A study comparing 30 diets found that a high-fat diet leads to the most weight gain.
Credit: Happy Lark

It seems like every week there’s a trendy new diet that offers crazy health benefits and dramatic weight loss. Most of these focus on a few macronutrients you must either avoid or focus on—carbohydrates, sugar, protein, fat.

Historically, dieters have focused on decreasing fat, increasing protein, and lowering carbohydrates. Some diets suggest lowering carbs and eating more fat, like keto or Atkins.

But new research took the question of what diet actually contributes to weight gain to the lab.

A study published in the journal Cell Metabolism found that mice who ate high-fat diets were more likely to become obese than ones on diets low in protein or high in carbohydrates. Researchers additionally found an increase in both saturated and unsaturated dietary fat led to genetic changes, creating an association between happiness and consuming fatty foods.

For more research on dietary fat:

Scientists exposed hundreds of male mice to 29 different diets ranging from 8.3 to 80 percent fat, 10 to 80 percent carbohydrates, 5 to 30 percent protein, and 5 to 30 percent sucrose (sugar) for three months. The findings were extraordinarily clear—only mice fed a diet that increased their fat intake by 60 percent became overweight or obese.

Credit: Cell Metabolism

Additionally, these mice experienced a dopamine, opioid, and serotonin spike when stimulated by fatty foods, meaning the foods gave them significantly more pleasure—and, thus, reason to overeat.

Researchers examined weight and body composition of the mice after the experiment, and found no other diet resulted in the same bodily changes. Afterwards, the scientists ran the same experiment on four addition mice breeds and found the same results.

The results are particularly surprising as fat, once widely vilified in health circles, has been making something of a comeback. When Cooking Light was founded, most foods marketed as healthy touted their low amounts of fat. These days high-fat foods like avocados and coconut oil are touted as health foods—and sugar has become the new demon. Curiously, the mice fed diets high in sugar had no change in weight.

Before you go tossing out that whole milk and digging into a pile of candy, however, it's important to, take this information with a grain of salt. For one thing, it is only one study, and for another it was completed on mice. While they have similar metabolisms to humans, mice are still not humans.

If you're trying to eat healthier, the most important thing you can do (and what all of Cooking Light's recipes are founded on) is also the least trendy: Eat moderate amounts of a wide variety of mostly plant-based foods, while enjoying other foods in moderation. That's still the only thing shown to have the greatest effect over the long term.