Diet and diabetes: how does a low fat diet compare with a low carbohydrate diet?

A Journal of the ADA

As long as you are going to deny yourself you might as well go for your best shot at weight loss. While you are at it, reducing blood glucose levels would be a good thing to optimize as well. Carbohydrates are big sources of dietary sugar so it would make sense to think that a diet which reduced the intake of this food type would be superior. Indeed this was the hypothesis of Dr. Nichola Davis and colleagues. They tested this hypothesis over the course of a year and published the results in the July issue of Diabetes Care.

The authors point out that historically, studies of low carbohydrate diets have been shown to work as well as other diets for non-diabetic individuals for losing weight. Additionally, short term low carbohydrate diets for people with type 2 diabetes has been shown to reduce postprandial hyperglycemia and improve insulin sensitivity. Glycemic control was improved in both short term and long term studies. However, a caveat to all of this work is that the studies were all generally done on small populations with little in the way of control groups and often for short observational periods. The goal of this study was to perform a larger randomized clinical trial over the course of a full year to better compare the results of a low carbohydrate diet to a low fat diet.

One hundred and five patients entered the study and were randomized to either receive a low fat diet or a low carbohydrate diet for a period of 1 year. The low carbohydrate diet was based on the Atkins diet. All patients were overweight with an average BMI of 36 (considered obese). The patients received nutrition counseling along with a gram allowance of carbohydrates or fat and structured menus with recipes for the first two weeks. Subsequently, the patients were given instruction in food selection that allowed them to meet their dietary goals. They met with the dietitian every two months. Diabetes medications were also adjusted to avoid inadvertent weight gain.

So what happened? Well, initially patients on the low carbohydrate diet did much better than the patients on the low fat diet. At 3 months they dropped their hemoglobin A1C levels by an average of 0.64% while the low fat group dropped their A1C by 0.26%. Weight loss was also better. The low carbohydrate diet resulted in an average loss of 11.4 pounds while the low fat diet resulted in a loss of 7 pounds. Interestingly, by one year, the low fat diet resulted in equal weight loss which ultimately was modest and A1C levels were unchanged from the beginning of the study.

While the authors limited their conclusion to the observation that these two diets had similar effects one could go a step further. Certainly the patients perceived themselves to have undergone deprivation for a year and had little to show for it. The study deliberately did not promote exercise as it was focused on the effects of diet and the population was clearly sedentary. The bottom line is that weight loss requires tremendous motivation. As mentioned in an earlier article, the body tries really hard to stay at its current weight and uses every metabolic and psychological trick in the book to make you break your diet. Exercise alone cannot succeed as the amount of work that an untrained overweight body can accomplish is minimal. What is needed is an entire lifestyle change similar to the Dean Ornish method for dealing with heart disease. For example, if you have friends who have successfully lost some weight and are continuing to lose weight and you see them a lot, you are much more likely to succeed in your diet as you now have that all important motivation: the respect of your friends. Additionally, you are likely to share recipes and get useful tips. If your friends exercise together and you exercise with them it becomes socializing and exercise becomes desirable. So perhaps, to lose weight, what one needs are a few close friends who have the same goal. Mutual friendship, respect, and affection will drive each person to succeed together rather than to fail alone.