Q&A: GLP-1 Monotherapy Is Not Enough—Jonathan Bonnet, MD, MPH, on the Lifestyle Prescription for Obesity

Jonathan Bonnet, MD, MPH, is a coauthor of a recent joint advisory that warns of the potential challenges associated with GLP-1 receptor agonist therapy for management of obesity. As use of the potent medications has grown increasingly widespread, so has documentation of adverse effects during treatment, including protein and other nutrient deficiencies and loss of lean mass and bone mass.

The advisory, titled “Nutritional Priorities to Support GLP-1 Therapy for Obesity: A joint Advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society,” doesn't just warn of the potential issues. It provides a comprehensive guide to patient assessment and the use of structured evidence-based nutritional and lifestyle strategies to address a wide range of challenges around GLP-1 treatment of obesity.

To gain more insight on the advisory, Patient Care sat down with Bonnet for a question and answer session and the transcript follows here. Bonnet is program director of medical weight loss at the Clinical Resource Hub Weight Management Center, Palo Alto VA, and holds an affiliate appointment at Stanford University. He is board-certified in family, sports, obesity, and lifestyle medicine.

The Q&A transcript has been lightly edited for style and clarity.

Patient Care: How did the concept for the joint advisory on nutritional priorities to support GLP-1 medication use in obesity come about?

Jonathan Bonnet, MD, MPH: I think by now most people have heard about GLP-1s—they’re being used pretty widely. We’re still figuring out how to use them in the best possible way so patients get great results without creating new problems. Any time there’s a new drug, there’s an art to it. It’s not just, “Here, take this pill and see what happens.” You need support and resources in place.

When you give a drug to thousands—or millions—of people, you learn a lot fast: the side effects, how it’s affecting people’s daily lives, what behaviors they are or aren’t changing. The question we asked was: how can we best support patients nutritionally—maybe even on the exercise side? What new challenges will they run into? And how do we make sure the benefits of the drug are backed up with lifestyle habits that help them succeed for the long haul?

PC: Beyond nutritional deficiencies, what other challenges does the advisory highlight?

Bonnet: First off, not everyone responds the same. Some people do great, some not at all, and a lot fall somewhere in between. Then there’s the side effects—GI issues are a big one. Nausea tops the list. Eating small, frequent meals and not skipping meals can help. For constipation, we push high-fiber, high-water foods. Reflux? Maybe it’s spicy foods, eating too late, or lying down right after meals—you can often fix that with simple changes.

The other big thing is that because these meds turn down appetite so much, people sometimes don’t get enough key nutrients—especially protein and fiber. Low protein puts them at risk for muscle loss, which is why we also talk about resistance training. And of course, there are the bigger-picture concerns: cost, and the fact that we still don’t have 10-year safety data.

PC: The advisory recommends a thorough baseline nutritional assessment before prescribing GLP-1s. Is that being overlooked, and what’s most often missed?

Bonnet: In obesity medicine, I’ve got more time to dig deep. In primary care, I know time is tight. But even then, there are a few non-negotiables. You’ve got to know the patient’s weight history—when they lost, when they gained, what was going on in their life. Did they start a new medication? Did something major happen?

You also need to know if they’ve ever had an eating disorder. A lot of people have tried every diet under the sun, and it’s not hard to end up with disordered eating along the way. And you need to get to the root cause. Is it poor sleep? Too much ultra-processed food? No physical activity? Medications? Depression? Anxiety? If you don’t figure that out, you’re just suppressing appetite without fixing the actual problem.

Plus, there are contraindications and a few drug interactions you don’t want to miss.

PC: The advisory stresses combining nutritional, behavioral, and lifestyle strategies with medication. How should primary care approach this?

Bonnet: You don’t have to do it all in one visit, and you don’t have to do it alone. Use your team—dietitians, behavioral psychologists, PTs, health coaches.

Like it or not, GLP-1s are here to stay. They’re probably going to be the biggest-selling drugs of all time—likely passing statins—unless something really unusual happens. And obesity? I’d argue it’s literally and figuratively our biggest healthcare challenge. Look at all the comorbidities: high blood pressure, high cholesterol, prediabetes, diabetes, sleep apnea, fatty liver, joint pain, heart disease, some cancers. If you treat obesity well, you move the needle on all of them.

Primary care docs already manage diabetes, and these drugs are part of that, so they’re not foreign territory. Sure, send the tough cases to an obesity specialist, but not every patient with obesity needs a referral—just like you don’t send everyone with arthritis straight to an orthopedist.

PC: Where is research most needed for integrating nutrition and medication in obesity care?

Bonnet: The big question: Are these forever drugs? Right now, the best data says… probably. There are ideas about weaning people off—alternate dosing, combining low doses of different meds, using intensive nutrition programs—but no rock-solid evidence yet that you can get people off GLP-1s without significant weight regain.

I’d also love more clarity on nutrient targets, especially protein. We suggested in our paper: 0.8 g/kg/day if you don’t adjust for body weight, or 1.2–1.6 g/kg of adjusted body weight per day if you do. That’s a big range. Same with other nutrients—we need to know what’s optimal during weight loss. And down the line, what does the “off-ramp” diet look like if you’re trying to transition someone off the drug without undoing all the progress?

PC: You’ve worked on guidelines for using lifestyle medicine in prediabetes and type 2 diabetes. What are the core principles of this approach?

Bonnet: The American College of Lifestyle Medicine has six pillars. I like the easy version: what you do with your feet, your fork, and your fingers; how you manage stress and sleep; and whether you have loving, meaningful relationships.

Translated: physical activity, healthy nutrition, avoiding harmful substances, restorative sleep, stress management, and social connection. There’s mountains of data showing these help prevent disease—and when done right, they can treat or even reverse some conditions.

They’re inexpensive, accessible, and work for the long run. That doesn’t mean ditch the meds. It’s lifestyle first, with medications as needed, so people can not just lose weight but keep it off and stay healthy for life.

PC: Would you leave us with 3 take-home suggestions for primary care from the advisory?

Bonnet: Certainly.

1. Take obesity as seriously as other chronic conditions. If someone walked in with a BP of 190/110, you wouldn’t just wave goodbye. Yet we do that with high BMI all the time. Address it respectfully, without judgment, and give patients something actionable.
2. Lead with lifestyle, use meds when appropriate. I’m a lifestyle-first guy. We often skip straight to pharmacology because it’s easier than walking through a lifestyle prescription—but lifestyle benefits everything you treat, not just weight.
3. It’s not “drugs or lifestyle.” It’s always “drugs plus lifestyle.” Use the right tools for the right patient, have the conversation about risks and benefits, and optimize lifestyle before jumping to meds.