On two popular diets, people gorge on steak and other high-fat foods while eschewing the carbohydrates in bread and pasta. On another, followers avoid meats, whole milk and avocados in favor of low-fat foods, which include the carbs dreaded by others. The tug-of-war between fad diets that are low-fat or low-carb has gone on for decades while more people gain weight. But, a surprising new government study shows that a low-fat diet is more effective than a low-carb one for those determined to drop those extra pounds.
For years, Atkins and Paleo diet promoters touted that a low-carb diet was more effective because it decreases insulin levels (which is better regulate fat tissue to allow people to burn more). A small study conducted at the U.S. National Institutes of Health (NIH) clinical center, however, shows that taking a low-fat approach to dieting may be better.
The head scientist, Kevin Hall, PhD, a metabolism researcher at the National Institute of Diabetes and Digestive and Kidney Diseases, previously reviewed countless studies over the last few decades. He then developed a mathematical model to offer a hypothesis on the different ways these two diet approaches work. That led to the new study, which was published in the most recent issue of Cell Metabolism, to test his hypotheses.
The study team recruited 19 obese adults as study participants, who agreed to be inpatients for more two almost two-week periods. This was done to ensure they adhere to the prescribed diet and researchers are aware of any variables that might affect results. “Unless we do the kind of study that we have done here, where we basically lock people up for an extended period of time, control everything, and make sure we know exactly what they eat…then we don’t have the kind of control that’s required to answer these really basic questions,” explained Hall.
The participants spent their first five days consuming a balanced diet. For the next six days, half of them reduced their calorie intake by 30 percent with a low-carb diet but kept their fat and protein consumption the same. Conversely, the other half reduced their intake via a low-fat diet, but continued to eat the same amount of carbs. After a break of a few weeks’ time, they did it all over again, except this time the two groups consumed the other diet. Using special equipment, the research team could follow exactly how the group’s bodies were burning both the calories and body fat.
The adults ended up losing weight on both diets, but they all lost more when they were on the reduced-carb diet. Over the study period, participants on the reduced-fat diet lost 463 grams of fat on average, compared to the 245 grams they lost on average while on the low-carb diet. The researchers predicted that, if the diets were to continue for six more months, the people on a low-fat diet would lose an estimated six pounds more than those in following a low-carb regimen.
Hall explained that the results were predictable. “We’ve known for quite some time that reduction of dietary carbohydrates causes an excess of water loss,” so he noted that weight lost on a low-carb plan may be due to water loss. There insulin levels also went down and fat burning increased. But the low-fat diet enabled followers to lose more fat, despite no change in insulin levels.
Hall cautions against assuming that his study proved definitively that a low-fat diet is more effective than a low-carb one, because the study sampling was small. Clearly, more research with larger sample sizes is needed. But, this study does offer food for thought.
Written and edited by Dyanne Weiss
Forbes: New Study Says Low-Fat Diet Trumps Low-Carb. But There’s A Bigger Message.
TIME: Does a Low-Carb Diet Really Beat Low-Fat?
Washington Post: Scientists (sort of) settle debate on low-carb vs. low-fat diets
Cell Metabolism: Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity
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