PROTEIN




















Weight Loss with Diets of Different Fat, Protein, and Carbohydrate Composition, NEJM (2009) [PubMed abstract]
  • A study in the NEJM enrolled 811 overweight adults
Main inclusion criteria
  • Age 30 - 70 years
  • BMI 25 - 40
Main exclusion criteria
  • Diabetes
  • Unstable cardiovascular disease
  • Use of medications that affect body weight
Baseline characteristics
  • Average age 51 years
  • Average BMI - 33
  • Female sex - 64%
  • Average weight - 205 lbs (93 kg)
Randomized treatment groups
  • Diet 1 - Low-fat, average-protein (204 patients) - 20% fat, 15% protein, and 65% carbohydrates
  • Diet 2 - Low-fat, high-protein (202 patients) - 20% fat, 25% protein, and 55% carbohydrates
  • Diet 3 - High-fat, average-protein (204 patients) - 40% fat, 15% protein, and 45% carbohydrates
  • Diet 4 - High-fat, high-protein (201 patients) - 40% fat, 25% protein, and 35% carbohydrates
  • Participants received continuous dietary counseling via group and individual sessions throughout the study. Daily meal plans were provided.
  • Participants were given individual caloric goals that provided a 750 kcal/day deficit
  • The study had a 2X2 factorial design that compared the low vs high fat diets and average vs high protein diets
Primary outcome: Weight loss at 2 years
Results

Duration: 2 years
Outcome High-protein Average-protein High-fat Low-fat Comparisons
Primary outcome 7.9 lbs 6.6 lbs 7.2 lbs 7.2 lbs p=0.22 for protein | p=0.94 for fat
  • There was no difference between the diets in patient reported cravings, fullness, hunger, and diet satisfaction scores
  • Participants in all groups did not reach their target macronutrient composition but did have changes in biomarkers (urinary nitrogen, respiratory quotient) from baseline that showed they modified their macronutrient intake in the direction of their goals
  • 80% of the participants completed the study

Findings: Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize
Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition, JAMA (2012) [PubMed abstract]
  • A study in JAMA enrolled 28 healthy people into an inpatient metabolic unit
Main inclusion criteria
  • Age 18 - 35 years
  • BMI 19 - 30
Main exclusion criteria
  • Smoker
Baseline characteristics
  • Average age - 24 years
  • Male sex - 64%
  • Black race - 64%
Randomized treatment groups
  • During the first phase, subjects were fed a weight-stabilizing (isocaloric) diet for 13 - 25 days
  • Subjects then entered a second phase for 8 weeks where they were overfed by about 950 calories a day
For the second phase, patients were randomized to 1 of 3 diets:
  • Group 1 - Low-protein diet (10 patients) - 6% of calories from protein, 52% from fat, and 42% from carbohydrates
  • Group 2 - Normal-protein diet (9 patients) - 15% of calories from protein, 44% from fat, and 41% from carbohydrates
  • Group 3 - High-protein diet (9 patients) - 26% of calories from protein, 33% from fat, and 41% from carbohydrates
Primary outcome: Change in body weight, body composition (measured by dual-energy x-ray absorptiometry), and calorie expenditure (measured by ventilated hood and doubly labeled water) from baseline to Week 7 - 8 of overfeeding
Results

Duration: 8 weeks
Outcome Low-protein Normal-protein High-protein Comparisons
Increase in body weight 7 lbs 13.3 lbs 14.3 lbs 1 vs 2 and 3 p=0.002
Increase in fat mass 8.1 lbs 7.6 lbs 7.6 lbs 1 vs 2 vs 3 p=0.91
Change in lean body mass -1.54 lbs +6.3 lbs +7.0 lbs 1 vs 2 and 3 p<0.001
Change in total energy expenditure +176 kJ/d +2186 kJ/d +1898 kJ/d 1 vs 2 and 3 p=0.007
Change in resting energy expenditure -86 kJ/d +669 kJ/d +949 kJ/d 1 vs 2 and 3 p<0.001
Change in nonresting energy expenditure +245 kJ/d +1296 kJ/d +756 kJ/d 1 vs 2 vs 3 p=0.24

Findings: Among persons living in a controlled setting, calories alone account for the increase in fat; protein affected energy expenditure and storage of lean body mass, but not body fat storage.