Vitamins and Supplements While Fasting: Do They Break It?

In 30 seconds

The fasting trials cited here allowed only water and energy-free drinks, and none of them tested supplements. Anything with sugar, protein or other calories, such as sugary gummies or protein powder, ends a strict fast. Plain tablets and capsules are a grey area, and taking them with your meal avoids the question.

• Gummies with sugar and protein or collagen powders provide energy, so they end a zero-calorie fast.
• Plain vitamin, magnesium and creatine products weren't tested in the fasting trials cited here.
• In a small study, vitamin D3 was absorbed better with a meal containing fat than with a fat-free meal.
• Magnesium, calcium and iron are among the supplements with the most documented medicine interactions.

Do vitamins and supplements break a fast?

It depends on what’s in them and how strict your fast is. The trials behind this guide defined the fast as no caloric intake and listed the drinks that were allowed; supplements weren’t on that list or tested. Check the label: if it lists sugar, protein, fat or calories, treat it as food.

In the 12-week TREAT trial, the time-restricted group was told to eat from noon to 8 p.m. and to completely abstain from caloric intake for the rest of the day.Source 11

In a 12-month randomized trial of eating only between noon and 8 p.m., participants were encouraged to drink plenty of water during the 16-hour fast and were allowed energy-free drinks such as black tea, coffee and diet sodas.Source 22

When should you take supplements if you fast?

With your meal is the simplest answer: it settles the fasting question and fits labels that say to take a product with food. For vitamin D, there’s also an absorption reason.

In a 1-day study of 50 healthy older adults, a single vitamin D3 supplement taken with a breakfast containing fat raised peak blood vitamin D3 by about 32% compared with a fat-free breakfast.Source 33

Can supplements interact with medicines?

Yes, some can. If you take prescribed medicines, ask a pharmacist before adding a supplement, and see taking medication during intermittent fasting for timing questions.

A systematic review of 1,491 documented supplement and herb interactions with medicines found that products containing St John's wort, magnesium, calcium, iron and ginkgo had the most, and that warfarin, insulin, aspirin and digoxin were among the medicines most often involved.Source 44

Here, what breaks a fast is defined by trial rules: no caloric intake, with water and energy-free drinks allowed. The vitamin D study measured absorption after one dose, and the interaction review counts documented cases, not how often harm happens.Source 11Source 22Source 33Source 44

Who should check first?

Frequently asked questions

Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.

Related guides

• What Breaks a Fast? Drinks, Gum and Medicines

  What breaks a fast? Trials allowed water, black coffee and tea, but no calories. Gum is untested; never change a medicine to keep fasting.

• Taking Medication During Intermittent Fasting

  Taking medication during intermittent fasting: water is allowed, but food instructions vary by medicine. Ask before changing a dose or its timing.

• What to Eat During Intermittent Fasting

  What to eat during intermittent fasting is ordinary food: vegetables, fruit, whole grains, pulses and protein, with fewer sugary drinks. Amounts count.

• Can You Work Out While Fasting?

  Working out while fasting gave strength and muscle results similar to fed training in small trials, but the studies are limited and safety comes first.

Frequently asked questions

Do vitamins break a fast?

Plain vitamin tablets weren't tested in the fasting trials cited here, so they're a grey area on a strict fast. Gummies with sugar do end a zero-calorie fast. Taking vitamins with your meal avoids the question.Source 11

Does magnesium break a fast?

It wasn't tested in the fasting trials cited here, so plain magnesium is a grey area. Check the label for sugar, and ask a pharmacist if you take medicines, because magnesium has many documented interactions.Source 11Source 44

Does creatine break a fast?

Plain creatine powder wasn't tested in the fasting trials cited here, so it's a grey area. Blends with sugar or protein end a zero-calorie fast.Source 11

Does collagen or protein powder break a fast?

Yes, on a strict fast. Protein provides energy, and fasting trials such as TREAT asked people to avoid all caloric intake during the fast.Source 11

Sources

1. 1

   Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical TrialDylan A. Lowe et al. American Medical Association (AMA), November 1, 2020.DOI: 10.1001/jamainternmed.2020.4153 · PMID: 32986097Human randomized trial

2. 2

   Time-Restricted Eating Without Calorie Counting for Weight Loss in a Racially Diverse Population: A Randomized Controlled TrialShuhao Lin et al. American College of Physicians, July 1, 2023.DOI: 10.7326/M23-0052 · PMID: 37364268Human randomized trial

3. 3

   Dietary Fat Increases Vitamin D-3 AbsorptionBess Dawson-Hughes et al. Elsevier BV, February 1, 2015.DOI: 10.1016/j.jand.2014.09.014 · PMID: 25441954Human randomized trial

4. 4

   Evaluation of documented drug interactions and contraindications associated with herbs and dietary supplements: a systematic literature reviewH.-H. Tsai et al. Hindawi Limited, November 1, 2012.DOI: 10.1111/j.1742-1241.2012.03008.x · PMID: 23067030Systematic review and meta-analysis

5. 5

   Fasting Safely with DiabetesMartin M. Grajower. National Institute of Diabetes and Digestive and Kidney Diseases, August 26, 2020.Official guidance