Feature Article: Does drinking water really help you lose weight?

We have all heard that drinking a lot of water helps you lose weight. But is this just another weight loss myth that has no scientific basis, or is it really true? According to the research literature, drinking water really can make it easier to lose weight. This post will summarize some of the important research in this field of study.

Research Evidence

1) In an investigation by the Harvard School of Public Health, the long term association between water consumption and weight was examined in a combined cohort of the Nurses’ Health Study, The Nurses’ Health Study II, and the Health Professional Follow-up Study (Reference 1). In total, there were 124,988 subjects included in this investigation that were followed for approximately 20 years. Participants reported their water consumption and their weight every 4 years throughout the study period. The researchers then calculated how 1 daily cup of water would impact weight each 4 year period. 

Here are the results:

1 cup of water resulted in .3 lbs. of weight loss over 4 years.

Substituting 1 cup of water per day for 1 cup of sugar sweetened beverages resulted in a weight loss of 1.1 lbs. over 4 years.

Although the results appear modest, they do offer evidence that by increasing water consumption, you can increase your rate of weight loss. This was particularly true if the water was substituted for more calorie heavy beverages, like soda.

2) Forty-eight adults were assigned to one of two diet groups for 12 weeks (Reference 2).  The first group was assigned a low calorie diet. The second was assigned the same diet, but was instructed to drink 16 oz. of water right before each meal. At the end of the 12 weeks, the group drinking the water prior to each meal lost an additional 4.5 pounds.

3) The Stanford University A to Z weight loss trial also examined water intake and weight loss (Reference 3). This trial was designed to compare the weight loss efficacy of 4 popular diets over a year in 173 young women. In a secondary analysis, they found that women who drank more than a liter of water each day (a little more than 4 cups) lost an additional 5 lbs. after a year.

Why Does Drinking Water Increase Rate Of Weight Loss?

While we don’t know for sure, there are several potential mechanisms by which water consumption increases the rate of weight loss:

1) Increased metabolic rate. Drinking water appears to increase sympathetic nervous system activity, which increases metabolism. Calories are also utilized to warm the water to body temperature. In the research literature, drinking 16 oz of water increased metabolic rate 30% in normal weight subjects (Reference 4) and 24% in overweight subjects (Reference 5).

2) Gastric distension. Water may also increase gastric distension, which has the potential to decrease hunger and subsequent energy intake. Fifty subjects participated in a trial that compared energy intake after consuming a water preload (Reference 6).  All subjects had access to an all you can eat lunch both with and without drinking 16 oz. of water, 30 minutes before the meal. Energy consumption at the lunches were compared. The subjects over 60 years of age consumed a statistically significant 58 fewer calories after drinking the water preload. Interestingly, this was not seen in the younger subjects.

3) Water replaces beverages containing calories. If you are drinking a lot of water, then you are probably not drinking a lot of soda or juice. The elimination of these calories over time can positively impact weight.

Recommendations

It is clear that drinking water can have a significant influence on ability to lose weight. I have my clients shoot for 8 cups of water each day. What counts? Filtered tap water, bottled water, hot or iced decaf coffee or tea, and flavored club soda from companies like Polar, and Poland Spring.

Any beverage that is high in caffeine does not count, since caffeine is a diuretic and may cause the body to excrete water.

References

1) Pan A et al. Changes in water and beverage intake and long term weight changes: results from 3 prospective cohort studies. International Journal of Obesity 2013; 37:1378-85.

2) Dennis EA, et al. Water consumption increases weight loss during a hypocaloric diet intervention in middle aged and older adults. Obesity 2010; 18:300-307.

3) Stookey JD, et al. Drinking water is associated with weight loss in overweight dieting women independent of diet and activity. Obesity 2008; 16:2481-88.

4) Boschmann M, et al. Water induced thermogenesis. Journal of Clinical Endocrinology and Metabolism 2003; 88:6015-19.

5) Boschmann M, et al. Water drinking induces thermogenesis through osmosensitive mechanisms. Journal of Clinical Endocrinology and Metabolism 2007; 92:3334-37.

6) Van Wallenghen EL, et al. Pre-meal water consumption reduces meal energy intake in older but not younger subjects. Obesity 2007;93-99.