October 6, 2026, 6:22 pm | Read time: 7 minutes

What Was Missing About Light Drinks and Weight Loss

Until now, it was unclear how light and zero-calorie drinks compare to water in terms of long-term weight loss and maintenance, as there are few long-term controlled studies on this.¹ This is precisely what scientists examined in the SWITCH study.²

How the Study Was Conducted

A total of 493 adults between 18 and 65 years old started with their assigned beverages. They were overweight or obese. Randomly, 246 participants were placed in the water group and 247 in the light drinks group. Each was to consume at least 660 milliliters of their assigned beverages daily.

The light group could choose from 20 different very low-calorie drinks, including light sodas and sweetened flavored waters. Aspartame, acesulfame K, and sucralose were primarily used as sweeteners. Additionally, these participants were allowed to drink water. The water group, however, was to avoid drinks with sweeteners–even in hot beverages.

First Lose Weight with Support, Then on Your Own

The study lasted two years. In the first 12 weeks, participants met weekly with a nutritionist and were to actively lose weight. This was followed by 40 weeks of monthly meetings to maintain weight as much as possible. During this first year, participants were also to gradually increase their physical activity, aiming for 60 minutes of walking six days a week.

Afterward, a voluntary second year followed. During this time, there were no regular meetings to support weight control. The focus was on the development of body weight. Additionally, scientists examined waist and hip measurements, blood pressure, various blood values, hunger levels, and the consumption of sugar and sweeteners. In a small group of participants, body composition was also measured more precisely.

Light Drinks Were Not Worse Than Water for Weight Loss

For the crucial evaluation after two years, complete weight data from 220 participants were available: 117 from the water group and 103 from the light group.

In the water group, participants lost an average of nearly 4 kilograms, while in the light group, it was nearly 5 kilograms. However, the difference of about 1 kilogram is not enough to derive a reliable advantage for light drinks. The study does not show that light drinks work better for weight loss than water. However, they did not perform worse in terms of long-term weight loss.

The most significant weight loss in both groups occurred during the first 12 weeks. Afterward, participants regained some weight. After two years, both groups still weighed less on average than at the start.

Changes in Waist and Hip Measurements

Waist circumference decreased by about 5 centimeters in the water group and about 6 centimeters in the light group. At the hips, it was around 3 centimeters in both groups. These measurements also showed no significant differences between the groups.

In 48 participants, body composition was examined more closely. In both groups, fat mass decreased, among other things. The results were overall similar.

No Evidence of Increased Hunger from Light Drinks

One concern with sweeteners is that the sweet taste without corresponding calories could negatively affect appetite. After two years, however, no reliable difference in hunger levels was found between the water and light groups. Sugar consumption was also lower in both groups at the end than at the beginning.

There were differences between the groups in some blood values and the lower blood pressure value. However, the authors assessed the changes in long-term blood sugar and lower blood pressure as too small to be medically significant. According to the authors, total cholesterol levels were in the healthy range in both groups.

Also interesting: Certain drinks can significantly increase the risk of stomach cancer

More on the topic

Not as Healthy After All? Nonalcoholic Beer Alters Blood Sugar and Gut Flora in Young Men

SWEET Study Study Finds Surprising Effect of Artificial Sweeteners

What the Results Mean for People Wanting to Lose Weight

The results do not suggest that light and zero-calorie drinks worsen long-term weight control compared to water. However, this applies to people who–like the participants in this study–are also participating in a weight loss program.

It is also interesting that part of the weight loss was maintained in the second year. Although participants no longer received regular support during this phase, the average weights in both groups remained below the initial values.

Light Drinks Alone Do Not Make You Slim

Participants did not simply swap regular soda for a light version and continue living as before. They received nutritional counseling, were to change their behavior, and increase their physical activity in the first year.

This does not imply that light drinks themselves were responsible for the lost pounds. Nor does the study show that consuming as many light drinks as possible leads to greater weight loss.

Weaknesses of the Study to Be Aware Of

Two points speak in favor of the study: Participants were randomly assigned to the two beverage groups, and the study lasted a total of two years. Such long-term controlled studies directly comparing water and light drinks are rare. However, there are several important limitations.

More Than Half Were No Longer Involved at the End

Of the original 493 participants, only 220 had complete weight data after two years. A total of 273 participants dropped out early or were excluded due to non-compliance with study requirements.

This means the most important evaluation after two years was based on less than half of the originally started participants. The scientists therefore conducted additional calculations to account for the missing data. Even then, no reliable difference in weight loss between water and light drinks was found. The high dropout rate remains an important limitation.

The Second Study Year Was Not Initially Planned

The last 52 weeks were voluntary and were introduced as an extension through a later change to the original study plan.

Possible reasons for the significantly lower number of participants after two years include the COVID-19 pandemic, the long study duration, and the voluntary nature of this final phase, according to the authors.

The Results Cannot Be Applied to Everyone

The study was conducted at a single site in England. Information on the ethnic background of participants was not collected. The authors themselves cite the potentially limited generalizability of the results as a weakness.

During the COVID-19 pandemic, some participants had to conduct measurements at home, and blood samples or other examinations could not be collected in some cases. However, additional analyses provided no indication that this significantly affected the body weight results.

Some Results Are Based on Very Small Groups

Not all examinations were conducted on all participants. For example, the more precise measurement of body composition after two years was based on 48 people. For various blood values, data were available for only about 30 participants.

The results for these additional health values should therefore be interpreted more cautiously than the main result on body weight. The authors also explicitly point out the small participant numbers for some blood values.

The Beverage Industry Funded the Study
The study was funded by the American Beverage Association, an industry trade group. According to the publication, the association was not involved in planning, conducting, data analysis, or interpretation, but a representative was allowed to review the manuscript before publication. Support from a medical writer was also funded by the association. Several authors also reported financial ties to the beverage, food, and pharmaceutical industries.

The funding does not automatically invalidate the study results, but it represents a potential conflict of interest that should be considered when interpreting them.