The widely used food preservative propionate may impair the action of insulin, according to US and Israeli researchers who have conducted a small study in humans and animals.

The short-chain fatty acid propionate, also known as proprionic acid, has potent anti-mould effects, and is generally recognised as being safe. It is endogenously produced by gut microbiota, the researchers say.

In a double-blind, placebo-controlled crossover study in 14 “lean and healthy” human volunteers, adding a typical preservative amount of propionate to a mixed meal increased glucagon and the levels of fatty acid-binding protein 4 and raised insulin resistance.

Furthermore, examination of serum samples from 160 overweight and obese volunteers taking part in a two-year dietary intervention trial showed that plasma propionate decreased with weight loss.