A starch supplement was linked to weight loss in a study. The same substance is found in leftover pasta.

• A resistant starch supplement has been linked to weight loss in a new study.
• Resistant starch is a hard-to-digest fiber thought to boost gut health.
• It occurs naturally in certain foods too, such as leftover pasta.

Taking a resistant starch supplement before meals has been linked to weight loss in a small study.

Resistant starch is a type of fiber that is harder to digest than regular starch, and is thought to boost gut health and help minimize blood sugar spikes.

"It doesn't get digested in the small intestine and then goes on to ferment," registered nutritionist Rhiannon Lambert previously told Business Insider.

In the study published in Nature Metabolism, 37 overweight people consumed a sachet of a resistant starch supplement mixed with water twice a day before meals for eight weeks.

After a four-week break, participants were given sachets containing regular starch and asked to do the same for another eight weeks. They were given three balanced meals a day throughout the experiment, and various health markers were monitored.

Participants lost an average of 2.8 kilograms (6.2 pounds) over the first eight weeks, and experienced no weight change while taking the regular starch.

Resistant starch supplements tend to cost about $1 per serving.

Leftover carbs contain more fiber thanks to resistant starch

While the study was too small to provide conclusive evidence, the authors said it's possible that the resistant starch boosted gut health, which in turn aided weight loss.

Stool samples taken during the study suggested that the resistant starch helped levels of several bacterial species in the participants' guts to increase.

The researchers said that dietary changes that affect the gut microbiome could be a "promising anti-obesity strategy."

Rebecca McManamon, a spokesperson for the British Dietetic Association, told New Scientist that the results of the study are "logical."

Resistant starch is also found naturally in certain foods. When cooked carbs such as pasta, potatoes, and rice are cooled, the levels of resistant starch increase and stay there even if leftovers are then reheated, Lambert said.

Resistant starch converts into sugar more slowly than regular starch and means the carbs' fiber content is higher. This helps reduce rises in blood sugar, which can be beneficial for those with diabetes or prediabetes.

However, more resistant starch isn't necessarily beneficial for everyone — those with irritable bowel syndrome sometimes find that it leads to bloating and discomfort, McManamon said.