To our knowledge, this is the first randomized controlled trial investigating the influence of increased water consumption on weight loss. Our results indicate that when combined with a hypocaloric diet, consuming 500 ml (~16 fl oz) of water prior to each of the three main daily meals (1.5 l/d) leads to ~2 kg greater weight loss over 12 weeks as compared to a hypocaloric diet alone (), among middle-aged and older adults. This difference was attributed to a 44% greater rate of weight loss among water group participants compared to nonwater participants over the 12-week period. This effect may be due in part to an acute reduction in meal EI following water ingestion, which we observed at the baseline laboratory test meal studies. A reduction in meal EI following water consumption is accompanied by increased sensations of fullness, which may facilitate a lower meal EI following water ingestion. However, it is not clear from our findings how long this effect is sustained, as we did not observe significant differences between meal conditions after the 12-week weight loss intervention.
Our data are consistent with prior reports. In a secondary analysis of a trial comparing several weight loss diets, Stookey et al.
) found that overweight women who reported drinking ≥1 l/d of water over a 12-month period increased weight loss by ~2 kg compared to those who did not increase water consumption. However, intentionally water consumption was not manipulated, and water consumption data was self-reported. Nonetheless, our data are in agreement with these findings in that they support a beneficial role of increasing water consumption while consuming a hypocaloric diet.
Though the exact mechanism responsible for the greater weight loss with increased water consumption is presently unknown, consuming water before
a meal or with
a meal reduces sensations of hunger, and increases satiety (15
). First, changes in subjective sensations of hunger and satiety are associated with an acute reduction in meal EI (16
), but prior to our study it was unknown if this acute reduction in meal EI could facilitate weight loss while consuming a hypocaloric diet. Advancing age is also associated with delayed gastric emptying (31
) that may play a role in reducing meal EI following a WP in middle-aged and older adults; this possibility warrants further investigation. We did not detect group differences in self-reported EI over the 12-week intervention, possibly due to the limitations associated with utilizing self-reported dietary intake measures (32
). Studies including objective measures of daily EI, such as those conducted on an in-patient metabolic research unit, are needed to more accurately quantify the potential daily reduction in EI associated with increased water ingestion.
Second, replacing energy-containing beverages in the diet with water may lead to a reduction in overall EI, as epidemiological data suggests that total beverage energy contributes >400 kcal to daily EI (33
). In our sample, beverage EI declined by ~100 kcal over the 12-week intervention, but did not differ between groups and is thus unlikely to explain our findings. As both groups were instructed to moderate their consumption of sweetened energy-containing beverages and alcohol, the lack of a group difference in beverage EI and nonwater beverage consumption is not unexpected. However, in the entire sample, a greater increase in water intake was positively associated with weight loss. In addition, overall dietary ED (food + beverages, including water) decreased significantly more in the water group than the nonwater group which may be attributed to an increased water intake among water group participants; reducing dietary ED is thought to be an effective weight loss strategy (34
Finally, it is possible that daily self-monitoring of water intake contributed to a greater weight loss in our water group participants, as others have demonstrated benefits of daily self-monitoring behaviors associated with weight management (i.e., daily self-weighing) (35
). Further research is warranted to determine the relative contributions of each of these possible physiological and behavioral mechanisms related to water consumption promoting weight loss.
There are some limitations that should be acknowledged. First, the sample size was small. However, this sample size provided sufficient power to detect physiologically and statistically significant effects in many outcome variables which were consistent with our hypothesis. Second, no standardized laboratory test is available to objectively assess compliance with the water intervention. We utilized urinary specific gravity, 24-h urine collections, self-reported daily compliance logs, and food intake records. These procedures provided reasonable indicators of compliance when comparing the two groups over time and there was consistency among most of these measures. Finally, these results may not apply to the general population, in that our study only included primarily white, middle-aged and older adults. Rolls et al.
) did not observe a difference in meal EI in young, normal-weight men who were given 8 and 16 oz of water 30 min prior to a meal as compared to no beverage. is observation is consistent with our findings in young adults (16
). Future studies examining premeal water intake in younger populations could address methodological changes such as increasing the quantity of the WP, or reducing the time between the preload ingestion and the ad libitum meal.
These findings may have clinical implications. Our prior work (16
) led us to hypothesize that premeal water consumption could reduce daily EI by ~225 kcal, and over a 12-week period, could produce an energy deficit of ~18,900 kcal and lead to ~2.5 kg weight loss. Although we recognize this is an extrapolation, it is consistent with our findings. Dietitians and other weight management practitioners often advise individuals desiring weight loss to increase their water consumption, and this strategy is often recommended in popular weight loss programs (36
). These findings provide an evidence-basis for this strategy among middle-aged and older adults. In addition, increasing water consumption is a simple, inexpensive behavioral change which can be recommended as a component of a hypocaloric diet to possibly enhance weight loss outcomes. Another potential health benefit of this strategy is improved hydration status, as habitual fluid intake among our population () was well below current guidelines (39
). us, our findings suggest benefits of increasing water consumption for weight management and health among middle-aged and older adults.
We conclude that for overweight or obese middle-aged and older adults, consuming ~2 cups of water prior to each of the three main daily meals may increase weight loss when combined with a hypocaloric diet, as compared to a hypocaloric diet alone. This strategy may aid in increasing fullness, thereby promoting a reduction in meal EI. Future studies, with larger sample sizes, are needed to confirm our findings as well as to determine how long the acute reduction in meal EI following water ingestion is sustained; if this increased weight loss with water consumption is maintained over time; and if increased water consumption facilitates long-term weight loss maintenance.