Here's an interesting meta-analysis demonstrating that during weight loss, different dietary intakes can impact the proportion of fat mass, lean mass, etc lost.
Effects of variation in protein and carbohydrate intake on body mass and composition during energy restriction: a meta-regression 1 ,2 ,3
James W Krieger1, Harry S Sitren1, Michael J Daniels1 and Bobbi Langkamp-Henken1
1 From the Departments of Food Science and Human Nutrition (JWK, HSS, and BL-H) and of Statistics (MJD), University of Florida, Gainesville, FL.
Background: It is unclear whether low-carbohydrate, high-protein, weight-loss diets benefit body mass and composition beyond energy restriction alone.
Objective: The objective was to use meta-regression to determine the effects of variations in protein and carbohydrate intakes on body mass and composition during energy restriction.
Design: English-language studies with a dietary intervention of 4200 kJ/d (1000 kcal/d), with a duration of 4 wk, and conducted in subjects aged 19 y were considered eligible for inclusion. A self-reported intake in conjunction with a biological marker of macronutrient intake was required as a minimum level of dietary control. A total of 87 studies comprising 165 intervention groups met the inclusion criteria.
Results: After control for energy intake, diets consisting of less than or equal to 35?41.4% energy from carbohydrate were associated with a 1.74 kg greater loss of body mass, a 0.69 kg greater loss of fat-free mass, a 1.29% greater loss in percentage body fat, and a 2.05 kg greater loss of fat mass than were diets with a higher percentage of energy from carbohydrate. In studies that were conducted for >12 wk, these differences increased to 6.56 kg, 1.74 kg, 3.55%, and 5.57 kg, respectively. Protein intakes of >1.05 g/kg were associated with 0.60 kg additional fat-free mass retention compared with diets with protein intakes 1.05 g/kg. In studies conducted for >12 wk, this difference increased to 1.21 kg. No significant effects of protein intake on loss of either body mass or fat mass were observed.
Conclusion: Low-carbohydrate, high-protein diets favorably affect body mass and composition independent of energy intake, which in part supports the proposed metabolic advantage of these diets.
For the record, Meta-Analysis isn't definative as all of the studies included had methodological differences and likely many design flaws. But Meta-Analysis does give us a general survey of the literature in a specific area and a review of what direction the literature points.
This review does point to the fact that perhaps calorie intake isn't the only important thing in governing the type of weight gained or lost with energy restriction.