|Could this large glass of water really be the "diet game changer" some mainstream media make it look like? Or, are we - once again - dealing with the abuse of science to attract readers by propagating dubious dieting myths?|
In other words: While we do have evidence that replacing caloric beverages with water/diet beverages works (Tate. 2012), we have little evidence that simply drinking more will accelerate weight loss and almost no evidence of the potential benefits water preloading before meals, in particular.
Quite surprising, isn't it. I mean, it should be obvious that drinking a glass or two of water before a meal would be a highly promising strategy to reduce meal energy intake by modifying an individuals’ perception of fullness prior to eating by, as Parretti et al. (2015) put it, "consuming a 'preload' of water". Nevertheless, Daniels' 2010 systematic review identified only two small laboratory studies that specifically investigated whether water preloading reduced energy intake. As Parretti et al. point out in the introduction to their own study,
"[b]oth studies compared participants given a water preload of 500 ml for 30 min before an ad libitum meal with those not given a preload and found that energy intake at the meal was lower for the preload group compared with the no-preload group" (Parretti. 2015).Thus, evidence to suggest that water preloading may improve the effectiveness of weight loss programs is there. Experimental evidence to confirm that is yet ultra-scarce. In fact, the only RCT (Dennis. 2015) to directly examine the effects of water preloading before meals on weight loss was published five years ago. In said study, 48 adults with overweight or obesity were allocated to a hypocaloric diet plus 500 ml of water before meals every day (water preload group) or a hypocaloric diet alone intervention (nonwater group) over 12 weeks.
|Figure 1: Dennis et al. were the first to show that drinking 500 ml of water before meals everyday can boost the weight loss success of overweight and obese individuals participating a 12-week diet intervention (Dennis. 2010).|
- a two-group randomized controlled trial with eighty-four adults with obesity
- all participants were given a face-to-face weight management consultation at baseline (30 min) and a follow-up telephone consultation at 2 weeks (10 min)
- participants were randomized to either drinking 500 ml of water 30 min before their main meals or an attention control group where participants were asked to imagine their stomach was full before meals (*)
- primary outcome was weight change at 12-week follow-up
|Table 1: Self-reported adherence for both groups - (I) intervention group, (C) control group (Parretti. 2015).|
|Table 2: Self-reported fullness and satiety scores for both groups - (I) intervention group, (C) control group; fullness and satiety scores can range from 1 to 10 (Paretti. 2015)|
|Figure 2: Weight loss (in kg) over the 12-week study period (unadjusted values | Parretti. 2015)|
- Daniels, Melissa C., and Barry M. Popkin. "Impact of water intake on energy intake and weight status: a systematic review." Nutrition reviews 68.9 (2010): 505-521.
- Dennis, Elizabeth A., et al. "Water Consumption Increases Weight Loss During a Hypocaloric Diet Intervention in Middle‐aged and Older Adults." Obesity 18.2 (2010): 300-307.
- Muckelbauer, Rebecca, et al. "Association between water consumption and body weight outcomes in children and adolescents: A systematic review." Obesity 22.12 (2014): 2462-2475.
- Parretti, Helen M., et al. "Efficacy of water preloading before main meals as a strategy for weight loss in primary care patients with obesity: RCT." Obesity (2015).
- Tate, Deborah F., et al. "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 (2012): 555-563.