It’s fat that makes you fat, study finds

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Our diet obviously plays a big role in our body weight but there’s little unanimity on which food types are the culprits. Sugar and fat are the usual targets and there has been an endless series of diets that claim to aid weight loss by emphasizing — or de-emphasizing — either fat or refined carbohydrates, also known as sugar.

Lately there have been promoters who have claimed that eating fat actually helps us lose weight. Another current theory is that hunger is based largely on the body’s need for protein and that if we get eat lots of protein, we won’t eat so much other stuff and will soon start shedding pounds.

Could be, but researchers in Scotland and China have just concluded what they say is the largest study of its kind, published in the journal Cell Metabolism, and the verdict, they say, is clear — it’s fat that makes us fat.

The reason? The researchers say that dietary fat stimulates the reward centers in the brain, causing us to want to eat more fat. This is a simple truth that nutritionists have known for decades — fat tastes great and when you eat a little of it, you naturally want more.

The researchers admit their study is somewhat limited because it was carried out on mice, but say there’s really no way around that.

“A clear limitation of this study is that it is based on mice rather than humans. However, mice have lots of similarities to humans in their physiology and metabolism, and we are never going to do studies where the diets of humans are controlled in the same way for such long periods. So the evidence it provides is a good clue to what the effects of different diets are likely to be in humans,” said Prof. John Speakman in a news release.

30 diets, 100,000 measurements

Scientists at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences in Beijing and the University of Aberdeen in Scotland conducted the study, which included 30 different diets that varied in their fat, carbohydrate (sugar) and protein contents. Mice of five different strains were fed these diets for three months, which is equivalent to nine years in humans.

In total, over 100,000 measurements were made of the mice’s body weight changes and their body fat was measured using a micro-MRI machine. The result of this enormous study was unequivocal — the only thing that made the mice get fat was eating more fat in their diets. Carbohydrates, including up to 30% of calories coming from sugar, had no effect.

Combining sugar with fat had no more impact than fat alone. There was no evidence that low protein (down to 5% of the total calories) stimulated greater intake, suggesting there is no protein “target.”

About the Author

Truman Lewis
Truman has been a bureau chief and correspondent in D.C., Los Angeles, Phoenix and elsewhere, reporting for radio, television, print and news services, for more than 30 years. Most recently, he has reported extensively on health and consumer issues for and