I make no secret of the fact that I favour protein-rich diets, particularly where weight loss and weight maintenance is concerned. Only last month I highlighted a study which found that a protein-rich diet was better for maintaining weight loss than a diet rich in carbohydrate.
In this particular study, the protein-rich diet had been supplemented with either casein or whey-derived protein. I was therefore interested to read a recently-published study which used two different amounts of casein to see what effect this had on a range of measurements that have some relationship to body weight .
In this study, 24 adults (average age 25) were tested with two different diets on separate days. One of these contained more protein and less fat than the other. The protein rich diet had 25 per cent of calories in the form of protein (casein), with 20 and 55 per cent of calories coming from fat and carbohydrate respectively. The lower protein diet had just 10 per cent of calories coming from protein, with fat and carb making up 35 and 55 per cent of calories respectively. For each of the study subjects, total calorie intake was the same on each diet.
For each diet, individuals spent 36 hours living in a ‘respiration chamber’, which allowed analysis of a range of things including energy expenditure and metabolic rate. The higher protein diet, compared to the lower-protein one, led to higher total energy expenditure, which seemed to be related to a higher metabolic rate during sleep.
These findings strongly suggest that when it comes to the impact food has on body weight, it’s more than mere calories that count. The form of the calories in this study appeared to have a significant impact on metabolic rate, and this has clear and important implications for those who are seeking to lose weight or maintain a healthy weight.
The setting of this study was very controlled, and really does not mimic what happens in the real world. However, it does clearly show that there may be some ‘metabolic advantage’ in eating a diet rich in protein if weight loss is the aim. Eating a diet rich in protein may help to enhance the rate at which protein is broken down and remade in the body (protein turnover), and this may have a positive influence on metabolic rate . In addition, a protein rich diet helps to preserve muscle mass, which also helps to maintain metabolic rate.
While the form of calories appears important in terms of its impact on body weight, the total number of calories also has some bearing here. Interestingly, the higher protein diet utilised in this study was found to be more satisfying than the lower protein one, echoing previous work which has found that protein has generally greater appetite-sating effect than carbohydrate or fat. Again, the implications of this with regard to weight loss are obvious.
1. Hochstenbach-Waelen A, et al. Comparison of 2 diets with either 25% or 10% of energy as casein on energy expenditure, substrate balance, and appetite profile
AJCN. Epub ahead of print 28 January 2009
2. Krieger JW, et al. Effects of variation in protein and carbohydrate intake on body mass and composition during energy restriction. Am J Clin Nutr 2006;83(2):260-74