A Professor of Public Health Nutrition, Ignatius Onimawo, has warned that overheating cooking oil increases the risk of heart attack, hypertension, and stroke. Onimawo, a former Vice-Chancellor of Ambrose Alli University, Ekpoma, Edo State, explained that overheating vegetable oil converts it into trans fat, which is harmful to health.
He stated that trans fats are the most dangerous type of fat one can consume, emphasizing their lack of health benefits and their significant role in cardiovascular diseases and strokes globally. Speaking to PUNCH HealthWise, Onimawo highlighted that excessive heating of vegetable oils transforms them into trans fatty acids, which lead to inflammation.
The former Nutrition Society of Nigeria President elaborated, “When you reuse vegetable oil or any cooking oil for that matter, and you do it more than twice, the tendency is that, if you are continuously heating the oil, the fatty acid composition of the oil can be transformed into trans fatty acid.
“When you are frying, the temperature of the oil is high. Then, after that, the same oil, you use it again, and the temperature is high. By the time you are using it the third or the fourth time, there is going to be a transformation of the fatty acid. They will be converted into what we call trans fatty acids. These trans fatty acids are responsible for cardiovascular diseases. They even cause cardiovascular diseases more than saturated fats. That is why we normally advise, that if you have used oil more than once or twice, it is better to discard it.”
Mayo Clinic has similarly noted that trans fats are considered the worst type of dietary fat. “Unlike other dietary fats, trans fats — also called trans-fatty acids — raise ‘bad’ cholesterol and also lower ‘good’ cholesterol. A diet laden with trans fats increases the risk of heart disease, the leading killer of adults. The more trans fats eaten, the greater the risk of heart and blood vessel disease,” the clinic said.
Onimawo explained that the body cannot properly process trans fats, leading to plaque deposits in arteries. “Because the body cannot handle them, they are the ones that normally form plagues or deposits along the arteries. Sometimes, they form these plagues along some of the organs. So, you find out that these trans fats are more deadly than saturated fatty acids,” he said.
He noted that saturated fats also lead to fat deposits in tissues, creating pressure on arteries and veins. “They deposit fats inside the arteries where blood passes through and sometimes, outside the arteries,” he said.
According to Onimawo, these fat deposits harden the arteries, which should remain flexible. This hardening restricts blood vessel expansion and leads to high blood pressure. He explained, “They (trans fatty acids) hardened the arteries which are supposed to be flexible. So, when the plagues are there, that particular blood vessel becomes non-flexible. And therefore, when it is not flexible, it cannot expand to accommodate pressure, and if that happens continuously, the blood pressure begins to increase, and sometimes, that is the origin of high blood pressure.”
Onimawo also pointed out that high blood pressure serves as a precursor to other heart-related diseases. “If this continues, you know that high blood pressure is a precursor to a lot of things that have to do with heart disease,” he added.
The World Health Organisation (WHO) confirms that heating and frying oil at high temperatures increases trans fat concentrations, which are linked to heart disease. According to WHO, trans fats increase the risk of heart disease and related deaths by 28%.
“On average, the level of trans fat has been found to increase by 3.67 g/100g after heating, and by 3.57 g/100g after frying. Approximately 540,000 deaths each year can be attributed to the intake of industrially produced trans-fatty acids. High trans fat intake increases the risk of death from any cause by 34 percent, coronary heart disease deaths by 28 percent, and coronary heart disease by 21 percent.
“This is likely due to the effect on lipid levels: trans fat increases LDL (‘bad’) cholesterol levels while lowering HDL (‘good’) cholesterol levels. Trans fat has no known health benefits,” WHO said.
Onimawo’s warnings align with global health advice to limit trans fat consumption. The reuse and overheating of cooking oils contribute significantly to the transformation of healthy fats into harmful trans fatty acids, making it a major concern for public health.
