Are High-Fat Diets Bad for Weight Loss?

Are High-Fat Diets Bad for Weight Loss?

A new study suggests that high-fat, low-carb diets like the Keto Diet can lead to weight gain, not weight loss.

  • A new study suggests that fat, not carbs, is directly linked to weight gain
  • The study looked at mice on 30 different types of diets. Researchers found that the mice on a high-fat, low-carb diet gained the most weight, while mice on a low-carb diet actually gained no weight at all
  • The findings suggest that trendy high-fat, low-carb diets might not be effective at helping you lose weight — but is that actually true?

If you’re trying to lose weight, you’ve probably jumped on the low-carb diet bandwagon at one point or another. Many weight loss gurus have claimed that cutting down carbs and increasing your fat intake can help you lose weight. This has contributed to the increasing popularity of diets like the keto diet, which suggests that if you stick to a high-fat, low-carb diet, your body will go into ketosis, thus prompting you to shed more pounds. But a new study suggests this might not be the case.

Published this month in Cell Metabolismthe study from the University of Aberdeen and the Chinese Academy of Sciences found that mice who ate high-fat diets gained more weight over a three-month period than mice who ate high-carbohydrate diets. In fact, surprisingly, the mice on high-carbohydrate diets did not gain weight at all. According to the researchers, eating fat is the only thing that made mice gain weight.

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For three months (the equivalent of nine years for humans), study co-author John Speakman of the University of Aberdeen studied how mice responded to 30 different diets, which varied widely in terms of their fat and carb content. The food was readily available for the animals, so they could eat whenever they liked and as much as they wanted.

At the end of three months, Speakman found that the mice that were put on 50 to 60% fat diets were the heaviest. He says that when his team looked at the animals’ brains, they found that genes linked to the reward system, which controls response to pleasurable activities like eating or sex, were activated in mice who consumed diets high in fat. There was no stimulation of the reward centers in mice placed on low-carbohydrate diets.

Contrary to popular belief that eating fat keeps you satiated, helping you eat fewer calories overall, Speakman theorizes that high-fat diets actually triggered the mice to consume more calories.

Interestingly, however, the researchers noticed that mice put on a diet that consisted of 80% fat gained less weight and weighed 15% less than the mice who adhered to 50-60% fat diets. Speakman isn’t sure why this is: while the average keto diet is also approximately 80% fat, he doesn’t think the mice on the 80% fat diets entered ketosis, because mice don’t require as many carbohydrates for energy, and therefore wouldn’t need to make ketones to fuel their bodies. But it’s possible the results indicate that adhering to an extremely high-fat, low-carb diet could lead to weight loss or at least weight maintenance, as opposed to a moderately high-fat, low-carb diet.


So what does this mean for humans?

Naturally, we want to know how these findings affects us. Well, the answer is complicated, according to Speakman and Dr. Konstantinos Spaniolas, Associate Director of the Stony Brook Metabolic and Bariatric Weight Loss Center in New York.

Because Speakman’s study was an animal study, it’s possible that it has no implications for humans at all. “It’s often really difficult to translate mice studies to humans,” Spaniolas tells

But Spaniolas does find it surprising that the mice on high-carbohydrate diets did not gain any weight at all. “A high-carbohydrate diet is not a recommendation for weight loss,” he says.

Further, he finds it “puzzling” that the mice who ate higher-fat diets ate more than the mice on higher-carb diets. Contrary to the results of Speakman’s study, most of his patients on high-fat diets typically don’t have as many cravings as people whose diets are more carb-heavy, he says.

So what’s the consensus on high-fat diets?

Despite the results of his study, Speakman says that high-fat diets aren’t the only cause of weight gain. In fact, Spaniolas says, “there is no question that ketosis does work in the short term” for humans, and most of the data on low-carb diets like the Keto Diet supports that.

Of course, there are numerous reasons why consuming obscene amounts of fat may be bad for your overall health, and there’s also evidence to suggest that weight loss from diets like keto is not sustainable in the long run. But this study doesn’t necessarily mean that high-fat, low-carb diets will make you fat, as other reports have suggested.

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