The Surprising Effects of GLP-1s; From hair loss to muscle mass — what the research really shows and how to protect your body
- sherrie@rootcauseclinic
- Jun 19, 2025
- 9 min read
Ozempic, Wegovy, Mounjaro. You can’t scroll through your phone, open a magazine, or walk past a beauty salon without hearing about them. GLP-1 receptor agonists — a class of medications originally developed for type 2 diabetes — have become the most talked-about weight loss tools of our generation, and for many people, they’re genuinely life-changing.
But here’s the thing that rarely makes the headlines: what you eat while taking them matters enormously. Not just for the number on the scales, but for your muscle mass, your hair, your energy, your thyroid, and your long-term relationship with your body. THis article covers the surprising effects of GLP-1s and what to eat to support your body.
As a Registered Nutritional Therapist and Functional Medicine Practitioner, I work with clients who are taking GLP-1 medications, thinking about starting them, or coming off them and navigating the rebound. In every case, the nutritional picture is central to how well things go. This guide brings together the latest research and my clinical experience to help you get the most from your medication — and protect your body while you do.
Why Weight Loss Stalls — and Why Nutrition Is the Missing Piece
GLP-1 medications work primarily by suppressing appetite and slowing gastric emptying. In the short term, this produces significant weight loss for most people. But studies consistently show that when medication is stopped, the weight tends to return. A landmark extension of the STEP 1 trial found substantial weight regain in the 12 months following withdrawal of semaglutide — largely because the underlying habits and physiology that contributed to weight gain in the first place hadn’t changed.
There’s also a plateau problem. Many people find that weight loss slows or stalls after the initial months, even while still taking the medication. Reducing calories alone — which is essentially what appetite suppression achieves — is not a sustainable strategy if the quality of those calories is poor. Your body will adapt, and it will do so by breaking down muscle, down-regulating thyroid function, and prioritising fat storage once the medication is removed.
The goal isn’t just to eat less. It’s to eat better. Here’s what the evidence now tells us you need to pay attention to.
The Hidden Risks: What the Latest Research Tells Us
The clinical picture around GLP-1 medications has become significantly clearer over the past two years. Here are the four areas every person taking these medications should know about.
1. Muscle Loss
This is arguably the most underappreciated risk of GLP-1 use. When the body loses weight rapidly, it doesn’t just lose fat — it loses lean tissue too. Recent research suggests that 20 to 40% of the weight lost on semaglutide can come from lean mass (muscle and bone), particularly when protein intake is inadequate and resistance exercise is absent.
Women and older adults appear to be at particular risk. Muscle loss matters far beyond aesthetics: it slows your resting metabolic rate (making future weight maintenance harder), weakens bones, compromises blood sugar regulation, and accelerates functional decline as you age.
The good news is that this is largely preventable with the right nutrition and movement strategy — which is covered in the sections below.
2. Micronutrient Deficiencies
A major 2026 review analysing nearly half a million adults on GLP-1 medications found significant rates of micronutrient deficiency, with vitamin D the most common — affecting over 13% of participants after just 12 months. Iron deficiency, anaemia, and B vitamin deficiencies were also identified.
The mechanism is threefold: people are eating substantially less overall, gastric emptying is slowed (affecting absorption), and food choices when appetite-suppressed often default to the path of least resistance rather than nutrient density. The result is a body that is losing weight but becoming progressively more depleted.
Nutrient | Why It Matters on GLP-1s | Food Sources |
Vitamin D | Deficiency affects immunity, mood, bone density, and thyroid function. Most at-risk nutrient on GLP-1s. | Oily fish, eggs, fortified foods, sunshine |
Iron & Ferritin | Required for energy, thyroid hormone production, and hair growth. Low ferritin is a primary driver of hair loss. | Red meat, lentils, dark leafy greens, pumpkin seeds |
Vitamin B12 | Critical for nerve function and energy. Absorption can be impaired by both medication and reduced food intake. | Meat, fish, eggs, dairy |
Zinc | Supports immune function, skin repair, thyroid, and hair follicle health. | Oysters, beef, pumpkin seeds, chickpeas |
Magnesium | Involved in over 300 enzymatic reactions; supports blood sugar regulation, sleep, and muscle function. | Leafy greens, nuts, seeds, dark chocolate |
Thiamine (B1) | Rare but serious deficiency linked to semaglutide in case reports, particularly with persistent vomiting. | Wholegrains, legumes, nuts |
📊 Know Your Numbers |
I recommend all clients on GLP-1 medications have a baseline nutrient check before starting, and a repeat panel at 6 and 12 months. Ask your GP or opt for testing via Medichecks is a convenient and cost-effective way to do this from home. |
Test via Medichecks: www.medichecks.com/?ref=ROOTCAUSECLINIC |
A full nutrient screen covering vitamin D, ferritin, iron, B12, folate, zinc, and magnesium will give you a clear picture of where you stand and where to focus supplementation. |
3. Hair Loss
Hair loss is one of the most distressing — and most Googled — side effects of GLP-1 medications, and it’s more common than most people realise. Clinical trials of Wegovy recorded hair loss in 2.5% of treated patients (versus 1% on placebo), with rates rising in those who lost 20% or more of their body weight.
The primary mechanism is telogen effluvium — a type of diffuse shedding triggered by physiological stress and nutritional depletion. The key drivers are low ferritin, zinc, biotin, and vitamin D, combined with thyroid hormone disruption that can occur during rapid weight loss. Hair follicles are exquisitely sensitive to nutritional status and hormonal shifts, and when both are disrupted simultaneously, the results can be significant.
What to Do About Hair Loss |
If you’re experiencing hair shedding on a GLP-1 medication, I recommend: |
1. Test ferritin, thyroid function (TSH, free T3, free T4), zinc, and vitamin D — these are the most common culprits. |
2. Prioritise protein at every meal (aim for 25–30g per sitting). |
3. Consider a targeted supplement protocol including iron (if deficient), biotin, zinc, and collagen peptides. |
4. Be patient — telogen effluvium typically resolves within 3–6 months once nutritional drivers are addressed. |
Medichecks offer a 'Hair Loss' finger piock blood test which is a good place to start https://www.medichecks.com/products/hair-loss-check-blood-test?ref=ROOTCAUSECLINIC |
4. A Note on Pancreatic Health and Thyroid
You may have read concerns about pancreatitis and thyroid risk with GLP-1 medications. It’s worth knowing that recent large-scale meta-analyses have not found evidence of a class-wide increased pancreatitis risk from semaglutide. However, if you have a personal or family history of pancreatitis, gallbladder disease, or medullary thyroid cancer, this should be discussed with your prescribing doctor before starting.
From a nutritional perspective, supporting liver and gallbladder function during weight loss is good practice regardless: adequate hydration, bitter greens (rocket, chicory, dandelion), and avoiding very high-fat meals during the early stages of treatment all help the gallbladder manage the increased bile demand that accompanies fat loss.
What to Eat: The Non-Negotiables
When appetite is suppressed, every mouthful counts. Here’s how to structure your eating so that the calories you do consume are doing maximum work for your body.
Prioritise Protein at Every Meal
Protein is the single most important macronutrient to focus on when taking GLP-1 medications. It is your primary defence against muscle loss, it keeps you fuller for longer, it supports hair and skin health, and it has a high thermic effect (meaning your body burns more calories digesting it).
Aim for 25–30g of protein per meal (roughly 1.2–1.6g per kg of body weight per day). Prioritise quality sources: eggs, Greek yoghurt, cottage cheese, oily fish, chicken, legumes, and tofu. If appetite is very suppressed, a high-quality protein shake can help you meet targets without volume.
Particularly if you are a woman or over 50, resistance training alongside adequate protein is the most evidence-based strategy for preserving muscle during GLP-1-assisted weight loss.
Make Your Carbohydrates Work Harder
Processed carbohydrates — white bread, pasta, pastry, ultra-processed snacks — are low in nutrients, spike blood sugar, and take up valuable space in a reduced-calorie diet. Swap them for nutrient-dense alternatives that also support stable blood sugar and beneficial gut bacteria.
Good choices include:
• Quinoa and amaranth — complete proteins as well as complex carbohydrates
• Sweet potato and butternut squash — rich in beta-carotene and potassium
• Lentils and chickpeas — protein, fibre, and iron in one
• Oats — soluble fibre supports cholesterol and gut health
• Plenty of non-starchy vegetables at every meal
Don’t Fear Fat
Healthy fats are satiating, anti-inflammatory, and essential for hormone production — including the thyroid hormones that regulate your metabolism. They are not the enemy.
Prioritise:
• Oily fish (salmon, mackerel, sardines) — omega-3 for inflammation and brain health
• Extra virgin olive oil — the most evidence-backed fat for cardiovascular and metabolic health
• Avocado — healthy monounsaturated fats plus potassium and folate
• A small handful of mixed nuts daily — a large study found that even half a serving of nuts per day was associated with slimmer waistlines over a 4-year period, making them an excellent long-term snack strategy
• Seeds (pumpkin, flaxseed, chia) — zinc, magnesium, and omega-3
Support Your Detoxification Pathways
As fat cells are broken down during weight loss, stored environmental toxins — pollutants, plasticisers, pesticide residues — can be released back into the bloodstream. Your liver’s job is to process and eliminate them. During periods of rapid weight loss, this load is amplified, which can contribute to fatigue, brain fog, and skin symptoms.
Support your liver and elimination pathways with:
• Cruciferous vegetables daily (broccoli, cauliflower, Brussels sprouts, kale) — activate phase 2 liver detoxification
• Bitter greens (rocket, watercress, dandelion) — support bile flow and gallbladder function
• Plenty of fibre to bind and eliminate toxins via the bowel
• Filtered water — minimum 1.5L daily; add a slice of lemon for gentle alkalisation
• Limit alcohol during active weight loss — your liver is already working hard
• Choose organic or ‘clean’ protein sources where possible: organic free-range meat, wild-caught fish
Supplements Worth Considering
I am not an advocate of supplementing blindly — testing first is always preferable so that any protocol is targeted rather than speculative. That said, given the consistent pattern of nutrient depletion on GLP-1 medications, there are some supplements that are clinically sensible for most people taking them.
Key Supplements to Discuss with Your Practitioner |
• Vitamin D3 + K2 — the most commonly depleted nutrient on GLP-1s; K2 directs calcium to bones rather than arteries |
• Magnesium glycinate — gentle on the gut, supports sleep, blood sugar regulation, and muscle function |
• Iron (if ferritin is low) — do not supplement without testing; excess iron is harmful |
• Vitamin B complex — supports energy, nerve function, and mood; look for methylated forms (methylfolate, methylcobalamin) if you have MTHFR variants |
• Zinc — particularly relevant for hair loss, immune function, and thyroid support |
• Collagen peptides — support skin elasticity and connective tissue during rapid body composition changes |
• Protein powder (whey isolate or plant-based) — useful if meeting protein targets through food alone is difficult |
Always choose practitioner-grade or independently tested brands. I source supplements for clients via The Natural Dispensary. |
Test before you supplement: www.medichecks.com/?ref=ROOTCAUSECLINIC |
Movement: Your Secret Weapon
Nutrition and movement are partners in this process. Exercise — particularly resistance training — is the most powerful tool available for preserving muscle mass during weight loss on GLP-1 medications. Even two sessions per week of bodyweight exercises, resistance bands, or weights makes a meaningful difference.
If the gym isn’t your thing, that’s absolutely fine. Brisk walking, swimming, yoga, Pilates, or a YouTube workout class at home all count. What matters is regularity and some degree of resistance (working against gravity or a load). Always check with your doctor or healthcare provider if you have any musculoskeletal or cardiovascular conditions before changing your exercise routine.
Want a Done-for-You Plan?
Knowing what to do is one thing — actually putting it into practice is another, especially when appetite suppression means the last thing you feel like doing is thinking about food.
I’ve created a suite of downloadable resources specifically designed for people on GLP-1 medications:
Resource | What’s Included | Price |
Nutrient-dense, high-protein, gut-friendly meals designed for when weight loss is stalling or appetite is suppressed. Includes shopping list. | £9 | |
Exactly what to test, when to test it, and how to interpret your results. Includes Medichecks panel recommendations and optimal ranges. | £9 | |
GLP-1 Supplement Stack | My clinical supplement recommendations by symptom — muscle loss, hair shedding, fatigue, GI side effects. With brand and dosage guidance. | £9 |
All three resources at a saving. Everything you need to support your body through and beyond GLP-1 treatment. | £22 |
Want More Personalised Support?
The guidance in this article is a strong foundation, but everyone’s biochemistry is different. If you’re experiencing persistent hair loss, fatigue, a significant plateau, or you’re planning to come off your medication and want to protect your results, working with a Registered Nutritional Therapist can make a significant difference.
I offer one-to-one consultations virtually, with a root cause approach that looks at your full health picture — not just the number on the scales.
Book a complimentary 10 minute call or learn more at rootcauseclinic.org/book-online.
References
Wilding JPH et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: The STEP 1 trial extension. Diabetes Obes Metab. 2022;24(8):1553–1564.
Urbina et al. Micronutrient and Nutritional Deficiencies Associated With GLP-1 Receptor Agonist Therapy: A Narrative Review. Clinical Obesity. 2026.
Harvard Health. Study: Taking GLP-1 drugs may increase risk of key nutrient deficiencies. March 2026.
Endocrine Society. Consuming more protein may protect patients taking anti-obesity drug from muscle loss. ENDO 2025.
Haykal D. Alopecia and Semaglutide: Connecting the Dots for Patient Safety. J Cosmet Dermatol. 2025.
Liu X et al. Changes in nut consumption influence long-term weight change in US men and women. BMJ Nutr Prev Health. 2019.
Jackson E et al. Adipose Tissue as a Site of Toxin Accumulation. Compr Physiol. 2017.
Cleveland Clinic Journal of Medicine. GLP-1 receptor agonists and pancreatitis: A reconcilable divorce. 2025.
Disclaimer: This article is for educational purposes only and does not constitute medical advice. Always consult your prescribing doctor or a qualified healthcare professional before making changes to your medication, diet, or supplement regimen.
© Root Cause Clinic 2026 | Sherrie Theis-Dunn BSc PgDip MBANT | rootcauseclinic.org
