Protein and weight loss (I)
In this post, we will briefly summarize the study of Weigle et al. (2005).
For this study 19 healthy participants (age = 41 ± 11, body mass = 72 ± 8.9, BMI = 26.2 ± 2.1) where recruited. They underwent 3 macronutrient configurations during 3 different but continuous periods of time.
1st period: for 2 weeks they were provided a weight maintenance diet, with 50% of the energy intake from carbohydrates (CHO), 15% from protein (PRO) and 35% from fat. Participants were asked to eat all the food they were provided to reach a fixed caloric intake.
2nd period: for another 2 weeks participants were provided with another weight maintenance diet, this time with an increased intake of protein and a subsequent reduction of fat (50% CHO, 30% PRO, 20% FAT). Again, participants were asked to eat all the food they were provided to reach a fixed caloric intake.
3rd period: for 12 weeks participants were provided with ad libitum (eat as much as you feel like) diet (50% CHO, 30% PRO, 20% FAT).
What they observed is that although the diets were isocaloric (same caloric intake) during the 1st and the 2nd period, the increased protein intake (2nd period) lead to an increase in the feeling of fullness and a reduction of hunger. However, this did not imply any weight loss.
Later, during the 3rd period, participants could eat as much as they wanted. One would have expected to probably observe an increase in the caloric intake, but this was not the case. Although hunger and fullness were not as affected as during the 2nd period, they seemed to play an important role during the last 12 weeks of the study. This could explain how average caloric intake was reduced and so it was body mass. Body composition was assessed by dual-energy x-ray absorptiometry (“gold standard” method). It is worth noting that the main contributor to weight loss was fat mass and not lean body mass (LBM) (which includes among others muscle mass). This point is important because generally, the term weight loss does not specify whether we talk about fat mass or LBM. We could say that our LBM is our life insurance, so losing weight at its expense should be avoided at all cost. Reached this point we now understand that out bathroom scale can be quite deceitful (it can’t measure our body composition).
In this great paper, Weigle et al. (2005) analysed many other variables at different time points such as resting metabolic rate, glucose, insulin, ghrelin, leptin… So, if you want to take a deeper look at it, we invite you to read some science.
Weigle, D. S., Breen, P. A., Matthys, C. C., Callahan, H. S., Meeuws, K. E., Burden, V. R., & Purnell, J. Q. (2005). A high-protein diet induces sustained reductions in appetite, ad libitum caloric intake, and body weight despite compensatory changes in diurnal plasma leptin and ghrelin concentrations. Am J Clin Nutr, 82(1), 41-48. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/16002798