Swapping half a pint of beer for a glass of water could slash the risk of obesity by one fifth, research suggests.

The Spanish study tracked almost 16,000 people for more than eight years. It found that swapping one high sugar beverage a day for water made a huge difference to obesity risks.

Reducing beer intake by half a pint a day had the greatest impact. But replacing a glass of sugary soft drink with water was almost as effective.

Experts at the world’s largest obesity conference said the simple change is an easy way of beating the bulge - and protecting against fat-related illnesses such as type 2 diabetes and heart disease.

Around two in three British adults are overweight or obese.

Spanish researchers followed 15,765 adults who were not fat at the start of the study. They measured their consumption of 17 different drinks and tracked their weight.

After eight years, 873 participants were obese. The study found drinking one less glass of beer daily (330ml) and having water instead, reduced the risk of being overweight by 20 per cent. And ditching a daily serving of sugary fizzy drink cut the chance of becoming obese by 15 per cent.