Healthy Cooking Columns

Low Fat Diets Don’t Make You Fat

There has been a lot of discussion and controversy about low-carb diets in the last few years. The inventors of diets like The Atkins Diet, Sugar Busters, South Beach Diet and The Zone Diet would have people believe that the rise in obesity is related to an increase in consumption of carbohydrates. They assert that by simply cutting all carbohydrates from the diet, people will lose weight and obesity will be cured. To support their claims they advance complex theories—none of which have been supported with well-designed research.

Much of the increasing problem with obesity is related to higher carbohydrate intake, but this is because soda and most of the snack foods that people eat today are carbohydrate based. Those foods, like potato chips, crackers, cookies, ice cream and baked goods, are generally very high in fat as well. Most diets, whether they are low-carb or low-fat, will eliminate many of these calorie-dense foods and people will lose weight.

The assertion by the inventors of fad low-carb diets is that it is the low-fat diet that is responsible for overall weight gain and the rise in obesity. This concept is refuted by the publication of a well designed research project on the effect of long term low-fat diet. The Women’s Health Initiative Dietary Modification Trial was designed to test the result of a low-fat, high-carbohydrate, high fiber diet on breast cancer, colorectal cancer and heart disease. The study was not designed as a weight loss program, and the participants were allowed to eat as many calories as they wished. (JAMA 2006; 295: 39-49)

They researchers enrolled a total of 48,835 post-menopausal women in the trial. About 60% were randomly assigned to a control group and were allowed to continue to eat the diets that they had been eating. The remaining 40% were in a group that was given instruction on how to eat a low-fat diet that increased consumption of fruits, vegetables and whole grains.

When the researchers looked at the effect of this diet on weight, however, they found that there was an initial weight loss of about 5 lbs. in the first year. After that, there was no significant gain in weight and the group that used the diet maintained their weight loss over 7 years. This effect was shared across all ethnic groups and it didn’t appear that there were differences in the effect in women who were obese, overweight, or of normal weight.

There was also evaluation of how the different dietary changes may have an effect on weight. Those women who ate less fat had the greatest weight loss. A small number of participants actually increased the amount of fat consumed and that group showed an increase in weight. Those who ate more fruits and vegetables showed a statistically significant weight loss, while eating more fiber showed the same trend (although eating more fiber was not definitively shown to promote weight loss).

This is a well designed large study of post-menopausal women over a period of time significant enough to allow for conclusions to be drawn with confidence. It shows that there is no significant weight gain on a low-fat, higher carbohydrate diet. It does help to refute the assertion that this type of diet is responsible for the trend toward obesity today.

The proponents of a low-carb diet have not had the opportunity to perform long term studies with such a large number of participants. The studies that have been done have been very short term and often show a higher weight loss on Atkins / Zone / Sugar Busters / South Beach type diets in the first three to six months, but weight loss is similar to low-fat, high carbohydrate diets when the studies are longer.

Eating well and eating healthy is about balance. It is not about giving up anything, but about using great fresh ingredients to make food that is delicious and satisfying. It’s pretty easy to reduce the amount of fat in the diet and not give up great flavor, but it is hard to replace great pasta, rice, potatoes, couscous, beans and fruit and eat great food. The research says that giving up carbohydrates isn’t the answer—but that eating a great balance of foods is.