— During your programme

Small portions,
complete nutrition.

During a Tirzepatide programme you naturally eat less. That's exactly the point — but when you eat less, less of everything your body needs comes in too. On this page we briefly explain what to watch for, and which multivitamin we recommend in our programmes.

Order Support-1 at FitForMe ↗ Read more first
For whom
Anyone on GLP-1 / GIP
Why
Reduced micronutrient intake
What we recommend
FitForMe Support-1
When to start
From the titration phase

What changes on GLP-1?

Tirzepatide and other GLP-1 medications work via a simple principle: they reduce appetite and slow gastric emptying. You feel full sooner, get hungry less quickly, and naturally eat smaller portions. That's great for weight — but it also has an unintended side effect.

When the total volume of food drops, almost everything scales down with it: not just calories, but proteins, fibre, vitamins and minerals too. With rapid weight loss, this can lead to deficiencies over a few months — similar to what we see in patients after bariatric surgery, only somewhat less pronounced.

That's no cause for alarm, but it is a reason to act. With good food choices (protein first, enough vegetables) and a targeted multivitamin, you cover most of the risk.

What might you notice?

Deficiencies build up gradually and aren't always immediately visible. The complaints we hear most often during programmes:

  • Persistent fatigue — not "tired after a busy day", but never feeling fully recharged
  • Hair loss, brittle nails or a dull complexion
  • Cramps in legs or hands, particularly at night
  • Less stamina during exercise than you're used to
  • Brain fog — trouble concentrating, searching for words
  • More sensitivity to cold, or more frequent colds

These symptoms aren't always caused by deficiencies — fatigue and hair loss can also occur in the first months of a programme simply from the weight loss itself. But it's worth raising in your progress check-in. When in doubt, we can check targeted blood values.

What does the science say?

Nutrition during GLP-1 therapy isn't an "extra"; it's a standard part of modern obesity care. Three recent studies show — in plain language — what happens and what helps.

— Butsch et al., 2025 Obesity Pillars · n = 461,382

1 in 5 GLP-1 users develops a diagnosed nutritional deficiency within a year.

In a large real-world analysis of nearly half a million US adults newly starting a GLP-1 medication (mostly semaglutide and tirzepatide), 22.4% had a new diagnosed nutritional deficiency within 12 months. Vitamin D was the most common (13.6% at one year), followed by other B-vitamins (2.6%) and iron-deficiency anaemia (3.2%). About 3% received a "muscle loss" diagnosis.

The authors conclude that structured nutritional screening during GLP-1 therapy is valuable — especially because many deficiencies go unnoticed without blood work.

What this means

Deficiencies aren't a fringe issue: roughly 1 in 5 GLP-1 users develops one — often without immediate symptoms. A good multivitamin covers most of this risk.

— Locatelli et al., 2024 Diabetes Care · narrative review

About 10% of the body weight you lose is muscle mass.

This review pooled data from major GLP-1 trials (including STEP-1 for semaglutide and SURMOUNT-1 for tirzepatide). The conclusion: of total weight loss with incretin medications, roughly 10% (~6 kg) is lean body mass — primarily muscle. That's comparable to what the body loses in ten years of ageing.

The good news: structured resistance training for more than 10 weeks can rebuild around 3 kg of lean mass and increase muscle strength by ~25%. The authors recommend making resistance training a standard part of GLP-1 therapy — not just to preserve muscle, but also to reduce weight regain after stopping medication.

What this means

It's not just "eat less, lose weight". A significant portion of the loss is muscle, with implications for energy, strength, and the risk of regain. Protein-rich nutrition and resistance training belong with the medication.

— Mozaffarian et al., 2025 Am J Clin Nutr · joint advisory

Four leading medical societies: nutrition belongs at the core of GLP-1 care.

A joint advisory from the American College of Lifestyle Medicine, American Society for Nutrition, Obesity Medicine Association, and The Obesity Society — four of the most authoritative organisations in this field. The expert panel (led by Mozaffarian of Tufts University) reviewed the literature and set out concrete priorities.

Their key recommendations for patients on GLP-1s: 1.2 to 1.6 grams of protein per kg of body weight per day during active weight loss (versus the standard 0.8 g/kg), eating protein-rich foods first in a meal to ensure adequate intake, structured resistance training to preserve muscle and bone, and attention to micronutrients. In the STEP-1 trial, 38% of total weight loss was lean body mass.

What this means

The international consensus is clear: GLP-1 alone isn't enough — nutrition, protein, and exercise make the difference between "short-term weight loss" and "lasting health gain".

Which micronutrients matter?

The following vitamins and minerals deserve extra attention during rapid weight loss. These are the same elements that post-bariatric care has been tracking for years:

— Vitamin D

Vitamin D3

Many people in the Netherlands run low year-round. Important for bones, muscles and the immune system.

— B-complex

B1, B12 and folate

Essential for energy, nerve function and the production of red blood cells. B1 drops first when food intake decreases.

— Minerals

Magnesium & potassium

For muscle function, heart rhythm and recovery. Cramps are often an early signal of a shortage here.

— Building blocks

Iron, zinc, selenium

Not for everyone — depends on blood values. Iron should only be supplemented when a deficiency is confirmed.

Which micronutrients matter most for you depends on your diet, your starting weight and any other conditions. When in doubt, we can run targeted blood values during a progress check-in.

What to look for in a good multivitamin.

Not every multivitamin is suitable for people on GLP-1. A few things we look out for:

— Our checklist

  • Active forms of B-vitamins (methylcobalamin, methylfolate) — better absorbed than cheaper variants
  • Vitamin D3 (cholecalciferol), not D2
  • Magnesium as glycinate or citrate — not as oxide
  • No mega-dose iron unless medically indicated
  • Dosages suitable for supplementation, not therapy — a multivitamin doesn't replace treatment
  • No unnecessary additives — sugars, dyes, flavourings
  • Preferably in a form that's easy to swallow — small portions also mean a sensitive stomach

What we recommend.

During our programmes we refer to FitForMe Support-1. FitForMe is a Dutch company that specialises in supplements for people after bariatric surgery and — more recently — for people on GLP-1 analogues. Support-1 was developed specifically for this purpose: the dosing and composition match the needs of someone who eats less.

— FitForMe Multivitamin for GLP-1 users

Support-1 — developed specifically for people on Tirzepatide and other GLP-1 analogues.

A complete daily multivitamin with the most relevant vitamins, minerals and trace elements in appropriate dosages, in active and well-absorbed forms.

  • Covers the most relevant micronutrients for people eating less
  • Contains active forms of B-vitamins, vitamin D3, magnesium and zinc
  • Dosages at supplementation level — no mega-dose iron
  • Dutch formulation, developed with dieticians and surgeons
View Support-1 at FitForMe

Full transparency: this is an independent recommendation. We have reviewed Support-1 ourselves for composition and dosing and find the product suitable for our patients. Lunaris Clinics receives no compensation on purchases — the link goes to a dedicated FitForMe landing page so they can recognise and assist our patients.

— Important caveats

This is not medical advice.

A multivitamin does not replace medical treatment and is not a fix for specific deficiencies. If symptoms persist — fatigue, cramps, hair loss that doesn't ease — please discuss with your doctor or specialised nurse, and have targeted blood work done if needed.

Extra caution with existing conditions: kidney problems (potassium and magnesium load), thyroid disease, blood thinners (interaction with vitamin K) or pregnancy. In those situations, always discuss before starting any supplement.

— Questions?

We're happy to think along.

Have questions about nutrition during your programme, or unsure whether a multivitamin is right for you? Bring it up during an appointment — our GP and specialised nurse are happy to look at it with you.

Book an appointment → Visit FitForMe →