There is some evidence in humans to suggest that water intake may determine food intake. Fat is the most efficient source of metabolic water (ie, water produced when a food substance is broken down). Fat yields 107g of water for every 100g fat oxidised compared, for example, to 60g of metabolic water from the oxidation of the same amount of carbohydrate. In studies on animals, dehydration leads to a preferential selection of fat in the diet for use as a metabolic fuel. A study of dehydrated adult humans showed that lipid levels fluctuated according to hydration status. This suggests that the amount of fat burned by the body was influenced by whether or not they were dehydrated.(i)
Dehydration may therefore be an important determinant of lipid metabolism in humans. Stookey suggests that there may be a link between poor hydration status and the development of obesity, if dehydration stimulates a preference for a fat-rich diet. A high fat diet would supply fat as an oxidative fuel and could therefore be part of a compensatory mechanism to deal with perpetually low water intakes, or increased water requirements due to high-protein and high-salt diets.(ii)
Childhood obesity may be related to fluid intake. Levine reviewed the role of fluid intake as a factor in childhood obesity and disease and recommended replacing soft drinks in the diet with milk or water to help with weight control.(iii) One study (in men) has shown that caloric drinks taken with lunch increased total energy intake in that meal. In addition, sucrose-sweetened drinks may decrease thirst less than water, hence promoting their greater intake.(iv) Drink flavouring and sodium chloride have been shown to be important promoters of drinking activity in children.(v)
There has been recent concern about the increasing prevalence of type 2 diabetes in childhood which closely parallels the increase in childhood obesity across the Western world. In particular, the noted increase in childhood obesity in the UK may precede an increase in the incidence of type 2 diabetes in both white and ethnic minority groups.(vi)
Drinking a lot of water is commonly espoused in weight loss regimens.(vii,viii) For example, drinking water before a meal can help to fill the stomach and decrease appetite, thereby increasing the chance of weight loss. The observation that “drinking a lot of water can take the edge off hunger” has been confirmed by two studies in adult and child populations.(ix,x)
Water is a vital component of any healthy diet, including weight loss regimens. Recently, Boschmann et al(viii) investigated the effect of water drinking on adipose tissue metabolism. They found that drinking 500ml of water increased the metabolic rate by 30%. This increase began within 10 minutes of water consumption and reached a maximum at 30-40 minutes after drinking. The effect was sustained for more than an hour. The authors estimate that increasing water ingestion by 1.5 litres would increase daily energy expenditure by approximately 200 kJ. Although this is only a small increase, over the course of a year, this additional metabolic activity would burn 17,400 kcal, or the equivalent of the energy content of 2.4 kg of adipose tissue. The study also revealed differences between men and women in the type of substrate used to fuel the increase in metabolism. In men, the increase in metabolic rate was mainly fuelled by lipids, whereas in women, carbohydrates formed the main energy source.
About 40% of the metabolic effect resulted from the energy supplied by the body to warm the water from 22 to 37oC. The remainder of the metabolic response appeared to result from sympathetic nervous stimulation, the mechanism for which remains unclear. The authors concluded that water has an important effect on energy expenditure and fuel utilization by the body. Water induced thermogenesis should be recognised as an important component of daily energy expenditure. For overweight and obese individuals, water induced thermogenesis may be a useful additional component to increase the energy expenditure.
Last updated: November 2004
(i) Campbell NR, Wickert W, Magner P, Shumak SL. Dehydration during fasting increases serum lipids and lipoproteins. Clin Invest Med. 1994;17:570-76
(ii) Stookey JD. Another look at fuel + O2 -> CO2 + H2O. Developing a water-oriented perspective. Medical Hypotheses 1999;52:285-290
(iii) Levine B. Role of liquid intake in childhood obesity and related diseases. Curr Concepts Perspect Nutr. 1996;8(2)
(iv) Rolls BJ, Kim S, Fedoroff IC. Effects of drinks sweetened with sucrose or aspartame on hunger, thirst and food intake in men. Physiology and behaviour 1990;48:19-26
(v) Kennedy WL, Chiu P. Influence of age on thirst and fluid intake. Medicine and Science in Sports and Exercise 2001;33:1524-32
(vi) Drake AJ, Smith A, Betts PR, Crowne EC, Shield JPG. Type 2 diabetes in obese white childen. Arch Dis Child 2002;86:207-8
(vii) Appleby M. Why Drinking Water Really is the Key to Weight Loss. Inch-aweigh.com: weight loss through fitness. 2004 (http://www.inch-aweigh.com/water.html)
(viii) Boschmann M, Steiniger J, Hille U, Tank J, Adams F, Sharma AM, Klaus S, Luft FC and Jordan J. Water-induced thermogenesis. Journal of Clinical Endocrinology and Metabolism 2003;88:6015-19
(ix) Wadhwa NK, Friend R, Gaus V, Taylor KL, Schneider MS. Weight reduction and fluid intake in an obese and fluid concompliant ESRD patieht. Clin Nephrol 1996;45:320-324
(x) Vido L, Facchin P, Antenello I, Bogger D, Rigon F. Childhood obesity treatment: double blinded trial on dietary fibres (glucomannan) versus placebo. Padiatrie und Padologie 1998;28:133-36
