Eating much less can make it hard to meet vitamin and mineral needs. A 2025 study of GLP-1 users found most fell short on vitamin D, iron, magnesium and potassium from food. Food-first choices and lab checks guided by a provider help.
When you eat substantially less, whether through dieting or a GLP-1 medication, it becomes harder to get enough vitamins and minerals from food alone. In research on people taking GLP-1 medications, the nutrients that most often fell short included vitamin D, calcium, iron, magnesium and potassium, along with fiber. Some shortfalls, such as low iron, cause no obvious symptoms at first. A food-first approach, sensible use of a multivitamin when your provider recommends one, and lab testing when there is a reason for it can keep small gaps from becoming deficiencies.
Vitamins and minerals come packaged with food. When portions shrink, intake of everything shrinks unless food quality rises to compensate. Newer antiobesity medications produce an average weight reduction of 15 percent or more, according to a 2024 review in the journal Obesity by Almandoz and colleagues, which means a long period of eating well below previous levels. The review recommends that clinicians identify preexisting nutritional risk factors before treatment, counsel patients on recommended intakes of protein, fiber, micronutrients and fluids, and monitor for inadequate nutrient intake during treatment.
A cross-sectional study published in Frontiers in Nutrition in 2025 asked 69 adults who had used a GLP-1 medication for at least a month to complete three-day food records. Average intake was about 1,748 calories a day. Participants met recommended intakes for B vitamins, copper, phosphorus, selenium and zinc. They fell short on fiber, calcium, iron, magnesium, potassium, choline, and vitamins A, C, D and E.
The largest gaps were striking. The share of participants below the recommended intake was 98.6 percent for vitamin D, 98.6 percent for potassium, 94.2 percent for choline, 89.9 percent for magnesium and 88.4 percent for iron. Protein was also below estimated needs for weight loss.
Keep the study's limits in mind. It was small, relied on self-recorded food diaries, did not measure blood levels, and did not include a comparison group of people not taking medication. The authors were affiliated with a supplement retailer. Still, the pattern lines up with the clinical guidance above: when appetite is low, nutrient gaps are likely unless meals are planned.
The recommended amounts below are for adults and come from the NIH Office of Dietary Supplements (ODS). Your own needs may differ.
| Nutrient | Recommended amount for adults (ODS) | Good food sources | Who is at higher risk |
|---|---|---|---|
| Iron | 18 mg for women 19 to 50; 8 mg for men and adults 51 and older | Lean meat, seafood, poultry, fortified cereals, beans, lentils, spinach | Women with heavy periods, pregnant women, frequent blood donors, people with GI disorders |
| Vitamin B12 | 2.4 mcg | Fish, meat, poultry, eggs, dairy, fortified foods | Older adults, people with absorption problems, people who avoid animal foods |
| Vitamin D | 15 mcg (600 IU) to age 70; 20 mcg (800 IU) at 71 and older | Fatty fish, fortified milk and plant milks, fortified cereals | People with limited sun exposure, darker skin or older age |
| Calcium | 1,000 mg for adults 19 to 50 and men 51 to 70; 1,200 mg for women 51 and older and everyone 71 and older | Milk, yogurt, cheese, canned fish with bones, kale, broccoli, bok choy, fortified foods | Postmenopausal women, people who avoid dairy |
The ODS notes that low iron often causes no obvious symptoms in the short term, because the body draws on its stores. When stores run low, iron deficiency anemia can cause digestive upset, weakness, tiredness, lack of energy, and problems with concentration and memory. Vegetarians need almost twice as much iron, because iron from plants is absorbed less well. Eating plant sources of iron with vitamin C foods, such as citrus, strawberries, sweet peppers, tomatoes or broccoli, improves absorption. Iron supplements must be kept away from children, because accidental iron overdose is a leading cause of fatal poisoning in children under 6.
Vitamin B12 is found naturally in animal foods, and plant foods contain none unless fortified. The ODS reports that deficiency affects between 3 percent and 43 percent of older adults, often because of reduced stomach acid, and recommends that people over 50 get most of their B12 from fortified foods or supplements. Some compounded GLP-1 formulations are prepared with added B12. Compounded medications are not FDA-approved, and the FDA states that it does not review them for safety, effectiveness or quality before marketing, so it is best not to assume a combination product covers your B12 needs without discussing it with your provider.
Very few foods naturally contain vitamin D, and fortified foods supply most of it in American diets. Almost all US milk is fortified with about 3 mcg (120 IU) per cup. The ODS notes that almost one in four people in the United States have blood levels that are too low or inadequate for bone and overall health. A blood test for 25-hydroxyvitamin D is the way to know your status. Because vitamin D is fat soluble, supplements are best absorbed with a meal or snack that includes some fat.
Dairy foods are the main calcium source for most Americans. The ODS notes that the body absorbs and retains less calcium after menopause. Calcium supplements can cause gas, bloating and constipation in some people, which is worth knowing if you already have digestive side effects.
Fiber and potassium were among the shortfalls in the 2025 study, and magnesium was one of the five nutrients with the largest gaps. Our guide to nutrition on a GLP-1 program covers fiber-rich food choices.
Not everyone does, but it is common for people eating much less to fall short on several nutrients. A licensed provider or dietitian can look at your diet, health history and medications and help you decide whether a multivitamin or a specific supplement makes sense.
Your provider decides based on your symptoms and risk factors. The ODS notes that vitamin B12 levels can be tested and that a blood test for 25-hydroxyvitamin D shows vitamin D status; tests for iron status are another common example.
Yes. More is not better for every nutrient, and some, such as iron, can be dangerous in excess, particularly for children. Check with a pharmacist or provider before adding supplements, especially if you take other medications.
If you are eating much less than you used to, a licensed provider can review your intake, order lab tests when appropriate, and help you build a plan that protects your health while you lose weight. Explore our weight loss programs to learn more. This article is educational and does not determine eligibility for any treatment.
Written by the NewDay Wellness editorial team from the sources above and checked against them before publication, and medically reviewed by Dr. Sean Arora and Dr. Shannon Arora of Arora Health & Aesthetics; see our editorial standards. This article is educational and does not diagnose conditions, establish eligibility for any medication, or replace care from a licensed provider. Compounded medications are not FDA-approved.
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