Guide · Food and modes · 3 min read
Vitamins and minerals when you eat less
GLP-1 medicines can cut how much you eat by a lot; in studies, calorie intake fell by 16% to 39%. 1 A drop this large can leave you short of vitamins and minerals, especially below about 1,200 kcal a day for women and 1,800 kcal a day for men. 1
Nutrients to watch
The joint expert advisory names iron, calcium, magnesium, zinc and vitamins A, D, E, K, B1, B12 and C as examples. 1 Stomach side effects can reduce how well nutrients are absorbed. 1
Food first
- Make small meals count with a variety of minimally processed foods: fruit, vegetables, whole grains, pulses, lean protein, nuts and seeds. 1
- Iron: red meat, beans such as kidney beans and chickpeas, nuts, dried fruit such as apricots, and fortified breakfast cereals. 3
- Calcium: milk, cheese and other dairy foods, green leafy vegetables such as kale or okra, soya drinks with added calcium, and fish eaten with the bones, such as sardines. 4
- Vitamin D: oily fish such as salmon or sardines, red meat, egg yolks and fortified foods. 2
Supplements
- Vitamin D: UK advice is that everyone should consider a daily 10 microgram supplement in autumn and winter. 2 Don't take more than 100 micrograms a day, as it could be harmful. 2
- Experts recommend vitamin or mineral supplements as needed, with your intake and nutrient levels checked during treatment. 1
- More is not better. Taking 17 mg or less of iron a day from supplements is unlikely to cause harm. 3 High doses of iron (over 20 mg) can cause constipation, feeling or being sick and stomach pain. 3 For calcium, 1,500 mg or less a day is unlikely to cause harm. 4
- In halal mode, check capsules: gelatin capsules are common for supplements, and gelatin can be made from cattle, pigskin or fish. 5
In CalJab
Add any vitamin or mineral you take in Health under Medicines; vitamin D, iron, calcium, B12, magnesium, zinc and multivitamins are among the often added ones. They show up in your doctor report under other medicines and supplements, and supplement reminders are in Reminders.
When to see a doctor
- Tiredness beyond what you'd expect, a lot of hair loss, flaky or itchy skin, muscle weakness, wounds that heal slowly or unusual bruising can be signs of a deficiency: talk to your doctor. 1
- If you've had a very low-calorie diet, weight-loss surgery, coeliac disease or a deficiency before, tell your doctor; tests may be needed before treatment. 1
- Heavy periods raise the risk of iron deficiency anaemia; a GP or registered dietitian can advise. 3
Ask your doctor or pharmacist before starting a supplement, especially if you take other medicines.
Sources
- 1Mozaffarian D, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint Advisory from ACLM, ASN, OMA and The Obesity Society. Obesity 2025;33(8):1475-1503. pmc.ncbi.nlm.nih.gov
- 2NHS: Vitamin D. Last reviewed 3 August 2020. nhs.uk
- 3NHS: Iron. Last reviewed 3 August 2020. nhs.uk
- 4NHS: Calcium. Last reviewed 3 August 2020. nhs.uk
- 5US Department of Agriculture (USDA AMS): Gelatin technical review. ams.usda.gov
Written by the CalJab team, with sources. It does not replace your doctor's advice. Found a mistake? Write to support@caljab.app.