The very high intake of total and saturated fat did not increase the calculated risk of cardiovascular diseases and had substantial improvements in several cardiometabolic risk factors, such as ectopic fat storage, blood pressure, blood lipids (triglycerides), insulin and blood sugar, found a Norwegian randomised controlled trial of 38 men with abdominal obesity.
A Norwegian diet intervention study (FATFUNC), performed by researchers at the KG Jebsen Centre for Diabetes Research at the University of Bergen, raises questions regarding the validity of a diet hypothesis that has dominated for more than half a century: that dietary fat and particularly saturated fat is unhealthy for most people.
The researchers found strikingly similar health effects of diets based on either lowly processed carbohydrates or fats. In the randomised controlled trial, 38 men with abdominal obesity followed a dietary pattern high in either carbohydrates or fat, of which about half 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,” says professor and cardiologist Ottar Nygård 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.”
Both groups had similar intakes of energy, proteins, polyunsaturated fatty acids, the food types were the same and varied mainly in quantity, and intake of added sugar was minimised.
“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,” says PhD candidate Vivian Veum.
“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,” says PhD candidate Johnny Laupsa-Borge.
Saturated fat has been thought to promote cardiovascular diseases by raising the “bad” LDL cholesterol in the blood. But even with a higher fat intake in the FATFUNC study compared to most comparable studies, the authors 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,” says Ottar Nygård.
“Future studies should examine which people or patients may need to limit their intake of saturated fat,” assistant professor Simon Nitter Dankel points out, who led the study together with the director of the laboratory clinics, professor Gunnar Mellgren, at Haukeland University Hospital in Bergen, Norway.
“But 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,” he says.
Background: Different aspects of dietary pattern, including macronutrient and food profiles, may affect visceral fat mass and metabolic syndrome.
Objective: We hypothesized that consuming energy primarily from carbohydrate or fat in diets with similar food profiles would differentially affect the ability to reverse visceral adiposity and metabolic syndrome.
Design: Forty-six men (aged 30–50 y) with body mass index (in kg/m2) >29 and waist circumference >98 cm were randomly assigned to a very high–fat, low-carbohydrate (VHFLC; 73% of energy fat and 10% of energy carbohydrate) or low-fat, high-carbohydrate (LFHC; 30% of energy fat and 53% of energy carbohydrate) diet for 12 wk. The diets were equal in energy (8750 kJ/d), protein (17% of energy), and food profile, emphasizing low-processed, lower-glycemic foods. Fat mass was quantified with computed tomography imaging.
Results: Recorded intake of carbohydrate and total and saturated fat in the LFHC and VHFLC groups were 51% and 11% of energy, 29% and 71% of energy, and 12% and 34% of energy, respectively, with no difference in protein and polyunsaturated fatty acids. Mean energy intake decreased by 22% and 14% in the LFHC and VHFLC groups. The diets similarly reduced waist circumference (11–13 cm), abdominal subcutaneous fat mass (1650–1850 cm3), visceral fat mass (1350–1650 cm3), and total body weight (11–12 kg). Both groups improved dyslipidemia, with reduced circulating triglycerides, but showed differential responses in total and low-density lipoprotein cholesterol (decreased in LFHC group only), and high-density lipoprotein cholesterol (increased in VHFLC group only). The groups showed similar reductions in insulin, insulin C-peptide, glycated hemoglobin, and homeostasis model assessment of insulin resistance. Notably, improvements in circulating metabolic markers in the VHFLC group mainly were observed first after 8 wk, in contrast to more acute and gradual effects in the LFHC group.
Conclusions: Consuming energy primarily as carbohydrate or fat for 3 mo did not differentially influence visceral fat and metabolic syndrome in a low-processed, lower-glycemic dietary context. Our data do not support the idea that dietary fat per se promotes ectopic adiposity and cardiometabolic syndrome in humans.
VL Veum, J Laupsa-Borge, O Eng, E Rostrup, TH Larsen, JE Nordrehaug, OK Nygard, JV Sagen, OA Gudbrandsen, SN Dankel, G Mellgren