Anti-mould ingredient in bread could be fuelling obesity epidemic, Harvard warns

A common preservative used to prevent bread and cakes going mouldy could be fuelling the obesity crisis by harming metabolism, scientists at Harvard University have warned.

Propionate is widely used in baked goods, animal feed and artificial flavouring but appears to increase levels of hormones which trigger weight gain and diabetes, according to new research.

Researchers at Harvard TH Chan School of Public Health carried out two studies, one in animals and one in humans, which showed propionate triggers a ‘cascade of metabolic events’ that can lead to insulin resistance and weight gain.

“Understanding how ingredients in food affect the body's metabolism at the molecular and cellular level could help us develop simple but effective measures to tackle the dual epidemics of obesity and diabetes,” said Professor Gokhan Hotam, Director of the Sabri Ulker Center for Metabolic Research.

Around two thirds of adults in Britain are now overweight or obese and there are around 4.6 million people living with Type 2 diabetes.

Experts have previously speculated that modern dietary ingredients used for preparation or preservation of food may be a contributing factor, but there has been little research.

For the study, the researchers administered propionate to mice and found it led to a surge in hormones, including glucagon, norepinephrine and a gluconeogenic hormone called fatty acid-binding protein 4 (FABP4).

This in turn led the mice to produce more glucose from their liver cells, leading to hyperglycemia - a defining trait of diabetes where there is too much sugar in the blood.

The researchers also found that a dose of propionate that was equivalent to the amount typically consumed by humans led to significant weight gain in the mice, as well as insulin resistance.

A further study in 14 humans found those who consumed the meal containing propionate had significant increases in norepinephrine as well as increases in glucagon and FABP4 soon after eating the meal.

Researchers say the findings indicate that propionate may act as a ‘metabolic disruptor’ that potentially increases the risk for diabetes and obesity in humans.

“The dramatic increase in the incidence of obesity and diabetes over the past 50 years suggests the involvement of contributing environmental and dietary factors,” said Dr Amir Tirosh, Director of the Institute of Endocrinology at Israel's Sheba Medical Center, Tel HaShomer.

“One such factor that warrants attention is the ingredients in common foods. We are exposed to hundreds of these chemicals on a daily basis, and most have not been tested in detail for their potential long-term metabolic effects.”

However scientists in Britain urged caution.

Prof Keith Frayn, Emeritus Professor of Human Metabolism, University of Oxford, said: “The study appeared to be of high quality in mice, but the human data were less convincing.

“More research in humans would be needed before condemning use of propionate as a food additive.”

The research was published in the journal Science Translational Medicine.