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The Crucial Workout and Nutrition Changes You Need to Make the Second You Start a GLP-1, According to Top Fitness Experts

By Dana Angelo White, MS, RDN, ATC Men's Journal

Updated May 19, 2026 9:52 AM

Weight loss medications have become a seamless part of everyday life for millions, but watching the number on the scale drop doesn't give you the full picture of what's actually happening to your body. While GLP-1 agonists are highly effective at stripping away body fat, they also come with a hidden cost, a significant reduction in muscle mass, which happens to be the ultimate currency for aging well.

According to recent data, men lose an average of seven percent of their starting weight on these prescriptions, but that deficit doesn't just come from fat. Lean body mass (the vital combination of muscle, bone, organs, and water) takes a hit, too.

True longevity is about more than just getting smaller. Preserving that lean mass as the years tick by is absolutely essential for sustainable, long-term health. To help you maximize your results, we asked top fitness and nutrition experts exactly how to protect your hard-earned muscle while taking a GLP-1.

How Can GLP-1 Medications Have a Negative Impact on Lean Body Mass?

The way GLP-1 medications can make a serious dent in lean body mass is simple.

The medication lessens appetite, creating a significant calorie deficit. Rapid weight loss typically follows, but this weight can be up to 40 percent lean body mass, according to Heidi Skolnik, MS, CDN, FACSM, author of the upcoming book Your GLP-1 Game Plan, What Your Doctor Didn't Tell You About How to Eat, Move and Thrive on Weight Loss Medication.

Fewer calories mean less energy, which turns into less fuel, so proper adjustments to both diet and training are needed. Michael J. Ranfone, BA, LMT, CSCS, Founder & Owner, Ranfone Training Systems, explains how rapidly this can occur.

"Any time someone is operating in a significant caloric deficit, the fundamental problem is a mismatch between energy demand and energy supply," says Ranfone. "The body simply doesn't have the resources to train hard, recover adequately, and protect muscle tissue simultaneously."

Because GLP-1 medications suppress your appetite, there's a good chance you won't eat enough to keep your energy levels up. If you're training hard and not eating enough because of the medication, not only does your training suffer, but your recovery will too.

"High volume, high frequency, or high intensity training in this state doesn't build or maintain muscle-it accelerates the breakdown of it," he adds.

This breakdown is not intentional or desirable, but the metabolic consequences of consistently not eating enough calories combined with training have a powerful impact on muscle protein synthesis.

"When the body is chronically underfueled, it shifts into a prolonged sympathetic state. Protein synthesis gets suppressed," Ranfone says. "The net result is an internal environment that is actively catabolic-add in the wrong type of training, and you have a recipe for muscle loss."

This doesn't make medications "bad" for muscle health-but shines a bright light on how they are not a magic pill; adjustments in habits are non-negotiable, as Skolnik underscores.

"The medication does not directly hurt muscle; it is the caloric deficit and weight loss that causes accelerated muscle protein breakdown."

Ranfone agrees, adding that the risk likely isn't the medications themselves but " the combination of a significant energy deficit, insufficient protein intake, and training that wasn't designed for a hypocaloric state," he says. "That combination creates the conditions for meaningful muscle loss over time-which is the opposite of what most people are trying to achieve."

What Are the Biggest GLP-1 Pitfalls?

Fasted workouts, inadequate hydration, and excessive training volume are just some of the most common mistakes people on GLP-1s make in the name of weight loss. Finding a new normal is essential.

"The single biggest mistake is trying to maintain the same training routine you had before starting a GLP-1. Whether that routine was high intensity, high volume, or high frequency-or all three-forcing your way through it while in a significant caloric deficit is a serious error," warns Ranfone.

Take the time to review your overall lifestyle and the demands of your schedule-all of our experts agree, time management, flexing on "old routines," and sustainability are paramount to long-term success with or without weight loss medications.

"An equally common mistake is letting the medication do all the heavy lifting while lifestyle fundamentals erode," he adds. "Sleep, hydration, food quality, and baseline daily activity are not optional supporting actors-they are load-bearing. GLP-1s are powerful, but they are one variable in a multifactorial equation."

A Guide to Measuring Real Progress Beyond the Scale

So how do you even know what kind of weight loss is occurring? It's a good idea to monitor changes in body composition. There are several ways to do this, including a good old tape measure, according to Greg Nichols, CPT, CES/BCS, and coach at F45 Training in Fairfield, CT.

"Take circumference measurements in three main areas," he says. "One from the belly button around the body, another around the widest part of the hips, and six inches above the knee. These measurements plus periodic weigh-in consistently at the same time under the same circumstances, first thing in the morning on Friday, works great."

In terms of frequency, Skolnik recommends monitoring body composition at the start of medication use and then every three to six months to help assess if training and diet are minimizing muscle loss.

"Bioelectrical impedance is the most accessible method, although some medical practices may have access to a DEXA machine," says Skolnik. Find a local gym or fitness facility with an InBody or other type of similar equipment and stay consistent with this tool to accurately assess changes.

A Strategic Approach to Weight Training and Cardio on GLP-1s

When asked what type and frequency of training would be best to help maintain lean body mass while in a calorie deficit from a GLP-1, the experts agree–it's quality over quantity when it comes to volume.

"Three days per week of full-body resistance training is the sweet spot for this population," suggests Ranfone. "In a hypocaloric state, recovery is the governing constraint-and three days respects that reality without sacrificing training quality."

How to Build an Effective Routine for Muscle Retention

When it comes to designing your training plan, this is not the time for total burnout, especially when it is isolated to one body part.

"Full-body training gives each muscle group a meaningful dose of stimulation across the week without overloading any single area on any given day," says Ranfone. "For the resistance training itself, prioritize mechanical tension techniques: lower rep ranges, eccentric emphasis, isometric holds, tempo manipulation, and lengthened partials. These tools allow you to generate a high-quality stimulus without needing excessive volume or load."

For the movements themselves, Nichols encourages sticking to compound, multi-joint exercises to get the absolute most bang for your buck. These foundational lifts engage multiple major muscle groups simultaneously, giving you a hyper-efficient workout that saves time while maximizing muscle retention.

"Depending on how many days you can consistently get to the gym, it'd be a great idea to create a split (different body parts or movement patterns for different days) that you can adhere to on most weeks," Nichols adds. "For example: total body push one day, and total body pull another, or back/biceps, chest/triceps, and legs for a 3-day split."

Despite what the internet tells you about grinding out hours of cardio for weight loss, the need for it is actually far less than you'd think. Ranfone encourages people to stick to just a few 30-to-45-minute Zone 2 sessions a week. This delivers a massive cardiovascular and metabolic benefit without adding a heavy burden to your recovery.

Skolnik agrees, stating, "Cardiovascular work is still important for heart health, but you do not need to ‘burn extra calories' – you can engage in strategic and time-efficient cardio."

How Can Diet and Supplements Help Support Lean Body Mass?

It's equally crucial to adopt solid nutrition strategies for maintaining as much lean mass as possible. Skolnik shares her four more important focus areas.

Prioritize protein (1.6 grams per kilogram of body weight) with 30 to 40 grams or so at each meal and some at snacks
Fiber-rich foods (aim for 6-10 grams per meal and some at snacks)
Make sure to stay hydrated
Eat enough to lose weight slowly! It's not a race. Slow weight loss along with resistance training will result in better body composition (and better for skin and mood!)

GLP-1s are also known to wreak havoc on digestion, leading to several unpleasant gastrointestinal symptoms, including nausea, vomiting, gas, bloating, and diarrhea. So it's important to tailor food choices to help sidestep these side effects.

"Foods that are harder to digest, particularly high-fat meals, can compound that effect and create unnecessary GI discomfort," Ranfone says. "Leaning toward carbohydrate-forward food choices from fruits, vegetables, and single-ingredient starches helps keep digestion moving and provides a more accessible fuel source for training and recovery. And pay attention to fiber-going too low for too long creates its own set of downstream problems, particularly for GI health and satiety."

If you're also adding in supplements, less is also more. Reliable, well- studied products like creatine monohydrate and essential amino acids (EAAs) can help support muscle maintenance. Properly dosed protein and electrolyte powders can help bridge gaps that lower calorie intake creates, and finally consider lower doses of stimulants like caffeine, if that is part of your routine.

"If a pre-workout is part of your routine, mild stimulants are fair game, but keep caffeine in check," suggests Ranfone. "If fatigue and recovery are already compromised, high stimulant intake will work against you."

This story was originally published by Men's Journal on May 19, 2026, where it first appeared in the Health & Fitness section. Add Men's Journal as a Preferred Source by clicking here.

This story was originally published May 19, 2026 at 8:25 AM.