Weight loss advocates recommend daily consumption of ample water, possibly up to a gallon (about 4.5 liters) for individuals looking to lose weight. The advocates argue that water aids in calorie burning and appetite reduction, facilitating weight loss. Although this has been championed for a while there is little evidence backing this claim.
Drinking water to burn calories is short lived
There is the presumption that water helps in burning calories but the effects may not last long. For instance in a study of adolescents, drinking 500 ml of water was found to increase resting energy expenditure by 24% but the effect was short lived (approximately an hour). Ordinarily an average adult is likely to use an extra 20 calories for each 500 ml of water they drink.
In another study, researchers observed an increase in energy expenditure whenever subjects took fridge cold water with a partly 4% surge in burned calories. The reason behind this could be because the body uses extra calories to bring the water o room temperature or because of the requirement of more energy to filter increased fluid volume through the kidneys.
While there is a scientific possibility that increasing water intake may lead to a slight increase in calorie expenditure, the actual impact is minimal. For instance, consuming an additional 1.5 liters of water daily would burn fewer calories than eating a single slice of bread.
Drinking water reduces appetite
The other claim is that drinking water with meals reduces appetite since the stomach will feel partly full. This is an assertion that is supported through a number of studies in older and middle aged adults and the reasoning behind advising people with poor appetite to avoid water before eating. However if you want to lose weight the science behind it is less straightforward.
Water alone isn’t very effective at controlling appetite, as demonstrated by the fact that prehistoric humans would have starved if it were. However, understanding appetite and feeling full can be a useful starting point for weight loss, even though they aren’t perfectly correlated.