A study published today in the New England Journal of Medicine suggests that cutting back on calories will help you lose weight, and it doesn’t matter if the cut calories are fats, proteins, or carbohydrates. These three main sources of calories are called macronutrients.
In other words: A calorie is a calorie is calorie.
Which is what was taught in medical school 30 years ago.
Short-term scientific studies over the last 15 years have suggested that the macronutrient composition of the diet was an important determinant of weight-loss success. Some studies favored low-fat diets, others low-carb diets. Others found no effect.
The study at hand was done under the auspices of the Harvard School of Public Health, Harvard Medical School, the Pennington Biomedical Research Center of the Louisiana State University System, and the National Heart, Lung, and Blood Institute. The study authors, who rank among the best obesity researchers in the world, write:
The possible advantage for weight loss of a diet that emphasizes protein, fat, or carbohydrates has not been established, and there are few studies that extend beyond 1 year.
811 overweight and obese adults were randomly assigned to one of four calorie-restricted diets with the following percentages of calories derived from fat, protein, and carbohydrates, respectively:
1) 20, 15, and 65%
2) 20, 25, and 55%
3) 40, 15, 45%
4) 40, 25, 35%
Participants were given group and individual instructional sessions frequently over a period of two years. Baseline levels of caloric intake were calculated for each participant, then they were instructed how to reduce that intake by 750 calories per day. The physical activity goal was 90 weekly minutes of moderate exercise. Low-glycemic index carbohydrates were recommended in each diet. Subjects were instructed to record food intake in a daily food diary and in a Web-based self-monitoring system. Average age was 51. Average weight was 93 kg (205 lb). Average body mass index was 33. Women were 64% of the subjects.
80% of the subjects completed the two-year study. Of these, average weight loss was 4 kg (8.8 lb).
Subjects in all groups lost about 6 kg (13.2 lb) on average, regardless of which diet they ate.
Subjects’ ratings of hunger, satisfaction, and satiety were similar for all diet groups.
People who faithfully attended instructional sessions definitely had better weight loss.
As measured after two years, weight loss amounts were quite similar whether someone ate 15% protein or 25% protein, 20% fat or 40% fat, 65% carbohydrate or 35% carbohydrate.
Fourteen or 15% of subjects over two years were able to lose at least 10% of their initial body weight.[Improved health usually requires loss of at least 5% of initial body weight.
Subjects who completed the study had an average weight loss of 6.5 kg (14.3 lb) at six months, which indicates a reduction of daily caloric intake of 225 calories (not the goal of 750).
Clinical markers of diet compliance confirmed that subjects generally had major problems adhering to their assigned diets.
Seven percent of participants had “serious adverse events,” with no difference among the diets. [No details provided.]
The Researchers’ Main Conclusion
Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize.
Losing excess weight is hard!
If you want to lose excess weight, reducing caloric intake is important. The researchers judged a food diary to be an important tool, and I agree.
Although average amounts of weight lost over two years is not much, some individuals do much better than average. That could be you.
In case you’re wondering, the Mediterranean diet is closest to dietary pattern #3 above. The Mediterranean diet is considered moderate or middle-of-the-road in terms of the three macronutients. Pattern #1 is a standard low-fat diet. Pattern #4 is reminiscent of the Atkins diet, which is low-carb.
Only one dietary pattern has been shown to prolong life and reduce rates of cancer (breast, colon, prostate, and uterus), cardiovascular disease (heart attacks and strokes), type 2 diabetes, dementia (both Alzheimers and vascular dementia, Parkinsons disease, chronic obstructive pulmonary disease, and melanoma. That’s the Mediterranean diet. Not low-fat. Not low-carb.
The authors surmise that unspecified “behavioral factors” rather than macronutrient metabolism are the main influences on weight loss. Allow me to name the major influential behavioral factors: commitment, discipline, and willpower. These seem to be verboten in some quarters of the obesity research community.
George Carlin had a famous comedy routine called “The Seven Dirty Words You Can’t Say on Television.” Well these are The Three Dirty Words You Can’t Say in Obesity Research Reports:
Commitment Discipline Willpower
Sacks, Frank M., et al. Comparison of Weight-Loss Diets with Different Compositions of Fat, Protein, And Carbohydrates. New England Journal of Medicine, 360 (2009): 859-873.
Parker-Pope, Tara. Study Zeroes In on Calories, Not Diet, for Loss. New York Times online, February 25, 2009. Accessed February 28, 2009.