Your prescriber told you to eat less. The medication made that remarkably easy. What nobody mentioned is that eating significantly less for months — even eating well — creates real nutritional gaps. Not in calories. In the specific vitamins and minerals your body needs to keep muscle, hold your mood steady, and stay healthy long-term.

These deficiencies don't announce themselves. They creep. You're a little more tired. Your hair seems different. Your mood is off in a way that's hard to name. Most women blame the medication, or stress, or not sleeping enough — and sometimes that's right. But often there's a nutritional gap quietly getting wider every month.

The mechanism is simple. GLP-1 medications suppress appetite so effectively that most women end up eating far less during active weight loss — often close to half of what they ate before. At that intake, hitting recommended micronutrient amounts through food alone is close to impossible.

The foods that disappear first — red meat, leafy greens, dairy, shellfish — are the primary sources of the nutrients most at risk. And there's a second issue: GLP-1s slow gastric emptying, which affects how well some nutrients are absorbed even from the food you do manage to eat. B12 in particular depends on adequate stomach acid, which drops when food intake drops.

Vitamin D is the single most commonly diagnosed deficiency in GLP-1 users. Zinc is the fastest to develop, because the body keeps almost no reserve of it. Iron is the one with the highest stakes for women who are still menstruating. Parts 2 and 3 of this series go deep on each.

The tricky part is that most of these overlap with what women already chalk up to GLP-1 side effects or rapid weight loss. Fatigue is fatigue. Some hair shedding is normal. But a few signs are worth more attention.

Hair shedding that starts around months 2–4. Some shedding is expected — it's a response to the physical stress of rapid weight loss and usually resolves. Shedding that's heavy, diffuse, or still going past month 5–6 often has a nutritional root, most commonly iron or zinc.
Fatigue that doesn't improve with rest. If you're sleeping and eating enough and still dragging, B12 and iron are the first places to look.
Tingling or numbness in hands and feet. Don't wait on this one. It's a nerve symptom that points specifically to B12, and it gets harder to reverse the longer it's left.
Persistent low mood or emotional flatness. Both vitamin D and magnesium affect mood, and both are easy to attribute to life rather than investigate.
Night cramps. Classic magnesium — and more common on GLP-1s than most people expect.

Standard panels don't include most of these. You have to request them by name — and it's worth doing at baseline, then again at months 3 and 6.

Food is always the better vehicle. But on a GLP-1, the gap between what your body needs and what you can realistically eat is real for most women. A standard multivitamin usually isn't enough: the doses are low, the forms aren't always well absorbed, and the two nutrients with the highest stakes — B12 and iron — need targeted attention.

A reasonable starting approach: supplement B12 preventively, get labs before touching iron, and add D3 with K2 and magnesium glycinate unless your diet is genuinely covering them. Don't start everything at once — leave yourself a way to tell what's working.

Continue to Part 2: B12 and iron — why these two hit women hardest →