Effects of variation in protein and carbohydrate intake on body mass and composition during energy restriction: a meta-regression 1.
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.


METHODS
English-language studies with a dietary intervention of > or =4200 kJ/d (1000 kcal/d), with a duration of > or =4 wk, and conducted in subjects aged > or =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 < or =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 < or =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.


CONCLUSIONS
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.
Department of Food Science and Human Nutrition and of Statistics, University of Florida, Gainesville, FL 32611-0370, USA.
James W
JW
Krieger
Harry S
HS
Sitren
Michael J
MJ
Daniels
Bobbi
B
Langkamp-Henken
D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism; D000328:Adult; D000368:Aged; D001823:Body Composition / Q000187:drug effects* / Q000502:physiology; D015992:Body Mass Index; D004038:Diet, Reducing; D004040:Dietary Carbohydrates / Q000008:administration & dosage*; D004044:Dietary Proteins / Q000008:administration & dosage*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D012044:Regression Analysis
D004040:Dietary Carbohydrates; D004044:Dietary Proteins