- Why eating less on a GLP-1 medicine can lead to nutritional gaps
- What the evidence shows on lean mass loss, and what is still unknown
- What studies show for each supplement, and the limits of that evidence
- What is known about semaglutide and the gut microbiome, and about probiotics
- Safety points to raise with your prescriber or pharmacist before adding any supplement
GLP-1 receptor agonists — semaglutide (Ozempic, Wegovy), tirzepatide (Mounjaro, Zepbound), liraglutide (Victoza, Saxenda) — are used in weight and metabolic management. In the STEP 1 trial, semaglutide at 2.4 mg produced a mean body weight reduction of 14.9% over 68 weeks, compared with 2.4% on placebo.3 In the SURMOUNT-1 trial, tirzepatide produced mean reductions of 15.0% to 20.9% at 72 weeks, compared with 3.1% on placebo.4
Like all medicines, they carry risks. In a meta-analysis of 76 randomized trials, GLP-1 receptor agonists were associated with a higher risk of gallbladder or biliary disease (relative risk 1.37), and the risk was higher in weight-loss trials (relative risk 2.29).5 Seek medical care promptly for severe upper-abdominal pain, fever or yellowing of the skin.
But the prescription conversation typically ends at the dosing schedule and side effect profile. What it may not cover is that eating much less for months can have nutritional consequences. Expert groups list nutritional deficiencies due to calorie reduction, muscle and bone loss, and gastrointestinal side effects among the challenges of GLP-1 treatment, and note that nutrition and lifestyle therapy alongside these medicines is not yet widespread.1 In a pooled analysis of three placebo-controlled trials lasting at least four weeks (209 participants), GLP-1-type medicines lowered energy intake at a standardized lunch by about 270 kcal.6 In a 12-week semaglutide trial in 30 adults with obesity, total energy intake across a day of ad libitum meals was 24% lower than on placebo, with less hunger and a lower preference for high-fat foods.7 Most abnormalities in nutrient status reported so far are subclinical or indirect, although meaningful consequences may occur in susceptible people, such as those with prolonged nausea and vomiting or a poor-quality diet.8
None of this diminishes the clinical value of these medications. This article covers where nutrition can fall short, what the evidence shows for each area, and where the evidence is limited. It is not a recommendation to take any supplement. Never start, stop, delay or change a prescribed medicine because of anything here. Ask your prescriber or pharmacist before adding any supplement, particularly if you take other medicines, have kidney disease, diabetes or thyroid disease, are pregnant or breastfeeding, or are considering a supplement for a child.
Why Nutritional Gaps Can Develop on GLP-1 Medications
Three Ways Nutrition Can Fall Short
1. Eating less without nutritional planning. GLP-1 receptor agonists reduce appetite and increase fullness. In a 12-week trial of semaglutide 1.0 mg in 30 adults with obesity, total energy intake across a day of ad libitum meals was 24% lower than on placebo.7 Lower intake can also mean lower absolute intake of protein, magnesium, B vitamins and other nutrients, particularly if meals are not planned with this in mind.1,2
2. Slower gastric emptying. GLP-1 medications slow gastric emptying, which helps limit blood sugar rises after meals; the effect lessens with prolonged treatment.9 Slower emptying can also change how some oral medicines are absorbed (see the clinical note below).10 Whether it affects nutrient absorption has not been established; a 2026 review lists delayed gastric emptying among several factors, alongside reduced intake and gastrointestinal intolerance, that may contribute to micronutrient risk.8 Gut bacteria may also change: in one small 12-week study of 15 adults with type 2 diabetes, the composition of gut bacteria shifted after starting semaglutide, but what this means for health is not known.11
3. Loss of lean mass during weight loss. Weight loss on GLP-1 medicines includes some loss of lean mass as well as fat. A 2026 systematic review of 35 studies found that, in the incretin groups, the median share of total weight loss attributable to reductions in muscle-based measures was 28.3% (interquartile range 15.9% to 39.9%); in the 13 studies that reported weight loss in lifestyle or placebo comparison groups, 38% also exceeded the same benchmarks, and no study reported objective physical function outcomes.12 In a SURMOUNT-1 substudy of 160 people measured by DXA scan, about 75% of the weight lost was fat and 25% lean mass, for both tirzepatide and placebo.13 Lean mass on a scan is not the same as muscle, and lean tissue loss does not necessarily indicate weaker strength or physical performance.14 The long-term health effects are not yet known. Expert groups recommend resistance training and an appropriate diet to help preserve muscle.1
Six Areas Where Nutrition Can Fall Short — and the Evidence Behind Each
Expert groups name preserving muscle mass, through resistance training and an appropriate diet, as a priority during GLP-1 treatment.1 How much protein is right depends on your size, kidney health and other conditions, so ask your clinician or a registered dietitian. For context, one 2026 narrative review proposed daily protein intakes of at least 1.2 g/kg of body weight (up to 1.6 g/kg in adults without chronic kidney disease) for people on these medicines. This is a proposal by the review author, not a trial result.15 An expert consensus statement notes that its recommendations are primarily derived from indirect evidence.2
When appetite is low, reaching a protein target from food alone can be harder, and some people use protein powders or shakes for that reason. In calorie-restricted weight-loss trials that did not involve GLP-1 medicines, higher-protein diets modestly mitigated the loss of fat-free mass (by about 0.4 kg in a meta-analysis of 24 trials),16 although a 2026 meta-analysis of 22 trials in adults without kidney disease found no significant effect of high-protein diets on fat-free mass.17 No trial has tested protein supplements specifically in people taking GLP-1 medicines. A 2026 review notes that protein supplements and nutritionally complete meal replacements may be useful when intake is insufficient.14
Spreading protein across meals may help: in a 7-day crossover study of 8 healthy adults, eating about 30 g of protein at each of three meals gave 25% higher 24-hour muscle protein synthesis than a pattern weighted toward the evening meal (about 11, 16 and 63 g).18 This small study was not done in people taking GLP-1 medicines. Higher protein intakes did not change serum creatinine in adults without kidney disease in a 2026 meta-analysis, but most trials were short and the long-term kidney effects are uncertain;17 a 2025 systematic review found too little good-quality evidence to judge the effect of protein intake on kidney disease.19 If you have kidney disease, ask your clinician for your protein target before using protein supplements.
Creatine monohydrate has been studied for decades, mainly in sport and exercise. Whether it helps preserve muscle during weight loss on GLP-1 medicines is a hypothesis, not an established benefit.
In healthy people and athletes, creatine supplementation raises muscle creatine concentrations and has been linked to better high-intensity exercise performance, and a position stand reports that supplementation of up to 30 g/day for 5 years was safe and well tolerated in healthy individuals.21 Creatine typically raises serum creatinine, a blood marker used to estimate kidney function: by 0.13 mg/dL on average in a meta-analysis of 19 randomized trials, with no significant change in estimated glomerular filtration rate.22 Other meta-analyses also found a rise in serum creatinine;23,24 one found that creatinine-based estimates of kidney filtration fell, but that kidney function measured by Cr-EDTA clearance did not change significantly, suggesting the change reflects creatinine metabolism rather than kidney injury.24 Tell your clinician if you take creatine before kidney blood tests. Concerns about its renal safety persist in people with impaired kidney function, so ask your clinician before using creatine if you have kidney disease.25
💪 Kasivit Creatine Monohydrate →Magnesium is a mineral involved in many processes in the body, including muscle and nerve function and glucose metabolism. In 2005–2006, about 48% of the US population consumed less than the required amount of magnesium from food.26 That is low intake, not a measured deficiency.
On a lower-calorie diet, magnesium-rich foods such as whole grains, legumes, leafy greens and nuts may be eaten less, so the gap between intake and need could widen; we did not find studies measuring this in people taking GLP-1 medicines. A 2026 review lists magnesium among several micronutrient signals in people taking these medicines, but notes that most abnormalities reported so far are subclinical or indirect.8 Poor sleep, muscle cramps and fatigue have many possible causes, and we did not find evidence that they are caused by low magnesium in people taking GLP-1 medicines. Discuss persistent symptoms with your prescriber.
Magnesium oxide is poorly absorbed (fractional absorption about 4% in a study of normal volunteers), while magnesium chloride, lactate and aspartate were absorbed significantly better and about equally well.27 Magnesium glycinate was not tested in that study, and we did not find trials showing that it is better absorbed or better tolerated than other forms. Magnesium supplements can cause diarrhea at higher doses.28 A systematic review of three small trials in 151 older adults with insomnia found that magnesium shortened the time to fall asleep by about 17 minutes compared with placebo, but the evidence was of low to very low quality and total sleep time did not change significantly; it has not been tested for sleep in people taking GLP-1 medicines.29 The US upper limit for supplemental magnesium in adults is 350 mg/day of elemental magnesium from supplements alone, based on diarrhea as the limiting effect; a 2023 perspective argues that this limit should be re-evaluated.28 If you have kidney disease, ask your clinician before taking magnesium supplements, and ask your prescriber or pharmacist whether magnesium could interact with your medicines.
🌙 Kasivit Magnesium Glycinate →B vitamins, including B12, B6 and folate, come mainly from animal foods, leafy greens and fortified foods, so eating much less could lower intake of them. A 2026 review lists vitamin B12 among the nutrients with signals of risk during GLP-1 treatment, but notes that most abnormalities reported so far are subclinical or indirect.8 We did not find evidence that GLP-1 medicines directly deplete a specific vitamin.
The link with metformin is better documented. In the Diabetes Prevention Program Outcomes Study, low vitamin B12 (200 pg/mL or less) was more common with metformin than with placebo at 5 years (4.3% vs 2.3%), but the difference was not significant at 13 years (7.4% vs 5.4%); combined low and borderline-low B12 was more common with metformin at both time points (19.1% vs 9.5% at 5 years; 20.3% vs 15.6% at 13 years). Neuropathy was more common in metformin users with low B12.30 The authors concluded that routine testing of B12 levels in people treated with metformin should be considered. If you take both metformin and a GLP-1 medicine, ask your clinician whether your B12 should be checked.
Whether a B-complex supplement is useful depends on your diet, your medicines and any blood test results. If B12 deficiency is confirmed, the dose and the route (by mouth or injection) should be set by your prescribing clinician.
⚡ Kasivit B-Complex #12 →Vitamin D is fat-soluble. Expert groups note nutritional insufficiencies associated with obesity itself,2 and vitamin D is one of the nutrients a 2026 review flags as a possible concern during GLP-1 treatment.8 One idea is that some vitamin D is diluted or held in body fat. A systematic review of weight-loss trials that did not use vitamin D supplements found that vitamin D status (blood 25-hydroxyvitamin D) rose with weight loss in 18 of 23 trials, but by less than would be expected if stored vitamin D were simply released into the blood.31
That review did not study GLP-1 medicines, so we cannot say how much vitamin D status changes on them. A blood test (25-hydroxyvitamin D) is the way to know your level, and your clinician can then advise whether a supplement is needed and at what dose.
In a meta-analysis of 20 comparative studies, vitamin D3 (cholecalciferol) raised total blood 25-hydroxyvitamin D more than vitamin D2 did.32 Vitamin K2 is added to some vitamin D products. A 2026 review describes the idea that K2 directs calcium into bone rather than artery walls as a candidate mechanism that remains insufficiently confirmed in humans,33 so we cannot say that adding K2 changes where calcium goes. Vitamin K also affects warfarin: in a study of healthy volunteers taking an oral anticoagulant, vitamin K2 (MK-7) at doses as low as 10 mcg a day lowered the INR in some people, and the authors concluded that MK-7 supplements need to be avoided in patients receiving vitamin K antagonist therapy.34 If you take warfarin or a similar medicine, do not take a vitamin K2 supplement without asking your prescriber. For vitamin D, a review states that 800–1,000 IU/day is safe for preventing or correcting low vitamin D, that an upper limit of 4,000 IU/day is consistently accepted for adults, and that larger doses over the long term should not be selected.35 Testing 25(OH)D lets your clinician choose a dose. Check the label of any product, and do not exceed the upper limit without medical advice.
☀️ Kasivit Vitamin D3 + K2 →Studies of gut bacteria during GLP-1 treatment are small. In one 12-week study of 15 adults with type 2 diabetes taking semaglutide, the composition of gut bacteria changed (for example, Bifidobacterium increased and Klebsiella decreased) alongside improvements in blood sugar, body weight and blood lipids. Samples were compared before and after treatment, with no probiotic arm.11 We did not find evidence on whether such changes influence side effects or health.
Some people choose a probiotic during GLP-1 treatment. There is no GLP-1-specific evidence on which strain or dose, if any, is useful. Probiotics are generally considered safe for most people, but serious infections and other effects have been described in susceptible individuals,36 and in a trial of 298 people with predicted severe acute pancreatitis, a multispecies probiotic was associated with higher mortality (16% vs 6%).37 A 2026 meta-analysis found the evidence insufficient to draw conclusions about long-term safety in at-risk groups.38 If you have a weakened immune system, pancreatitis or a serious illness, ask your clinician before taking a probiotic.
🦠 Kasivit High Potency Probiotic + Prebiotics →Berberine: What the Evidence Shows, and Why to Ask First
Berberine is a plant compound sold as a supplement for blood sugar and cholesterol, and it is often marketed alongside GLP-1 medicines as "nature's Ozempic".39 It has not been studied together with GLP-1 medicines, and it is not a substitute for them.
In trials, berberine lowered blood glucose modestly: a meta-analysis of 20 randomized trials found reductions in fasting glucose of 0.52 mmol/L and in HbA1c of 4.48 mmol/mol (7 studies).40 A meta-analysis of 18 placebo-controlled trials found small reductions in LDL cholesterol (0.46 mmol/L, about 18 mg/dL) and triglycerides (0.34 mmol/L, about 30 mg/dL), with gastrointestinal side effects reported in 2–23% of berberine groups compared with 2–15% of placebo groups.41 A small 3-month pilot in 36 adults with newly diagnosed type 2 diabetes found a blood sugar effect similar to metformin, and 34.5% of patients in the pilot reported transient gastrointestinal adverse effects.42
Supplements Discussed — At a Glance
This table summarizes the sections above. It is not a protocol or a recommendation. Direct evidence in people taking GLP-1 medicines is limited for all of these,2 and doses and timing should be decided with your prescriber or pharmacist. Expert groups point to resistance training and an appropriate diet as the main strategies for preserving muscle.1
| Supplement | Dose or Limit in Sources | Timing | What the Evidence Shows |
|---|---|---|---|
| Protein (supplement) | Target set with your clinician or dietitian | Spread across meals; about 30 g per meal was used in one small study | Higher-protein diets modestly mitigated fat-free mass loss in weight-loss trials without GLP-1 medicines; ask first if you have kidney disease |
| Creatine Monohydrate | No dose tested with GLP-1 medicines; follow the product label | Follow the product label | Plausible add-on, not yet tested with GLP-1 medicines; raises the blood marker creatinine; ask first if you have kidney disease |
| Magnesium Glycinate | Up to 350 mg/day of elemental magnesium from supplements (adult upper limit) | Follow the product label | Low dietary intake is common; diarrhea at higher doses; ask first if you have kidney disease |
| Probiotic + Prebiotic | No GLP-1-specific dose established; follow the product label | Follow the product label | Not tested for GLP-1 side effects; ask first if you have a weakened immune system, pancreatitis or a serious illness |
| B-Complex (with B12) | 1 capsule/day (per product dosing) | Morning with food | Low intake is possible when eating less; B12 testing should be considered with metformin |
| Vitamin D3 + K2 | Up to 4,000 IU/day vitamin D (adult upper limit); 800–1,000 IU/day is considered safe for correcting low levels | Follow the product label | Check your 25(OH)D level first; vitamin K2 can interact with warfarin |
| Berberine | The most common dose in trials was 0.9–1.5 g/day; not tested with GLP-1 medicines | Follow the product label | Modest glucose and lipid effects in trials; may add to blood sugar lowering and can interact with other medicines; ask your prescriber first |
Kasivit Products Related to the Topics Above
Each of the supplements above is available individually from Kasivit — free from unnecessary fillers. All are vegan or vegan-compatible. None of these products has been tested in people taking GLP-1 medicines, so ask your prescriber or pharmacist before adding any of them.
Creatine Creatine Monohydrate $44.99 
Magnesium Magnesium Glycinate $34.99 
Probiotic Probiotic + Prebiotics $34.99 
B Vitamins B-Complex #12 $28.00 
Vitamin D + K2 Vitamin D3 + K2 $34.99 
Berberine Berberine $39.90
Three Kasivit supplements in one bundle. It has not been tested in people taking GLP-1 medicines, so talk to your prescriber or pharmacist before using it. Vegan-compatible, no unnecessary additives.
Shop the GLP-1 Bundle → $92.99GLP-1 Nutrition Gap: Common Questions Answered
What the Evidence Does and Does Not Show
GLP-1 medications produced substantial weight loss in the STEP 1 and SURMOUNT-1 trials.3,4 This article does not question their value. It looks at the nutrition questions that can come with eating less.
Eating less can reduce intake of protein and some micronutrients, although most abnormalities reported so far are mild or indirect.8 Strategies to address this are largely based on indirect evidence, and expert groups note that direct evidence is urgently needed.2 Lean mass is lost during weight loss with or without these medicines, and what that means for strength and health is not yet clear.12,14 We did not find trials of creatine,20 probiotics or berberine in people taking GLP-1 medicines.
Expert groups point to protein, resistance training and an appropriate diet as the main strategies to help preserve muscle.1 The other supplements discussed here are options some people ask about, not requirements. Whether any of them is appropriate depends on your diet, your medicines, your kidney health and whether you are pregnant or breastfeeding. Talk to your prescriber or pharmacist first, and never start, stop, delay or change a prescribed medicine because of this article.
Medical Disclaimer: This article is written for educational purposes and reflects a review of peer-reviewed literature. It is not medical advice and does not establish a clinician-patient relationship. GLP-1 medications are prescription drugs requiring physician oversight. Supplement information in this article is general and may not be appropriate for all individuals — particularly those with kidney disease or thyroid disease, who are pregnant or breastfeeding, who are considering a supplement for a child, or who take several medicines. No prescribed medicine should be started, stopped, delayed or changed on the basis of this article. These statements have not been evaluated by the Food and Drug Administration. Products mentioned are not intended to diagnose, treat, cure, or prevent any disease. Always consult your prescribing clinician before adding supplements to a regimen that includes GLP-1 medications, metformin, insulin, or other glucose-lowering agents. Individual nutritional needs vary and may require personalized assessment.
