Adults Assigned Diet Drinks Lost About as Much Weight as Water Drinkers Over Two Years
Adults in a two-year weight-loss trial who drank diet sodas and other artificially sweetened beverages ended up with about the same results as adults who drank only water. Among participants who finished, those who drank water had lost an average of 8.2 pounds after 104 weeks, while those who drank diet beverages had lost 10.6 pounds, a gap too small to rule out plain chance.
Researchers at the University of Liverpool in England followed 493 adults with overweight or obesity through a structured weight-loss program, then checked in for a full extra year with no coaching at all. Only 220 stayed to the end, and those who did still weighed less than they had at the start of the study.
Diet drinks have long drawn suspicion as a saboteur of weight-loss plans. The World Health Organization advises against using non-sugar sweeteners to control weight, and some observational studies, the kind that spot patterns but cannot prove cause and effect, have linked diet drinks to weight gain. The study’s authors argue that guidance leaned mostly on that type of research rather than on randomized trials like this one. People already gaining weight may simply reach for diet drinks more often, one reason such studies can mislead. Known as SWITCH, the trial provides rare long-term randomized data comparing diet drinks directly with water for weight management, and the results appear in the British Journal of Nutrition.
Nearly 500 Adults Were Assigned Diet Drinks or Only Water
Volunteers were adults ages 18 to 65 living with overweight or obesity, with an average age of about 45 and a typical starting weight near 200 pounds. Roughly 70% were women. All lived within 50 miles of Merseyside, the region that includes Liverpool, and already drank at least three cold beverages a week. Anyone with diabetes, cardiovascular disease, digestive disease, food allergies, or a history of weight-loss surgery was left out, as were current and recent smokers.
Random assignment sent 246 people to water and 247 to diet drinks, and everyone was asked to drink at least two 330-milliliter servings a day, roughly 11 ounces each. The researchers supplied the drinks. The diet drink group chose from 20 branded options, including diet colas, diet fruit drinks, and flavored waters, sweetened mostly with aspartame, acesulfame potassium, and sucralose. The water group gave up all artificially sweetened drinks, even sweeteners stirred into coffee or tea.
Everyone also attended group weight-loss sessions with a nutritionist, weekly for the first 12 weeks and monthly for the next 40. A final 52-week stretch was optional and came with no coaching sessions, though measurements continued monthly. Enrollment ran from 2016 to 2021, so the COVID-19 pandemic disrupted some in-person visits. Researchers tracked weight, waist and hip size, and hunger ratings throughout.
Diet Drinks and Water Led to Similar Weight Loss After Two Years
By the two-year mark, 117 people remained in the water group and 103 in the diet drink group. Among them, about 98% in both groups kept to their daily drink target near the end, according to beverage logs. High dropout means the two-year results come from the people who stayed.
Both groups followed the same arc. Weight came off fastest in the first 12 weeks. Diet drinkers hit their lowest average weight around week 36, about eight months in, and water drinkers around week 44, roughly ten months in. Both groups then slowly regained some weight, though regain was slower with diet drinks. Even so, both stayed clearly below their starting weights at week 104. Re-running the numbers with estimates filled in for dropouts led to the same conclusion about the two groups.
Waists and hips shrank by similar amounts, with waists down roughly 2 inches in both groups. A subset of 48 volunteers who had body scans lost fat and some lean tissue at similar rates in each group. Hunger ratings rose slightly in both groups over two years, though only the diet drink group’s rise was big enough to stand out from chance, and the two groups did not differ from each other. Water drinkers sharply cut their sweetener intake, as expected, and sugar intake dropped in both groups.
Source : https://studyfinds.com/diet-drinks-match-water-weight-loss/
