The slimming effect of drinking water at mealtimes

If you want to lose weight you’re best off drinking ordinary water with your meals. This way you’ll automatically consumer fewer calories than if you drink juice, milk or soft drinks. Nutritionists at the University of North Carolina drew this conclusion from a metastudy in which they reviewed the evidence from experimental studies.

Lies, damned lies & statistics
You have to be a bit careful with metastudies. Researchers produce them after wielding an impressive array of statistical gymnastics. Not that there’s anything wrong with statistics, but the programmes that researchers use these days make it very easy to twist the truth: if nothing shows up from the initial metastudy, then most self-respecting programmes will indicate which observations or studies you need to get rid of to produce some statistically significant correlations.

So, if you hear that an arbitrary university, which happens to be funded by the dairy industry, analyzes seventeen studies on the effect of milk on the cardiovascular system, eliminates thirteen of these and concludes on the basis of the remaining four that milk protects against heart attacks, then a healthy dose of scepticism is not misplaced. [Am J Clin Nutr. 2011 Jan; 93(1): 158-71.] [ 20 October 2011] To say the least.

But even with this cautionary note, the metastudy that researchers at the University of North Carolina published in 2010 in Nutrition Reviews is still worth reading. The researchers collected experiments in which test subjects drank with a meal either nothing, water, milk or juice, and in which the researchers measured how many calories the subjects consumed. The results are interesting for everyone who wants to lose weight.

The researchers discovered that drinking milk or juice instead of water with or just before a meal boosts caloric intake by about 15 percent.


Replacing water with soft drinks sweetened with sugar or high fructose corn syrup also boosted caloric intake, but a little less so than milk or juice. This may be because of the bubbles in fizzy soft drinks: they make you feel fuller.


Replacing water by ‘light’ drinks reduced caloric intake by a few percent. The researchers regard the effect as so small that they devote few words to it.

“This review suggests promising results for promoting water as a replacement beverage”, the Americans conclude. “As shown elsewhere, the proportion of water in the average diet has diminished over time as individuals have shifted consumption patterns to a range of beverages that contain either one or many of the following: sugar, caffeine, natural and artificial flavorings, nonnutritive sweeteners, and carbonation. The beverage revolution in the post World War II period truly shifted drinking patterns and possibly even total fluid intake. The question that remains to be answered completely is ‘Will there be a benefit to shifting back to water’?”

And you can guess where they’re headed: the researchers, who have just ploughed through a whole bookcase of studies, argue that more research is needed on the matter. We forgive them though – they have to keep the home fires burning. But maybe you don’t need to wait for more studies. Maybe you already know what you need to know.

Impact of water intake on energy intake and weight status: a systematic review.


The effects of consuming water with meals rather than drinking no beverage or various other beverages remain under-studied. This systematic review of studies reported in the English-language literature was performed to compare the effects of drinking water and various beverage alternatives on energy intake and/or weight status. Relevant clinical trials, epidemiologic studies, and intervention studies were identified and findings across the literature were summarized. From the clinical trials, average differences were calculated in total energy intake at test meals (DeltaTEI) for each of several beverage categories in comparison with water. The available literature for these comparisons is sparse and somewhat inconclusive. However, one of the most consistent sets of findings was related to adults drinking sugar-sweetened beverages (SSBs) versus water before a single meal. In these comparisons, total energy intakes were 7.8% higher (DeltaTEI range, -7.5 to 18.9) when SSBs were consumed. Studies comparing non-nutritive sweeteners with water were also relatively consistent and found no impact on energy intake among adults (DeltaTEI, -1.3; range, -9 to 13.8). Much less conclusive evidence was found in studies replacing water with milk and juice, with estimated increases in TEI of 14.9% (range, 10.9 to 23.9%). These findings from clinical trials, along with those from epidemiologic and intervention studies, suggest water has a potentially important role to play in reducing energy intake, and consequently in obesity prevention. A need for randomized-controlled trials to confirm this role exists.

PMID: 20796216 [PubMed – indexed for MEDLINE] PMCID: PMC2929932