Article at a Glance:

  • Fasting can affect the benefits of some vitamins, supplements and medications.
  • Some prescription drugs are time-sensitive, so ask your doctor before you try intermittent fasting.
  • For best absorption, some supplements are meant to be taken with only water, and others with food.
  • If you follow Bulletproof Intermittent Fasting, you can take fat-soluble vitamins and some supplements in the morning with your Bulletproof Coffee.
  • Do some careful experimentation — if taking a pill on an empty stomach makes you nauseous, next time take it with your Bulletproof Coffee or during your eating window.

Intermittent fasting improves your focus, torches body fat, and gives aging a run for its money. It promotes autophagy, the process through which your cells get rid of built-up waste. Fasting may also cause your body to secrete a protein called fasting-induced adipose factor (FIAF), which signals that it’s time to burn fat.

Will taking vitamins, supplements and coffee end your fast? Can you take supplements during your fasting periods and still get the benefits? Which ones are beneficial to take while fasting? There’s no black-and-white answer here. Whether or not you can take a supplement during your fast depends on what you’re taking and how your body responds.

Here’s the bottom line on taking vitamins and supplements while fasting.


Generally, you can continue taking supplements and still get the fat-burning benefits of an intermittent fast.

You want to be mindful of your supplements because some of them can affect your body’s function during your fast. They can:

  • Drop your blood sugar, zapping your energy and giving you brain fog
  • Raise your insulin levels, taking you out of ketosis (the whole point of fasting)
  • Pass through your body without being absorbed unless taken with food
  • Make you want to puke (if taken on an empty stomach)

Taking vitamins and supplements while intermittent fasting requires some experimentation. Being Bulletproof is all about paying attention to how your body feels, and adjusting accordingly.

If you’re looking for some guidance on what vitamins and supplements will supercharge an intermittent fast, check out the 10 basic supplements that almost everyone should take to provide their bodies with essential nutrients that are missing from most diets.


If you have a health concern, some vitamins and supplements can cause negative health effects. So before you add any vitamins or supplements to your diet, be sure to consult your doctor.

To get the most from your supplements, make sure you take them at the right time of day. For example, some vitamins are made to be taken with food. Usually, that means they’re fat-soluble, which means they absorb better when they’re paired with fat. Other supplements complement each other when they’re taken together, like vitamins A, D and K.

Here’s the breakdown on the top vitamins and supplements — how to get the most from them during your intermittent fast.


You’ll get the most benefit from taking these vitamins and supplements on an empty stomach because they are best absorbed that way. Spread them out during your fasting period to reduce the potential for stomach upset. And if one of them makes you feel sick, you can easily pinpoint the culprit.

  • Water-soluble vitamins: You can take vitamins B and C with water during a fasting period. Vitamin C is usually pretty easy on an empty stomach, but B vitamins taken on an empty stomach are notorious for making people feel nauseous. If that happens to you, try taking vitamin B after a cup of Bulletproof Coffee (the quality fats may help prevent stomach upset). Or, just take these vitamins when you break your fast.
  • L-tyrosine: No worries here — this is meant to be taken on an empty stomach. If it makes you feel nauseous, take it with Bulletproof Coffee or when you break your fast. Learn more about the benefits of L-tyrosine.
  • Zinc and copper: These two minerals work better together, so you’ll often see them combined in a pill form. They work best if taken on an empty stomach, so take these during your fasting period.


Some of these supplements are best absorbed with food in your stomach, or the food you eat actually makes them work better. Some can just make you puke if you take them on an empty stomach. When you’re intermittent fasting, take these supplements during your eating window.

  • Fat-soluble vitamins: Fat-soluble vitamins (vitamin E, A, D and K) don’t dissolve with water, so take them during your eating window. If you’re Bulletproof Intermittent Fasting, you can take fat-soluble vitamins with your Bulletproof Coffee, which is made with quality fats like grass-fed butter and Brain Octane MCT oil.
  • Amino acids: L-glutamine and branched-chain amino acids (BCAAs) are usually a no-go while fasting because they can kick you out of ketosis by raising your insulin levels. Take with food, or if you want to take these supplements while staying in ketosis, add Brain Octane MCT oil, which supplies your body with extra ketones.
  • Iodine: For maximum absorption, take your kelp powder or potassium iodide capsules with food. And pass on iodized table salt — common iodized table salt is made with anti-caking agents, contains unwanted compounds and is chemically bleached. Learn more about different salts.
  • Magnesium: When beginning a magnesium supplement routine, some people report getting disaster pants (loose stool or worse). If you have a sensitive stomach, consider taking your magnesium with food. This can reduce the likelihood of negative effects. If you’re taking magnesium to help you sleep, take it after your last meal of the day.
  • Curcumin and krill oil: Supplements like these are easier for your body to absorb when they’re taken with food. So, have them during your eating window (or with your Bulletproof Coffee).
  • Chr omium and vanadium:These minerals can actually drop your blood sugar levels too low while you’re fasting. If your insulin levels dip, you run the risk of hypoglycemia — aka low blood sugar. Even a small bout of hypoglycemia can lead to problems adjusting and managing your moods. Take these supplements when you break your fast.


Before you even consider mixing supplements and fasting, talk to your doctor about any issues this might cause with your prescription medication. Combining vitamins and supplements with some medicines can be bad for your health. Also, some medications have to be taken within specific timeframes, and taking them on an empty stomach or within restricted eating windows can mess with their effects.

If you have to temporarily step away from intermittent fasting because of your medication, that’s okay. You can upgrade your health and wellness in other ways, like boosting your sleep quality or taking care of your gut health.


Caffeine isn’t technically a supplement, but it does have vitamin-like superpowers. It turns out that caffeine improves memory recall and has antioxidant effects. And, of course, coffee has been shown to boost your mood, improve your focu, and reduce your risk of chronic degenerative disease.

During your fasting periods, you can drink black coffee, no matter what intermittent fasting method you follow. If you follow the Bulletproof Diet, you can drink Bulletproof Coffee (aka butter coffee) during your intermittent fast. This creamy beverage is made with just three ingredients: coffee, MCT oil and grass-fed butter (or ghee). It curbs cravings, boosts ketone production and helps you power through your fast without feeling hangry. And because your body processes fat differently than carbs or protein, your liquid breakfast won’t interrupt autophagy — one of the biggest benefits of intermittent fasting.

If you don’t drink java but still want caffeine, drink high-quality green tea. Be cautious with black tea, which is fermented and can increase your risk of mycotoxin exposure.

The bottom line: Yes, you can use supplements while you’re fasting. If your vitamins and medication upset your stomach or need to be taken with food, take them during your eating window (or with Bulletproof Coffee). Experiment to find what works for you and helps you thrive.