The fat vs carb debate: Weight loss more complicated than previously thought, says NIH study

25 Jan 2021 --- Plant-based low-fat diets may result in more significant weight loss than low-carbohydrate diets that include animal products, a study from the US National Institutes of Health (NIH) suggests. The small but highly controlled trial results contradict mainstream beliefs about dietary models and their impact on health.

Weight loss regimens such as the ketogenic and Atkins diets have popularized the idea that consuming high quantities of carbohydrates causes excess insulin secretion, thereby promoting energy intake and fat accumulation. 

Reducing carbohydrate intake, therefore, should theoretically have the opposite effect. A significant rise in products marketed toward these diet plans has been seen in recent years. 

The rise of keto diets marked a shift from previous thinking that diets with lowered fat intake would result in increased fat loss. 

“To help us achieve good nutrition, rigorous science is critical − and of particular importance now, in light of the COVID-19 pandemic, as we aim to identify strategies to help us stay healthy,” says Griffin Rodgers, director at the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Some mainstream weight loss diets recommend low-carbohydrate intake.The new study sought to compare the effects of high-fat and high-carbohydrate diets on calorie intake, hormone levels, body weight and more.  

The findings, now published in Nature Medicine, suggest the answer is more complicated than previously believed, highlighting benefits in both regimens and pointing to the significance of eating unprocessed foods. 

Study methods 
Twenty participants, 11 men and nine women, were housed for four continuous weeks in the NIH Clinical Center’s Metabolic Clinical Research Unit. 

None had diabetes, and each participant was given three meals a day, plus snacks, and was free to eat as much as they desired. 

Half of the participants received a plant-based, low-fat diet and the other half an animal-based, low-carbohydrate diet for two weeks. After this period, each group followed the other diet for a further two weeks.

The plant-based, low-fat diet contained 10 percent fat and 75 percent carbohydrate, while the animal-based, low-carb diet was 10 percent carbohydrate and 75 percent fat. 

Both diets contained about 14 percent protein and were matched for total calories presented to the subjects, although the low-carb diet had twice as many calories per gram of food as the low-fat diet. 

On the low-fat menu, a typical example of a dinner meal was a baked sweet potato, chickpeas, broccoli and oranges. Meanwhile, the low-carb dinner might be a beef stir fry with cauliflower rice.

Difference in weight loss but not in hunger 
The main results showed that participants on the low-fat diet consumed an average of 550 to 700 fewer calories per day than when on the low-carb diet. The results contradict some current philosophies surrounding weight loss.

Despite the large differences in calorie intake, participants reported no differences in hunger, enjoyment of meals or fullness between the two diets. 

Participants also lost weight on both diets, but only the low-fat diet led to significant body fat losses, given that each participant was free to consume as much as they pleased. However, the study authors warn that the results are not intended to create diet recommendations for weight loss. 

“Despite eating food with an abundance of high glycemic carbohydrates that resulted in pronounced swings in blood glucose and insulin, people eating the plant-based, low-fat diet showed a significant reduction in calorie intake and loss of body fat,” says lead author Kevin Hall. 

“This challenges the idea that high-carbohydrate diets lead people to overeat per se. On the other hand, the animal-based, low-carb diet did not result in weight gain despite being high in fat.”

Further research needed
The study authors point to several holes in the research design and findings, including the small sample size of only 20 participants.

Moreover, the highly controlled environment inside the research unit makes generalizing the results to the outside world more difficult, despite ensuring the accuracy of the data. 

Traditional assumptions regarding weight loss and low-carbohydrate diets call for further investigations say the researchers, especially during the COVID-19 pandemic. 

“This study brings us closer to answering long-sought questions about how what we eat affects our health,” Rodgers concludes.

Edited

By Louis Gore-Langton