Water is one of the most mundane yet important substances on earth. Over 50% of our body is made up of water, with the average water content slightly higher in men than in women. Most of us probably have heard the slogan that tells us to drink 8 glasses (or 2 litres) of water a day and yet, it was reported that around 75% of the population in America (Australian data not available) may be suffering from chronic dehydration due to a lack of water intake or/and an excessive amount of dehydrating beverage intake. We don't drink enough water. While drinking water has obvious benefits such as thirst quenching and life sustaining, it is the weight loss effect of water drinking that motivated me to write this article and to share this unusual information with you.
Drinking room temperature water (22°C) can induce a thermogenic response, partly due to the fact that the body has to warm up the water to 37°C after ingestion. How much energy does it take for the body process water? Boschmann et al found in 2 independent studies using healthy male and female subjects that drinking 500mL of room temperature water can increase metabolic rate by up to 30% over the course of 60 minutes after ingestion. This energy-burn generally begins from 10 minutes after water ingestion and reaches maximum at around 30-40 minutes after ingestion. It's estimated that 100kj of extra energy is spent by the body to process 500mL of water. That is 400kj of extra energy expenditure per day if you drink the recommended 2 litres of water, which is equivalent to roughly 20 minutes of moderate-intensity exercise. This may not seem much to some, but for those who want to lose weight, every calorie counts, especially when you can burn them by just drinking the recommended amount of water. The catch however, is that researchers found drinking a small amount of water (50mL) does not induce a thermogenic response, you have to do it in relatively large quantities, i.e. 500mL portions (Boschmann et al 2003 and 2007, Journal of Clinical Endocrinology and Metabolism). So the recommendation of 8 glasses of water 8 times a day should be modified into 8 glasses of water, 4 times a day, 2 glasses each time, if you want to take advantage of the thermogenic effect of water for weight loss.
The timing of water consumption may also help with weight loss. It was found that premeal water consumption (again in 500mL portion) could significantly reduce energy intake during a meal. A 44% greater reduction in weight was also observed in middle-aged and older adults with BMI of 24 - 40 after 12 weeks of premeal water treatment while on a low calorie diet compared to those on a low calorie diet alone without the water (Dennis et al 2010, Obesity). Other studies have also confirmed the energy intake reduction property of consuming 375 - 500mL of water before a meal in healthy and obese adults aged 55 and above (Van Walleghen et al 2007, Obesity; Davy et al 2008, Journal of American Dietetic Association). However, this energy intake reducing effect was not observed in young health adults aged between 21 - 35 (Van Walleghen et al 2007). No studies that examined the effect of premeal water consumption on energy intake reduction in obese young adults were found during my literature research while writing this article. Therefore, while drinking 500mL of water before a meal may help you to lose weight by reducing energy intake if you are over 55, I cannot comment on the effectiveness of this strategy if you are under the age of 35.
Drinking enough water can ensure good health and increase energy expenditure, which could help with weight loss. I hope this article gives you enough incentive to follow the doctor's recommendations on water drinking. Go fill up your glasses and drink up.