On many diet plans, as long as you stay within the calorie level provided, the world of food is your oyster. You are free to pick and choose those foods that met your preferences. Sure all credible diet plans talk about healthful eating and provide basic macronutrient guidelines to follow, but the amount and type of nutrients are secondary to the total number of calories consumed. Want to lose weight – eat less and exercise more. Either fewer calories going in or more calories coming out means a new you with fewer pounds.
Lately there have been many studies showing that not all calories are created equal and not all calories are handled in the same way in different people. Now none of this is gospel yet, but now another study by Cara B. Ebbeling, PhD and colleagues at the New Balance Foundation Obesity Prevention Center has stuck an additional pin into the sacred cow of weight loss.
Their study entitled “The Effects of Dietary Composition on Energy Expenditure during Weight-Loss Maintenance” appears in the June edition of Journal of the American Medical Association (JAMA.)
The study focused on resting energy expenditure, or REE, and how it’s affected by different nutrients. REE is a measure of how many calories you need when your body is at rest. The higher your REE the more calories you burn at rest.
Understanding how different nutrients may modify this number is important because weight loss, especially a loss of more than 10 percent of body weight, resets your internal combustion engine to a new lower level .
For example, if you used to weigh 110 pounds and then gained weight, dieted and lost it so that you once again weigh 110 pounds, you would need to consume fewer calories now to maintain your weight than when you previously weighed 110 pounds. Therefore any diet composition that prevents a reduction in REE levels without deleterious side effects is preferable.
The researchers looked at results produced by the nutrient composition of three popular diet types during the maintenance phase of weight loss. First, all of the study participants followed a diet containing 45 percent carbohydrate, 30 percent fat and 25 percent protein for a 12-week period to achieve a reduction in body weight of between 10 and 15 percent.
Once they lost the weight, they were assigned to rotate among three weight maintenance diets in random order. The three diets were a low- fat diet (similar to a Dean Ornish program) with 20 percent of calories provided by fat, a low- glycemic index diet with a GI of 32.9, and a very low- carbohydrate diet (similar to Atkins’) with 10 percent of calories drawn from carbohydrate. Both the very low carbohydrate and low fat diets used nutrient percentages significantly below what people in the general population both with and without diabetes follow.
The results were interesting. Both hormonal parameters and resting energy expenditure were different among the three groups. Participants had the most reduction in REE during the low-fat diet maintenance phase and the least during the very low carbohydrate phase with the low GI diet coming out in-between.
In addition, hormones associated with energy metabolism, such as leptin and thyroid stimulating hormone, were also most favorably influenced by the very low carbohydrate diet.
The very low- carbohydrate diet was NOT the winner however. In addition to maintaining REE and leptin, it increased cortisol levels which are associated with increased fat stores, insulin resistance and cardiovascular disease. Overall the low GI diet maintained REE and hormonal status the best without increasing cortisol levels excessively.
The participants in the study did not have diabetes, but Osama Hamdy, MD, PhD, FACE, Medical Director of the Obesity Clinical Program at Joslin Diabetes Center, thinks these findings relate to people with diabetes as well.
“The major difference in this [well-controlled] study is that the dietary composition suggested for comparison was maintained throughout between the three comparative groups. The results are in line with the Joslin nutrition guidelines for overweight and obese patients, which indicate that a diet lower in carbohydrate load, lower in glycemic index with a modestly higher protein and better quality of fat has greater impact on body weight and other metabolic parameters.”
Now a few upfront caveats—the study wasn’t perfect. It was quite small with only 21 study subjects completing the protocol. The participants were on the maintenance diet only a short time; dietary adherence wasn’t measured, which can throw a wrench in the results. Also, the low glycemic index diet and low fat diet had different carbohydrate percentages so there isn’t a clear way of parsing out the direct effect of the GI from the change in carbohydrate concentration.
And we have no way of knowing if these results are transferable to the real world. The subjects in this study were highly motivated and were monitored over the long haul. Motivation and monitoring have been shown to be effective tools in achieving and maintaining weight loss.
So while these initial findings are potentially valuable, we will have to stay tuned to see if larger, more “real world” follow-up studies yield similar results.