A new study has found rapid weight gain from the consumption of polyunsaturated fats leads to lower levels of bad cholesterol in the blood, compared with a rapid increase in bad cholesterol from the consumption of saturated fats.

Slices of cake with food on a table.Share on Pinterest
Baked treats such as muffins and cake are slightly healthier if made using polyunsaturated rather than saturated fats.

Researchers conducted a weight-gain study to analyze the roles of different dietary fats in regulating cardiometabolic risk – the risk of an individual developing heart disease, diabetes or stroke. For the 7-week study, participants consumed muffins rich in either polyunsaturated or saturated fats.

The study, funded primarily by the Swedish Research Council and published in the Journal of the American Heart Association, observed a difference in cholesterol levels despite the fact both polyunsaturated and saturated fats led to equal weight gain.

“Even in early adulthood, it is important to avoid high-calorie foods and weight gain, but also it is important to consume sufficient amounts of polyunsaturated fats from non-hydrogenated vegetable oils,” says Dr. Ulf Risérus, associate professor of Clinical Nutrition and Metabolism at Uppsala University, Sweden.

There are two forms of cholesterol: low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol. LDL cholesterol is regarded as “bad” cholesterol due to it contributing to plaque formation that can clog arteries. HDL cholesterol is referred to as “good” cholesterol as it aids the removal of LDL cholesterol from the arteries.

“The lowering of the cholesterol/HDL cholesterol ratio by polyunsaturated fat is of special interest,” continues Dr. Risérus, “because recent large studies have shown this ratio seems to predict heart disease risk even better than LDL levels alone.”

For the study, participants were followed for 7 weeks and asked to eat three muffins a day in addition to their regular diets. A total of 39 otherwise healthy adults participated in the study, with an average age of 27.

Participants were divided into two groups; one group eating muffins made with unsaturated sunflower oil and the other eating muffins made with saturated palm oil.

The aim was for each participant to gain around 3% of their body weight over the duration of the study. Weight gain was observed throughout the study and single muffins were added to or subtracted from the diets of the participants in order for them to reach this target weight.

All muffins used had high carbohydrate and sugar contents, and the average weight gain for both groups was 2.2%. Both groups also registered an increase in insulin resistance, a common signifier of future adult-onset diabetes.

However, the researchers found that only the muffins made using the saturated palm oil led to concerns regarding the participants’ cholesterol levels. The difference in LDL levels between the eaters of saturated oil muffins and polyunsaturated oil muffins was 9%. Overall cholesterol/HDL cholesterol ratios were also found to differ by as much as 18% between the groups.

Dr. Risérus believes the short-term adverse metabolic changes observed by his team could shed light on why certain overweight people are at a higher risk of developing cardiovascular disease and type 2 diabetes in the long term.

“Dietary fat composition thus seems to be important during weight gain,” write the authors, “which is a novel finding that could have clinical implications in the long term.”

The short duration of the study and the small number of the participants limits the findings somewhat, as does the fact that the average weight gain for the participants was below the target of 3%.

Despite this, the researchers believe that their findings could be useful for people who are at risk of gaining weight through excess calorie intake and a lack of physical exercise. Excess calories gained from polyunsaturated fats result in a slightly more metabolically favorable form of weight gain than calories derived from saturated fats.

Future research will examine whether the effects of a high-saturated-fat diet can be reversed. A new trial will follow participants for a month after a period of weight gain. Dr. Risérus discusses the importance of this research:

Studies using these oils in weight-stable participants have demonstrated that the adverse effects on LDL seems to disappear shortly after they stop consuming foods with saturated fats, and this may also be the case here. Such data would be important to encourage people who gained weight to lose their weight and lower their metabolic risk.”

Recently, Medical News Today reported on another study suggesting that a Mediterranean diet high in nuts and extra-virgin olive oil could reverse metabolic syndrome.