Which Types Of Fat Are Bad For The Heart?

Many people believe that diets high in fat will lead to a greater risk of heart disease in later life however this is not necessarily the case. Countries such as Spain, Greece, Italy, and France all have remarkably low rates of heart disease while consume a Mediterranean style diet that is relatively high in fat.

Recent scientific studies point instead to two specific types of fat, trans fats and saturated fats, which are thought to increase the risk of cardiovascular disease.

The largest study on the effects of fat intake on heart disease was published in The New England Journal of Medicine in 1998. The research was conducted at the Harvard Medical School and involved more than 80,000 women from the Nurses’ Health Study (NHS) who were followed over a 14 year period.

Over the course of the study, 939 of the women developed heart disease. The researchers found that both saturated and trans fats led to an increase in the risk of heart disease while polyunsaturated and mono-unsaturated fats both reduced heart disease risk.

The researchers calculated that a 5% increase in calories increased heart disease risk by 17% (relative to carbohydrate calories). A 2% increase in energy due to trans fats was calculated to increase heart disease risk by 93%. This means calorie for calorie, trans fats have almost ten times the impact on heart disease compared to saturated fats.

In contrast, a 5% increase in energy due to mono-unsaturated fat and poly-unsaturated fat was found to decrease heart disease risk by 19% and 38% respectively.

The authors also found that animal fats as a whole increased heart disease risk while fat from plant sources reduced risk slightly. A small positive trend was observed between dietary cholesterol and heart disease however the relationship was not statistically significant.

Trans fats are produced in an industrial process where unsaturated fats are partially hydrogenated in order to increase their melting point. Both saturated and trans fats are thought to increase heart disease risk by increasing levels of LDL cholesterol. Trans fats are further thought to lower levels of the beneficial HDL cholesterol. It is thought that trans fats are responsible for more than 35,000 heart disease deaths each year in the United States.

Trans fats are not widely found in natural foods but are common in processed goods such as french fries, spreads, dips, biscuits, pies, and other snack foods. A small amount of trans fat is also present in animal milk and fat. Foods high in saturated fat include beef, pork, coconut oil, palm oil, full-fat milk, butter, cream, eggs, and bacon.

Mono-unsaturated and poly-unsaturated fats on the other hand are thought to increase HDL cholesterol while decreasing LDL cholesterol levels. Rich sources of unsaturated fats include avocados, seeds, nuts, soybean oil, canola oil, olive oil, and most varieties of oily fish.