Traditional wisdom about dieting has always said that limiting the calories going into the body or increasing the calories going out of the body will allow the dieter to lose weight. This can be accomplished by eating less, and thus decreasing calorie intake. Alternatively, participating in activities that require a lot of energy will increase the amount of calories going out. In recent years, it has been proposed that not only decreasing caloric intake but also modifying the type of calories that are consumed will help in weight loss. Dr. Robert Atkins was one of the very first proponents of modifying the type of calories in a diet to increase weight loss. The Atkins diet consists of a low carbohydrate, high fat, high protein diet that ultimately has a ketogenic effect. The Atkins diet has become extremely popular because of the success that the dieters have in losing weight.
Researchers working at Children’s Hospital Boston and Brigham and Women’s Hospital, lead by Dr. David Ludwig, have studied the effect of various diets on the weight maintenance phase of weight loss and have found that diets high in fat and protein and low in carbohydrates allow weight that is lost to remain off. The results of their study are published in the Journal of the American Medical Association. The investigators studied 21 overweight and obese adults after they had lost 10-15% of their weight to determine the type of diet that would allow them to keep the weight off. Three diets were used: a low fat diet, a low carbohydrate diet, and a low glycemic diet. The low carbohydrate diet was similar to the Atkins diet. The low glycemic diet had fruits and vegetables but was designed so that high blood sugar spikes did not occur. The researchers found that during the weight maintenance phase of dieting, when the dieters were trying not to regain the weight, the low carbohydrate diet produced the best results. When the dieters used the low carbohydrate diet, measurement of energy expenditure showed that their bodies burned an additional 300 calories compared when they used the low fat diet. That is equivalent to one hour of exercise per day, without actually having to exercise. This difference was obtained by using a low carbohydrate diet instead of a low fat diet alone. The authors of the study wrote that the exact mechanism for this difference was not understood.
We have previously discussed the addictive nature of sugar, and the theories of Dr. Robert Lustig regarding sugar’s toxicity. In a commentary article in the Los Angeles Times, Dr. Robert Lustig is quoted as saying, “To borrow a phrase from Bill Clinton: It’s the insulin, stupid”. His comments were meant to point out the probable mechanism for the success of the low carbohydrate diet in allowing the dieters to keep the weight off in the maintenance phase. Diets that are high in sugar and carbohydrate cause the pancreas to secrete insulin in order to lower blood sugar. Atkins type diets, such as the low carbohydrate diet used in the study, result in the lowest levels of insulin secretion by the pancreas. If we look at the physiological effects of insulin, we will understand why these diets allow us to keep weight off. Insulin is well known for lowering the blood sugar level, and it is used to treat type 1 diabetics and medication resistant type 2 diabetics. Insulin also has several other physiological effects that promote weight gain. Insulin causes glucose storage in the liver, increases lipid synthesis, forces adipose tissue to make fats, decreases lipolysis, and decreases proteolysis.
Thus, the most likely mechanism that allows dieters using low carbohydrate diets to maintain weight loss is by producing low insulin secretion levels. This study is important because it shows that not all calories are equal when dieting and when trying to keep the weight off. One of the key factors may be the insulin levels that a particular diet produces. Future studies should focus on obtaining data to substantiate this hypothesis.
Ebbeling CB, Swain JF, Feldman HA, et al. “Effects of Dietary Composition on Energy Expenditure During Weight-Loss Maintenance” JAMA 2012;307(24):2627-2634. doi:10.1001/jama.2012.6607
Eryn Brown “Robert Lustig on JAMA calorie study: ‘Insulin is the bad guy‘ Los Angeles Times / For the Booster Shots blog June 28, 2012