Swap Sugary Drinks for Diet Versions to Lose Weight, Study Finds—But Water Is Still Best

A new study suggests that swapping sugary drinks for artificially sweetened ones may help people shed pounds. But researchers say water is still the healthiest choice.

Scientists from the Harvard T.H. Chan School of Public Health in Massachusetts found that replacing sugar-laden beverages with either diet drinks or water can lead to weight loss. Their analysis showed that people who switched to artificially sweetened drinks lost a modest amount of weight over time, especially those who were overweight or obese and drank a lot of sugary beverages at the start of the study.

Participants who replaced diet drinks with water also experienced modest long-term weight loss, while those who swapped sugary drinks for water lost the most weight.

The findings were published in the American Journal of Clinical Nutrition.

Experts not involved in the study caution that while artificial sweeteners may help with weight loss, they come with health risks. Water, they say, is a much better substitute.

“Avoiding sweeteners entirely by choosing plain water is the better option,” said Dr. Mir Ali, a bariatric surgeon at MemorialCare Surgical Weight Loss Center in California. “This avoids the bad effects of both sugar and artificial sweeteners and is good for weight loss.”

“Water provides hydration and has no additives,” added dietitian Kristin Kirkpatrick, who works at the Cleveland Clinic. “Both sugary drinks and diet drinks are ultra-processed. So choosing water is a great way to start cutting back on processed foods.”

For the study, Harvard researchers looked at data from about 143,000 people who took part in three long-term health studies. Participants were between ages 26 and 65 and were followed for 24 to 32 years. They filled out questionnaires every two years about their health, lifestyle, and body measurements.

On average, participants gained about 2.8 pounds every four years. But replacing just three sugary drinks per week with diet versions was linked to losing about 3 pounds. Similar results were seen when people swapped sugary drinks for water. Replacing diet drinks with water led to only small weight loss.

Experts say there are a few reasons why switching to diet drinks might help with weight loss.

“It’s possible this happens mostly because you’re cutting calories,” Kirkpatrick said. “People in the study may also be trying to eat better overall, which can lead to better habits and weight loss.”

“It confirms what you’d expect: replacing a drink with calories with one that has none leads to weight loss because you’re taking in fewer calories,” said Dr. Jonathan Long, a professor at Stanford University who was not part of the study.

The latest U.S. dietary guidelines say that no amount of added sugar or artificial sweeteners is considered part of a healthy diet. They also recommend that one meal should contain no more than 10 grams of added sugar, which is less than 2.5 teaspoons.

The main sources of sugar in the American diet include sugary drinks, desserts, and sweet snacks like cookies, cakes, pies, ice cream, and pastries. Americans consume about 22 teaspoons of added sweeteners each day.

Artificial sweeteners are found in many foods and drinks labeled “sugar-free” or “diet,” including baked goods, soft drinks, candy, puddings, and dairy products. These sweeteners can be 180 to 13,000 times sweeter than sugar.

The health risks of eating too much sugar are well known. According to the CDC, high sugar intake can raise the risk of obesity, heart disease, and type 2 diabetes. It may also increase the risk of cancer, depression, aging, and kidney disease, and can harm dental health.

The risks of artificial sweeteners are less widely reported, but experts have concerns. In 2023, the World Health Organization advised against using artificial sweeteners for weight control, citing worries that long-term use could raise the risk of heart disease and type 2 diabetes.

Dr. David Cutler, a family medicine doctor in California who was not part of the study, said artificial sweeteners may also affect insulin resistance, change the gut microbiome, and harm dental health.

“The bottom line is that while they are safer than sugary drinks, they are not risk-free,” Cutler said.

Ali agreed. “Artificial sweeteners can have bad effects, like changing the gut microbiome, which can increase chronic inflammation,” he said. “They may also trigger insulin release in some people, which could lead to insulin resistance.”

Experts agree that the best weight loss plans focus on healthy eating and regular exercise. A healthy diet should include unprocessed foods like fruits, vegetables, legumes, whole grains, nuts, seeds, eggs, and dairy. It should be low in processed foods and sugar.

Long said diet drinks can be a helpful step for people trying to quit sugary sodas.

“Drinking water is the best option—it’s hydrating and doesn’t have the other stuff that diet drinks do,” he said. “But it’s very hard for people to replace juice or soda with water. So as a middle step, replacing sugary drinks with something sweet but calorie-free is better than giving up and going back to regular soda.”

Kirkpatrick, however, warned that this approach has risks. “This study shows diet drinks might be a useful bridge for people trying to cut back on sugar. But my worry is that people might see this and think diet colas are a healthy choice,” she said.

“As a dietitian, I often find that diet drinks make it harder for people to reduce sugar intake because they still deliver a lot of sweetness, which can keep cravings high,” she added.

Cutler noted that drinking diet beverages might cause some people to eat more calories overall. “Possible reasons include messing with appetite regulation, so people eat more because they think they’re saving calories in their drink,” he said. “And the sweet taste may change how the brain feels rewarded by eating.”

Experts agreed that a healthy lifestyle is the main goal.

“Overall, to keep a healthy diet and lifestyle, try to eat a variety of foods, not too much, and everything in moderation,” Long said.

“There are many parts to staying healthy and preventing disease. Diet, exercise, stress management, and sleep are all connected,” Kirkpatrick added.

“From a nutrition standpoint, one of the easiest and most effective starting points is to keep foods as close to their natural state as possible,” she said. “That means limiting additives, cooking more at home, and eating a variety of colorful plant foods, lean proteins, and healthy fats.”

Kirkpatrick also noted that the best approach to a healthy lifestyle varies from person to person. “It’s important to remember that there is no one-size-fits-all plan. Individual needs, preferences, and health goals matter,” she said.