In this post I’m going to examine a recent study (1) concerning the ‘Effect of Dietary Protein Content on Weight Gain, Energy Expenditure and Body Composition During Overeating’. I’ll give a brief overview of the study, it’s results and conclusions, and what I see as limitations in the methodology or interpretations. In Part II, we’ll look at the contrasting interpretations of that study by (Prof) Marion Nestle (2) and (Dr) John Briffa. (3)
This was a randomised controlled trial with intake and expenditure measurement methods with accurate, high-tech instruments. Using a metabolic ward, the researchers measured food intake (set meals, staff on hand to ensure compliance, no sneaking snacks or feeding the cabbage to the dog!), body composition (fat and lean body mass/muscle tissue), resting energy expenditure (base metabolism) and total energy expenditure (metabolism + activity).
The objective of the trial was “to evaluate the effects of overconsumption of low, normal and high protein diets on weight gain, energy expenditure and body composition.”
They took 25 healthy, American, weight-stable male and female volunteers, aged 18 to 35 years with a body mass index between 19 and 30. (Make sure you check out the section on BMI, it’s strengths and limitations below)
After eating a weight-stabilizing diet for 13 to 25 days, participants were randomized to diets containing 5% (low protein), 15% (normal protein), or 25% (high protein) of energy from protein. They were overfed during this last 8 weeks of their 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 about 950 extra calories per day.
The Results were as follows: (showing average changes from baseline)
| Diet Group | Weight gain (kg) | Body fat (kg) | Lean body mass (kg) | Resting energy expenditure | Total energy expenditure |
|---|---|---|---|---|---|
| Low protein | + 3.16 | + 3.66 | – 0.70 | – 20 cal/day | + 42 Cal/day |
| Normal Protein | + 6.05 | + 3.45 | + 2.87 | + 160 Cal/day | + 522 Cal/day |
| High Protein | + 6.51 | + 3.44 | + 3.18 | + 227 Cal/day | + 453 Cal/day |
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.
My take on this study:
The study conclusion represents the results. My question is – are they asking the right questions?
This study shows that if you gorge yourself – you’ll gain weight. Is weight quantity or quality what’s important? (Check out Mariusz below) The weight gain in the low protein group was only from increased body fat, whereas those in the normal and high protein groups also gained lean body mass and improved energy expenditure.
Are 25 people divided into 3 groups a large enough sample to give us meaningful results that can be applied to the general population?
Is a “weight gain through forced overeating” study useful? When are people ever forced to overeat?
Should data on satiety (the feeling of fullness after a meal) have been noted and included in this study? (4)
In this study, the proportion of carbohydrates in the diet are held almost exactly constant (42% in the low protein group, 41% in the medium and high protein group). Isn’t this study equally consistent with the claim that it’s carbs that cause fat?
It would have been nice to see an experiment where carbs, fat, and protein were evaluated, plus a high and low exercise variable. While this study did a great job of controlling variables and measuring results, it seems to fail in the design: Carbs were held constant, and fat level was adjusted to compensate for the variation in protein level. In the “low protein” group, the fat was over 50% of calories. Couldn’t the chart have been labeled “high, medium, and low fat” … and results attributed to fat, not protein?
A calculation of someone’s body fat percentage seems more significant to a determination of what constitutes healthy eating habits than does a calculation of what that person weighs in the absolute.
This study shows that if you gorge yourself – you’ll gain weight. The question: Is weight quantity or quality what’s important?
Mariusz Pudzianowski - 1.86m, 116kg, BMI 33.5 - No one calls him obese!
Body mass index for adults (5)
Body Mass Index (BMI) is a common method of estimating total amount of fat. A healthy BMI for an adult is considered to be between 20 and 25.
Once BMI is measured, healthy weight range can be determined. If BMI is:
Under 18 – considered very underweight and possibly malnourished.
Under 20 – underweight and could afford to gain a little weight.
20 to 25 – healthy weight range for young and middle-aged adults.
26 to 30 – overweight
Over 30 – obese.
Exception to the rule
BMI does not differentiate between body fat and muscle mass.
Related reading: (PubMed studies)
Protein, weight management, and satiety http://www.ncbi.nlm.nih.gov/pubmed/18469287
Dietary protein, weight loss, and weight maintenance http://www.ncbi.nlm.nih.gov/pubmed/19400750
Protein intake and energy balance http://www.ncbi.nlm.nih.gov/pubmed/18448177
Benefits of high-protein weight loss diets http://www.ncbi.nlm.nih.gov/pubmed/18769212
References:
1. Bray GA, et al. Effect of Dietary Protein Content on Weight Gain, Energy Expenditure, and Body Composition During Overeating – A Randomized Controlled Trial. JAMA 2012;307(1):47-55
2. http://www.foodpolitics.com/2012/01/the-new-study-of-protein-and-weight-gain-calories-count/
3. http://www.drbriffa.com/2012/01/06/new-study-on-protein-and-weight-is-interesting-but-lets-get-to-the-nub-of-the-issue/
4. Protein induced satiety http://www.ncbi.nlm.nih.gov/pubmed/18282589
5. http://www.betterhealth.vic.gov.au/bhcv2/bhcsite.nsf/pages/bmi
6. http://en.wikipedia.org/wiki/Mariusz_Pudzianowski
