Treating yourself to regular morning croissants or biscuits can “silently” increase the risk of serious heart problems even if you do not put on any weight, a study shows.
A trial by Oxford University found that if people spent three weeks eating buttery foods such as pastries and cakes every day it took a major toll on heart health.
A group of volunteers followed a diet high in saturated fat for 24 days, including foods such as butter, croissants, sausages, cakes and chocolate.
They were weighed and had blood tests and MRI scans at the beginning and end of the study. The number of calories was controlled, meaning they did not put on any weight, but there were still concerning changes to “invisible markers of heart health” after three and a half weeks.
Their cholesterol rose by 10 per cent on average, while there was also a 20 per cent rise in the fat in their liver, increasing the risk of type 2 diabetes and heart disease, which can cause heart attacks and strokes.
The study, which was presented at the European Society of Cardiology conference in London, sought to examine how changing the type of fat in a diet could affect the heart, even if overall calories remained the same.
Even though the participants in the trial did not put on weight, their heart health deteriorated when they ate saturated fat regularly
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There were 24 participants, and half were put on the saturated fat diets of butter and pastries. The other half ate lots of polyunsaturated fat for three and a half weeks, including oily fish such as mackerel and salmon, sunflower oil, walnuts and sesame seeds.
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This polyunsaturated fat actively protected the heart. The group experienced a drop in total “bad” cholesterol levels of about 10 per cent, and an increase in energy reserves in their heart muscle, even though their body weight and calorie intake was unchanged.
The lead researcher, Nikola Srnic, a PhD student at Oxford, said it showed that “even when you are not gaining weight, different fats can have drastically different effects on our health in a short timeframe. 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.” He said people who were eating healthily but not losing weight should be reassured that they were getting beneficial effects even if the numbers on the scale did not change, adding: “If you’re not losing weight, you shouldn’t lose hope.”
He encouraged people to make simple substitutions to replace saturated fat for healthier polyunsaturated fat.
The researchers also looked at heart muscle cells in the lab, finding that cells found it easier to break down polyunsaturated fat and use it for energy, explaining how polyunsaturated fat could help the body lower the level of fats in the blood.
Professor James Leiper, the associate medical director of the British Heart Foundation, said: “This study 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.”
Scientists have long been puzzled by the “French paradox”, of how a nation famed for its croissants — although they came from Austria — has relatively low levels of heart disease.