Eight Glasses of Water

Chapter summary

• Your body needs some water. Drink water, but you do not need eight 8-oz glasses (1.9 litres) a day.
• Count tea and coffee in your total.
• Avoid sugar-sweetened beverages (SSBs). That includes gin and tonic and rum and Coke. Have spirits on the rocks.

The “8 x 8” claim

• Dr Karl of ABC Australia pointed out that the advice appears everywhere, from newspaper health columns to university pamphlets, with no scientific base.
• The conventional rule is 1ml of fluid per calorie burned, about eight 8-oz glasses for 2,000 calories. It rests on panel advice and not on evidence. Valtin (2002) searched for evidence for “8 x 8” and did not find it.
• The claim that we are chronically dehydrated and our bodies are not sensitive enough to make us thirsty is, from a physiological point of view, “rubbish”.
• You get water from green leafy vegetables and fruit. If you eat processed food, you may need more.
• Drinking constantly means frequent toilet trips and possible loss of minerals.

Two views

• Official dietary panel: The US Institute of Medicine panel (2005) gives total water intake guidance, with most coming from drinks.
• The author: Adequate hydration is essential for blood volume, kidney function and avoiding constipation, but it does not need to be forced. Drink when thirsty.
• Coffee: Some say it should not count. The author says it should.

Where water does help

• Water has no calories or additives, is cheap, widely available and generally safe.
• Energy intake is 9% (194 kcal a day) lower in water drinkers than non-water drinkers (Popkin 2005).
• German schoolchildren given water instead of SSBs for a year cut their risk of being overweight by 31% (Muckelbauer).
• Replacing sweetened drinks with water is linked to lower energy intake (Stookey 2007).
• Water before or with a meal reduces hunger. Middle-aged and older adults on a low-calorie diet lost more weight when they drank more water (Dennis 2010).
• Sweet drinks, including artificial sweeteners, can affect appetite (Black 1993).

Take-away points

• The benefit is in replacing sugary drinks, not in the volume.
• Keep water handy, drink when thirsty and skip the target.

References

• Valtin, H. (2002) “Drink at least eight glasses of water a day.” Really? Am J Physiol Regul Integr Comp Physiol 283:R993-1004.
• Popkin, B., Barclay, D. and Nielsen, S. (2005) Water and food consumption patterns of U.S. adults from 1999 to 2001. Obes Res 13:2146-2152.
• Muckelbauer, R. et al. (2009) Promotion and provision of drinking water in schools for overweight prevention. Pediatrics.
• Stookey, J. et al. (2007) Replacing sweetened caloric beverages with drinking water is associated with lower energy intake. Obesity 15:3013-3022.
• Dennis, E. et al. (2010) Water consumption increases weight loss during a hypocaloric diet intervention. Obesity.
• Jequier, E. and Constant, F. (2009) Water as an essential nutrient. Eur J Clin Nutr.
• Black, R., Leiter, L. and Anderson, G. (1993) Consuming aspartame with and without taste. Physiol Behav 53:459-466.