The more water in the food you eat, for example in yoghurt, fruit, meat or fish, the thinner you are likely to be. And the other way round, a diet consisting largely of foods that contain little water leads to obesity. Japanese epidemiologists have published an article on the subject in Nutrition.
Drinking water during a meal does not help to reduce caloric intake, but if you prepare rice dishes using more water, then the caloric intake does decrease, studies have shown.
The Japanese examined the relationship between bodyweight and the amount of water you consume daily through drinks and through solid foods. They collected data on bodyweight and body composition of 1200 women between 18 and 22, and asked them what they ate.
The researchers calculated the amount of water the women consumed daily through solid food and drinks, and then made quintiles: they divided the women according to their water intake into five equal-sized groups. Then they calculated the average BMI and waist-measurement for each quintile. The results for the first and fifth quintiles – the groups with the lowest and the highest water intake – are shown below.
The amount of water the women consumed through drinks had no influence – but the amount of water consumed through food did. The more water in the solid food, the thinner the women.
The researchers do not know how exactly why this is so. The wetter the food, the more proteins and the less carbohydrates it contains, according to the information in the table below. We have also simplified this table to show only the first and fifth quintiles.
The Japanese don’t know what it is in water-rich products that makes them slimming. Is it that they contain more protein? Or because they contain fewer carbohydrates? Fewer joules? Or the water itself? They really have no idea. "Any firm conclusions regarding the influence of intake of water from foods and from beverages on obesity require additional studies", they conclude.
Nutrition. 2008 Oct;24(10):925-32.