The recommendation to consume ample water daily for weight loss is widely circulated, sometimes even suggesting a gallon (around 4.5 liters). Proponents argue that water aids calorie burning and curbs appetite, leading to weight loss. However, these assertions lack substantial scientific backing.

Amount of calories burnt by drinking water insignificant

The idea that drinking water helps burn calories is a common myth. For instance a small study on 14 young adults showed that drinking around 500ml of water boosted resting energy expenditure by around 24%, with the effect lasting only for an hour. This would result in a minimal difference,. However for a 70kg adult it will require adding about 20 calories for every 500ml one drinks.

Another study on eight young adults found a 4% increase in calories burned when drinking cold water, possibly due to the body needing to warm the water or filter the increased fluid volume. However, this effect was also short-lived, lasting about an hour. In reality, the actual increase in calories burned is insignificant. Even consuming an extra 1.5 liters of water per day would save fewer calories than a slice of bread.

Drinking water before meals reduces appetite

The other myth is that drinking water with meals can reduce appetite in older and middle aged adults and individuals with poor appetites. However, the connection between water consumption and weight loss is less straightforward. Research indicated that middle-aged and older adults lost 2kg over 12 weeks when they drank water before meals, while younger participants (21-35 years old) did not experience weight loss regardless of water intake. Nevertheless, the overall calorie reduction from this practice is minimal, with an additional 1.5l of daily water intake saving fewer calories than a single slice of bread.

While water might have some appetite-dulling effects, it’s unlikely to lead to significant weight change over time. This effect could be attributed to making deliberate dietary adjustments. It is important to note that water alone is insufficient for regulating appetite, and this is because if it were effective, prehistoric humans might have faced starvation.