Did you know that drinking water is the real key to losing weight? Well, not exactly. CNN says they have dug up some “serious evidence” that says drinking water or eating water-loaded fruits and vegetables when your stomach starts growling could help with weight management. The evidence, though, comes from a cross-sectional study in which the authors state “these data… cannot be used to infer causation.”
Chang and colleagues recognized that the relationship between weight status and hydration status is still relatively unknown. So, using data pulled from 2 recent National health and Nutrition Examination Surveys (NHANES), the researchers set out to see if there was an association between obesity and urine osmolality as a cursor of hydration status. No research had been conducted on this area of interest prior to this study, as urine osmolality was only added to the national survey in 2009. Additionally, the researchers only categorized study participants into two categories of weight: Body Mass Index (BMI) > 30 kg/m2 or BMI < 30 kg/m2 . So after combining the results from the 2009-2010 and 2011-2012 NHANES surveys, what did they find?
The University of Michigan researchers found that hydration status could be quantified as adequate over 800 mOsm/ kg or inadequate below 800 mOsm/ kg. The overall average urine osmolality was 631.4 mOsm/ kg, well below the adequate hydration marker. Hydration status was associated with age, race, sex, poverty level, and BMI in this study. They reported that adults who were inadequately hydrated had a mean BMI of 1.32 30 kg/m2 more than hydrated individuals. Additionally they stated that the odds of being obese were 1.59 times higher for inadequately hydrated individuals compared with hydrated individuals. Interestingly, about 68% of those who were classified as adequately hydrated were obese. The exact percentage of the 9,528 participants who fell about the BMI of 30 kg/m2 is never reported.
As this is not a causation study, the researchers inferred reasons for the lower hydration status of obese individuals but made only suggestions and educated guesses. Even in CNN citations, Chang states that it could just be because “a bigger person needs more water than a smaller person to stay hydrated.” This would make sense, as urine osmolality is measured in mOSM/ kg. In the study discussion, higher sodium intakes from “unhealthy” foods and increased metabolism of individuals with higher BMIs were cited as a possible causes for decreased hydration. Overall, the reasoning has not been researched, though Chang encouraged new studies in this area. Clinicians can also take this into consideration for counseling weight loss clients, although water intake as a weight loss tool is not an evidence based recommendation. As for individuals trying to lose weight, eating more fruits and vegetables with higher in general is a great idea and replacing soda and other sugar-sweetened beverages can definitely help with weight loss. Unfortunately, for now, there is no single key to weight loss as it involves changing a multitude of daily behaviors and habits.
Though the conclusions are not scientifically sound, an article like this circulating around CNN at least (more than likely) won’t have outward negative effects. If a person reads this article and decides “Alright, I’m going to drink more water!”, likely only positive benefits will come from it. I love that they specifically note “Water containing fruits and vegetables” AS IF the WATER is the sole part of those nutritional powerhouses driving the reduced weight effect. These correlation to causation studies are so common on the interwebs and it is comical to me that “drinking water and eating fruits and vegetables” is being repackaged, rebranded and resold to the public like it’s some new knowledge. Though maybe hearing this information in multiple different ways is what’s important. Maybe once people learn healthy foods “hydrate you”, “decrease cancer risk”, “promote healthy bowel movements”, “help your immune system”, “improve your microbiome”, “make your hair grow”, “reduce anxiety”, etc. etc. ETC.–they’ll start eating them; we can hope, right?
This is an interesting study and article. I would speculate that those who fall in the overweight or obese category are turning sugary drinks vs. water when they experience thirst. These high sodium, high sugar drinks not only dehydrate, but add unnecessary calories and sugars. They make reference to the fact that foods higher in calories and fat tend to contain less water in contrast to foods with lower calorie and higher fiber. This in combination with hydration being associated with more efficient metabolic functions makes it easy to make the association between hydration and weight status. There have been other studies that relate to this on preloading water prior to meals as a weight loss strategy. (http://onlinelibrary.wiley.com/doi/10.1002/oby.21167/abstract) Although they state that this study does not infer causation it seems as though the research supports that staying hydrated has tangible benefits in weight control. This seems obvious and pretty much every fitness and health magazine has covered this topic on some level, but unfortunately most of us still don’t stay adequately hydrated.
My first two thoughts after reading this post mirrored Staci’s exactly. Firstly, at least this misrepresentative media posting wouldn’t have negative effects, as drinking more water is hardly ever a bad thing. Secondly, why is water being promoted as the primary nutritional and weight loss factor of fruits and vegetables? However, despite its inaccurate translation of the research, an article such as this could potentially have positive effects. The large majority of people are under-hydrated, and I see this daily with my athletes. We constantly have to promote hydration as a consistent part of their day, when in reality, you would think water wouldn’t be too difficult of a thing to consume. Incorporating water into the diet to replace carbonated or sweetened beverages would be a great first step to improving adequate hydration levels. More research related to this area may eventually prove a causation, and thus media articles such as this would still be promoting a positive habit, only one with an actual scientific basis.