Weight loss and metabolism: Is water best?

Losing weight and maintaining a lower body weight thereafter can be challenging. A common misconception amongst people who want to lose weight is that drinking fruit juice is healthy. However, fruit juice contains calories, is usually drunk in excess and often contains added sugar. Another misconception is that energy drinks are healthy. Frequently, advertising for these high-calorie drinks depict athletes drinking them, whereas the significant majority of the population is sedentary. The beverage industry has done a good job in changing attitudes, and perhaps even palates, and water generally seems to be avoided. Then there is the bottled water industry, which discourages drinking tap water and prices its bottled water higher than some sugar-sweetened beverages. Individuals often switch to “diet” labelled beverages in order to aid weight loss and avoid weight gain.

Which is better for weight loss: diet beverages or water? To answer this question, Madjd and colleagues conducted a 24-week randomised controlled trial (summarised alongside) that included 81 obese women with type 2 diabetes undergoing a weight loss programme. The women were randomised to drink either water or a diet beverage after their main meal (lunch). The primary outcome was weight loss at 24 weeks. Women who drank water lost more weight, although the between-groups difference was small (just over 1 kg). Similar weight loss has been observed in obese women without type 2 diabetes in a previous study by the same group (Madjd et al, 2015).

Interestingly, at 24 weeks, the water group were consuming fewer calories (about 42 kcal less per day) and had lower carbohydrate intake (16.1 g less) than the diet drink group. This fits in with previous suggestions that artificial sweeteners in diet beverages increase a person’s desire for high-sugar, high-energy food and drinks. Of particular interest was the greater improvement in insulin sensitivity and reduction in insulin dose in the water-drinking group.

There were several limitations to this study, including its small numbers, short-term nature and lack of more accurate measures of body composition. The timing of drink intake in relation to the meal is also likely to be important. Parretti et al (2015) observed that water preloading before meals was associated with around 1 kg greater weight loss. It is also difficult to exclude the behavioural effect of being in a particular group, difficult to monitor adherence and difficult to determine the volume of drinks consumed.

In another recent study, Wong et al (2017) examined whether giving advice on water intake had beneficial effects on body weight in adolescents. The study included 38 adolescents who reported drinking four cups of water or fewer per day. The water advice group were advised to drink eight cups of water per day. Both groups were drinking around two cups of water daily at the beginning. At 6 months, the water advice group reported drinking 4.8 cups per day compared to 3.5 cups per day in the control group. Only one individual in the water advice group drank more than eight cups a day. Energy intake was non-significantly lower in the water advice group by 13 kcal, and carbohydrate intake was also reduced non-significantly. There was no difference in BMI between the groups at 6 months. In this study, an insufficient number of adolescents achieved the recommended level of water intake, which could have diminished the significance of the outcome.

The study by Madjd and colleagues provides key data regarding the impact of water, as opposed to diet beverages, on body weight and metabolic parameters. It appears, however, that persuading adolescents to increase their water intake is a major challenge. Sadly, adolescents are a key target for the beverage industry. Further studies will be needed to examine the impact of water intake on weight loss. In the meantime, continuing with the common dietary advice that water is best seems most appropriate.

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