A CALORIE IS A CALORIE? THE DEBATE CONTINUES
Have you heard the latest headlines? All foods are not equal, researchers now say. Too many carbs decrease the metabolism, making it harder to maintain a weight loss. Does this new piece of research lend support to those who favor high protein low carbohydrate diets? Do the flashy headlines accurately describe the science?
In a provocative study published in the June 27th issue of the Journal of the American Medical Association (JAMA) and seized upon by journalists and bloggers, the authors describe their research which was designed to evaluate whether what we eat, calories being equal, can have an impact on whether we will maintain a weight loss. The study design was strong. Subjects were placed on a low calorie diet so that they lost 12.5% of their body weight in 12 weeks. Then in a randomized fashion each subject spent 4 weeks following one of 3 diets, all providing the same number of calories: high glycemic index low fat (20% of calories from fat), low glycemic index high fat (40% of calories from fat), or low carbohydrate high fat (60% of calories from fat). After 4 weeks, each individual switched to another diet and then again to the third so each subject spent 4 weeks on each diet. Energy expenditure was measured at the beginning of the study and after each diet.
It is known that metabolic rate, or the number of calories our body uses to stay alive, decreases after weight loss, and this was indeed what the researchers found. Interestingly, though, they found that the drop was greatest after subjects followed the low fat diet and least following the low carbohydrate diet. The authors concluded that it is not only the number of calories we eat that is important, but also the source of those calories. Noting that the low carbohydrate high protein (and fat) diet increased markers for heart disease, they did not recommend this diet for weight control. Rather, they stated that focusing on glycemic load rather than fat content might be the best way to control weight and reduce risk of heart disease. Meaning cut out the pastries, ice cream, chips and bagels, and focus on more minimally processed foods including whole grains, beans, fruits and vegetables.
Some reporters have taken this to mean that high carbohydrate low fat diets are not the way to manage body weight, and have misled their readers by omitting important aspects of the research. While the researchers did observe a difference in metabolic rate, no one diet improved weight maintenance – all 21 subjects (it was a very small study) maintained their weight loss on each of the diets. Suggesting that a low carbohydrate diet is the best way to maintain weight is speculation. Other aspects of this report to consider include:
- The specifics of the prescribed diet, as well as the subjects’ actual intake, were not reported so we don’t know just which foods they were eating. Researchers commonly find that prescriptions are not rigidly adhered to, affecting study results.
- The study was only 4 weeks long. This does not give us any information about long term adaptations which the body may make.
- The calorie level of the weight loss diet was quite low to enable the loss of about 30 pounds in 12 weeks. This may have affected the results.
- The amount of physical activity and moderate to vigorous intensity exercise was different between trials, which may have affected the results
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And while the low carbohydrate high fat diet lowered metabolism less than the other diets, this came at a huge cost. The researchers observed increases in cortisol and CRP, markers of increased risk of cardiovascular disease, when subjects were on this diet even for this short period of time. The importance of this finding is emphasized by another recent report in which a large (43,396 subjects) long-term (15 years) study found increased cardiovascular events among those who ate less carbohydrate and more protein. Taken together, these results should convince anyone that omitting fruits and whole grains is not the way to achieve health and happiness. We can also not ignore the strong evidence coming from the National Weight Control Registry, where those who have maintained a weight loss of at least 30 pounds for 1 year are tracked. Analyzing the habits of these successful individuals has found that they overwhelmingly maintain their weight loss by eating a low fat diet and engaging in high levels of physical activity averaging 1 hour a day.
So this study, while interesting, does not change the best advice. Anyone hoping to lose weight and maintain that loss would benefit from making regular physical activity of about 1 hour a day an essential part of the equation. Avoiding carbohydrates beyond what is needed to control calories will not improve weight loss or maintenance. As the researchers in the “calorie is not a calorie” study concluded, best results will come from eating a more plant-based, minimally processed diet including whole grains, beans, fruits and vegetables. So have oatmeal or shredded wheat with blueberries for breakfast, not bacon and eggs. Eat salads, but include high fiber, nutrient dense grains like brown rice, quinoia, and whole wheat. Throw in some beans, fish, and fat free milk and yogurt for high quality protein.
Combining this way of eating with increased physical activity is your best bet to improve body weight and reduce your risk of health problems in the future.