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Jennifer Grebow is editor-in-chief of Nutritional Outlook.
Want to lose body fat? A low-fat diet-as opposed to a low-carb diet-may be the way to go, NIH research shows.
Amidst the many diet fads consumers follow, it’s difficult to know which is approach is best. National Institutes of Health (NIH) researchers are cutting through the noise with new study data published online last week in the journal Cell Metabolism. With researchers pegging fat loss “a more important goal than weight loss in the treatment of obesity,” the results of their highly controlled study show that, for purposes of body fat loss, a low-fat diet outperformed a low-carb diet.
The researchers performed their study on obese people: 10 males and 9 females with a mean BMI of 35.9 ± 1.1 kg/m2. To ultimately control subjects’ dietary intake, subjects were housed as inpatients at the NIH Clinical Center for two-week inpatient periods, separated by a 2–4 week washout period.
For the first week of each study period, subjects were fed diets similar to what they typically consumed in terms of carbohydrate (50%), fat (35%), and protein (15%) content, with a total energy intake of 2,740 ± 100 kcal/day. Subjects were also made to exercise on a treadmill for one hour daily to establish a constant level of physical activity.
During the following week, subjects were fed either a reduced-carb diet (140 g carbohydrate and 108 g fat) or a reduced-fat diet (352 g carbohydrate and 17 g fat), keeping total caloric and protein content between the two diets constant. Overall, both diets were 30% lower in calories compared to the subjects’ typical (baseline) diet.
Subjects on the reduced-carb diet did experience decreased insulin secretion, increased fat oxidation, and increased body fat loss compared to baseline.
Subjects on the low-fat diet did not exhibit significant changes in insulin secretion or body fat oxidation-but they did lose significantly more body fat (89 ± 6 g/day of body fat) compared to those on the reduced-carb diet (53 ± 6 g/day of body fat).
Discussing the results, the researchers acknowledged the current popularity of low-carb diets. “While low-fat diets were popular in the latter part of the 20th century, carbohydrate restriction has regained popularity in recent years, with proponents claiming that the resulting decreased insulin secretion causes elevated release of free fatty acids from adipose tissue, increased fat oxidation and energy expenditure, and greater body fat loss than restriction of dietary fat.”
But citing their data, they continued, “This study demonstrated that, calorie for calorie, restriction of dietary fat led to greater body fat loss than restriction of dietary carbohydrate in adults with obesity. This occurred despite the fact that only the carbohydrate-restricted diet led to decreased insulin secretion and a substantial sustained increase in net fat oxidation compared to the baseline energy-balanced diet,” they wrote. “In contrast to previous claims about a metabolic advantage of carbohydrate restriction for enhancing body fat loss, our data and model simulations support the opposite conclusion when comparing the [reduced-fat] and [reduced-calorie] diets.”
This may be good news to those already following a low-fat diet, but the researchers also made sure to point out that these study results are not easily replicated outside of a controlled lab setting. “Translation of our results to real-world weight-loss diets for treatment of obesity is limited since the experimental design and model simulations relied on strict control of food intake, which is unrealistic in free-living individuals. While our results suggest that the experimental reduced-fat diet was more effective at inducing body fat loss than the reduced-carbohydrate diet, diet adherence was strictly enforced. We did not address whether it would be easier to adhere to a reduced-fat or a reduced-carbohydrate diet under free-living conditions.”
In addition, they pointed out, longer-term studies are needed: “It could be argued that perhaps the fat balance and body fat changes would converge with continuation of the diets over the subsequent weeks.”
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