For years, obesity treatment has often been judged by one question: How much weight did someone lose?
A new Scientific Statement from the Endocrine Society says that is too narrow. The authors argue that treatment should also be judged by whether a person’s health actually improves, including changes in blood sugar, blood pressure, sleep apnea, liver health, mobility and quality of life.
The statement, published in Endocrine Reviews, is not a treatment guideline. Instead, it reviews what researchers know about obesity today and highlights some of the biggest questions still unanswered, especially as GLP-1 medications such as semaglutide and tirzepatide make larger amounts of weight loss possible.
Several authors reported financial relationships with companies that develop obesity medications, including Eli Lilly, Novo Nordisk, AstraZeneca, Amgen, Roche and Pfizer. One author became an AstraZeneca employee after the statement was written. Those ties do not invalidate the work, but they are important context given the statement’s focus on obesity medications.
“This Statement highlights major advances in obesity science and outlines areas of research needed to improve our understanding of the disease, optimize treatment, personalize care and improve long-term health outcomes for people living with obesity,” said lead author Daniel J. Drucker of Mount Sinai Hospital in Toronto.
One reason the authors want a broader definition of success is that the same amount of weight loss can mean very different things for different people.
Some health improvements can begin with relatively modest weight loss. The statement notes that losing about 2% to 5% of body weight can improve blood sugar and triglycerides in some people. Other conditions, including sleep apnea and knee osteoarthritis, may require more substantial weight loss before symptoms improve.
Newer obesity medications have also raised another question: Are some health benefits happening because of the weight loss itself, because of the medication or because of both?
For example, semaglutide has been shown to lower the risk of major cardiovascular events in some adults with overweight or obesity and established cardiovascular disease. Tirzepatide has been approved for adults with obesity and moderate to severe sleep apnea. Semaglutide has also been approved for a form of metabolic liver disease.
That means someone could lose less weight than expected but still see important improvements in their health.
The authors say obesity research needs better ways to measure those outcomes.
Right now, clinical trials often focus on the percentage of body weight lost. But that does not capture everything that may matter, such as whether blood sugar improves, sleep gets better, mobility increases or a person feels and functions better day to day.
The statement also points out that treatment goals may need to look different depending on the person.
For one person, the main goal may be lowering the risk of type 2 diabetes. For another, it may be improving sleep apnea or making it easier to move without pain. Older adults may need more attention to muscle strength and bone health during weight loss, while children and teens need different measures because they are still growing.
Researchers also know that people respond very differently to obesity treatment.
Some lose much more weight than others, even when they receive the same medication, follow the same type of diet or undergo the same surgery. Researchers still cannot reliably predict who will respond best to a particular treatment or who is most likely to regain weight later.
That is why the authors say more personalized treatment is an important goal, even though the science is not there yet.
The statement also emphasizes that obesity is a chronic disease, not simply a matter of willpower. It is shaped by a mix of biology, genetics, the brain, environment and other factors.
That matters when treatment stops.
Studies of semaglutide and tirzepatide have shown that many people regain weight after discontinuing the medication. Some improvements in blood pressure, cholesterol and blood sugar can also begin to fade.
The authors say that does not necessarily mean the medication failed. They compare obesity treatment with treatment for other chronic conditions, where health can worsen when an effective treatment is stopped.
Still, many practical questions remain. Researchers do not yet know whether everyone needs to stay on the same dose long term, whether lower doses may work for maintenance or whether switching to another treatment could help some people maintain their progress.
Safety is another major concern as these medications become more widely used.
The most common side effects of GLP-1-based medications involve the digestive system, including nausea, diarrhea, constipation and vomiting. These side effects are often more noticeable when treatment begins or doses are increased.
Researchers are also paying closer attention to what happens when people lose a large amount of weight quickly.
Some loss of muscle and other lean tissue happens with weight loss from many methods, not just GLP-1 medications. The bigger question is whether that loss affects strength, balance or day-to-day function, especially in older adults or people who are already frail.
The statement says more research is needed on whether exercise, diet quality, protein intake and a slower pace of weight loss can help protect muscle and bone health.
Researchers also want better information about rare or long-term side effects. Many obesity medication trials last about one to two years and do not include every group of people who may eventually use these drugs. That makes longer follow-up important as use continues to grow.
Lifestyle still matters in this new treatment landscape, but the role may be changing.
Rather than expecting diet and exercise alone to produce large, lasting weight loss, the statement suggests looking at how healthy eating, physical activity, sleep and stress management can work alongside medication to improve overall health.
That could mean helping preserve muscle, improving fitness, supporting good nutrition and making it easier to maintain daily function, even if those changes do not lead to more pounds lost.
“The rapid adoption of highly effective obesity medications has changed the treatment landscape, but important questions remain about their long-term use, individualized treatment strategies, side effects and the best ways to measure treatment outcomes,” Drucker said.
The Scientific Statement was developed by the Endocrine Society. Several authors reported research funding, consulting work, advisory roles, speaking fees, stock holdings or other financial relationships with pharmaceutical and health companies, including companies that develop obesity medications.