Last night I came across a news story comparing calories vs protein intake in regards to weight gain. I went to the news story only to find out who the authors were and where the study was published. I found it today and it is available free for anyone to read by clicking on this link.
I did not keep the link to the news paper story but you could probably find it easily through a web search. It is a little complicated - three groups of people ate an additional 900 or so calories from their stable baseline, but different amounts of fat and protein within that same calorie amount.
One of the groups gained less weight (pounds), but the other two gained leaned body mass. The extra calories seemed to turn into fat and were provided as fat. The amount of protein did not impact weight gain, but it does appear that one of the groups increased what is called metabolic efficiency. This is a number - a ratio - determined by the increase in calories divided by the number of pounds gained. Thus having a low denomenator (fewer pounds gained) creates a higher 'score' indicating efficiency. The weird thing is that the group which gained the least and had the greatest score, lost lean mass whereas the less efficient groups gained lean mass!
But what I really wanted to tell you about was the intricate details of the study because the news paper article doesn't give the low down. Trust me that what they did in the lab - well - it won't be happening at your house!
First there were only 25 people in the whole study and these people were put into one of three conditions so that each group had less than 10 people in it. (in research the best studies are said to be controlled - but they are expensive and use fewer people - another marker of good research is having a large amount of subjects! It is hard to get both of these things)
There were men and women in the experiment and they were between the ages of 18 and 35. More participants were black than white and all lived in Louisiana. They all had normal BMIs at the start of the study.
The participants stayed in the center for the duration of the project. The scientists used fancy, expensive and ultra sensitive equipment to determine each persons total energy intake, as well as resting, non resting and total energy expenditure. The scientists then fed each person the amount of calories necessary to make sure their baseline weight remained stable (the test lasted four days). Stable meant that the weight could not fluctuate more than 2 pounds. They tried this up to three times and if the weight wasn't stable when everything else was being held constant - the people were sent home (:(.
(During the study, the meals were prepared by the 'metabolic kitchen' staff and sent to a lab for analysis - later in the study, when the people were put into separate groups, the people and the scientists who measured their body changes did NOT know who was getting which protein amount- in other words, it was "blind.")
During the stabilization phase, the caloric amounts were the same and the breakdown of macro nutrients was protein 15%, fat 25% and carbs 60%. The people were then randomized into the three groups - low, normal and high protein intake.
The carbohydrate amount was not manipulated and stayed around 40% of total calories for all three groups. The low protein group had 47g protein per day (6% of total cals) with 52% calories from fat, the normal protein had 15% and 44% fat while the high protein (228g) or 26% of total cals and 33% from fat. They all started off at about 2400 calories a day and added 900 cals a day in the 8 weeks of overfeeding.
If you look at the information above carefully, you can see what the problem may be. The groups did not only change protein - they changed fat percent as well and the low protein group ate the most fat. They also gained on average 6 pounds compared to 12+ pounds for the other two groups. They ate more calories from fat but gained the least pounds. The other groups gained more pounds, but also gained lean tissue mass.
The conclusion offered by the researchers - calories impact fat storage while protein impacts energy expenditure (burn) and lean body mass - do not carry over to practical application, that I can see. I.e the group with a higher energy expenditure at rest still gained more weight.
We know from this study that if you eat more calories than you need you will gain weight (which is old news). It also looks like the amount of calories that you consume in fat grams will have a negative impact on body composition and metabolism (this is related to how nutrients in fat are metabolized and is beyond the scope of this blog).
The problem with the outcome is that the low protein group did not increase their total expenditure (where as the other two did [no group changed activity level - this is all related to the intake]) and still the low protein group gained the least amount of weight.
Other studies have noted that over time, if people continue to overconsume, the increase energy burn from the protein increase will abate and they too would stop gaining lean tissue.
PS - the participants stayed in the lab an extra day or two after the overfeeding to get their cals back to normal.
PSS - this was a very well controlled laboratory experiment! and super fun to read and there are lots of charts you can see in the actual study if you go to the journal article.