In a recent paper, of 81 overweight and obese women with type 2 diabetes who usually consumed diet beverages and were on a weight loss program, those who substituted water for diet beverages after their lunch for 24 weeks had a greater decrease in weight (-6.40 vs. -5.25 kg) and body mass index (-2.49 vs. -2.06 kg/m2) compared with those who continued to consume diet beverages.

Specifically, the water group had a greater decrease in weight (water, −6.40 ± 2.42 kg; DBs, −5.25 ± 1.60 kg;  P = .006), in BMI (water, −2.49 ± 0.92 kg/m²; DBs, −2.06 ± 0.62 kg/m²; P = .006), in FPG (water, −1.63 ± 0.54 mmol/L; DBs, −1.29 ± 0.48 mmol/L, P = .005), in fasting insulin (water, −5.71 ± 2.30 m lU/mL; DBs, −4.16 ± 1.74 m lU/mL, P = .011), in HOMA IR (water, −3.20 ± 1.17; DBs, −2.48 ± 0.99, P = 003) and in 2 hour postprandial glucose (water, −1.67 ± 0.62 mmol/L; DBs, −1.35 ± 0.39 mmol/L; P = 0.027) over the 24-week period. However, there was no significant time × group interaction for waist circumference, lipid profiles and HbA1c within both groups over the 24-week period.

Since both contain zero calories what could explain that?

There is no metabolic pathway proposed. or a related hypothesis, it is a tiny sample where people were engaging in healthier lifestyles overall, and in the diversity of the human condition some people lost more weight than others. Reasonable enough, but the authors, some of whom are employed in diet clinics, chose to ignore the many confounders and conclude that diet soda prevented weight loss. 

Substituting water for high-calorie drinks like fruit juice, smoothies or soda obviously makes sense in a diet, but diets are already difficult. Denying people who already overeat, or they wouldn't have gained weight and gotten type 2 diabetes, a treat in the form of a diet soda after lunch, in addition to the struggle they already have, seems unnecessarily punitive, especially based on a short-term study. It's another flavor of the 'quit or die' mentality that plagues academics when dealing with addiction.

There is no magic bullet for weight loss, no fat-burning miracle pill and no special food that causes or eliminates weight gain. It comes down to burning more calories than consumed, which can be difficult in a world where treats are not special, they can be found in every store.

If you're a biologist and have a legitimate biological hypothesis that hasn't been debunked, please let us know in the comments and we'd like to interview you.

Citation: Madjd A , Taylor MA , Delavari A , Malekzadeh R , Macdonald IA and Farshchi HR . Beneficial effects of replacing diet beverages with water on type 2 diabetic obese women following a hypo-energetic diet: A randomized, 24-week clinical trial, Diabetes Obes Metab, 2016. doi: 10.1111/dom.12793