Years Later:  Is A Calorie Really A Calorie

George A. Bray, MD; Steven R. Smith, MD; Lilian de Jonge, PhD; Hui Xie, PhD; Jennifer Rood, PhD; Corby K. Martin, PhD; Marlene Most, PhD; Courtney Brock, MS, RD; Susan Mancuso, BSN, RN; Leanne M. Redman, PhD. Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating. JAMA. 2012;307(1):47-55.
Objective To evaluate the effects of overconsumption of low, normal, and high protein diets on weight gain, energy expenditure, and body composition.
Design, Setting, and Participants A single-blind, randomized controlled trial of 25 US healthy, weight-stable male and female volunteers, aged 18 to 35 years with a body mass index between 19 and 30. The first participant was admitted to the inpatient metabolic unit in June 2005 and the last in October 2007.
Intervention After consuming a weight-stabilizing diet for 13 to 25 days, participants were randomized to diets containing 5% of energy from protein (low protein), 15% (normal protein), or 25% (high protein), which they were overfed during the last 8 weeks of their 10- to 12-week stay in the inpatient metabolic unit. Compared with energy intake during the weight stabilization period, the protein diets provided approximately 40% more energy intake, which corresponds to 954 kcal/d (95% CI, 884-1022 kcal/d).
Main Outcome Measures Body composition was measured by dual-energy x-ray absorptiometry biweekly, resting energy expenditure was measured weekly by ventilated hood, and total energy expenditure by doubly labeled water prior to the overeating and weight stabilization periods and at weeks 7 to 8.
Results Overeating produced significantly less weight gain in the low protein diet group (3.16 kg; 95% CI, 1.88-4.44 kg) compared with the normal protein diet group (6.05 kg; 95% CI, 4.84-7.26 kg) or the high protein diet group (6.51 kg; 95% CI, 5.23-7.79 kg) (P = .002). Body fat increased similarly in all 3 protein diet groups and represented 50% to more than 90% of the excess stored calories. Resting energy expenditure, total energy expenditure, and body protein did not increase during overfeeding with the low protein diet. In contrast, resting energy expenditure (normal protein diet: 160 kcal/d [95% CI, 102-218 kcal/d]; high protein diet: 227 kcal/d [95% CI, 165-289 kcal/d]) and body protein (lean body mass) (normal protein diet: 2.87 kg [95% CI, 2.11-3.62 kg]; high protein diet: 3.18 kg [95% CI, 2.37-3.98 kg]) increased significantly with the normal and high protein diets.
Conclusions 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.

Figure 1-4. Changes in Body Weight, Body Fat, and Lean Body Mass During 8 Weeks of Overeating. The blue horizontal lines indicate individual participants. The error bars in the change from baseline graphs indicate 95% confidence intervals. The amount of energy that the subjects in the low protein diet group burned remained stable; in the other two groups the amount rose.

Figure 5. Changes in Resting Energy Expenditure During 8 Weeks of Overeating. The blue horizontal lines indicate individual participants. The error bars in the change from baseline graph indicate 95% confidence intervals.

Figure 6. Relationship of Energy Intake and Protein Intake With Change in Body Fat and Change in Lean Body Mass A higher protein intake resulted in more lean body mass build up, and did not correlate with the growth in fat mass.

In this study 25 healthy, 16 weight-stable males and 9 females aged 18 to 35 years, with a BMI between 19 and 30, were recruited. Researchers wanted to find out if overeating a low or high protein diet would produce less weight gain than overeating a normal protein diet. All the food was provided and participants resided in a metabolic unit for 10 to 12 weeks with no prescribed or regular exercise program. Alcohol and caffeine were prohibited throughout the study and smokers were excluded.

The researchers divided the subjects into three groups. The low protein diet group were given The low protein diet had 6% of energy from protein, 52% from fat, and 42% from carbohydrates. The normal protein diet group got 15% of energy from protein, 44% from fat, and 41% from carbohydrates. The high protein group got 26% of energy from protein, 33% from fat, and 41% from carbohydrates.

The researchers determined how many calories a day we needed for each individual to keep their weight stable. After the subjects reached weight stability they were given 954 calories a day more than they burned for eight weeks.

At the end of the 8 weeks it first appeared that the low protein group had done best. This group had 'only' put on 3.6 kg. The normal protein diet subjects had put on 6.1 kg and the high protein diet subjects had put on 6.5 kg. The subjects in the low-protein diet group had lost 0.7 kg of body weight; the subjects in the normal protein diet group had gained 3.2 kg and the subjects in the high protein diet group had gained 4.0 kg. Once researchers looked in to body composition they found the as protein increased, lean body mass also increased as part of the weight gain. Explaining the weight gains.

The key finding of this study is that calories are more important than protein while consuming excess amounts of energy with respect to increases in body fat. Calories alone, however, contributed to the increase in body fat. In contrast, protein contributed to the changes in energy expenditure and lean body mass, but not to the increase in body fat.

Amazingly enough, the subjects in this study did no exercise. Had they been participating in weight training, the results no doubt would have been even better.