A new diet intervention study (FATFUNC), performed by researchers at the KG Jebsen center for diabetes research at the University of Bergen in Norway, raises questions regarding the validity of a diet hypothesis that has dominated for more than a half-century: that dietary fat — particularly saturated fat — is unhealthy for most people.

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The researchers found strikingly similar health effects of diets based on either minimally processed carbohydrates or fats. In the randomized controlled trial, 38 men with abdominal obesity followed a dietary pattern high in either carbohydrates or fat, about half of which was saturated. Fat mass in the abdominal region, liver and heart was measured with accurate analyses, along with a number of key risk factors for cardiovascular disease.

"The very high intake of total and saturated fat did not increase the calculated risk of cardiovascular diseases," said professor and cardiologist Ottar Nygard, who contributed to the study. "Participants on the very-high-fat diet also had substantial improvements in several important cardiometabolic risk factors, such as ectopic fat storage, blood pressure, blood lipids (triglycerides), insulin and blood sugar."

High-quality food is healthier

Both groups had similar intakes of energy, proteins and polyunsaturated fatty acids; the food types were the same and varied mainly in quantity, and intake of added sugar was minimized.

"We here looked at effects of total and saturated fat in the context of a healthy diet rich in fresh, lowly processed and nutritious foods, including high amounts of vegetables and rice instead of flour-based products," University of Bergen doctoral candidate Vivian Veum explained. "The fat sources were also lowly processed — mainly butter, cream and cold-pressed oils."

Total energy intake was within the normal range. Even the participants who increased their energy intake during the study showed substantial reductions in fat stores and disease risk.

"Our findings indicate that the overriding principle of a healthy diet is not the quantity of fat or carbohydrates but the quality of the foods we eat," doctoral candidate Johnny Laupsa-Borge said.

Saturated fat increases "good" cholesterol

Saturated fat has been thought to promote cardiovascular diseases by raising the low-density lipoprotein (LDL), or "bad" cholesterol, in the blood. However, even with a higher fat intake in the FATFUNC study than most comparable studies, the researchers found no significant increase in LDL cholesterol.

Rather, the "good" cholesterol increased only on the very-high-fat diet.

"These results indicate that most healthy people probably tolerate a high intake of saturated fat well, as long as the fat quality is good and total energy intake is not too high. It may even be healthy," Nygard said.

"Future studies should examine which people or patients may need to limit their intake of saturated fat," said assistant professor Simon Nitter Dankel, who led the study together with professor Gunnar Mellgren, director of the laboratory clinics at Haukeland university hospital in Bergen, Norway.

"The alleged health risks of eating good-quality fats have been greatly exaggerated. It may be more important for public health to encourage reductions in processed flour-based products, highly processed fats and foods with added sugar," Dankel said.