If you’re a really serious athlete, the answer is probably no. The problem, says William Evans, chief of the nutrition, metabolism and exercise lab at the University of Arkansas for Medical Sciences, is that “whenever you work out hard, you use glycogen, the body’s stored form of glucose (sugar). If you don’t eat much carbohydrate, your muscles will have ever-diminishing levels of glycogen and it will be difficult to continue exercising. There’s a lot of research that demonstrates that a high carbohydrate diet is important for people who do a lot of exercise.”
For people who aren’t serious athletes but exercise moderately and want to lose weight via a low-carb diet, there may be enough carbohydrates from the fruits and vegetables you get in the later stages of low-carb diets, says Barry Braun, an exercise biochemist at UMASS/Amherst. The real value of such diets is probably “more mental than biochemical,” he adds. They work “by making people more aware of what they’re eating and helping them cut out junk food and sugary snacks.”
But beware. There is a lot of water tied up chemically with glycogen, says Evans. So you may lose weight early on. “But as soon as you start eating carbs again,” he says, “you replenish glycogen and the water comes back with it. What you haven’t lost is fat.”
The bottom line, once again, is not news. Exercise for half an hour a day and eat sensibly.