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.
Krieger
James W
JW
Department of Food Science and Human Nutrition and of Statistics, University of Florida, Gainesville, FL 32611-0370, USA.
Sitren
Harry S
HS
Daniels
Michael J
MJ
Langkamp-Henken
Bobbi
B
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