A lot of people find they can lose excess weight reasonably effectively. However, maintaining that weight loss can be another matter. It’s not uncommon for the pounds that have been shed to slowly return, often with a bit of additional interest too. The reasons for failure in this respect are varied and are perhaps the subject of a separate post, but they include a slide back to less healthy eating, and the fact that caloric restriction can put a dent in the metabolism.
The chronic failure of weight loss diets in the long term have led some doctors and scientists to explore what factors might affect the loss maintenance. One such study was published recently on-line in the American Journal of Clinical Nutrition [1]. In this this piece of research, overweight and obese study subjects (average BMI 39) were subjected to a very low calorie diet (500-550 calories per day ) for three months. At the end of this intervention, average weight loss was 16.5 kg (36 lbs). After this initial phase, the group was then randomised to eat either a high-carb diet or a high-protein diet for a year. The prescribed diets contained 15 and 30 per cent protein respectively. Both groups were advised to keep fat intake to less than 30 per cent of calories. Subjects were advised of the number of calories to consume that, theoretically, should maintain their weight.
During this phase subjects generally gained weight, but still ended up an average of 14.5 kg lighter than their original starting weight. There was no significant difference between the high-protein and high-carb groups, which might lead some to conclude the higher protein diets have no particular merit over lower ones.
However, while one prescribed diet had twice the protein level of the other (30 v 15 per cent), the subjects may have ended up having more similar protein intakes than this. Protein intakes were calculated using food diaries and urine analysis (urea). Average protein intakes were calculated to be 30.2 and 21.7 per cent respectively. However, the number of people completing these tests was very low. And normally, it’s the most compliant individuals that are most motivated to fill out food diaries or have other assessment of compliance.
Other studies have found that higher-protein diets may have some advantages regarding the maintenance of weight loss or fat loss. In one study of similar design to the one above, individuals were put on a low-calorie diet for a month [2]. After this, individuals were split into two groups, one of which had their diet supplemented with 30 g of protein each day over a 6-month period. The protein-supplemented group regained less than 1 kg in weight, compared to 3 kg in the other group. However, none of the weight regained in the protein-supplemented group came in the form of fat. This was not true for the other group, however. Higher protein intake was also associated with a reduction in waist circumference, compared to a gain in the other group.
In another study [3], obese individuals were put on a very low-calorie diet for 5-6 weeks to induce weight loss. After this, though, individuals were instructed to eat a low-fat diet. Some of the individuals supplemented their diet with carbohydrate (in the form of maltodextrin), while others supplemented their diet with protein (50 g of casein or whey protein each day). Individuals could eat as much of their new diet as they liked for a period of 12 weeks, at which point they were assessed in terms of weight and various biochemical measurements.
At the end of the study, compared to the carb-supplemented individuals, those supplemented with protein lost an average of 2.3 kg more. Crucially, this lost weight was almost entirely composed of fat.
Other research had individuals eat either a higher protein (1.6 grams of protein per kg of body weight per day) or lower protein (0.8 grams of protein per kg of body weight per day) for a year [17]. The first four months was designed to provide individuals with a calorie deficit of 500 calories a day, and for the following 8 months the calorie intake was designed for weight maintenance (rather than loss). At the end of the year, while weight loss was not significantly different between the two groups, fat loss was: those on the higher protein diet did better on this measure. As a group, they had improved body composition (more lean body mass and less fat) compared to those eating the lower-protein diet.
This last finding ” improved body composition ” is important. When people lose weight, some of this can be muscle, and this is not generally a good thing. Higher protein diets can reduce the loss of lean mass (including muscle) during weight loss [5].
Overall, there is good evidence, I think, that higher protein diets help weight loss maintenance and lead to improvements in body composition.
References:
1. Delbridge EA, et al One-year weight maintenance after significant weight loss in healthy overweight and obese subjects: does diet composition matter? Am J Clin Nutr 30 September 2009 [epub ahead of print]
2. McAuley KA, et al. Comparison of high-fat and high-protein diets with a high-carbohydrate diet in insulin-resistant obese women. Diabetologia 2005;48(1):8-16
3. Claessens M, et al. The effect of a low-fat, high-protein or high-carbohydrate ad libitum diet on weight loss maintenance and metabolic risk factors. Int J Obes (Lond). 2009;33(3):296-304
4. Layman DK, et al. A Moderate-Protein Diet Produces Sustained Weight Loss and Long-Term Changes in Body Composition and Blood Lipids in Obese Adults. Journal of Nutrition. 2009;139: 514-521
5. Krieger JW, et al. Effects of variation in protein and carbohydrate intake on body mass and composition during energy restriction: a meta-regression 1. Am J Clin Nutr. 2006;83(2):260-274
