We don’t have strong evidence that diet drinks in themselves cause weight gain, as some media headlines have suggested. Some scientific studies have found an association between people drinking diet drinks and obesity. However, these studies observed people over time rather than asking people to make specific changes to the drinks they chose, so it’s possible that this association was due to obese people being more likely to choose diet drinks. Studies where researchers give people diet or sugary drinks and monitor their diet and weight, generally find that those given diet drinks consume fewer calories and, in the longer term, have lower bodyweight than those who consume sugary drinks.

What happens when you have diet instead of sugary drinks?

When you have a diet drink, or indeed any low-calorie drink instead of a sugary drink you consume fewer calories. Studies suggest that, when the effects of having low-calorie drinks instead of sugary drinks are tested in a controlled trial, people tend not to consume more of other foods and drinks to fully make up for having fewer calories from the diet version. Short-term studies (that last 1 day or less) show they consume fewer calories overall and, in longer term studies (over weeks or months)  people tend to have lower bodyweight. However, it’s important to remember that this only works when you don’t replace the calories saved with extra calories from other foods and drinks – if calorie intake from the diet overall isn’t controlled then this won’t help with weight control.

Does having diet drinks make you eat more?

It has been suggested in the past that having a sweet taste without any calories could make you feel hungrier and therefore eat more. However, this has not been supported by more recent research. It is possible that people might use choosing diet drinks as an excuse to eat more, but this hasn’t been found in studies that have looked specifically at the effects of replacing sugary drinks with diet versions.

Will choosing diet drinks help me lose weight?

If you swap from sugary drinks to diet versions (or any other low-calorie option) then you can make significant calorie savings and, over time, this can help you to lose weight, provided the rest of your diet is calorie-controlled. However, to lose weight and keep it off you need to make changes across your diet and lifestyle to have a healthy, balanced diet and to keep active.