A recent study finds that if you drink more water, you can lose more weight and stay slimmer. Wait, does it say that?
Well, you would believe so, if you depended on these internet breaking news headlines.
I love the last one, as if water - the magical cure for weight gain - was sitting under our nose (or toilet seats) the entire time. Move over fountain of youth, hello fountain of fat proof.
But, the authors never say that drinking more water will lead to greater weight loss or make you thinner. Here is the actual study.
So, What Did They Actually Find?
Based on urine samples, the study looked at those who were adequately hydrated versus those who were not. Here is the table that shows the body mass results (see highlighted area).
Most 'breaking news' articles have focused on the finding that the average body mass index (BMI) was higher in the 'inadequately hydrated' group (29.2 kg/m2) than the 'adequately hydrated' group (28.3 kg/m2).
However, the difference is slight (1 BMI unit). For a 5'6" person, this would be about a 5.5 lbs difference (181 lbs vs. 175.5 lbs, respectively).
In either case, both groups were still classified as overweight (25.0 to 29.9 kg/m2), and nearly 'obese' (30 kg/m2).
However, notice too that there was actually a higher percentage of people classified as 'obese' in the 'adequately hydrated ' group (67.7%) than the 'inadequately hydrated' group (59.7%). Yet, there were more people who were not classified as obese in the 'adequately hydrated' group (40.3%) than those who were adequately hydrated (32.3%). These results are more telling than the mean.
Odds of Being Obese
They also found that, "The odds of being obese were 1.59 times higher [35% to 88% higher] for inadequately hydrated individuals compared with hydrated individuals."
Note, however, "Our findings also suggest that individuals with higher BMIs may behave in ways that lead them to be inadequately hydrated." For example, obese individuals might require more water based on current recommendations, and might not be getting adequate amounts for their weight.
For example, "the water requirements for a 5-foot, 10-inch man who weighs 160 pounds (healthy weight) and a 5-foot, 10-inch man weighing 210 pounds (obese) would differ by more than 1 L." [33 oz]
Less Water, More Soda?
Perhaps those with higher body weight do not have as healthy a diet, so they choose to drink other options throughout the day besides water – soda, juice, energy drinks, or margaritas (who knows)?
This is why research finds that reducing sugar-sweetened beverages leads to weight loss, and improved obesity-related diseases.
Also, other research has found that replacing sugary beverages with diet drinks resulted in the same amount of weight loss as replacing them with water. So, again, it might not be the less water intake that leads to more weight, but that obese individuals might simply drink less water in lieu of other, more sugary or unhealthy options.
We Cannot Say 'Causes'...
However, the intent of this cross-sectional study was not to show causation – that water 'causes' us to be thinner. Even the authors point out this limitation for us, "First, these data are cross-sectional and cannot be used to infer causation." Yet, the 'breaking news' skips over this part.
All 'cross-sectional' means, is that the researchers looked at a large group or 'cross-section' of people surveyed at single time point. They then broke the people into two groups, those who were hydrated, and those who were not. They only can look at correlations, not causation.
For causation, we would look to studies like this one, which showed that a group of overweight adults drinking 500 ml (16 oz) of water before each meal plus eating 500 calories less per day lost about 4.5 more pounds than a group that only ate 500 calories less per day. The authors conclude, "This strategy may aid in increasing fullness, thereby promoting a reduction in meal energy intake."
Also, as this study found, getting 1.5 to 2.0 liters per day (50-67 oz/day) in addition to 25g/day of fiber significantly increased stool frequency (pooping). So, as I have written about before, pooping more can lead to a small difference in weight loss.
Move over fountain of youth, hello fountain of poop?
The study discussed in the media, although very interesting and quite good, does not say that if you drink more water, you will be slimmer. Water is not a miracle weight loss treatment, keeping us slim. This is the fault of the internet heading, and not the original study.
So, at the present time, this one is busted.
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- Chang, T., Ravi, N., Plegue, M. A., Sonneville, K. R., and Davis, M. D. (2016). Inadequate hydration, BMI, and obesity among US adults: NHANES 2009-2012. Annals of Family Medicine, 14, 320-324.
- Dennis, E. A., Dengo, A. L., Comber, D. L., Flack, K. D., Savla, J., Davy, K. P., & Davy, B. M. (2010). Water consumption increases weight loss during a hypocaloric diet intervention in middle‐aged and older adults. Obesity, 18(2), 300-307.
- Hu, F. B. (2013). Resolved: there is sufficient scientific evidence that decreasing sugar‐sweetened beverage consumption will reduce the prevalence of obesity and obesity‐related diseases. Obesity Reviews, 14(8), 606-619.
- Tate, D. F., Turner-McGrievy, G., Lyons, E., Stevens, J., Erickson, K., Polzien, K., ... & Popkin, B. (2012). Replacing caloric beverages with water or diet beverages for weight loss in adults: main results of the Choose Healthy Options Consciously Everyday (CHOICE) randomized clinical trial. The American Journal of Clinical Nutrition, 95(3), 555-563.