Effects of protein intake and gender on body composition changes: a randomized clinical weight loss trial

Journal Title (Medline/Pubmed accepted abbreviation): Nutr. Metab.
Year: 2012
Volume: 9
First Page : 55
doi : 10.1186/1743-7075-9-55

Summary of background and Research Design

Background: Males and females differ in the way that they store excess body fat (generally, men in the trunk/abdomen, women in the thighs/buttocks) due to hormonal influences.  Therefore, the genders may also differ in the best way to lose excess body fat.
Some research suggests that high protein/low carbohydrate diets are more effective at reducing fat mass and retaining lean mass as carbohydrate diets with the same caloric deficit.

Hypothesis: A high protein/low carbohydrate diet would help males more than females lose body fat while retaining lean mass because they typically have a greater amount of lean mass and therefore higher protein requirements.

Subjects: Men (n = 58) and women (n = 72), age 40-56 y, body mass index (BMI) 26 kg/m2 or larger, body weight 140 kg (308 lbs) or larger

Experimental design: Subjects were blocked by BMI and randomized into one of the two groups

Treatments : About 1700 kcal/day for females, 1900 kcal/day for males
Low carbohydrate: protein diet (PRO): 1.6 g protein/kg body weight per day (about 30% energy from protein), 40% carbohydrate, 30% fat.
High carbohydrate: protein diet (CARB): 0.8 g protein/kg/day (about 15% energy from protein, 55% carbohydrate, 30% fat).

Protocol : For 10-20 days (the “baseline period”), the participants followed the dietary habits that they had over the last 6 months and recorded food intake.  After an overnight (12 hour) fast, they were measured for height and weight.  They were then assigned to one of the diet treatments.  The first 4 months of the intervention focused on weight loss while the subsequent 8 months focused on weight maintenance.  Meetings with participants in each treatment group met once per week for one year where they were weighed and provided with education on healthy nutritional and exercise practices.  At 4, 8, and 12 months they were assessed for weight and body composition (using dual energy X-ray absorptiometry, DXA) after an overnight fast.

Summary of Research Findings
  • After 12 months, 18/36 CARB females, 18/30 CARB males, 14/36 PRO females, and 9/28 PRO males dropped out. (reasons not provided; this number was not compared to attrition rates in past weight loss interventions)
  • Total energy intakes were similar between diets.
  • In total, the participants lost 8.2% of their body weight after 4 months and 10.5% of their baseline body weight at 12 months.  There was no significant difference between males and females or PRO vs. CARB.
  • Percent fat decreased for whole body, trunk, and legs with the most fat loss in PRO males (p < 0.01).

Key practice applications

All participants, regardless of gender or diet composition, lost approximately 10% total body mass in 12 months on a calorie-deficit diet.  It is important to consume protein during caloric deficit periods in order to maintain lean muscle mass.  When in search of a weight loss diet, it is most important to choose a diet that you can maintain so that you can maintain celebrated weight loss and prevent oscillating between healthy and unhealthy body compositions.

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