Moderate evidence Tested in GLP-1 users
In real-world use, people on GLP-1s probably fall short on fiber, calcium, iron, magnesium, potassium, and vitamins including D, and often on protein relative to body weight. The data is early and observational, and one key study is authored by a shake seller, so cite the gap, not its remedy.
What it rests on
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Frontiers nutrient intake 2025 1
A study recorded three days of food intake for 69 people on GLP-1s. They fell short on fiber (about 14.5 vs 28 g), calcium, and vitamin D (below the reference in about 99%), and only 43% hit the protein target. It was funded by a supplement seller whose suggested fix is its own shakes.
69 GLP-1 users (supplement-seller funded)
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Urbina 2026 2
A review pulling together reports of nutrient shortfalls in people on GLP-1s. Vitamin D deficiency rose from about 7.5% to 13.6% between 6 and 12 months, with additional signals for iron and thiamine, including rare case reports of serious thiamine deficiency.
Review of GLP-1 users
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Mozaffarian 2025 advisory 3
A joint advisory from four medical societies summarizing current best practice for supporting people on GLP-1s. It is an expert consensus document, not a trial, and is the standard reference for what the field recommends and where evidence is still missing.
Four-society expert consensus
Moderate evidence Not tested in GLP-1 users
People with obesity are frequently already low in several micronutrients, including vitamin D, B12, folate, and magnesium, before starting any drug. You can be overweight and undernourished at the same time. This baseline research does not involve GLP-1s.
What it rests on
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Kobylinska 2022 4
A review of malnutrition in obesity showing people with obesity are often already low in vitamin D, B1, B12, folate, and magnesium before any drug, from low-nutrient diets and altered absorption. It does not mention GLP-1s; the link to these drugs is our inference.
General obesity, not GLP-1
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Mozaffarian 2025 advisory 3
A joint advisory from four medical societies summarizing current best practice for supporting people on GLP-1s. It is an expert consensus document, not a trial, and is the standard reference for what the field recommends and where evidence is still missing.
Four-society expert consensus
Moderate evidence Tested in GLP-1 users
The nutrients of greatest concern during GLP-1 weight loss are iron, calcium, magnesium, zinc, and vitamins A, D, E, K, B1, B12, and C. This is a review-based watch list; several prevalence figures come from bariatric and general-obesity groups, and one source is drug-maker funded.
What it rests on
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Almandoz 2024 5
A clinical review listing the nutrients to watch on obesity medications: iron, calcium, magnesium, B12, and vitamins A, D, E, and K. It suggests considering a multivitamin but states plainly that no study has tested whether supplementing improves outcomes on these drugs. It is drug-maker funded.
Review (drug-maker funded)
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Urbina 2026 2
A review pulling together reports of nutrient shortfalls in people on GLP-1s. Vitamin D deficiency rose from about 7.5% to 13.6% between 6 and 12 months, with additional signals for iron and thiamine, including rare case reports of serious thiamine deficiency.
Review of GLP-1 users
Moderate evidence Not tested in GLP-1 users
Eating less, even under supervision and without a crash diet, can still leave persistent micronutrient shortfalls, which is why food quality matters and not just quantity. The evidence is a single-arm study in 70 dieting women, not GLP-1 users.
What it rests on
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Poli 2017 6
A study followed 70 women through a year of supervised dieting with counseling. Even with intake down about 18% and no crash dieting, most tracked micronutrients stayed below the recommended level, showing food quality matters, not just quantity.
70 women, not GLP-1
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Mozaffarian 2025 advisory 3
A joint advisory from four medical societies summarizing current best practice for supporting people on GLP-1s. It is an expert consensus document, not a trial, and is the standard reference for what the field recommends and where evidence is still missing.
Four-society expert consensus
Early / weak evidence Tested in GLP-1 users
If you are barely eating, thiamine (B1) deficiency is a rare but serious risk that can, in the extreme, cause a medical emergency. This rests on a handful of case reports, so it is a know-the-warning-signs flag and a reason to seek care, not a common event or a reason to buy a supplement.
What it rests on
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Urbina 2026 2
A review pulling together reports of nutrient shortfalls in people on GLP-1s. Vitamin D deficiency rose from about 7.5% to 13.6% between 6 and 12 months, with additional signals for iron and thiamine, including rare case reports of serious thiamine deficiency.
Review of GLP-1 users
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Mozaffarian 2025 advisory 3
A joint advisory from four medical societies summarizing current best practice for supporting people on GLP-1s. It is an expert consensus document, not a trial, and is the standard reference for what the field recommends and where evidence is still missing.
Four-society expert consensus
Strong evidence Not tested in GLP-1 users
A clinician may reasonably consider a multivitamin, calcium, vitamin D, or B12 for someone at risk, but no trial has shown that supplementing improves outcomes in GLP-1 users, and the papers pushing supplements are funded by drug makers and supplement sellers. Food first; supplement only to fill a demonstrated gap.
What it rests on
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Almandoz 2024 5
A clinical review listing the nutrients to watch on obesity medications: iron, calcium, magnesium, B12, and vitamins A, D, E, and K. It suggests considering a multivitamin but states plainly that no study has tested whether supplementing improves outcomes on these drugs. It is drug-maker funded.
Review (drug-maker funded)
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Frontiers nutrient intake 2025 1
A study recorded three days of food intake for 69 people on GLP-1s. They fell short on fiber (about 14.5 vs 28 g), calcium, and vitamin D (below the reference in about 99%), and only 43% hit the protein target. It was funded by a supplement seller whose suggested fix is its own shakes.
69 GLP-1 users (supplement-seller funded)
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Mozaffarian 2025 advisory 3
A joint advisory from four medical societies summarizing current best practice for supporting people on GLP-1s. It is an expert consensus document, not a trial, and is the standard reference for what the field recommends and where evidence is still missing.
Four-society expert consensus
What would change this grade
A randomized trial of a multivitamin and mineral supplement in GLP-1 users (NCT06981936) is underway. Until it reports, the honest statement is that no supplement is proven to help.