Hard-to-digest starch supplements may help people lose weight

A supplement containing a kind of carbohydrate that takes longer to be digested, called resistant starch, has helped people lose a modest amount of weight in a small trial.

Resistant starch is naturally found in beans, wholegrains, raw oats and green bananas, and also forms when common starchy foods like potatoes, pasta and rice are left to cool down after being cooked.

There are several different forms of resistant starch, but what they have in common is that the structure of the molecules means they can’t be easily digested and absorbed in the small intestine.

The starch therefore reaches the large intestine, further along the gut, where it is digested by bacteria, meaning it is classed as a prebiotic.

While some previous studies have suggested that this starch can help people lose weight, Huating Li at Shanghai Jiao Tong University School of Medicine in China and her colleagues investigated its effects on our gut bacteria.

They asked 37 overweight people to consume a sachet of starch mixed with water twice a day before meals. For eight weeks, they were given resistant starch, while, for another eight weeks, the packet contained ordinary starch as a comparison. Participants were also provided with three balanced meals a day and various health indicators were measured.

After having the resistant starch for eight weeks, people lost an average of 2.8 kilograms, while the ordinary starch had no effect on weight. The resistant starch also caused less of a rise in blood sugar after meals, which may be good for health.

Stool samples revealed that while people were taking resistant starch, several bacterial species became more numerous in their guts. When these bacteria were transplanted into mice that were given a high-fat diet, they seemed to have a weight-reducing effect.

Rebecca McManamon, a spokesperson for the British Dietetic Association, says the trial was too small to be definitive, but the findings are plausible. “It’s logical that these results would happen,” she says.

However, some people with irritable bowel syndrome may find that eating resistant starch results in bloating and discomfort due to the bacteria creating gas as they break it down, she says.