Macronutrient ratios have been extensively investigated in nutritional research, and a growing body of evidence suggests that higher protein and lower carbohydrate diets cause weight loss. This is despite general public health advice that advocates high carbohydrate low protein, low fat diets for overweight and obese individuals. Research suggests that diets containing more than 1.4 grams/kg/d protein, with less that 150 grams per day of carbohydrate, increase fat loss and prevent catabolism of lean mass thereby improving body composition. The main problem with calorie restricted diets is that the weight loss they achieve is often not maintained for long term benefits. High protein diets show promise in maintaining weight loss long term. The exact reasons for this are not know, but improvements in satiety, lean mass maintenance and the thermic effects of protein are all though to contribute.
Researchers1 have investigated the effects of a higher protein diets on weight loss and maintenance in obese individuals. Subjects with a mean age of 45 and a BMI of 32.6kg/m2 were fed a calorie restricted high protein or high carbohydrate diet (-500 kcal/d) for 4 months. The high protein diet consisted of 30% protein (1.6 grams/kg/d), 40% carbohydrate and 30% fat. The high carbohydrate diet contained 15% protein (0.8 grams/kg/d), 55% carbohydrate and 30% fat. After 4 months the weight of the two groups was not statistically different, but the high protein diet group had lost significantly more fat (5.6 kg compared to 4.6kg). During the following 8 months both groups maintained their weight loss such that the high protein group retained their improved body composition compared to the high carbohydrate group. However, more of the carbohydrate group failed to complete the study.
These results suggest that high protein diets are effective in inducing weight loss in obese individuals. Protein may be effective in aiding weight loss because of all the macronutrients it has the greatest thermic effect. Protein is also known to delay gastric emptying which contributes to a feeling of fullness for longer. Because of this increased transit time through the gut, protein can also stabilise blood sugar and lower glycaemic response to carbohydrate foods. Protein is also thought to stimulate the release of a number of gut peptide hormones that are involved in inducing satiety. The fact that more subjects completed the study from the high protein group suggests that high protein diets are easier to follow long term. The high protein diet group also had greater reductions in triglyceride levels and greater increases in HDL cholesterol compared to the carbohydrate diet group suggesting better improvements in cardiovascular health.
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