New analyses from the Norwegian randomized controlled trial CARBFUNC show that more than doubling saturated fat intake over a two-year period can promote favorable changes in several cardiovascular risk markers, without increasing apoB, the main suspected risk factor. ApoB is a protein found in the particles that transport cholesterol in the blood, and can be used to assess the risk of cardiovascular disease.

The study is led by Professor Simon Dankel at the Department of Clinical Science, UiB, and is published in the renowned journal eBioMedicine, part of the Lancet family, with PhD candidate Cathrine Loddervik as first author. The study is unique in that no previous study has prescribed such a high intake of saturated fat over such a long period, with close to a third of energy coming from saturated fat, while less than a tenth is typically recommended.

The study included 193 adults with obesity in the area around Bergen in Western Norway. They were randomly assigned to three different diets and followed for up to two years. One group ate a diet high in total and saturated fat, but very low in carbohydrates (under 10 percent of energy). The other two groups ate a more standard diet in line with dietary guidelines, with carbohydrates from either refined or minimally refined sources.

All three diets provided an energy intake that could be sustained over time, around 2,500 calories for men and 2,000 for women. The diets also had the same protein intake, added sugar reduced to around 1-2 percent of energy, and a recommendation of 500 grams of vegetables per day.

LDL cholesterol increased somewhat, but only the larger particles

– An interesting result is that LDL cholesterol only showed a modest increase on the high-fat diet, explained by larger, less dense particles, while several other blood lipid values changed in a favorable direction, says Loddervik.

– This shows the importance of looking at more than a single risk factor when assessing how saturated fat, carbohydrates and diet in general affect the body.

Higher levels of LDL cholesterol are associated with increased risk of cardiovascular disease, together with apoB, a protein that these cholesterol particles are built around.

In the study, LDL cholesterol increased by 5-10% among participants who ate a low-carbohydrate, high-saturated-fat diet. The increase was mainly due to an increase in larger LDL particles. Previous research has found that small, dense LDL particles are associated with greater risk than larger particles, and these did not change appreciably.

– We cannot necessarily conclude that the moderate increase in LDL cholesterol is without significance, Loddervik explains. But it shows that we need to understand what happens to cholesterol particles in the context of the many other blood lipids and the overall metabolic health, which is also affected by carbohydrates.

Several of the other changes measured in the lipid profile, such as triglycerides and HDL cholesterol, are linked to insulin resistance, type 2 diabetes and metabolic syndrome. The triglycerides and HDL cholesterol moved in a considerably more favorable direction in the low-carbohydrate group. Triglycerides were reduced by as much as 20-35% on the high-fat diet, while HDL cholesterol rose by 5-18%, whereas the values remained fairly unchanged flat on the diets with more carbohydrates.

No difference in coronary artery calcification

The researchers also examined possible changes in calcium deposits in the coronary arteries supplying blood to the heart, at baseline and after 12 months on the diets, using CT scans. No clear increase was found on the high-saturated-fat diet, and no difference between the diet groups in the development of calcium deposits.

– The study gives us important knowledge about how the body reacts when we replace carbohydrates with fat as the primary energy source, says Dankel. A key take-home message is that an increase in LDL cholesterol should not be interpreted in isolation.

The carbohydrates in the diets were primarily whole grains, which are considered to give a more favorable blood lipid profile. The high-fat diet cut out most grains.

– The most striking finding is that apoB on the high-fat, low-carbohydrate diet neither increased nor changed appreciably differently from the two diets with more carbohydrates and less fat, Dankel points out.

Dankel emphasizes that more research is needed into what the combined changes in several blood lipid values and risk factors mean for long-term health, when people adapt to a diet low in carbohydrates and higher in saturated fat.

– But the study challenges the contention that a higher intake of saturated fat has an inherent negative impact of overall disease risk. A low-carbohydrate high-fat diet cannot be dismissed as a good, or even better, alternative for many, if overall disease risk is lowered – at least in people with obesity, he concludes.

The study was published on October 24 in eBioMedicine under the title: «Lipid dynamics and cardiovascular risk profiles on carbohydrate- or saturated fat-based diets: secondary analysis of the CARBFUNC trial».

The research was supported by Kostfonden, Sweden, as well as the Trond Mohn Foundation, the University of Bergen and Haukeland University Hospital.

LINK TO THE STUDY: Lipid dynamics and cardiovascular risk profiles on carbohydrate- or saturated fat-based diets: secondary analysis of the CARBFUNC trial - eBioMedicine