Not all processed fats are bad, study finds

Two types of industrially processed hard fats, widely used in everyday foods such as bakery products, margarines and spreads, are unlikely to affect heart health when consumed in levels achievable in most people’s diets.

The study, led by researchers at King’s College London and Maastricht University and published in the American Journal of Clinical Nutrition, investigated the health effects of interesterified (IE) fats which are rich in either palmitic acid (from palm oil) or stearic acid (from other plant fats).

These fats are often used by the food industry as alternatives to other hard fats, including trans fats and animal fats, which have known risks to heart health.

In the trial, 47 healthy adults took part in a double-blind randomised crossover trial, meaning neither the participants nor the researchers knew which type of fat was being tested during the study period. Each person followed two different diets for six weeks each, which included muffins and spreads made with either palmitic acid-rich fats or stearic acid-rich fats, providing around 10% of their daily energy intake.

The researchers assessed a comprehensive set of cardiometabolic health markers, including cholesterol, triglycerides, insulin sensitivity, liver fat, inflammation and blood vessel function.

The findings showed no significant differences between the two fats in blood cholesterol or triglyceride profiles, including the ratio of total to HDL cholesterol, a key indicator of cardiovascular risk. The study also found no adverse effects on inflammation, insulin resistance, liver fat or vascular function.

Sarah Berry, senior author and Professor of Nutritional Sciences at King’s College London, said: “With the current demonisation of everything processed, this research highlights that not all food processing is bad for us! The process of interesterification allows the generation of hard fats in place of harmful trans fats, whilst also enabling manufacturers to reduce the saturated fat content of spreads and foods. Given the widespread use of the process of interesterification of fats and the fearmongering around food processing, this research is timely.”

The results suggest that both palmitic acid- and stearic acid-rich interesterified fats, when consumed in feasible amounts, do not increase short-term risk factors for heart disease.

Wendy Hall, lead author and Professor of Nutritional Sciences at King’s College London, said: “Our findings provide reassuring evidence that industrially processed fats currently used in everyday foods, whether rich in palmitic or stearic acid, are unlikely to have harmful effects on cardiovascular health when consumed in amounts that people could achieve in their everyday diets. This is important given the widespread use of these fats in processed foods such as margarines, pastries and confectionery.”

While the trial lasted six weeks, which is sufficient to detect meaningful changes in cholesterol and other cardiovascular risk factors, further studies are needed to evaluate longer-term effects.

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