Emmaline studies Dietetics and Kinesiology at the University of Illinois at Chicago and will be eligible to sit for the registered dietitian exam in December of 2012. She is an avid food and nutrition enthusiast as well as a certified yoga teacher.
In a nation where the number of overweight and obese individuals is rampant enough to be referred to as an “epidemic,” coupled with an aesthetic culture that emphasizes weight, it is of no surprise that many adults have contemplated or attempted weight loss at some point in their lives. While energy-restricted diets can elicit substantial weight loss and provide associated favorable benefits on cardiometabolic risk factors(1), the potential effects of the macronutrient profile in an energy-restricted diet prescription on these outcomes should not be discounted.
A cornerstone of energy-restricted diets for the treatment of obesity is the attention to low fat intake, yet there has been an apparent lack of definitive evidence or analysis that specifically evaluates the potential effects of a modified carbohydrate:protein ratio in controlled and structured studies matched for energy-restriction level. Recently, the American Journal of Clinical Nutrition published ameta-analysis of 24 randomized controlled trials that evaluated the effects of high and standard protein diet prescriptions on weight loss, body composition, resting energy expenditure (REE), and cardiometabolic risk markers in isocalorically restricted low fat diets. Based on exclusion criteria, there were a total of 520 high protein (HP) and 542 standard protein (SP) participants (N= 1063).
Findings of the meta-analysis revealed that the high protein diets elicited a small but significant 0.79 kg greater weight loss than standard protein diets. Additionally, there were favorable effects on body composition as demonstrated by greater loss of fat mass with mitigated reductions in fat free mass and REE. Reductions in triglyceride levels were significant in the group consuming a high protein diet as well. Though only 5 of the studies included in the analysis evaluated satiety as an outcome, it is noteworthy that greater satiety was reported in 3 of the 5 studies among the high protein group.
A 0.79 kg difference in weight loss may seem modest; however, it is significant that in the high protein group a relatively larger portion of the weight lost was fat mass, with a greater preservation of fat free mass. Fat free mass—specifically skeletal muscle—is the primary metabolically active tissue in the body, which draws a potential connection between the mitigated decrease in REE and the relative preservation of fat free mass seen in the high protein group.
Because loss of fat free mass typically contributes to approximately 20% of total diet-induced weight loss (2), macronutrient distribution—with special attention to protein intake—could be paramount in both mediating and augmenting certain outcomes of weight loss and subsequent maintenance.
Knowing there are many factors that may impact results, the study does show modest benefits in areas of interest, especially as we look forward to more long term studies.