It’s not carbs or sugar. Eating more fats makes you fat, study on mice shows
Joint research by Chinese and British scientists links weight gain in mice to the amount of fat in their diet, not protein or sucrose
Among dieters, it’s an eternal debate: what is the best way to keep weight off? A high-carb diet? Low-sugar? All-protein?
Now, new joint research by Chinese and British scientists suggests something simpler – and maybe something we already knew in our gut: to avoid putting on the pounds, avoid fat in your diet.
The Chinese government-backed study, published last week in the scientific journal Cell Metabolism, showed that weight gain in mice was linked only to dietary fat levels, not to protein or sucrose.
An increased intake of dietary fats was found to drive obesity in mice more than an increase in protein or carbohydrates. In other words, the bigger the proportion of fat in their diet, the more likely they were to overeat, which led to a higher likelihood of obesity.
The research involved a collaboration between Chinese and British researchers at the Chinese Academy of Sciences and the University of Aberdeen in Scotland. The study was the biggest nutrition study of its kind in 50 years, according to the team.
The ultimate aim of the study was to find out which macronutrient had the biggest impact on body weight gain, in the face of varying results from other nutrition studies, according to Hu Sumei, a postdoctorate fellow at the Chinese Academy of Sciences and one of the paper’s authors.
“In other nutritional studies, the diet composition had several variables – while in this study, we were able to control the amount of protein, fat or sucrose in their diet even more precisely,” said Hu, referring to the mice.
For years, low-carb, high-protein and high-fat diets like the Atkins Diet and the ketogenic diet have gained huge followings worldwide for their presumed weight-loss benefits.
The team of scientists carefully monitored the weight of a group of 30 male mice put on a variety of diets over three months, the equivalent to nine years in a human lifespan, said Scottish biologist John Speakman, another of the paper’s authors.
The same strictly controlled diets would have been impossible to replicate in testing on humans over the same time period, he said.
“We found that the only macronutrient that caused an increase in body fat was dietary fat. So if you ramped up the fat in their diet from 10 to 60 per cent, the mice progressively got fatter and fatter,” Speakman said.
An increased amount of fat triggered the release of feel-good hormones like dopamine and serotonin from the brain’s reward centres, making it more pleasurable to overeat, he said. If one’s diet had a relatively low percentage of fat, those reward centres were not activated.
The team found that adjusting other macronutrients, like the amount of protein or carbohydrates, had no impact on the weight of the mice.
“We didn’t find any evidence that high levels of protein suppressed appetite and reduced body weight,” Speakman said.
Speakman and Hu advised caution when applying the study’s findings to dieting for weight loss. The experiment, they stressed, focused on preventing weight gain in mice that were already thin, instead of reducing the body weight of obese mice.
“If we started out the experiment on mice that were already fat, we might get a different answer,” Speakman said.
“But if you were already slim and presuming that humans respond in the same way as mice, we anticipate that the best way to avoid becoming fat is to reduce the amount of fat in your diet.”
However, he did not dismiss low-carb, high-protein diets such as the Atkins Diet as an effective method for weight loss, since that was not the focus of the study.
Speakman also noted that results might have been different had they experimented on female mice as well as mice at different stages in their lives.
“Based on our findings, you have to have some fat in your diet since they’re essential for the human metabolism,” he concluded.
“We found the mice that gained the least weight were on a diet of 10 to 20 per cent fat – that seems to protect individuals from consuming excess calories.”
The typical amount of fat in a standard American diet is 35 per cent, according to a 2006 study.
Hu said that in the future, the scientists hoped to fine-tune their results by researching the effects of different types of fat and carbohydrates on one’s diet.