Those who replace unhealthy drinks with water once a day for four years also lose weight, according to a study of nearly 16,000 people.
A 200ml glass of fizzy drink, swapping it for water, you will cut your risk of becoming obese by 15 per cent.
Beer and fizzy drinks are so calorific may be to blame.
A bottle of beer typically contains 142 calories, while a 200ml glass of soft drink such as Coca-Cola typically contains 78 calories.
Those who drink beer are also more likely to consume extra calories, such as on a night out, while people who drink sugary drinks probably also have unhealthy diets.