Water: a dieter's best friend?
We all know that water is the most vital requirement for human life. While our bodies can survive without food for around 3 weeks, without water we can only live for 3 days. There are many myths surrounding water and weight loss, but can drinking water really help you lose weight?
In recent years, drinking large quantities of water has become one of the mantras for healthy living. Every magazine has had its version of ‘drink water and be healthy’ or ‘drink water and lose weight’. However, despite the fact that most diets call for drinking at least 8 glasses of water a day, few studies have been carried out to determine if this practice actually speeds weight loss.
Can drinking water speed up your metabolism?
Myth: drinking a glass of ice-cold water first thing in the morning will make you lose weight
Researchers in Germany have reported that water consumption actually increases the rate at which people burn calories (1). They tracked energy expenditure among 14 healthy, normal weight subjects and found that after drinking 500 ml of water, the subjects' metabolic rates - or the rate at which calories are burned - increased by 30% for both men and women. The increases occurred within 10 minutes of water consumption and reached a maximum after about 30-40 minutes.
The total thermogenic response was about 100 kJ. They noted that up to 40% of the increase in calorie burning originated from the body's attempt to heat the ingested water from 22-37°C. The study also showed that the increase in metabolic rate differed in men and women. In men, burning fat fueled the increase in metabolism, whereas in women, carbohydrates were mainly used as the energy source.
The researchers estimated that a person who increases their water consumption by 1.5 litres a day would augment daily energy expenditure by approximately 200 kJ. This means that, over the course of one year, energy expenditure would increase by 73,000 kJ (17,400 kcal) for a weight loss of approximately 2.4 Kg or 5 lbs.
While this study appears to support the myth that drinking cold water will make you lose weight, larger studies are clearly needed to confirm this extremely modest weight-loss effect. And, even if the findings are confirmed, the clinical implications for overweight/obesity treatment are likely to be slight.
Can drinking water make you feel full?
Myth: drinking a glass of water 30 minutes before a meal will make you lose weight
Drinking water before a meal helps to fill the stomach and increases the chance of weight loss by making the person eat less. A recent study (2) conducted in 48 overweight/obese middle-aged and older adults found that drinking 500 ml (2 cups) of water 30 minutes before each meal combined with a low calorie diet led to a 44% greater rate of weight loss than a low calorie diet alone. This translated into a 2 Kg greater weight loss over 12 weeks.The authors concluded that this effect was probably due to an increase in fullness following water ingestion, thereby promoting a reduction in energy intake from the meal.
However, while the effectiveness of pre-meal water consumption for weight loss has been seen in overweight and obese middle-aged and older adults, there is less evidence for its benefit in younger people (3), suggesting there may be age-related differences in the ability of water to acutely reduce energy intake. It is known that gastric emptying slows down as people age, which may be why water helps older people feel fuller for longer.
While drinking water may make you feel fuller and therefore satisfied eating a bit less, drinking water alone may not have this effect. In order to feel satiated, our bodies need bulk, calories and nutrients.
While drinking water is not a magical solution for weight loss, it is certainly a helpful tool for dieters. It has no calories, it may help you feel fuller so that you eat less and, as an added bonus, it will help you burn a few extra calories. Replacing caloric beverages with water will also save you extra calories for a faster weight loss (4). Drinking tap water is fine and it is free, so keep drinking!
Written by Victoria Trowse
1. Boschmann, M. et al. (2003). Water-induced thermogenesis. Journal of Clinical Endocrinology and Metabolism, 88 (12): 6015-6019.
2. Dennis, E.A. et al. (2010). Water consumption increases weight loss during a hypocaloric diet intervention in middle-aged and older adults. Obesity, 18: 300–7.
3. Van Walleghen, E.L. et al. (2007). Pre-meal water consumption reduces meal energy intake in older but not younger subjects. Obesity (Silver Spring), 15: 93–99.
4. Tate, D.F. et al. (2012). Replacing caloric beverages with water or diet beverages for weight loss in adults: main results of the Choose Healthy Options Consciously Everyday (CHOICE) randomized clinical trial. American Journal of Clinical Nutrition. Published online February 1 2012.