Replacing sugary drinks with diet beverages does not undermine long-term weight management, according to the SWITCH trial published in the British Journal of Nutrition. Researchers from the University of Liverpool and the University of Leeds followed 493 adults with overweight or obesity for 104 weeks to compare the effects of artificially sweetened drinks versus water.
Two-Year SWITCH Trial Results and Weight Outcomes
The SWITCH trial initially randomized 493 adults aged 18 to 65 with body mass index values between 27 and 35. Participants were assigned to drink either water or commercially available beverages containing non-nutritive sweeteners for 104 weeks while participating in a structured behavioral weight-management program. Those in the diet-drink group consumed at least two 330-milliliter servings each day, including products containing aspartame, acesulfame potassium, and sucralose. The water group avoided non-nutritive sweetened beverages and sweeteners added to hot drinks.
By the end of the 104-week study, 220 participants remained, comprising 117 in the water group and 103 in the diet-beverage group. Among those who completed the full two-year trial, participants assigned diet beverages lost an average of 4.8 kilograms from their baseline weight. Participants assigned water lost an average of 3.7 kilograms. Investigators noted the difference was not statistically significant, indicating equivalent weight outcomes between the two hydration strategies.
Behavioral Phases and Body Composition Changes
The trial incorporated a structured lifestyle intervention beginning with a 12-week active weight-loss phase focused on weekly behavioral sessions. This period was followed by a 40-week assisted maintenance period featuring monthly meetings and a voluntary final year with no routine weight-management sessions. Most weight loss occurred during the first three months, with both groups reaching their lowest average weights during the first year before gradually regaining some weight. Average body weight remained significantly below baseline after two years in both cohorts.
Additional body composition assessments revealed that waist and hip measurements declined significantly in both groups. A smaller subset of participants underwent body scans, which showed reductions in fat mass and shifts in regional body fat without significant differences between the water and diet-beverage groups. Sugar intake also dropped across both arms of the study.
Appetite Regulation and Metabolic Findings
Researchers evaluated whether tasting sweetness without consuming calories would disrupt appetite regulation or trigger compensatory eating. Self-reported hunger increased slightly over the two-year period in both groups, reaching statistical significance within the diet-beverage cohort. However, the difference between the diet-drink and water groups was not statistically significant.
“This latest finding shows that concerns about sweeteners disrupting appetite or causing weight gain are not supported when tested in a rigorous, long-term randomised trial,” said Joanne Harrold of the University of Liverpool. Metabolic markers improved from baseline across both study arms, and the trial indicated that consuming non-nutritive sweeteners within a structured weight-management program produced weight outcomes comparable to water.
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