Science
Research reveals hidden dangers of high saturated fat diet
A diet high in saturated fat is more dangerous for the heart than a diet high in unsaturated fat, even when there has been no weight gain, according to new research funded by us and presented at the European Society of Cardiology Congress 2024 in London.
The study found concerning changes to regularly measured invisible markers of heart health in people who ate a high saturated fat diet and didn’t see a change their body weight. People on this diet had a roughly 20 per cent rise in fat in their liver and around 10 per cent higher blood cholesterol levels after just 24 days, compared to before they started the diet.
Nikola Srnic, MD/DPhil Candidate at the University of Oxford, who led the research said:
“We want to study how the type of fat that a person eats affects their risk of heart and circulatory disease beyond a change in body weight. The results suggest that a diet high in saturated fat may negatively change cardiovascular disease risk factors even when a person does not gain weight.
“On the other hand, we saw protective effects if a person ate a diet high in polyunsaturated fat. Although our study is ongoing, our findings so far suggest that even when you are not gaining weight, different fats can have drastically different effects on our health in a short time frame.”
Heightened risks
Saturated fats are found in foods including butter, fatty meats, cakes, pastries and biscuits. Polyunsaturated fats, including omega-3 and omega-6, supply the body with essential nutrients and are found in foods including oily fish, like mackerel and salmon, sunflower oil, and some nuts.
During the study, 24 participants were asked to follow a diet high in either saturated fat or polyunsaturated fat for up to 24 days. Each participant had an MRI scan and blood test at the beginning and end of the study to assess the impact of the type of fat they consumed on known risk factors for heart and circulatory diseases.
Body weight was unchanged in both groups after 24 days, yet the participants who ate more saturated fat had test and scan results that are linked to an increased risk of heart disease. This group’s levels of total cholesterol and non-HDL cholesterol – known as ‘bad’ cholesterol – in the blood were approximately 10 per cent higher than before the study.
The saturated fat group also saw a roughly 20 per cent increase in the amount of fat stored in their livers. Too much fat being stored in the liver heightens the risk of person developing type 2 diabetes and cardiovascular diseases.
Protective role for some fats
The group which ate a diet high in polyunsaturated fat saw very different changes after 24 days. They experienced a drop in total blood cholesterol and ‘bad’ cholesterol levels of around 10 per cent, and an increase in energy reserves in their heart muscle, compared to before the study.
The effects seen in this group underline the protective role that some fats can play, reinforcing the benefits of including polyunsaturated fats as part of a balanced diet.
The researchers also assessed the mechanisms in heart muscle cells that may help to explain these observations. They grew these cells in conditions enriched with saturated or polyunsaturated fats and measured how the cells responded.
If cells were grown in conditions with more polyunsaturated fat, they became more active in taking up fat and breaking it down for energy. This could be one way in which a diet high in polyunsaturated fat could help the body lower the level of fats in the blood.
Professor James Leiper, our Associate Medical Director, said:
“Saturated fat has long been understood to cause a much higher risk of heart and circulatory disease. This study adds to this consensus and gives us evidence that saturated fat may silently start to pose a risk to heart health very quickly, without causing any changes to a person’s weight.
“The results the researchers saw in lab-grown heart cells will hopefully improve our understanding of how these changes happen. Longer studies with more participants are needed to confirm these findings and show whether these short-term changes increase people’s risk of serious heart problems in the long term.”