Low-carb dieting has been all the rage in Norway recently – not only depleting butter stores but also with likely detriment to people’s overall health, cardiovascular health, and fitness. Bearing this in mind, a paper by Bray and colleagues published in the latest issue of JAMA seems particularly relevant and adds to our understanding of metabolic efficiency and the role of individual nutrients in weight gain.
The prospect of preventing weight gain simply by changing the nutrient composition of what you eat is beguiling. In the past, studies have indicated that a low protein content might mitigate the effects of overeating. But as they say, if it sounds too good to be true, it probably is too good to be true. Bray and colleagues performed a blind, randomized controlled study to see what effect the protein content of a diet would have on weight gain, energy expenditure and body composition in average people.
The researchers chose 25 healthy, weight-stable men and women between 18 and 35, all non-smokers and physically inactive. After determining their normal metabolic demands, the participants were randomly assigned to three different groups; low protein, normal protein or high protein diets, with respectively 5%, 15% and 25% of the energy coming from proteins. The carbohydrate content was kept constant at 41%, and the fat content was varied so all the diets were isocaloric. The participants were housed in the metabolic unit and overfed for 8 weeks, where they were given roughly 40% more calories than they needed, which corresponded to an increase by approximately 950 kcals per day.
Through the use of a controlled environment and rigorous statistical analysis, they found several very interesting results:
- All participants gained weight, and there were no differences by sex or race. On average the participants in the low-protein group gained 3 kg, and the normal and high-protein groups gained 6 kg and 6.5 kg, respectively. The rate of weight gain in the low protein group was significantly lower than in the other two groups.
- The overall increase in fat mass did not differ significantly between the groups. They all gained approximately 3.5 kg, with the low protein group adding on average more than 200g of fat, corresponding to roughly 2000 kcal.
- The lean body mass increased in the normal and high protein groups, and decreased in the low protein group. The loss of lean mass was roughly 0.7 kg for the low group, and the gain was respectively 2.9 and 2.3 kg for the normal and high groups.
- Overeating led to a significant increase in resting energy expenditure in both normal and high protein groups starting soon after the overeating began. By contrast the resting energy in the low protein group did not change. The total energy expenditure also increased significantly in the normal and high protein groups compared to the low protein group.
- The changes in body composition were able to account for the changes in energy expenditure. The smaller weight gain in the low protein group was accounted for by their failure to increase lean body mass. It was found that the low protein group was below the protein intake required to prevent the loss of lean body mass by approximately 40 %.
Low protein – loss of muscle and slowed metabolism
Although a cursory glance at the results might give the impression that a low protein diet is significantly better for controlling your weight and improving your health, the opposite is in fact true. Bray concludes,
“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.”
There was no significant difference between the energy expenditure and energy intake between participants in the three groups, and they all gained the same amount of body fat.
While the weight gain was blunted on a low protein diet, it came at a cost; more than 90% of the excess energy was stored as fat on a low protein diet, compared to 50% in the other groups. Additionally the loss of lean body mass – essentially muscle – is detrimental and a very undesirable result of dieting. The coup de grace for the low protein diet was the fact that the metabolism slowed when overeating on a low protein diet as opposed to accelerating on a normal or high diet. It begs the question, if muscle breakdown and a slowed metabolism isn’t a recipe for obesity, what is?
The carb connection: low protein = high fat
To tie it all back to Norway’s (hopefully) dying low carb fad, this rigorous study potentially carries a strong message. While the carbohydrate content was kept the same between the three groups, the fat content varied inversely with the amount of protein. In a sense, the low-protein group essentially was a high-fat group too. Might not the results have some bearing on the high fat component so often found to accompany a low carb diet? In the past, both animal models and epidemiological studies have shown a relation between high fat diets and the development of insulin resistance.
While the study showed that the protein composition of diet has an effect on weight gain and that it is too simplistic to treat all nutrients as equal, ultimately it was the energy balance – the caloric intake – that determined the increase in body fat. This leaves us with a chilling thought, courtesy of Time. The participants consumed an excess of roughly 50,000 calories over the course of 56 days, and gained an equal amount of weight in 8 weeks than an average person gains over the course of 10 years. If you divide that all out, that means it only takes an excess of 100 kcal per week if all else remains the same.
But remember, all else need not remain the same – the choice is up to you! The study used couch potatoes who never exercised. But you can do better! If your motivation drops, remind yourself of the many benefits of exercise over the course of a long life, not the least of which is upping your metabolism so you can eat that extra cookie without guilt.
Written by Hanna Sofie Ellingsen at CERG.