While unwanted pounds undoubtedly come from eating more calories than the body burns, the process is far more complicated than the overly simplistic calories in/calories out paradigm, according to a new study published today in the Journal of the American Medical Association.
Those extra calories we eat, whether protein, fat, or carbohydrates, all result in the same extra padding of body fat, but how much lean muscle we put on is dependent upon the amount of protein we consume.
In the study, 25 volunteers agreed to live in a research lab for two months and consume 1,000 extra calories a day with varying amounts of protein. Those who were randomly assigned to eat a low-protein diet -- with just 5 percent of their calories from protein -- gained seven pounds, about half as much weight as the two other groups, which were given 15 percent or 25 percent of their calories from protein.
But that smaller weight gain was deceiving since the low protein group shed muscle mass, while the other two groups gained calorie-burning muscle cells and had a metabolism boost that could help them more easily shed the extra fat when they return to their old eating habits, said study co-author Leanne Redman, an obesity researcher at the Pennington Biomedical Research Center. (The followup data on what happened when participants returned to their previous diet haven’t yet been analyzed.)
“We knew from previous research that people gained less weight when their excess calories came from fat instead of protein,” said Redman, “but our study looked at how excess calories are used by the body for fat storage, to build muscle, or to be burned off as heat.”
In the low-protein group, the body siphoned off 95 percent of the excess calories to pad the body with more fat, burning off 5 percent as heat while shedding muscle due to a lack of protein. In the higher protein groups, the body used 50 percent of the extra calories for fat while burning off 40 percent as heat and depositing 10 percent into new muscle.
The study underscores the limitations of relying solely on a bathroom scale to monitor weight over time, especially as the body ages and begins to shed muscle and accumulate fat. “Many people can be at a healthy weight on the outside with a high percentage of body fat on the inside and that can lead to many health problems over time like frailty and falls,” said Dr. David Heber, director of the University of California Los Angeles Center for Human Nutrition who co-wrote an editorial that accompanied the study.
Where the findings could prove to be most useful is for dieters who want to accomplish the ultimate hat trick of shedding pounds without losing precious muscle, a feat most can’t accomplish.
“Many people make the mistake of cutting back on protein or skipping meals when they’re trying to lose weight,” said Dr. George Blackburn, chief of the Nutritional/Metabolism Laboratory at Beth Israel Deaconess Medical Center in Boston. “But most of us need about 45 to 55 grams of protein each day spread over three meals to keep the body from losing muscle.”
One eight-ounce glass of milk has 8 grams of protein, while three ounces of lean beef, chicken or fish has about 21 grams; a cup of dry beans has 16 grams, and an eight-ounce container of yogurt has about 11 grams, according to the US Centers for Disease Control and Prevention.
Only about half of Americans, Blackburn added, get adequate amounts of protein throughout the day, and as a result of this deficiency we may find it harder to retain muscle and fight the mid-life spread.
The study, though, didn’t address an issue pressing to many followers of high-protein, low-carbohydrate diets like Atkins: whether eating an excess amount of protein and calories will lead to weight loss if carbohydrates are kept to a minimum. (Carbohydrates made up a substantial 41 percent to 42 percent of the calories in all three study groups.)
“I can’t comment on it,” said Redman, “but what I found most intriguing was the differences in weight gain among participants within each group.” Some in the low-protein group, for example, gained just 4 pounds overall while others gained 32 pounds. There was far less of a range in the higher-protein groups, with those at the lowest end gaining about 10 pounds while others gained as much as 17.
If researchers could tap into the secrets that allow some individuals to gain less weight from overeating, she said, that could eventually provide some novel solutions for the obesity epidemic.
Deborah Kotz can be reached at firstname.lastname@example.org. Follow her on Twitter @debkotz2.