Drinking 500 mL of water increases the metabolic rate by 30%, with a peak observed between 30 and 40 minutes, and a different use of energy substrates (lipids vs. carbohydrates) depending on sex.

noli's read

This advice is based on a study published in the Journal of Clinical Endocrinology & Metabolism (PMID 14671205). It is accurate that this study observed an increase in energy expenditure of approximately 30% after the ingestion of 500 mL of water in the 14 participants. However, it is important to note that this effect is transient (lasting about one hour) and represents a fairly modest total caloric increase over the course of a day. The claim regarding the metabolic distinction between men (lipid oxidation) and women (carbohydrate oxidation) is indeed mentioned in the results of this small observational study. It should be kept in mind that the sample size is very limited, which restricts the generalizability of these conclusions to the entire population. In summary, the effect is real but physiologically minor for significant weight loss.

the sources

No named source held this one up — that absence is part of the verdict.