A study conducted at the University of Pennsylvania has challenged the widespread belief that consuming large amounts of refined carbohydrates (such as white bread, sweets, and other processed carbs) poses the greatest threat to health.

The findings were published in the Journal of Nutrition.

Researchers set out to compare the effects of different diets on overall health, particularly metabolism and liver function, using mouse models fed various dietary patterns.

The experiment included four types of diets: high-carbohydrate, high-fat, ketogenic (very high in fat and almost no carbohydrates), and a control diet rich in whole grains, fiber, and moderate amounts of fat. Protein accounted for roughly the same proportion of calories in all diets, meaning the primary differences lay in the ratio of fats to carbohydrates.

The results showed that mice on high-fat and ketogenic diets gained more weight and developed more severe metabolic disturbances than those consuming high-carbohydrate diets. These animals also exhibited impaired glucose processing, inflammation, and increased fat accumulation in the liver — markers associated in medicine with a higher risk of metabolic diseases. In contrast, mice fed a high-carbohydrate diet combined with fiber and whole foods experienced fewer of these negative effects.

The most pronounced adverse outcomes were observed in the ketogenic group: the near absence of carbohydrates and high intake of saturated fats led to the most significant metabolic and liver-related impairments.

The authors emphasize that results obtained in mice cannot be directly applied to humans, as metabolic processes differ between species. However, the findings clearly suggest that an excess of saturated fats alone may be particularly harmful, and that health depends not only on the quantity of carbohydrates consumed but also on the balance between fats, fiber, and high-quality carbohydrates in the diet.