Eating Less on a GLP-1? The Nutrients to Watch and How to Cover Them

Medically reviewed by Chad M. Ferguson, MD, on October 18, 2026.

A smaller plate carries fewer nutrients

GLP-1 medications such as semaglutide and tirzepatide work largely by reducing appetite. In a 20-week trial, adults taking semaglutide 2.4 mg ate 35 percent less at a lunch where they could eat as much as they wanted, compared with adults taking placebo. A joint advisory from four obesity and nutrition societies puts the observed reductions in calorie intake on these medications at 16 to 39 percent.

That reduction is how the medicines produce weight loss, and it is also why nutrition needs attention. When you eat a third less food, you take in roughly a third fewer vitamins and minerals unless you change what you eat. The advisory warns that intakes below about 1,200 calories a day for women and 1,800 calories a day for men make it hard to meet vitamin and mineral needs.

Eating less, not absorbing less

You may have read that GLP-1 medications stop your body from absorbing nutrients. The evidence points mainly to intake instead. These medications can slow stomach emptying, which contributes to fullness, bloating and nausea. However, the same 20-week semaglutide trial found no evidence of delayed stomach emptying at week 20 using an indirect test, even though participants were eating far less. For most people, the practical problem is the amount of food, and the solution is to make each meal count.

What the real-world data show

In an analysis of insurance claims for 461,382 adults who started a GLP-1 medication, a nutritional deficiency was diagnosed in 12.7 percent within 6 months and in 22.4 percent within 12 months. Vitamin D deficiency was the most common diagnosis, recorded in 7.5 percent at 6 months and 13.6 percent at 12 months. Most people in that study had type 2 diabetes, and a claims database records only the deficiencies that someone tested for and coded. These figures therefore describe a pattern rather than your personal risk.

The nutrients that deserve the most attention

• Protein. Protein supports muscle, skin and the repair of tissue, and it is usually the first thing to fall when appetite drops. The joint advisory notes that targets of 1.2 to 1.6 g per kilogram of body weight per day have been proposed during active weight loss, often calculated on an adjusted body weight for people with obesity. Our article on keeping muscle while losing weight before surgery explains these targets in more detail.
• Vitamin D and calcium. The advisory names vitamin D and calcium among the nutrients for which supplements can be considered proactively. It also notes that substantial and rapid weight loss is associated with loss of bone, which makes these nutrients and resistance training more important during treatment.
• Vitamin B12. The advisory lists B12 as well. Many people with type 2 diabetes take metformin alongside a GLP-1 medication, and the metformin label states that metformin may lower B12 levels and recommends measuring B12 every two to three years.
• Iron. Iron needs vary widely with sex, age and diet. Ask your provider whether to check your iron stores, usually with a ferritin test, before you start an iron supplement.
• Fluids and fiber. Nausea, vomiting or diarrhea can lead to dehydration, which the advisory notes can cause acute kidney injury. Constipation is also common, and the advisory recommends adequate fluids and fiber from food.

Watch for the warning signs

The advisory lists signs that can indicate a true nutrient deficiency: fatigue beyond what you would expect, excessive hair loss, flaky or itchy skin, muscle weakness, poor wound healing and unusual bruising. Any of these signs deserves a call to your provider rather than a guess in the supplement aisle.

A practical plan

1. Build each meal around protein, and eat the protein first, before you feel full.
2. Choose foods that carry the most nutrition per bite, such as fish, eggs, dairy or fortified alternatives, beans, vegetables, fruit and whole grains.
3. If nausea limits what you eat, try smaller meals every three to four hours, drink fluids through the day, and avoid fatty foods while a new dose settles in. The advisory describes each of these strategies.
4. Ask your provider or a registered dietitian whether a complete daily multivitamin at moderate doses makes sense for you when a smaller diet leaves likely gaps, rather than a long list of high-dose single supplements.
5. Ask your provider which laboratory tests make sense for you, and repeat them if you stay on treatment.

How Truthe products fit

Truthe Daily Support is a two-capsule daily multivitamin. Each serving provides 1,000 IU of vitamin D3, 500 mcg of vitamin B12 as methylcobalamin, 680 mcg DFE of folate as 5-methyltetrahydrofolate, 15 mg of zinc as zinc bisglycinate chelate and 500 mg of vitamin C. It contains no iron, which leaves the iron decision to you and your provider. Truthe Nutrition Blend adds 20 g of whey protein per scoop, and the two products are sold together as Core Nutrition.

Tests to discuss with your provider

• Ask about a 25-hydroxyvitamin D level, because vitamin D deficiency was the most common diagnosis in the claims analysis.
• Ask about a vitamin B12 level, especially if you also take metformin.
• Ask whether a complete blood count and a ferritin level make sense if you have unusual fatigue or heavy menstrual periods.
• Ask about kidney function tests if you have had significant vomiting or diarrhea.

If surgery is on your calendar

Nutrient gaps matter most when the body has extra work to do, and recovery from surgery is extra work. If you take a GLP-1 medication and have an operation planned, read our guide to nutrition around surgery and our article on surgery while taking a GLP-1.

About Truthe Rx

If you are considering a GLP-1 medication, the Truthe Rx LEAN program and the Truthe Rx MICRODOSING program connect you with a licensed provider. Truthe does not prescribe, and an independent licensed provider decides whether a prescription is appropriate for you.

Disclaimer: This content is for educational purposes only and is not medical advice. Talk with your surgeon and a licensed healthcare provider about your situation. Statements about dietary supplements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.

Sources

1. Friedrichsen M, et al. The effect of semaglutide 2.4 mg once weekly on energy intake, appetite, control of eating, and gastric emptying in adults with obesity. Diabetes Obes Metab. 2021;23:754-762. doi.org/10.1111/dom.14280
2. Mozaffarian D, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory from the American College of Lifestyle Medicine, the American Society for Nutrition, the Obesity Medicine Association, and The Obesity Society. Obes Pillars. 2025;15:100181. doi.org/10.1016/j.obpill.2025.100181
3. Butsch WS, et al. Nutritional deficiencies and muscle loss in adults with type 2 diabetes using GLP-1 receptor agonists: a retrospective observational study. Obes Pillars. 2025;15:100186. doi.org/10.1016/j.obpill.2025.100186
4. Metformin hydrochloride tablets, prescribing information, section 5 (vitamin B12 deficiency). DailyMed, US National Library of Medicine. dailymed.nlm.nih.gov