Weight loss effects of water
The apparent weight loss effects of water are still a subject for further research, but there is some evidence that suggests that drinking water can be associated with appetite reduction (for middle-aged and older people), consuming fewer calories, burning slightly more calories, and eating more fruits and vegetables[fn 1]. Increased water consumption, or replacement of energy-containing beverages with energy-free beverages, or consumption of water-rich foods such as fruits and vegetables with a lower energy density, may help in weight management. Popular advice to children regarding water consumption is often inaccurate.
This evidence has been used by some of the scientists who worked on this research, and by others, to bolster suggestions that people who are trying to lose weight can benefit from augmenting – but not replacing – their dietary programs by drinking water, either before meals or at any time. Such advice had previously been given by dieticians even before the most recent research was published.
In the case of appetite reduction, the apparent effect has been reproduced in a published study in adults aged 55–75, half of whom were instructed to drink 500ml of water before every meal, while following a low-calorie diet. This behaviour led to the water-drinking cohort losing weight faster over a 12 week period. On average, the water-drinking cohort also continued to lose weight - although at a slower rate - over the following 12 month period, even though they had ceased their low-calorie diets. The study authors attribute this to the fact that those participants continued to drink water before meals.
Possible appetite reduction effect
Drinking water prior to each meal may help in appetite suppression. A promising approach to reducing appetite which does not involve taking any drugs, and is very safe, is to drink a moderate amount of water before a meal. Though this had been a folk remedy for overeating for many years, and is recommended by some dieticians and stipulated in some scientific studies, it was only recently that the approach was subjected to a scientific randomised controlled trial to see how much effect it had.
In a prior study, researchers had found that water drinkers ate 75 to 90 fewer calories per meal. However, they wanted to know whether this effect made a difference to weight loss, or whether it was cancelled out by subjects eating more through the day, and so they did a randomised controlled trial to find this out.
Davy et al. randomised controlled trial
Davy et al. took a group of 48 overweight and obese Americans aged 55 to 75 who were considered inactive, and divided them randomly into two equal-sized groups. The control group simply followed a calorie-controlled diet equating to approximately 1500 calories per day for the men and 1200 calories per day for the women. The second group followed exactly the same diet, but drank 500 millilitres of water before each meal. Both groups kept up the diet for 12 weeks. Although both groups lost weight on average – as scientists would expect to happen, because such calorie-controlled diets are known to be effective – the water-drinking group lost about 5 pounds more on average, which made the diet 30% more effective. Because the water-drinking group reported feeling both more full and less hungry, the researchers believe that the water acts to suppress appetite. The researchers also recommended that people wishing to lose weight should replace sweetened calorie-containing drinks with water.
Subjective effects also reported by the water-drinking group were a clearer mind and a better ability to think. There were no negative effects reported.
A 12-month-long followup to this study was presented to a meeting of the American Chemical Society in August 2010. However, since this follow-up study has only been reported at a conference, and not yet published in a peer-reviewed publication, it must be treated as provisional. The followup found that while the control group had, on average, gained some weight after discontinuing the diet, the water-drinking group weighed, on average, slightly less than they did after discontinuing the diet. The water-drinking group had voluntarily chosen to continue drinking water before meals, even though they were not following the strict diet any longer. This suggests that drinking water before meals is also effective in preventing weight loss rebound, if continued after the end of a diet. Since many people experience great difficulty keeping weight off permanently after dieting, this could make the water technique more attractive.
Provisos and criticisms
There has been relatively little research carried out on this topic. However, this study is "promising", according to Barry Popkin, director of the University of North Carolina Nutrition Obesity Research Center (who has himself carried out empirical research on water and weight loss).
The researchers caution that while drinking moderate amounts of water (as the subjects did in this study) is safe, drinking extremely large amounts of water over a short period of time can lead to serious health problems, a very rare phenomenon known as water intoxication. It can cause low sodium levels, seizures, swelling of the brain and even death.
The study only looked at people aged between 55 and 75. The effect is not known to work in younger people: previous research has shown that in those aged 18–35, drinking more water at the meal did not cause them to eat fewer calories at the meal. This is believed to be because water travels out of the stomach almost immediately in younger people.
In the past, some believed that drinking at the same time as eating was unhealthy because it dilutes the stomach acid. In fact, studies have repeatedly shown that the acidity level of the stomach does not change very much when a person does this, and therefore it is not seen as a cause for concern.
Carla Wolper, an assistant professor in the Eating Disorders Center at Columbia University, cautioned that it can be more difficult to get people to follow dietary advice outside of a scientific study – so even if it works, people might not have the discipline to follow it. She noted that other simple things that people can do to lose more weight, such as cutting portion sizes and writing down what they eat, do work if followed, but it is very difficult to get people to carry out these simple actions.
How it might work
As stated above, a hypothesis of Davy et al. (who conducted the original trial) is that the water reduces appetite. The water also displaced calorie-containing beverages in the diets of the water-drinking group in the trial. However, Davy does not believe that this explains away the results of the trial, because both groups had to keep their calorie intake within predefined limits.
Registered dietician Dawn Jackson Blatner, who was not involved in the study, says "Many of us confuse hunger and thirst signals so drinking water through the day and before meals makes sense to take the edge off thirst which leaves us with a more accurate feeling of true hunger."
Concomitant dietary changes
Template:Expand section Research by Barry Popkin et al. has shown that people who drink lots of water eat more vegetables and fruits, drink fewer sugary beverages, and consume fewer total calories. The reason for drinking less sugary beverages would likely be that the increased water substitutes for them in the diet, quenching the thirst so that the person does not feel as much need to drink sugary beverages.
Some claim that drinking cold water aids in calorie burn as the body has to work to heat the cold water in the body and hence burning calories. This idea may be similar to the idea of eating Celery as a Negative calorie food. However the number of calories generated by drinking cold water may be minimal, since the body's response to cold conditions is to first reduce heat loss, not create new heat. It does this mainly by reducing blood flow to the skin, which reduces heat lost through the skin. If this isn't sufficient to maintain body temperature, new heat is created through shivering. A study found that drinking that approximately 518 mL (18 ounces) of near-freezing water (3°C) only burned approximately 4 kcal, well below the theoretical energy cost of warming the water to body temperature.
A study in Germany in 2003 reported that after drinking 17 ounces of water, the subjects' metabolic rates increased by 30%, starting at 10 minutes after water consumption, and peaking at 30 to 40 minutes. However, exercise physiologist Daniel Moser commented that the effect of this on weight loss would be "extremely modest", and said that more studies were needed to confirm the effect.
However a study by a different research center in 2006 failed to confirm that drinking water significantly increases metabolism. Drinking room temperature water had no effect on the metabolic rate, and drinking near-freezing water (3°C) raised metabolism by only 4.5%, much less than the 30% found by the other research center.
- Eating more fruits and vegetables is often recommended by dieticians and governmentsTemplate:Who, both to aid weight loss, and because of its other potential health benefits, such as a reduction in the risk of heart disease and type 2 diabetes.