The scale is moving in the direction you want, and your clothes are starting to fit again. Yet you’re tired by mid-afternoon, your face looks a little hollow in photos, and you can’t remember the last time you finished a full meal.
GLP-1 medications like semaglutide mimic a gut hormone that slows digestion and reduces appetite. For many people, they work well. But eating substantially less food means taking in fewer nutrients, with GLP-1 side effects you won’t see on the bathroom scale — including muscle loss, skin changes, and nutrient deficiencies.
Healthy aging requires more than weight loss. Along with healthy food and proper medical care, a daily foundation like NOVOS Core can help cover gaps created when appetite drops on GLP-1 medications.
Quick Overview
- In the STEP 1 trial of semaglutide, roughly 45% of the weight lost came from lean mass; in SURMOUNT-1 with tirzepatide, about 26%.
- GLP-1 users report eating 700 to 800 fewer calories per day than non-users.
- GLP-1 side effects may include deficiencies in vitamin D, iron, calcium, thiamine, and B12.
- Resistance training plus 1.2–1.6 g of protein per kg of body weight daily are evidence-backed ways to protect muscle.
- Supplements complement a nutrient-dense diet and your doctor’s guidance. They don’t replace either.
GLP-1 Side Effects: Why These Medications Can Affect More Than Your Weight
Two things typically happen at once on GLP-1 medications: You eat less, and you lose weight quickly. Eating less drains your nutrient stores. Rapid weight loss changes your body’s makeup.
Appetite Suppression Changes Your Nutritional Intake
A 2025 review cites survey data showing GLP-1 users consume 700 to 800 fewer calories daily than people not taking these drugs. That drop doesn’t come evenly out of every food group.
Protein is often one of the first to go. It’s filling, it takes effort to prepare, and when nausea or early fullness sets in, a piece of fish is often the last thing that appeals.
Micronutrients follow: A 2025 narrative review covering more than 480,000 adults found vitamin D deficiency in 7.5% of users at six months and 13.6% at 12 months. Over 60% were eating below estimated requirements for calcium and iron. When you’re eating less, every calorie has to carry more nutritional weight.
Rapid Weight Loss Alters Body Composition
With weight loss comes lean tissue loss. A 2024 analysis in Diabetes, Obesity and Metabolism found that in STEP 1, semaglutide participants lost 15.3 kg on average, 6.92 kg of it lean mass (about 45%). In SURMOUNT-1, tirzepatide participants lost 22.1 kg with 5.67 kg from lean mass (closer to 26%). The authors note variations across studies, with some reporting lean mass losses of 15% or less.
4 Common Challenges While Taking GLP-1 Medications
The issues below appear most often in the research and in what patients report to their doctors.
1. Muscle Loss
Muscle isn’t only about strength. It’s where most of the glucose in your bloodstream gets stored after a meal. It burns calories at rest. And grip strength and walking speed predict how independently people live in their 70s and 80s.
How much you lose is partly within your control. A 2025 case series followed three patients on semaglutide or tirzepatide who prioritized lean tissue: resistance training three to five days a week and protein at 1.6–2.3 g per kg of fat-free mass. Two of the three gained lean soft tissue while losing 13% to 27% of their body weight. Three patients isn’t a trial, and the authors present it as a case series, but the result matches what resistance training does during any period of eating in a deficit.
Hitting protein targets is challenging when appetite drops. The NOVOS Bar can help fill the gaps. With 15 g of plant protein, up to 20 superfoods, and five longevity supplements, one bar works as a snack, two as a meal. It was developed by longevity scientists, a registered dietitian, and a pastry chef formerly of The French Laundry — so it tastes like something you’d want when nothing else appeals.
2. Nutritional Gaps
GLP-1 medications don’t cause malabsorption the way some bariatric procedures do. The problem is simply that there’s less food and thus fewer nutrients being consumed.
A 2025 paper in the International Journal of Obesity points out that bariatric surgery comes with mandatory nutritional monitoring, while GLP-1 therapy has no equivalent framework, despite comparable risk of shortfall. You get full quickly, and foods you used to like may not sound appetizing. When you eat a narrower range of foods, your iron, B12, vitamin D, calcium, and thiamine may run low. Ask your doctor about testing vitamin D, B12, iron, and ferritin before and during treatment.
NOVOS Core can help fill nutritional gaps and was designed to address all 12 hallmarks of aging. It delivers compounds including glycine, alpha-ketoglutarate, magnesium, fisetin, and hyaluronic acid that are hard to get from food alone, and harder still when you’re eating less. Likewise, the NOVOS Bar adds 21 essential vitamins and minerals from food sources, which helps on days when a full meal isn’t happening.
3. Skin Changes & Loss of Elasticity
“Ozempic face” describes hollowed cheeks, deeper folds, and looser skin along the jaw and neck. A 2025 systematic review found that these changes come from rapid weight loss, not from the drug itself. Fat leaves the face faster than the skin can shrink to fit it; bariatric surgery and crash diets do the same thing.
Collagen is the protein that gives skin its structure and lets it snap back when it’s stretched, such as after weight loss. Your body needs specific raw materials to rebuild collagen — which are harder to come by when you’re eating less. Glycine is one of the main amino acids in collagen itself, and vitamin C is required to build it. Both are in NOVOS Core, along with hyaluronic acid, which holds water in the skin.Â
Losing weight more slowly gives skin more months to retract, so ask your prescriber whether a lower dose or slower titration makes sense.
4. Fatigue & Brain Fog
Fatigue often comes down to calories. People eating fewer than 800 calories per day aren’t getting all the fuel their bodies need to run well and maintain mental sharpness.
Low iron, low B12, and low thiamine each affect energy and concentration, and all three appear in the GLP-1 deficiency data. Dehydration adds to the problem, as much of daily water intake comes from food.
NOVOS Vital can provide essential support in a calorie deficit. It targets seven organ systems that decline with age, including the brain, heart, and gut. If the fatigue lasts more than a few weeks or gets worse, ask for a blood panel rather than adding another supplement.
How To Stay Healthy While Using GLP-1 Medications
Beyond your doctor’s recommendations, these habits protect the muscle, skin, and nutrient stores that rapid weight loss puts at risk:
- Prioritize protein. Aim for 1.2 to 1.6 g per kg of body weight daily, spread across meals. Anchor each meal around a protein source and eat that part first.
- Lift heavy twice a week. Whether at the gym or at home, incorporate resistance training to preserve muscle and enhance longevity.
- Drink more water. Less food means less water from food, and dehydration can lead to fatigue and dizziness.
- Cover your micronutrients. Vitamin D, iron, calcium, B12, and thiamine are the ones to monitor. Get them tested.
- Watch fiber intake. These drugs slow stomach emptying, and low fiber on top of that causes constipation. Beans, lentils, vegetables, and whole grains help.
- Don’t fear healthy fats. Fat in a meal makes the gallbladder squeeze out bile, preventing it from sitting stagnant and forming stones. Olive oil, avocado, nuts, and seeds all do the job.
- Protect your sleep. Muscle rebuilds during sleep. Short sleep also raises hunger hormones, which fights the appetite control you’re getting from the medication.
- Keep your follow-up appointments. You won’t feel low iron or low vitamin D immediately, and bloodwork can catch deficiencies earlier.
Our guide to the best diet for longevity covers which eating patterns have the most evidence behind them. We’ve also written separately on why the NOVOS Longevity Diet goes beyond the Mediterranean diet.
Weight Loss Is Only Part of Healthy Aging
GLP-1 medications have changed what’s possible in weight management, and for many people, they’ve been life-altering. But the number on the scale doesn’t tell you what’s happening in your body.
Two people can lose the same 40 pounds. One keeps her muscle, tests her vitamin D and iron twice a year, and lifts weights twice a week. The other loses lean tissue that she won’t rebuild easily and learns of her low B12 two years later. The difference is protein, resistance training, nutrient density, and bloodwork.
FAQ About GLP-1 Side Effects
What supplements should I take while on GLP-1 medications?
Talk to your doctor first, ideally with recent bloodwork. The nutrients most commonly low in GLP-1 users are vitamin D, iron, calcium, B12, and thiamine. A daily foundation like NOVOS Core plus adequate protein covers most of these, but test rather than assume.
Why does my skin look older after losing weight on GLP-1 medication?
Facial fat pads shrink faster than skin can retract, resulting in hollowing and laxity. Research indicates this change reflects the speed of weight loss, not a direct effect of the medication on facial tissue.
Can GLP-1 medications cause vitamin deficiencies?
Drastically reduced food intake means fewer nutrients consumed. Observational data has documented deficiencies developing within 12 months, with vitamin D the most common.
Does GLP-1 medication cause brain fog?
Cognitive complaints are commonly reported, although brain fog isn’t a formally recognized side effect. Likelier explanations are very low calorie intake, dehydration, and nutrient shortfalls. Persistent symptoms warrant a conversation with your doctor.
How can I prevent muscle loss while taking GLP-1 medications?
Prioritize adequate protein intake and resistance training two to three times weekly. Most people should aim for 1.2 to 1.6 g of protein per kg of body weight daily, but anyone with kidney disease needs individualized guidance. Convenient, tasty options like the NOVOS Bar help when appetite is the obstacle.
What are the long-term side effects of GLP-1 drugs?
Long-term data is still accumulating. The documented concerns are lean mass loss, nutritional deficiencies, gallstone risk during rapid weight loss, and weight regain after stopping. Regular bloodwork and follow-up appointments are key to catching issues early.
Consult your healthcare provider before making changes to your medication, diet, or supplement routine.
