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Sounds a little unbelievable but could just drink water help you lose weight? According to the results of two recent studies the answer may be yes. In one investigation German researchers validated some of their work showing that drinking simple tap water increased thermogenesis. This time they had subjects come into the laboratory 3 separate times to measure the number of calories they burned after ingesting either 500 mL (about 2 cups) of tap water, 500 mL of water with saline (salt water), and 50 mL water. Energy expenditure started to increase rapidly after 500 mL of water reaching a maximum of 24% above resting after 60 min. This was greater than both the saline and 50 mL water trial. The total calories burned above resting over 90 min was 23 kcal during the 500 mL trial compared to 7 kcal during 50 mL water and 10 kcal during 500 mL saline. Exactly how tap water but not an equal volume of saline increases thermogenesis remains unclear but the authors suggested it was due to the lower osmolarity and stimulation of osmosensitive structures. In a separate study researchers tested whether consuming water before a meal could reduce the amount of calories consumed at that meal. They had overweight adults consume 500 mL of water or nothing 30 min before breakfast. Total calories consumed was 13% less when 500 mL of water was consumed before breakfast. These studies show that simply consuming 500 mL of water has a dual effect of increasing thermogenesis and decreasing appetite and food consumption. While the magnitude of the thermogenic and appetite suppressing effect might be considered relatively small, the cumulative effect could be substantial over a period of months.

Boschmann M, Steiniger J, Franke G, Birkenfeld AL, Luft FC, Jordan J.

J Am Diet Assoc. 2008 Jul;108(7):1236-9. Water drinking induces thermogenesis through osmosensitive mechanisms. J Clin Endocrinol Metab. 2007 Aug;92(8):3334-7. Epub 2007 May 22.

Davy BM, Dennis EA, Dengo AL, Wilson KL, Davy KP. Water consumption reduces energy intake at a breakfast meal in obese older adults. J Am Diet Assoc. 2008 Jul;108(7):1236-9