Are High-Carb Diets Fattening?

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Are High-Carb Diets Fattening?

With nearly 2 out of every 3 American adults now either overweight or obese, there is a growing debate about what is the best diet to eat to lose excess body fat or maintain a healthful weight. Recently, diets restricting carbohydrates to about 40% or less of energy have received a lot of favorable publicity in the press based on the results of a few short-term studies. However, a review of very-low-carbohydrate diets concluded these diets produce weight loss only when they reduce calorie intake.

Of course any diet that temporarily cuts calorie intake will result in weight loss. But this weight loss often can lead to increased hunger and calorie intake and weight gain. The National Weight Control Registry (NWCR) has now documented more than 4,500 Americans who have lost at least 30 pounds and kept it off for at least a year. By far, the majority of these long-term weight control success cases utilized a diet considerably higher in carbohydrate and much lower in fat than the average American diet. Only a very small percentage of these long-term success cases have used a very-low-carbohydrate approach advocated by Atkins and others.

Diets such as ?Enter the Zone? and ?Sugar Busters? restrict the percent of calories from carbohydrate to 40% or less of total calories but as with the more carbohydrate-restrictive diets there are few documented cases of long-term weight control successes on these lower-carbohydrate diets.

A recent study evaluated the diets of a sample of U.S. adults whose customary diets varied in the amount and percent of calories from carbohydrate. The data used came from the USDA?s Continuing Survey of Food Intakes by Individuals 1994-1996. The sample included more than 10,000 free-living adults and divided them into 4 groups according to the percent of carbohydrate calories in their diets.

Of those who consumed the lowest-carbohydrate (less than 30% of calories) diets the percent of men and women who were overweight or obese was significantly higher than those consuming the highest-carbohydrate (greater than 55% of calories) diets. Indeed, 58.9% of the women consuming the highest-carbohydrate diets had a normal weight for their height (BMI<25). By contrast, most of the women (54.5%) consuming the lowest-carbohydrate diets were overweight or obese (BMI>25 or >30). The prevalence of being overweight or obese in the two other groups consuming either 30-45% carbohydrate calories or 45-55% carbohydrate was also significantly higher than those consuming the highest percentage (>55%) of their calories from carbohydrate.

The higher prevalence of obesity in those consuming lower-carbohydrate diets compared to those consuming the most carbohydrates could not be attributed to differences in physical activity. The higher average BMI of those eating more fat and protein and less carbohydrate was due to a higher calorie intake. The finding of this new study contradicts the oft repeated mantra that ?diets higher in protein make you feel fuller on fewer calories? or that ?adding more fat to the diet increases satiety, enabling people to eat fewer calories without being hungry.?

As the authors of this new study noted, it is not so much the ratio of macronutrients in the diet that determines calorie intake. Rather the lower calorie density of most minimally processed, high-carbohydrate foods help most people feel more satisfied on fewer calories. High-carb foods with a low calorie density include fruits, vegetables and whole grains (e.g., oatmeal, pasta and rice). The lower-carbohydrate diets had far more saturated fat, cholesterol and salt on average than the diet highest in carbohydrate. And they had less fiber and lower levels of most vitamins and minerals. The authors of this study conclude, ?A study of diets of free-living adults in the U.S. showed that diets high in carbohydrate were both energy restrictive and nutritious and may be adopted for successful weight management.?1 However, high-carbohydrate diets full of sugar and refined grains are calorie dense and nutrient poor and clearly not the best choice for weight loss and good health.

Bottom Line:

The results of this study and the NWCR seriously undermine the claims that a diet with less carbohydrate and more fat and protein is the key to long-term weight control.

By James J. Kenney, PhD, RD, LD, FACN.

Reference:

1. J Am Coll Nutr 2002;21:268-74

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