The problem is that there are currently many fad diets and diet supplements that claim to change total body weight and waist circumference. However, the aim of any weight loss attempt is the reduction of fat mass rather than lean mass. The standard measurement for overall body weight change gives total mass lost with no distinction between fat mass and lean mass. It is known that a diet that consists of decreased calorie intake and exercise leads to body-composition changes. Visceral adipose tissue (abdominal fat around the organs) is considered to be “bad fat” because it is associated with obesity complications (especially cardiovascular disease in the elderly).
The researchers of this study were interested in comparing changes in total and visceral fat mass and lean mass with diets that varied in macronutrient composition: fat, protein and carbohydrates. There have been other studies to look at weight loss and its effect on uptake of liver fat. A caloric restriction has been shown to increase liver insulin sensitivity (ability for insulin to allow cells to uptake glucose for energy).
The participants included men and women who were 30–70 years of age and have a BMI between 25 and 40.
The following 4 diets were tested in this study: 1) a low-fat, average-protein diet 2) a low-fat, high-protein diet 3) a high-fat, average-protein diet and 4) a high-fat, high- protein diet. Each participant was asked to consume 750 kcal fewer than their estimated energy requirements each day for 2 years. The dietary intake of 50% of the participants was assessed at 6 months and at a 2-year follow-up.
It was found that reduction of total energy intake was the most important determinant for fat loss and the particular macronutrient content of the diet was not as significant. The same amount of weight loss of about 10 pounds was seen in all four diets. An interesting finding was that overall, women lost more fat than men. A reduction of total calorie intake of the participant resulted in a greater weight loss; each of the four diets had a similar effect on lean mass and fat mass loss. However, it was found that any participant that lost weight decreased liver fat deposits.
The limitations of the study were that not all participants were able to meet the macronutrient target that was asked of them, especially after 6 months. However, this is a normal limitation in studies that were done previously. There was also a 20% dropout rate from the participants, but the dropouts were fewer than in previous trials.
The implications of this study are that the loss of body fat, abdominal fat, and liver fat are dependent on calorie intake. The macronutrient composition of the diet does not play a significant role in changes of body composition in overweight or obese individuals.
The full report is titled “Effects of 4 weight-loss diets differing in fat, protein and carbohydrate on fat mass, lean mass, visceral adipose tissues and hepatic fat: results from the POUNDS LOST trial”. It is in the 18 January 2012 issue of the American Journal of Clinical Nutrition (volume 95, pages 614-25). The authors are Russell J de Souza, George A Bray, Vincent J Carey, Kevin D Hall, Meryl S LeBoff, Catherine M Loria, Nancy M Laranjo, Frank M Sacks, and Steven R Smith.
Written by Diana Naser and Samantha Nuzio, Dept. Nutritional Sciences, Rutgers University-NewBrunswick Edited by SA Shapses PhD, RD