Pills that expand in the stomach could provide doctors with an effective new tool for the fight against obesity.

The capsules, taken with water before lunch and dinner, mix with food and liquid to create a gel-like mass that gives a feeling of fullness despite eating smaller portions.

Scientists behind the innovation say the pills are made from the “naturally derived building blocks” cellulose and citric acid.

Classed as a medical device rather than a drug, the treatment does not have the side-effects associated with weight-loss aids that rely on stimulants.

Harry Leider, chief medical officer of the manufacturer Gelesis, told The Times: “We are really optimistic that millions of people will benefit.

“There really is an unmet need for new treatments that are effective for the majority and are really well tolerated.”

There are hopes the pills will help obese patients lose weight without the need for gastric band surgery or medication.

A study of nearly 440 overweight and obese adults showed six out of 10 had a “meaningful response” after taking the pills, which are marketed as Plenity.

The participants lost an average of 10% of their weight, the equivalent of 22lb (10kg) or 3.5in (9cm) from their waist.

The results were presented at the European Congress on Obesity in Glasgow.

A major study revealed at the event suggested that being obese is linked to a significantly higher chance of serious disease and early death than being a healthy weight.

Research on more than 2.8 million adults found that people with a body mass index (BMI) of 30 to 35 were at 70% higher risk of developing heart failure than their healthy weight peers.

Even a BMI of 25 to 30 increased the risk by 20%, while a BMI of 35 to 40 more than doubled the risk and a BMI of 40 to 45 almost quadrupled the risk compared with people of a normal weight.