Anyone who has any interest in weight loss knows there has been a long-running debate regarding the primary factor that causes weight gain. Go to the weight-loss section of any bookstore and you will see the calorie, fat, carbohydrate and protein camps, each of whom insists they are the key to weight loss.
However, when I retrieve and read the evidence, I often find flaws based on lack of control regarding subject supervision. Occasionally I will come across a study that is well-controlled, but they are always short since it isn’t practical to have people live in a lab for more than a few days.
Therefore, I was intrigued when I read about a study that paid people to live in a metabolic setting for three months. By allowing researchers to measure every unit of energy expenditure, the result would be expected to be much more accurate than the typical questionnaire-based study or three days in a laboratory type of experiment.
The study researchers, based in Florida and Louisiana, hired 25 people (16 men and nine women) ages 18 to 35 with body mass indexes ranging from normal weight to overweight. They were then studied for 14-28 days to establish their exact calorie amount required for body-weight stabilization. Then the subjects spent eight weeks eating one of three diets that provided 40 percent more energy than they required. All three diets averaged 934 additional calories. See Table 1 for the macronutrient breakdown.
|Table 1: Macronutrient Profile of Neutral and High-Calorie Diets|
|Diet||Protein (%)||Carbs (%)||Fat (%)|
|Stabilization (neutral calorie)||15%||60%||25%|
|High calorie 1||6%||42%||52%|
|High calorie 2||15%||41%||44%|
|High calorie 3||26%||41%||33%|
Each of the three weight-gain diets differed by protein and fat percentage, while carbohydrates and total calories remained stable. The researchers wanted to see if macronutrient manipulation with the same amount of excessive calories would cause differences in the amount of weight gain. Results are summarized in Table 2.
|Table 2: Body Weight, Lean Mass and Fat Mass Changes After Eight Weeks of Overeating|
|High-Calorie Diet||Body Weight (lbs)||Lean Mass (lbs)||Fat Mass (lbs)|
|Diet 1 (low protein)||+7.0 lbs||-1.5 lbs||+8.0 lbs|
|Diet 2 (moderate protein)||+13.3 lbs||+6.3 lbs||+7.6 lbs|
|Diet 3 (high protein)||+14.3 lbs||+7.0 lbs||+7.6 lbs|
The results of this study were a real eye opener, as table 2 demonstrates. The findings were:
- To gain body fat, the type of calorie makes little difference when a person eats more than they need.
- To gain body weight, which includes muscle and fat, extra protein will add muscle even without exercise.
- The average amount of protein in grams does not make much difference once the requirements are met. (Table 3)
|Table 3: Average Protein Intake Per Day, Per Diet|
|Stabilization phase||90 g|
|Diet 1 (low protein)||47 g|
|Diet 2 (normal protein)||139 g|
|Diet 3 (high protein)||228 g|
|Maintain lean body mass*||78 g|
|*Calculated by the authors as the amount of protein required to prevent loss of muscle.|
The subjects were all closely monitored and did not exercise, although they did expend energy on activities of normal living. These results were from eating too much; they support strategies recommend higher percentages of dietary protein when total calories are insufficient because we diet to lose fat, not muscle.
- Bay GA. Smith SR. et al. Effect of dietary protein content on weight gain, energy expenditure and body composition: a randomized controlled trial. JAMA, 2012;307(1):47-55.
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