Impact of Water Intake on Weight Loss

As previously discussed, water intake is vital but can also be done to excess.  When it comes to weight loss (fat loss), though, does water intake make a difference?  Can increased water intake increase metabolism and/or fat burning?  The answer is not as clear as your water should be, and there are several possible mechanisms at play.

1. Appetite

Drinking excess water (e.g. 1.5 L water over and above one’s usual daily intake) appears to decrease appetite.  This strategy may take the form of an increased intake throughout the day or of loading the stomach with water prior to a meal, thereby contributing to a sense of fullness.

It’s worth nothing that it is common for humans to misinterpret sensations of thirst as hunger.  Thus, when you feel hungry, it is prudent to first address possible thirst, as hydration may alleviate that hunger sensation.

2. Calorie burning

Water intake certainly has an impact on our physiology.  In individuals with autonomic failure (impaired function of the nervous system), water drinking causes a significant rise in blood pressure.  (In healthy individuals, with an intact autonomic nervous system, the body adapts quickly to a bolus of water to prevent a spike in the blood pressure.)   In addition, water drinking appears to cause a slight increase in energy expenditure.  Both of these appear to be due to activation of the sympathetic nervous system – the “fight or flight” response.

Here’s where it gets confusing.  A study in 2003 demonstrated that drinking 500 mL of water caused an increase in metabolic rate by 30%.  Several other studies, however, refuted that finding, including one demonstrating only a 4.5% increase in energy expenditure after drinking chilled water and others with no effect of water drinking on metabolic rate.  So, which is it?  Keep reading . . .

3. Displacement of caloric beverages

Sugar-sweetened beverages, such as juice and soda, have little nutritional value and are associated with poor metabolic health – weight gain, diabetes, cardiovascular disease, and cancer.   Thus, there is a clear benefit to drinking water as a calorie-free replacement for them.  This benefit likely extends beyond the sugar-sweetened beverages to other calorie-containing beverages.

4. Water intake and Glucose Tolerance

The hormonal response to dehydration (increased vasopressin, i.e. antidiuretic hormone) appears to be related to elevated blood glucose concentration and may be a risk factor for cardiometabolic disease.  An interventional study is underway to investigate if supplementing water in individuals with elevated vasopressin can reduce their fasting glucose levels and other cardiometabolic disease.

 

Best evidence for water and weight loss

The closest thing to a definitive answer comes from a systematic review of 6 randomized controlled trials.  The overall reduction in weight after a water consumption intervention was 5.15%.  Intervention strategies included increased water intake, replacement of caloric beverages, and loading with water before meals.  Replacing caloric beverages with water was the most effective approach for weight loss.  One limitation of the evidence from this review, however, is that the quality of the included studies was rated low to moderate.

Takeaway

There is promising evidence that increased water intake is beneficial for weight loss.  The first priority should be replacing caloric beverages with water, which appears to be the most effective intervention in terms of water drinking.  Then, one should focus on consuming water when one feels hungry and before meals.  Though not likely to have a substantial impact on weight, a strategy of increasing water intake likely provides modest benefits.