The Food Journal and Food, Nutrition & Science

An alliance between The Lempert Report and The Center for Food Integrity

Carbs and Obesity

Carbs and Obesity

Health and Wellness

July 26, 2009

Low carb diets like Atkins and the Zone have been all the rage for years now, and many swear by them in their quest to achieve a leaner physique. But a new study from the University of South Carolina suggests that most people who maintain optimum body weight do not consume a diet low in carbohydrates.

Researchers used a 2004-2005 cross-sectional survey of 4,451 Canadians aged 18 years and older – and the results were staggering. People consuming 290 to 310 g/day carbohydrates (47% to 64% of calories from carbs) were least likely to be overweight or obese compared to those in the lowest intake category.

Those that consumed the highest level of carbohydrates tended to be younger and female, with lower intakes of calories and fats and higher intakes of fiber. Compared to the lowest carb intake category (179 g/day), weight and obesity risk was lower by 37% for those consuming 234 g/day and by 42% for those consuming 269/day. 

Proponents of low carb diets hypothesize that consuming fewer carbohydrates allows the body to break down fat, instead of sugar, to provide energy. Data has shown that low carb diets are effective at inducing weight loss in the short term. However, a recent study showed that high and low carbohydrate diets were equally effective in achieving and maintaining weight loss for up to two years. 

Dr. A. T. Merchant is an associate professor in the Department of Epidemiology and Biostatistics at the University of South Carolina and the author of the recent study. He says that the main drawback of any extreme diet, be it one based on high or low carbohydrate intake, is that is it difficult to adhere to over the long term. 

“We found that most healthy people who maintained optimum body weight in Canada did not consume very low or very high carbohydrate diets. This is important to know because participants in our study were average, healthy, adult Canadians, not those choosing to participate in clinical trials,” says Merchant.

One drawback to many low carb diets is the lack of complex carbohydrates that are rich in soluble and insoluble fiber, he says. In fact, according to one estimate, Canadians consume less than one whole-grain serving per day on average. Similarly, in this study, Merchant found that participants who consume fewer carbs also consumed less than the recommended levels of fiber. Overall, participants ate 13 to 22 g/day of fiber versus the recommended 38 g/day for men and 25 g/day for women.

Meanwhile, participants who consumed more carbohydrates typically ate more fruit, vegetables and fiber. It has been well documented that diets low in whole grain, fiber, fruit and vegetables, and high in calories, are associated with an increased risk of overweight or obesity and poor overall health, and these findings point out some of the limitations to eliminating carbs, especially those with potential health benefits.

“Fiber in the diet comes mostly from whole grains, fruits and vegetables, beans and legumes,” says Merchant. “If these foods are eaten instead of refined grain, red meat, and high fat dairy, not only will fiber in the diet increase but saturated fat will also decrease.”

Researchers say that populations on a low carb diet could benefit by choosing whole grains, increasing fiber and decreasing calories, and remaining physically active. Indeed, those found to have the lowest overweight and obesity risk were more physically active than those in both the lowest and highest carbohydrate intake categories. And retailers have a role to play too.

“Retailers can encourage people to eat healthy foods by displaying healthy foods prominently on their shelves and flyers, and keeping their prices lower than those of unhealthy alternatives. For example, whole grain bread should cost less than white bread. The healthy choice should also be the easy choice,” Merchant adds.