Water is an essential component of human health, and studies suggest that water consumption, in its pure form, is decreasing as other beverages become cheaper and more widely available. Water is required by cells in order to maintain the aqueous medium that allows chemical reactions to occur, and this is a tightly regulated homeostatic mechanisms. Studies suggest that drinking water may increase metabolic rate and estimates of this increase have shown that it may be as high as 30 % following consumption of 500 mL of cold water. This effect has been shown to occur 10 min post consumption, and peak 30 to 40 min post consumption. However, while some studies have shown a thermogenic effect for water, some have failed to detect a rise in the thermogenic rate following consumption of water. This may relate to methodological differences between these studies. For example, heating the water to 37 ℃ attenuated the the thermogenic effects of water, suggesting that the temperature of the water is an important consideration.
One study1 administered a 7.5 mL water per kg body weight (~518 mL water), a 0.9 % saline drink or a 7 % sucrose drink to health human volunteers and then monitored that rise in resting metabolic rate subsequently. Neither the plain water nor the saline drink caused an increase in resting metabolic rate compared to the baseline readings in the subjects. However, the sucrose drink did cause an increase in resting metabolic rate, likely due to the oxidation of the sugars in the drink, a phenomenon known as the thermogenic effect of food (TEF). Therefore it is not exactly clear as to the thermogenic effect of water, as studies to date have been inconsistent. Although a thermogenic effect of water may be perceived to cause weight loss in obese subjects if found to exist, the real advantage of drinking water may be that its substitution for colorific drinks results in a decrease in total sugar intake. The recommendation to drink more water is therefore still valid even in the absence of a known thermogenic effect.
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