If you believe that weight loss is dependent solely on your caloric balance, then you would have lauded the latest study by George Bray, et. al., fresh off the presses at JAMA – get it while you can!: http://jama.ama-assn.org/content/307/1/47.full (PDF here)
Most mainstream media outlets are taking this study as confirmation of the “calories in/calories out” theory – that weight gain/loss is totally dependent on the difference between the calories you eat and the calories you expend each day – and it’s hard to imagine why they wouldn’t. Let’s take a quick look at the parameters of the study:
- 25 people were overfed for 8 weeks to the tune of roughly 40% over their baseline consumption. Meaning, they ate an extra 954 calories each day.
- There were 3 groups: A 6% (low) protein group; a 15% (normal) protein group; and a 25% (high) protein group.
- All groups gained different amounts of weight, but similar amounts of body fat (about 7.7lbs in each group).
Seems pretty cut and dried – despite the amount of protein the groups ate, they ended up gaining the same amount of weight. Let’s pack up for home, right? Wrong. Let’s take a closer look at the data.
One necessary aside: The subjects were overfed for 8 weeks in a metabolic ward (Warning: PDF), which is about as a controlled, lab-rat environment that you can put people participating in a nutrition study in. For those of you unaware of what metabolic ward testing entails, it’s like sleep-a-way camp: There are organized times for data collection and feeding; all you can eat is what the research facility provides; and you get to enjoy all the fun of being cooped up in a “controlled environment“. What this implies is that we can assume the data in this study is legit. No misreporting, no sneaking in a Snickers bar after lights out, no bad food surveys or faulty recall (”What did I have for breakfast yesterday?”) – all their food was measured and prepared in the metabolic unit kitchen.
I’ll save you a whole lot of reading and reprint the Table from the study:
As reported, all three groups had nearly the same amount of gain in Fat Mass (3.66kg, 3.45kg, and 3.44kg) at the end of the study. But look at the differences between groups. The low-protein group lost Lean Mass (read: muscle) and correspondingly impaired their metabolisms, but not by much (see Resting Energy Expenditure, -86.1 kJ/day, which is about 21 calories, if you’re keeping score) whereas the normal and high-protein groups both raised their lean body mass (2.87kg and 3.16kg; 6.3lbs and 7lbs respectively). So even though all groups were consistently overfed by about 1000 calories a day, very different outcomes resulted (and personally I wouldn’t be too happy if I were in the low-protein arm. Gaining fat, losing muscle, and lowering my metabolism are not high priorities on my health watch-list). Since all groups were overeating by the same amount (roughly 954 calories), then according to the calories in/calories out model, shouldn’t they have gained the same amount of weight? If all the surplus calories they ate went to fat storage, then where the heck did all that new muscle come from in the normal and high protein groups?
But wait, there’s more! Check out line item Non-Resting Energy Expenditure. The normal protein nearly doubled their expenditure from a baseline level of 1979 kJ/day (that’s 473 cal/day) to 3275 kJ/day (1979+1296; that’s 782 cal/day). The high protein group also increased their expenditure, by 181 cal/day. The low protein group decided it would be better to kick back a little, raising expenditure by a paltry 59 cal/day (maybe they were tired from the loss of muscle). Now, one wonders what could possibly account for such wild variance. Well, the table has an answer for you: Physical Activity. Although the lead researcher has stated that there was no formalized exercise during the 10-12 week trial, it’s well established that energy expenditure can increase significantly through NEAT (warning: PDF). If the calories in/calories out model held true, wouldn’t the normal and high protein groups have gained less fat than the low protein group, since all 3 groups were eating roughly the same amount of calories, but were burning significantly different amounts of calories?
Is there any way to reconcile the fact that all of the groups gained roughly the same amount of fat? Aside from calories, was there anything else held constant in all three groups? Quoted from the study:
Absolute carbohydrate intake was kept constant throughout the study.
All groups consumed 41% of their calories from carbs – that’s about about 250 grams of carbs per day. And they were exactly the kinds of carbs you’d expect; foods that drive up insulin and promote fat storage:
The eating plans that Bray and his colleagues used included food you’d find in the typical American diet: eggs, bacon, biscuits or cereal for breakfast, for instance; tuna salad, turkey sandwiches and chips for lunch; pasta, rice, pork chops or casserole for dinner, accompanied by salads and fruit; and plenty of baked goods, candy and other processed sweets for snacks and dessert.
So, mystery solved: You could posit that the reason the three groups all gained the same amount of fat is that they were all eating enough carbohydrate to cause high levels of insulin, which would promote fat storage, particularly if you were, say, eating an extra thousand calories a day (which all three groups were). This would neatly explain why the higher protein groups gained muscle while the low protein group lost muscle (and slowed down their metabolisms in the process) and would explain the thorny issue of different energy expenditure (and consequently, different caloric balances) between the three groups.
So we arrive at three conclusions based on Bray’s research:
1) Low intake of protein while overeating seems to have compound negative effects. It slows metabolism and results in loss of lean tissue. So despite what your latest cleanse guru told you, there is a minimum amount of protein intake necessary to “run the ship”, and that minimum is probably higher than the official government recommendations.
2) It’s unlikely that caloric balance was responsible for the similar fat gain between the low, normal, and high protein groups, since the three groups exhibited big differences in expenditure. In other words, the math doesn’t work out. What’s more likely is that similarities in the diet composition (the carb intake, in other words) caused the fat gains to be equal across the groups.
and
3) Always check the data. It’ll tell you what the real story is.
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