If you don’t drink enough water, you can easily become dehydrated. Many actually mistake their thirst for hunger, and this is one of the basic premises behind the idea that drinking water may alleviate hunger and help you lose weight.

Many studies support this idea though, so it’s not just pure hype. Most recently, researchers found that adults who were chronically under-hydrated had higher body mass index (BMI) and were more likely to be obese compared to well-hydrated adults.^1,2,3,4,5

A BMI of 25 is considered overweight; 30 obese. Those deemed sufficiently hydrated had an average BMI of 28 whereas inadequately hydrated individuals had an average BMI of 29.

While this study does not prove drinking more water will help you lose weight, it does suggest staying well-hydrated is associated with slightly lower body weight.

On the other hand, a 2013 systematic review of 11 studies and two other meta-analyses concluded that while high-quality studies were still lacking, increasing your water consumption when on a diet does appear to be helpful for weight loss.⁶

Studies looking at general populations that were not necessarily trying to lose weight found that increasing water consumption yielded inconsistent results.