July 22, 2026, 3:01 pm | Read time: 4 minutes
Many people lose weight, gain it back later, and then start the next diet attempt. Such repeated weight fluctuations, also known as the yo-yo effect or “weight cycling,” could have consequences that aren’t visible on the scale. A new study suggests that this could lead to long-term muscle loss.
Yo-Yo Effect Leads to Muscle Loss
According to a recent study, people with repeated weight loss and subsequent weight gain lost significantly more thigh muscle over four years than those with stable body weight. Both groups weighed about the same at the end of the observation period as they did at the beginning.1
The press release for the study states that those affected lost about four times as much thigh muscle as participants without comparable weight fluctuations. Thomas Link, one of the study’s lead authors, also says: “With weight fluctuations, those affected lose not only fat but also a significant amount of muscle mass, which they do not regain.”2
How the Study Was Conducted
For the study, researchers at the University of California, San Francisco analyzed data from 1,433 adults from the “Osteoarthritis Initiative,” a large U.S. long-term study on knee osteoarthritis. The participants were on average about 61 years old. All included individuals had less than a five percent weight difference after four years compared to the start of the study and were therefore considered long-term weight stable.
Within this group, however, the researchers distinguished between people whose weight fluctuated multiple times over the four years and those whose weight remained largely constant. Simply put, some participants lost and regained weight intermittently, ending up close to their starting weight, while others showed only minor weight fluctuations over the entire period.
Based on regular BMI measurements, the scientists categorized participants into those with pronounced “weight cycling” (repeated weight loss and gain) and those with a more stable weight trajectory. They then evaluated MRI scans of the thigh and knee.
The researchers wanted to know if repeated weight loss and gain affected muscle mass and fat distribution. They were particularly interested in whether such changes occur even when overall body weight remains stable.
Body Weight Alone Says Little
Of the total 1,433 participants, 77 were classified as so-called “weight cyclers.” These are people whose weight repeatedly increased and decreased significantly over the years. The study’s key finding: They lost an average of 3.7 percent of their thigh muscle mass over four years. In contrast, participants with relatively stable weight lost only about one percent. The difference was statistically significant.
The situation was different for fat deposits. Although both the fat tissue stored between the muscles and the fat tissue near the knee increased during the study, there were no significant differences between participants with and without strong weight fluctuations.
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What This Specifically Means
According to the authors, the results suggest that repeated weight loss and regain could be associated with a greater loss of thigh muscle volume, even if body weight remains largely stable over the years. Changes in fat tissue, however, could not be demonstrated.
The study thus highlights that changes in body composition should not be assessed solely based on body weight. Rather, it may be important to also focus on maintaining muscle mass, especially in the context of weight reduction. The study did not include individuals taking GLP-1 medications. With the growing use of these medications for weight loss, the aspect of muscle preservation is likely to gain importance.
Strengths and Weaknesses of the Study
The strengths of the study include the large number of participants, the four-year observation period, and the detailed assessment of muscle and fat tissue using MRI. Additionally, the researchers considered numerous potential influencing factors such as age, gender, BMI, and lifestyle.
However, since it is an observational study based on existing data, no cause-and-effect relationships can be derived from the results. Another, albeit small, limitation of the study lies in the selection of participants. Since all participants had an increased risk of knee osteoarthritis, the results may not be directly applicable to the general population.