Throughout most of human history, our ancestors ate a diet that was nearly perfect in its balance between two essential fatty acids, omega-3s and omega-6s, which have crucial, though opposite, roles to play in metabolism.

In the last few decades, however, this delicate balance has been thrown out of whack, with most of us eating too many omega-6s, which come chiefly from corn and safflower oils, and far too few omega-3s, found in fatty, cold-water fish such as salmon and tuna as well as walnuts, canola, soy and flax seed oil. This nutrient imbalance is believed to contribute to arthritis, cystic fibrosis, heart attacks and other diseases.

“We are drowning in omega-6 relative to omega-3’s,” says Dr. George L. Blackburn, associate director of nutrition in the Division of Nutrition at Harvard Medical School.  Throughout evolution, the ratio of omega-6 to omega-3 was two 6’s to one 3, he says. “Now it’s about 20 to one. We have wiped out a lot of sources of omega-3 and have a huge intake of omega-6-heavy products like corn and safflower oils.”

“We need some of both,” adds Dr. Walter Willett, chair of the department of nutrition at the Harvard School of Public Health. The goal is to bring back a balance “by increasing omega-3s, not by decreasing omega-6s.”

Omega-6 fatty acids get converted in the body to substances that rev up the immune system and inflammatory response – a good thing for fighting infections, but detrimental in people prone to auto-immune problems such as arthritis. Omega-6s also boost clotting – a benefit if you’re bleeding to death, but potentially harmful in terms of increasing clots that can lead to heart attacks or strokes.

“We have doubled omega-6s in our food supply in the last 40 years” says Willett. “That’s one of the most important reasons that heart disease mortality has declined by 50 percent since the 1950s…Omega-6 lowers cholesterol and has some benefits on platelets and anti-arrhythmic effects as well….We need the 6s. We don’t want to reduce those.”

Omega-3s, by contrast, get converted in the body to substances that decrease the immune response, a benefit for people with auto-immune problems, and increase the time it takes for blood to clot, a benefit for people at risk of heart disease. Omega-3’s also decrease potentially fatal cardiac arrhythmias and are crucial to the healthy development of the spinal cord, brain and retina in infants and to healthy brain functioning in older people as well. 

Because Americans are relatively deficient in omega-3s, doctors and scientists are now scrambling to find ways to increase omega-3s in our diet.

Last week, researchers at Massachusetts General Hospital announced that they had genetically altered mice to produce omega-3 fatty acids. Scientists from Beth Israel Deaconess Medical Center and UMass Memorial Medical Center in Worcester also reported on research that suggests that people with cystic fibrosis may be helped by increasing omega-3s.

Later this month, the Institute of Medicine, an arm of the National Academy of Sciences, is expected to issue a report evaluating the methods used to assess the safety of additives to infant formula, including DHA, an omega-3 fatty acid, and AA, an omega-6. European countries have long added DHA and AA to baby formulas; American manufacturers began doing so two years ago to bring formulas closer to the composition of breast milk.

Because there are now so many products, particularly dietary supplements, out there in health food stores, supermarkets and pharmacies, it’s worth taking a moment to understand the terminology on product labels and ads.

There are many kinds of omega-6 fatty acids, and the one people need to consume in the diet – that is, the “essential” fatty acid – is linoleic acid. This gets converted in the body to arachidonic acid (AA) (which cannot be obtained from the diet) and which boosts the immune system and clotting by increasing a hormone called prostaglandin E2.

There are also many kinds of omega-3 fatty acids, the most important of which are DHA (docosahexaenoic acid) and EPA (eicosapentaenoic acid), both of which are found in fish. DHA can also be made by the body from its precursor, an omega-3 called linolenic acid, which comes from soy, canola, walnut and flaxseed. EPA can also be made from linolenic acid. The body’s biochemical machinery uses these acids to make prostaglandin E1, which slows down the immune system and increases the time it takes for blood to clot.

Omega-6 and omega-3 are both in the family of “PUFAS,” or polyunsaturated fatty acids. Fatty acids are long chains of carbon atoms hooked to each other and linked hydrogen bonds. If there are no “double bonds” between carbons, the fat is said to be saturated.  If there is a “double bond” anywhere in this chain, the fat is unsaturated. If there are lots of double bonds, the fat is polyunsaturated.

Polyunsaturated fats are considered  “good” because every double bond causes a 37 degree kink in the chain, which makes the fat more fluid. That in turn makes it easier for the fat to do one of its major jobs, slink into the fatty membrane around cells.

Because omega-3 fatty acid suppresses immune function and increases the time it takes for blood to clot, one might think that an excess could lead to an increase in infections and bleeding problems. This does not appear to be the case. “We’re not even close to those dangers – maybe the Eskimos are,” says Dr. Ernst Schaefer, chief of the lipid metabolism laboratory at the Human Nutrition Research Center at Tufts University.

The bottom line? Don’t stop eating omega-6 oils, but increase omega-3 however you can. This means eating more fish – yes, even salmon despite the risk of pollutants such as mercury, dioxin or PCBs. It also means breastfeeding if you can, or choosing formulas containing DHA and AA if you can’t.

If you hate fish, try taking 1 gram a day of fish oil supplements containing omega-3 fatty acids. But beware: Fish oil capsules vary greatly in quality. To reduce the chance that the supplements have the same pollutants as in fish, it may be wise to stick with well-known national brands. 

The patient was so obese – more than 700 pounds – that it took seven nurses to turn him over. Three nurses at the New England hospital where he was in intensive care went out on workman’s compensation after injuring their shoulders and backs trying to move him.  

Because it was so hard to turn him over, he developed bedsores that got so large “you could see his colon – you could have put a basketball in there,” recalls a nurse. During one admission, when the man needed a CT scan, he had to be taken to a nearby aquarium.

“Toiletting,” in the discreet phrase of medical professionals, became horrific. A urinary catheter solved one problem, but the man couldn’t be moved onto a bedpan, so doctors put in a rectal tube to withdraw his bowel movements. Taking his blood pressure was hard, too  – he needed extra-large cuffs around his lower arms or legs or a catheter placed into an artery in his arm.

 America’s obesity epidemic is creating a nightmare for hospitals, both medically and economically. It’s no day at the beach for patients, either. Lynn McAfee, a spokeswoman for the Council on Size and Weight Discrimination in Mount Marion, N.Y., says obese patients often face hostility and discrimination from health professionals.  “No matter why we are fat,” she says, “right now we exist. And we deserve the best possible medical care, just as anyone else is who is another size.”

According to the federal Centers for Disease Control, 64 percent of adult Americans, or 135 million people, are overweight or obese. One third of all Americans – 68 million – are obese.  (Overweight is defined as having a body mass index, or BMI, of 25.0 to 29.9. Obesity is defined as having a BMI of 30 or more. BMI is calculated by taking weight in pounds and multiplying by 703; this number is then divided by height in inches squared.)

People with a BMI of 40 or more are now called severely or extremely obese, a category that includes  12.3 million people, says Dr. George Blackburn, director of the center for the study of nutrition medicine at Beth Israel Deaconess Medical Center in Boston. “Super morbid” obesity is defined as a BMI of 50 or more, a category that includes 5.9 million Americans, and “mega obesity” as a BMI of 70 or more, which includes 1 million Americans.

The burden that “people of size,” the politically correct term for obese people, is putting on hospitals is huge. It takes special expertise to get an intravenous tube in a place “where you can feel the vein,” Blackburn says. “You can’t feel the liver. Bowel sounds are distant. Detection and treatment of pneumonia are more challenging because you can’t hear breath sounds as well. You can’t see subtleties on X-rays because the thickness of the fat creates a haze on the image.”

Regular beds are nowhere near big or strong enough, either. Nor are operating tables. Or chairs. Or walkers, or ventilators, or hypodermic needles. Nurses need stools to to reach an obese person’s chest.

But capitalism being capitalism, adaptation to the needs of obese patients has become a growth industry.

In the last six years, the instruments needed for bariatric surgery (in which most of the stomach is stapled off and the remaining 5 percent is connected to the small intestine) have gotten larger as patients get heavier, says Dr. Michael Schweitzer, assistant professor of surgery at Johns Hopkins University.  Surgeons have needed ever- larger instruments for laparoscopic surgery – done through several small incisions rather than one large one – and “companies have responded.”

Bariatric surgery itself is booming, too. According to the American Society for Bariatric Surgery, there are now more than 100,000 such operations a year. Five years ago, it was 25,800, and five years before that, 16,800.

Just as dramatic, the industry that supplies over-sized beds, wheelchairs, operating tables and the like to hospitals is growing, by about 20 percent a year, says Lynne Sly, vice president for marketing for Kinetic Concepts, Inc., based in San Antonio, Texas.

Demand is growing for bari-beds with “pressure relief” air mattresses – the mattress inflates and deflates section by section to relieve pressure sores. Gore-Tex sheets allow a patient’s skin to “breathe,” which helps prevent skin breakdown. There’s even a device called “AirPal” that helps heavy patients slide from one bed to another.

Susan Ross, clinical manager of the medical Intensive Care Unit at Rhode Island Hospital, says caring for  obese patients is “a challenge, let me tell you.”  One woman had so much fat hanging down her legs she developed a fungal infection in the skin folds. Just feeding obese patients – often through intravenous lines or naso-gastric tubes- is a major task because “these people require thousands of calories a day,”  she adds.

All of this gets expensive. The cost just for the extra-large bed needed for the 700-pound New England man was $5,568, for less than a month.

Renting an extra-large bed runs an extra $650 a day, says Dawn Arthur, a nursing director at the Santa Monica-UCLA Medical Center in Santa Monica, CA.  Normal wheelchairs cost $750, she says; super-sized ones cost $1200.

But the demand for such products is clearly growing. Since the Stryker Corp. in Kalamazoo, Mich. introduced its 650-pound capacity cot for ambulances last year, it has become a top-seller, says Dean Bergy, chief financial officer for the company.

Despite such accommodations to obesity, some hospitals may still not be doing enough, says McAfee of the size and weight council.  McAfee, who weighs 416, says hospitals “should look in their hearts and ask, “If that were me, would I really think the hospital was doing enough?”

The ramifications seem endless. Well, not quite. As the New York Times reported recently, even the funeral industry is  having to adapt to obese bodies – with extra-large coffins, and super-sized burial plots.

If you haven’t heard of it yet, get ready to grapple with the “glycemic index,” the latest wrinkle in America’s endless diet debate.

On the surface, the glycemic index is a simple concept – a way to measure how much blood sugar goes up in the two hours after eating carbohydrates. Carbohydrates with a high glycemic rating, like cake with icing, trigger huge, rapid spikes in blood sugar, followed by steep spikes in insulin, the hormone that escorts sugar into cells. Carbohydrates with low glycemic ratings, like whole grains and fresh fruits and vegetables, trigger more modest, slower rises.

The basic idea is that high glycemic carbohydrates are bad because they leave the stomach fast and trigger a rapid rise in blood sugar and insulin, which is soon followed by a crash in blood sugar that prompts renewed hunger. The result can be more calories consumed and more weight gained.

Using the index in real life is dicey. For instance, carrots have a high glycemic rating, but they’re good for you. French fried potatoes could be interpreted as having a better (lower) rating than a naked baked potato, because they contain fat, which causes slower emptying of the stomach and hence, a more modest rise in blood sugar and insulin, notes Karen Chalmers, a registered dietician and director of nutrition services at the Joslin Diabetes Center in Boston.

But what is important about the glycemic index is its symbolic value as a reminder to ever fatter, ever more confused Americans that carbohydrates, the big no-no of current fad diets, are not a monolithic entity. There are “good” carbs – found in whole grains, fruits and veggies – and “bad” ones, found in highly refined baked goods, candy and many processed foods, a message that some nutritionists, most notably Dr. Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health and author of “Eat, Drink and Be Healthy, have long been trying to get across.

The glycemic index has actually been around for 20 years, but a series of recent studies, and popular books like “The Glucose Revolution” by Jennie Brand-Miller et al, have propelled it to center stage.

In the last several years, for instance, Dr. David Ludwig, director of the obesity program at Children’s Hospital in Boston, and others have published studies suggesting that obese people put on low-glycemic diets lose more weight than those on reduced-fat diets.

 In one such study, Ludwig gave some obese youngsters high glycemic index meals and others, low-glycemic ones. The number of calories given to both groups was the same. But the kids on the high glycemic diet ate almost twice as much when allowed free access to food as the others. Obviously, more snacks mean more calories and more weight gain.

That said, there are limits to the logic behind the glycemic index. It is incorrect to infer, as some do, that sugar is “addictive.”  Nor is it correct, as some diet gurus say, that carbohydrates turn into body fat more easily than fat. It’s fat that’s most efficiently converted into body fat, that is, it takes the fewest calories for the conversion. Carbohydrate is the next most efficient, then protein.

More important, a calorie is still a calorie is still a calorie. No matter what combination of protein, fat and carbohydrate you eat, if you take in more calories than you burn, you’ll get fat.

And getting fat triggers a dangerous cascade of biochemical events. Excess body weight causes the pancreas to work overtime to produce enough insulin, a phenomenon called insulin resistance, notes Dr. Edward Horton, director of clinical research at the Joslin Diabetes Center in Boston.

Insulin resistance, in turn, is associated with a whole cluster of metabolic problems, even if it never leads to outright diabetes. Syndrome X, also called Insulin Resistance Syndrome or Metabolic Syndrome, is characterized by elevated triglycerides (fats), low HDL (“good” cholesterol), high blood pressure, changes in blood clotting patterns and a build-up of plaque in artery walls. High insulin prevents fat cells from dumping fatty acids into the blood stream (thereby making the body store more fat) and makes the liver convert more fatty acids to triglycerides, which raises the risk of heart disease.

High insulin can also raise the level of PAI-1, or plasminogen activator inhibitor, which prevents the breakdown of potentially dangerous clots. With high PAI-1 levels, clots are not broken down and the risk of heart attack and stroke goes up. Insulin resistance is also associated with high levels of C-reactive protein, a marker for heart disease.

Eating too many calories – from any source, protein, fat or carbohydrate – can lead to obesity. But part of the problem today – two-thirds of Americans are overweight and one third, obese – is that for years, we were all told to cut down on fats. There’s still some truth in this message-saturated fats and trans-fats (like those in some margerines) are dangerous because they boost cholesterol and the risk of heart disease. Some fats, though,  are good, notably the monounsaturated and polyunsaturated fats found in olive, canola or peanut oils, nuts, other plant products and fish. These fats can lower the bad kind of cholesterol (LDL) without lowering the good (HDL).

The lesson that most of us have absorbed over the years, however, was not this mixed message but a starker one: all fat is bad. That, not surprisingly, prompted consumer demand for “low fat” foods, the food industry responded, with a vengeance.  

 In recent years, “the food industry has screwed around with fat-free foods to keep the taste up,” says Dr. David Heber, director of the University of California, Los Angeles Center for Human Nutrition and author of “What Color is Your Diet?”

“They lowered the fat content but raised the sugar,” he says, noting that many processed foods are now loaded with high fructose corn syrup, in part because “corn is subsidized by the federal government.” Indeed, one reason for the current obesity epidemic is all the high fructose corn syrup added to processed foods.

So whee does this leave us, besides fat and frustrated? It’s pretty straightforward, actually. Don’t take the glycemic index itself too literally. It’s too complicated and you could spend hours trying to calculate the glycemic rating for each food on your plate.  

But do use the concept as a valid, potent way of remembering that not all carbohydrates are created equal. After all, as Ludwig points out, lumping all carbohydrates together as a diet rationale has clearly not worked to help people lose weight.

Bottom line? Stick to whole grains and fresh fruits and veggies, avoid refined carbohydrates as much as you can. Chances are, you’ll be less hungry and much healthier.

Three very fat Turkish people, all cousins, got very lucky this year, when they spent a few months in Los Angeles getting injections of leptin, the “satiety” hormone discovered in 1994 and immediately hailed as the long-awaited magic bullet to cure obesity.

The three, a 27-year old man who weighed 312 pounds, a 35-year old woman who weight 253 pounds and a 40 year old woman who weighed 194 pounds, were all miserable.

The man was so fat, he said through an interpreter, that he couldn’t get a job, or a girlfriend. One woman had to work at home as a seamstress because people made fun of her if she went out. The other had given up her dreams of marriage, devoting herself to taking care of her parents.

By the time they headed back to Turkey in July after their treatments, they had each lost roughly half of their body weight, says the researcher who treated them, Dr. Julio Licinio, professor of psychiatry and medicine at the David Geffen School of Medicine at UCLA.

A pair of obese Pakistani cousins living in England, both born, like the Turkish family, with defective genes for leptin, also lost significant amounts of weight with leptin injections.

And that’s pretty much it, folks. That’s the good news: A handful of obese people who get better with leptin, and  – let’s be generous here- maybe several thousand  more helped modestly and temporarily by other drugs.

After all the hoopla, all the hype, all the hope and all the research, anti-obesity drugs, at least so far, have largely been a bust. And barring some secret miracle concoction now in development, there will simply not be a pharmaceutical fix for fatness in the near future.

It’s all rather depressing.

Two-thirds of Americans are now overweight, the latest government figures show, and one in every three is obese. Obesity is defined as having a Body Mass Index (BMI) of 30 or more and being overweight, by having a BMI of 25 to 30. (To calculate your BMI, multiple your weight in pounds by 703; then divide that number by your height in inches squared.)

Yet, aside from repeating the old mantra of diet and exercise, and maybe a mention of gastric bypass surgery, there’s still very little that doctors have to offer the millions of Americans stuck in weight loss hell.

“There is certainly nothing on the horizon in terms of a drug that will solve obesity,” says Dr. Eric Colman, medical team leader for the metabolic and endocrine division at the US Food and Drug Administration.

“It would be wonderful if there were something that was highly effective and without side effects. But nobody should be waiting for that pill to arrive,” adds Dr. Walter Willett, chairman of the department of nutrition at the Harvard School of Public Health.

The more researchers try to find a magic bullet for weight loss, the more they are discovering that the biochemical pathways in the brain that control appetite and weight maintenance are devilishly complicated. 

At the moment, for instance, there are only two prescription weight-loss drugs on the market that are approved for long term use – Meridia (sibutramine) and Xenical (orlistat).

Meridia works promotes a feeling of satiety by increasing levels of serotoninn, norepinephrine and dopamine, chemical messengers in the brain. But, as the Harvard Heart Letter of March, 2002, notes, the drug only works as long as you take it, and even then, only modestly, resulting in a 5 to 10 percent weight loss. This amount of weight loss can help lower blood pressure and cholesterol but may not make a huge dent in what you see in the mirror.

Nor is Xenical a magic answer. It acts in the digestive tract to stop absorption of fat from foods by blocking enzymes called lipases. Like Meridia, it can result in a 5 to 10 percent weight loss, but all that unabsorbed fat can cause uncontrollable bowel movements, messy underwear and frequent passing of fatty gas.

There used to be more choices, but they weren’t terrific either. In 1997, the US Food and Drug Administration asked manufacturers to remove two highly popular anti-obesity drugs from the market, fenfluramine (part of the combination called “fen-phen”) and dexfenfluramine (Redux) because of an apparent increase in the risk of heart disease and serious lung problems.

There still are a few other weight-loss drugs on the market, including those containing phentermine (the “phen” of the old fen-phen combo). But these aren’t approved for long term use (which obese people need) and many are stimulants that can cause nervousness, rapid heartbeat and similar symptoms. These drugs can trigger brief spurts of minor weight loss, but they often lose their effectiveness over time.

So where does this leave the millions of Americans who are either overweight or obese? Still fat and still desperate.

Some people resort to gastic bypass operations – surgery to reduce the size of the stomach, which limits the amount of food a person can take in.  In 2000, 40,000 Americans underwent this procedure, almost double the number performed five years earlier, reports Ellen Ruppel Shell, co-director of the Knight Center for Science Journalism at Boston University, in her highly-readable new book “The Hungry Gene.”

But the costs are high. “Gastric bypass surgery kills one out of every hundred patients on the operating table, and not everyone recovers from the complications,” notes Shell.

On the other hand, gastric surgery may work not just by limiting stomach volume – but biochemically as well, according to a recent paper in the New England Journal of Medicine.

Cells in the stomach produce a chemical called ghrelin that has been shown to stimulate feeding and obesity in animals. Unlike the weight loss induced by dieting, weight loss induced by gastric bypass may lead to longer term maintenance of  weight loss because of  reduced ghrelin levels, note Drs. Jeffrey Flier, an endocrinologist and chief academic officer at Beth Israel Deaconess Medical Center and Eleftheria Maratos-Flier, director of the obesity section at the Joslin Diabetes Center in Boston in an editorial accompanying the research. This suggests that a grehlin-blocking drug might work where others have failed.

And someday, there may be other pharmaceutical options.

Some scientists are hopeful that a drug now in clinical trials called CNTF, for ciliary neurotrophic factor, may work out.

Others are looking at a compound called MLN 4760, made by Millenium Pharmaceuticals in Cambridge, MA, which has been working on obesity drugs for years. So far, says Lou Tartaglia, vice president of metabolic diseases, none of the drugs in the works are yet ready for marketing, but MLN 4760 is now in early human safety trials. The company will not say exactly how it works except that it block an enzyme called carboxypeptidase.

Farther back in the Millenium pipeline is a drug that would activate a receptor molecule called MC4 that seems to act in the brain, at least in mice,  to decrease body weig

Tartaglia thanks that the reason that drugs marketed so far have failed is that they are crude and act essentially “by hitting the brain with a hammer.” New drugs could work better because they are targeted to more specific molecules in the brain.

But even then, there are no guarantees. Take leptin, for exaple, a highly specific drug. 

Amgen, a company based in Thousand Oaks, Calif., has been trying for years to develop a leptin-based drug, with no success. Company spokeswoman Barbara Bronson Gray says Amgen researchers have conducted several trials but the drug “did not achieve clinical or commercial hurdles needed for an obesity drug in this population.”

Why? For one thing, obese people often turn out to have perfectly normal or even higher than normal levels of leptin, which is made in fat cells and travels to the brain to deliver “satiety” or “I’m full, stop eating” signals.

The Turkish cousins were genuinely – and genetically – leptin-deficient, so giving leptin to them worked. But most obese people are not leptin deficient, perhaps in part because of the sheer number of their fat cells. These fat cells, which never go away, even when a person loses weight, keep cranking out leptin but, obese people, one current theory goes, may become resistant to their own leptin, much as people susceptible to diabetes can become insensitive to their own insulin.

Maybe, some day, the growing understanding of all the biochemistry involved in appetite and weight regulation will result in a magic pill.

Until then? It’s same old, same old: Diet and exercise. Turn off the TV and take a walk instead. Don’t adopt a “low fat” diet that allows you to eat endless carbohydrates. Eat more veggies and less processed junk. At the very least, if you are already overweight, don’t give up and let the problem get even worse.

In the swampy world of nutrition books, clarity and credibility are as scarce as tofu and sprouts at Dunkin’ Donuts.But clarity and credibility are precisely the reasons you should toss out your old diet books, forget the government’s famous but flawed food pyramid, and get your hands on a new book, “Eat, Drink and Be Healthy,” by Walter Willett, a nutritionist based at Harvard University.

His book is powerful not only for its independence from both doctrinaire nutritionists and New Age nonsense, but for its no-holds-barred attack on the nutrition advice doled out by the US Department of Agriculture in posters and brochures that reach millions of schoolchildren each year.

Among other things, the USDA food pyramid utterly fails to make clear that there are both good (unsaturated) and bad (saturated and trans) fats, as well as good (whole grain) and bad (refined) carbohydrates.The Agriculture Department, citing longstanding policy, declined to comment on Willett’s criticisms.

Willett, whose lean figure is visible proof that he follows his own advice, is one of the nation’s leading nutrition researchers and chairman of the nutrition department at the Harvard School of Public Health.

Unlike most nutrition books out there, his is based on mountains of data from huge epidemiological studies. And his willingness to simply say that the federal pyramid is wrong is welcome news to nutrition researchers in a country where so much of the debate about diets is based on special-interest advertising (“Beef: It’s what’s for dinner”) or celebrity endorsements of fad weight-loss plans.

Perhaps this is the summer of science in the nutrition debate. Tufts University nutritionist Miriam Nelson, virtually a one-woman health advice industry, also has written a diet book, “Strong Women Eat Well,” that finds Americans get lousy nutrition advice from many quarters.

For instance, Americans who load up on refined carbohydrates, including supposedly healthful low-fat cookies, which are actually high in calories, have been getting steadily fatter, often without violating USDA guidelines, noted Nelson, an associate professor at the university’s School of Nutrition Science and Policy.

Half of all adults Americans are now overweight, studies show, and more than 20 percent are obese, twice as many as in 1960; diabetes also has risen nearly 40 percent in the last 20 years.

Yet, you could look at the USDA pyramid and conclude all sorts of bad nutritional habits are fine – for instance, that it’s OK to eat three servings a day of red meat. It’s not: Red meat is loaded with artery-clogging saturated fat.

You could also figure, looking at the food pyramid, that it’s OK to eat six to 11 helpings a day of Wonder Bread. Wrong again: White breads are made from refined carbohydrates, which lower good HDL cholesterol and can lead to weight gain.

The reason the pyramid gives such erroneous messages, Willett said, is that it was cooked up primarily by the Agriculture Department and was”yanked this way and that by competing powerful interests,” which include the formidable meat, dairy and sugar industries.

The pyramid, in Willett’s view, “was built on shaky scientific ground back in 1992” and has been steadily eroded by new data ever since.   

But, when one looks, as Willett does, not at industry’s claims but at data from big research projects, the picture becomes far more nuanced, and presumably, accurate. Willett uses large studies such as the Nurses’ Health Study of 122,000 women; the Physicians’ Health Study of 22,000 male doctors; the Health Professionals’ Follow-up Study of 52,000 male doctors, dentists and veterinarians; the Iowa Women’s Health Study of 42,000 women; and numerous others.

Among other things, the emerging data show it’s time to re-think how we classify carbohydrates. The old way was to label them “simple” or”complex,” depending on the number of sugar molecules linked together.   

A better distinction, Willett said, is between whole grains (good carbohydrates) and refined (bad). The good category includes brown rice, oats, whole-wheat pasta and beans, and you should base your diet on these. The bad ones are regular pasta, white bread, white rice, some cereals and commercially baked cookies and the like made with refined flour.

Why are pasta and the other refined carbohydrates such no-nos? Because they are essentially simple sugar. The minute you swallow these starches, your digestive system transforms them into glucose and pumps it into the bloodstream almost as fast as if you had eaten jelly beans. The result is a spike of insulin, the hormone that escorts sugar into cells. Once glucose enters cells, your blood-sugar levels plummet, your brain interprets that as a hunger signal and you want to eat again. Worse yet, this sugar-insulin roller coaster can lead to diabetes and heart disease.

In fact, Willett said, it is now clear that the bad carbohydrates – the refined ones that the body rapidly metabolizes – are more likely to cause heart disease, probably by lowering good cholesterol and raising triglycerides (three fatty acids linked together), than some good kinds of oil, like the unsaturated fats in walnuts.

Dr. Gerald Reaven, professor of medicine at Stanford University School of Medicine, agreed. People trying to reduce cholesterol “would do better by eating less carbohydrate and substituting good fats” such as those in nuts, he said.

Just as the USDA food pyramid lumps all carbohydrates together at the bottom of the pyramid, it lumps all fats and oils together at the top of the pyramid, with a “use sparingly” label. That’s partly right: Bad fats should be used sparingly. These are the saturated fats (from whole milk or red meat) and the trans fats (trans-fatty acids) found in vegetable shortenings and some margarines. Saturated fats contribute to clogged arteries, resulting in heart attacks and strokes, and trans-fats are even worse, Willett said.

In fact, trans-fats are so worrisome that Nelson recommends sometimes eating butter despite its high saturated fat content because many margarines contain trans-fats.

But just as important as avoiding the bad fats is increasing the good fats in your diet, Willett said. The good fats are the monounsaturated and polyunsaturated types found in olive, canola or peanut oil, nuts, other plant products and fish. These fats can lower the bad kind of cholesterol without lowering the good.

Willett also has weighed in in favor of moderate alcohol consumption. Although more than one drink of alcohol a day can raise the risk of breast cancer, for instance, he noted that this risk can be offset by the B vitamins, particularly folate, that are standard in most multivitamins.

And what about the current darling of health-food industry advertising, soy? It does help lower cholesterol, Willett noted, but it doesn’t reduce hot flashes in menopausal women much. And in high doses (three to four glasses of soy milk a day or supplements), it may actually drive proliferation of breast-cancer cells, not retard it.

Unlike many nutritionists who often stick to an”eat-your-vegetables-or-else” line, Willett also advocates a multivitamin a day, on top of loads of fruits and vegetables.

As for potatoes, both Willett and Nelson take a dim view. Nelson said it’s OK to eat a small one occasionally. Willett said that because the starch in a potato turns to sugar soon after digestion, it shouldn’t even be dignified by the term vegetable.

Willett also attacks those annoying milk mustache ads, noting that, despite what the USDA says, there are more reasons not to drink milk in large amounts than there are to drink it – among them the high calories and saturated fat in whole milk. Nelson takes a somewhat softer line, arguing the milk campaign is “not ridiculous” for children and young adults who may not get enough protein otherwise.

The bottom line? Eat more good fats and fewer bad ones. Eat more good carbohydrates and fewer bad. Substitute a small handful of walnuts for a midafternoon cookie. Get more of your protein from beans and nuts, fish, poultry and eggs, and less from red meat. Drink alcohol, but not to excess, and pop a multivitamin while you’re at it.

Most important, get or keep your weight low and stable. Health risks may begin to accrue at a shockingly low body mass index of 22, suggesting that a 6-foot man weighing 165 pounds could have a weight problem. (To calculate your body mass index, or BMI, divide your weight in pounds by your heightin inches; divide that number by your height in inches and multiply that number by 703.) 

The benefits to eating right are huge – a lower risk of heart attack, stroke, high blood pressure, high cholesterol, diabetes and certain cancers, including those of the uterus, colon and kidney and, for women past menopause, of the breast.

On balance, that seems well worth trading your morning bagel for a nice big bowl of kashi.

Let’s face it: We were brainwashed. For years, nutritional gurus strummed a one-note samba: All fats are bad. And many of us played along, giving up some of our favorite foods. Like nuts.

“Eighty to 90 percent of calories [in nuts] are from fat. So they were labeled as a high-fat food,” said Frank Hu, an assistant professor of nutrition at the Harvard School of Public Health. And, for the last two or three decades, he said, “health-conscious people tended to avoid them to lose weight and avoid heart disease.”

“We’ve been so biased about fat,” said Jeffrey Blumberg, a nutrition professor at Tufts University. “The thinking was that any high-fat food is bad.”

At long last, nutritionists are changing their tune. Now, they concede, there are both good fats and bad fats, and nuts are good again because they contain “the good kind of fat,” said Dr. George Blackburn, director of the center for nutrition and medicine at Beth Israel Deaconess Medical Center. They’re also good, he said, because “they satisfy in small portions.”

The emerging consensus is that saturated fats (the kind found in meat and dairy products) are the bad ones because they raise LDL or bad cholesterol in the blood. Monounsaturated and polyunsaturated fats (the kind found in nuts and olive, canola, corn, safflower and sunflower oils) are good because, though high in fat and calories, they do not raise LDL. In fact, polyunsaturated fats can actually lower LDL.

The same principle holds for peanuts and peanut butter, too, even though peanuts, despite their name, are technically classified as legumes, not nuts. Peanuts are good for you because they’re high in monounsaturated fats.

For the record, It’s only fair to note that this good-fat, bad-fat message is heavily promoted by some food industry groups, including the International Tree Nut Council, which sponsored a conference on the health benefits of nuts this fall at Georgetown University. The nut folks are also sponsoring a number of ongoing studies of the nutritional pros and cons of nuts.

But, with that caveat in mind, consider the growing evidence that nuts are good for you:.

The Iowa Women’s Health Study of 34,000 women, conducted between 1986 and 1992, found that women who ate nuts had a 35 percent reduction in heart attacks, compared to those who didn’t.

In 1992, a California study of 34,000 Seventh Day Adventists (who don’t drink or smoke) found that those who ate a small handful of nuts five days a week had 50 percent fewer heart attacks than those who didn’t. And no matter how the researchers sliced up the data looking at men alone, women alone, young people, old people, vegetarians or meat-eaters, the protective effect of nuts on the heart held up, said Dr. Gary Fraser, leader of the study and a cardiologist at Loma Linda University. The gist of 20 other studies, he said, is that regular consumption of nuts lowers blood cholesterol 8 to 10 percent.

In 1998, the Nurses Health Study of 86,000 female nurses confirmed the heart benefits of nuts, showing that women who ate at least 5 ounces of nuts a week had 40 percent fewer heart attacks than those who didnt. Many of the women who ate nuts substituted nuts for greasy steaks and fries, but the protective effect of nuts held true even for those who made less-drastic diet changes, said Hu, of Harvard, the lead author.

Preliminary results from a similar study, the Physicians Health Study, suggest that there are fewer sudden deaths among men who eat nuts, suggesting a similar heart-protecting effect in men, although, so far, the research has not been published.

It’s much less clear whether eating nuts helps prevent cancer. So far, limited data in human studies suggests no dramatic benefit. In rats, a study paid for by the Almond Board of California and conducted by Paul Davis, a research nutritionist at the University of California at Davis, found that rats that were fed almonds were less likely to develop precancerous changes in the colon after being injected with a cancer-causing chemical, compared to rats that didn’t get almonds.

Naturally, there’s a downside to this good PR for nuts: Because of their high-fat content, nuts are loaded with calories. But that doesn’t automatically mean they’re diet-busters. In fact, a nibble or two of nuts a day may actually help with weight loss, provided you don’t go overboard on overall calories.

In research presented last year at a scientific meeting, Kathy McManus, a registered dietitian at Brigham and Women’s Hospital in Boston, studied 101 overweight people who were put on either low- or moderate-fat diets that didn’t exceed 1,200 calories a day for women or 1,500 for men.

At the end of the 18-month study, the people on the low-fat diet had typically dropped out and regained some of their lost weight, while the moderate fat group was maintaining weight loss. Those on the moderate fat diet ate an ounce of nuts a day (170 calories worth), plus a tablespoon of oil and a teaspoon or two of peanut butter.

“The point is that, with a moderate-fat diet, people seem to be able to stay with a diet longer,” said McManus, whose research was paid for by three industry groups – the Institute and the International Tree Nut Council.

International Olive Oil Council, the Peanut

Among other things, she said, having an ounce or so of nuts in late afternoon can ward off the hungry horrors. You’re not so ravenous when you walk in the door, which means you’re less likely to eat a lot while you’re cooking dinner.

And there’s yet another reason to eat nuts: They are full of arginine, an amino acid that helps the body make nitric oxide, which helps blood vessels dilate, thus lowering blood pressure. They’re also loaded with vitamin E and other antioxidants, which prevent damage to DNA and cells from chemicals called free radicals.

The bottom line is that nuts are no longer taboo. If you want to add them to your diet, you probably should try eating them instead of something like cream or red meat. And keep portions modest, like the small packets of nuts that airlines hand out. In other words, don’t go totally nuts.

SIDEBAR: Going Nuts Over Nuts

For years, nuts were regarded as unhealthy because they are high in fat. But researchers believe nuts got a bad rap: they contain no cholesterol and are high in both polyunsaturated and monounsaturated fats, which are considered good because they promote a healthy heart. And nutrients in nuts compare favorably to common foods such as chicken and hamburger.

Calories (kcals)

Protein (grams)

Cholesterol (mg)

Saturated fat (grams)

Mono- un saturated fat (grams)

Poly unsaturated fat (grams)

Total fat (grams)

Almonds

578

21

0

4

32

12

51

Cashews

574

15

0

9

27

8

46

Hazelnuts

628

15

0

4

46

8

61

Macadamian

716

8

0

12

59

1

76

Pecans

691

9

0

6

41

22

72

Pistachios

567

21

0

4

25

14

46

Walnuts

654

15

0

6

9

47

65

Lean hamburger

268

24

78

7.2

8

1

18.3

Chicken

173

31

85

1.3

1.5

1

4.5

Butter

108

0.1

33

7.6

3.5

0.5

12.2

Note: Nutrient information is based on 3.5-ounce servings, except butter, which is based on one tablespoon. SOURCES: USDA Nutrient Database for Standard Reference, Bowe and Church’s Food Values of Portions Commonly Used

In the early 1990s, while almost nobody was looking, the biotech industry pulled off quite a coup.

Led by industry giants like Monsanto, DuPont, Novartis and Aventis, genetic engineers began commercializing an idea they’d worked on for years – tinkering with genes to make crops more resistant to insects and herbicides.

The basic idea was clever. If, say, a gene could be inserted into soybean seeds so the plants would be resistant to an herbicide, farmers could spray their fields with that herbicide, killing the weeds without fear that it would harm the cash crop. If a gene could be introduced into corn that would produce a protein toxic to corn-eating caterpillars, farmers could grow that kind of corn without using high quantities of pesticides.

The idea has not only worked – it’s worked too well in the eyes of the anti-biotech crowd, which has been staging counter-demonstrations this week in Boston during BIO2000, the biotech industry’s annual gig. Yesterday, four protesters were arrested on disorderly conduct charges for dumping 30 gallons of “genetically altered” soybeans outside the Hynes Convention Center, marring otherwise orderly demonstrations.

Worldwide, the area planted with transgenic crops has soared from 2 million hectares in 1996 to nearly 40 million in 1999, according to the Worldwatch Institute, a research organization based in Washington. In the United States, the world leader in growing genetically modified foods, half of the soybean crop carried the herbicide-resistant gene last year while a third of the corn crop carried the anti-caterpillar gene.

The problem, opponents say, is that in the rush to get “GM,” or genetically modified, food out of the lab and into the mouths of consumers – who had not been clamoring for it – the biotech industry did not completely answer the one question that consumers care most about: Are GM foods safe to eat?

In theory, they should be. After all, we eat DNA all the time (we just call it steak or fish), so what’s an extra gene or two? We eat corn that over the centuries has been cross-bred so many times – the old, Mendelian way – that it bears little resemblance to its wild ancestors.

And, even if a transplanted gene, or a special kind of DNA called a promoter, did have a destructive effect, the damage would likely show up in the plant into which it was inserted, not the humans who ate the plant. Besides, our digestive enzymes should chew up GM food the same way they process everything else we eat.

Among other things, that means that it’s unlikely that, say, a gene from a flounder that’s inserted into a tomato (as scientists are doing to make tomatoes more resistant to freezing) would somehow lodge itself forever in the human genome. In fact, if it were that easy to transfer genes, scientists wouldn’t have to resort to sophisticated tricks to create transgenic animals in the lab: They could just feed them GM food.

Indeed, there’s no evidence that any human has ever been harmed by eating GM food. (This is in contrast, by the way, to evidence that some herbal products, which people assume are safe because they’re “natural,” can be harmful.)

Given that 60 percent of the processed food now on the American market contain ingredients that have been genetically engineered (a fact many people don’t realize), chances are that if the stuff were dangerous, somebody would have noticed.

But none of this is what really irks consumers – including this one – on both sides of the Atlantic. What is irksome is that, even though GM foods may be safe, there’s too little testing to say for sure – and there are no labels to guide us.

We don’t know, for instance, whether the proteins made by genes inserted into plants could cause serious, even fatal, allergic reactions. In one notorious case, scientists inserted a Brazil nut gene into soybeans to increase protein. When the hybrid was lab tested in 1996, human antibodies reacted to the nut gene, a sign that the product could have caused allergies in people.

“Bioengineering could produce novel protein combinations that the human body has never seen before, potentially resulting in serious allergies that would be difficult to diagnose,” said Martin Teitel, executive director of the Council for Responsible Genetics, a Cambridge-based watchdog group.

Another concern is that gene-altered foods may have different nutrient value than standard foods. Though the biotech industry disputes it, GM soybeans may have fewer phytoestrogens than normal, a potentially important change, since some consumers eat soybeans precisely to get the hormone-like effects of these plant estrogens.

Opponents of GM foods also worry that gene-altered crops might contain pesticide residues or, worse in the eyes of some opponents, genes that make pesticides in every cell in the plant. (On the other hand, with some gene-altered crops, farmers can use fewer pesticides than normal.)

And then there’s the concern that these crops could increase antibiotic resistance.

Bioengineers use antiobiotic-resistance genes as markers to see whether the genes they put into plants get into the DNA. The worry is that eating the altered food could allow the marker genes to pass into bacteria in the human digestive system, making people resistant to potentially life-saving antibiotics.

“That argument is totally bogus for two reasons,” fumed Val Giddings, a geneticist and vice president for food and agriculture at the Biotechnology Industry Organization in Washington. “Number one, the antibiotic resistance genes used as markers in biotech do not [cause] resistance to antibiotics used to treat human disease. Number two, those resistance genes are already present in the human digestive tract.”

Furthermore, he said, “crops improved by biotechology have been subjected to more scrutiny in advance, depth, detail and rigor than any other foods introduced into the food supply in human history.”

But have they?

In 1992, faced with the imminent onslaught of GM foods, the FDA decided to regulate those products the same way as new foods created by old-fashioned plant breeding, said Laura Tarantino , deputy director of the office of premarket approval at the FDA’s Center for Food Safety and Applied Nutrition.

The agency also decided not to consider genes inserted into foods as “additives,” which would have required FDA approval before marketing. That means, she acknowledged, that, as of now, “there is no requirement that someone come in for premarket approval” of GM food just because it is “made by recombinant DNA.”

This stance so outraged lawyer Steven Druker, executive director of the Alliance for Bio-Integrity, a nonprofit watchdog group based in Iowa, that he and others filed a lawsuit against the FDA in 1998 seeking mandatory safety testing and labeling of GM foods. That suit is still pending.

In Europe, consumer pressure against “Frankenfoods” has grown so intense that some grocery chains are tossing transgenic products off their shelves. That, in turn, is making farmers around the world uneasy about growing gene-altered crops.

Indeed, after four years of rapid growth, farmers are expected to reduce planting of genetically engineered seeds by as much as 25 percent this year, the Worldwatch Institute predicts.

Giddings of the biotech organization counters that, at least in the United States, farmers are increasing their plantings of biotech soybeans. They are planting less GM corn, he conceded, but that’s not because of consumer resistance but because that crop, engineered to resist a European corn-borer, is no longer endangered by that pest.

The bottom line is that, even if GM foods are safe, and they seem to be so far, consumers have a right to demand labels so they know what they’re eating.

Margaret Mellon , a lawyer, molecular biologist and director of the agriculture and biotechnology program at the Union of Concerned Scientists in Washington, put it this way:

Consumers “deserve the opportunity to know which foods have been altered and to make a choice about whether they want to take any risk at all, even if that is a very tiny risk.”

 

SIDEBAR

QUESTIONS REMAIN ON `ORGANIC’ LABEL

If you want to avoid genetically modified foods, the only way to do that with certainty is to buy foods labeled “organic.”

The US Department of Agriculture recently developed new labeling standards to clarify what “organic” means. Among other things, the new standards prohibit organic labeling on any foods produced with genetic engineering.

Organic foods, however, may have their own problems. Since they’re often grown without pesticides, you may get some pests with your food. Organic food is often more expensive as well.

If you want to find out more about the controversy over genetically modified foods, visit these Web sites:

• www.ucsusa.org (Union of Concerned Scientists)
• www.gene-watch.org (Council for Responsible Genetics)
• www.biointegrity.org (Alliance for Bio-Integrity)
• www.fda.gov
• www.monsanto.com
• www.bio.org (Biotechnology Industry Organization)
• www.ificinfo.org (International Food Information Council)
• www.gmabrands.com (Grocery Manufacturers of America)