SIMPLE’s comprehensive guide to supplements for fasting

Written by Aly Owen

Medically reviewed by Louise Bula, RD

Published on October 4, 2023 | Updated on March 28, 2024

Intermittent fasting is a food routine that can unlock a range of health benefits, like improved energy levels and metabolic changes such as enhanced insulin sensitivity and improved blood lipids [1,2,3], as well as things like weight loss and fat burning, especially in people who are overweight or living with obesity.[4,5] 

However, if you’re eating less or less often, you might run into some sticking points around hitting the nutrient levels you need each day — especially if you’re focusing on less nutrient-dense food sources (like refined carbs or ultra-processed snacks like chips or pastries) or following a vegetarian or vegan intermittent fasting plan.[6] 

While we recommend getting your nutrients through natural, health-promoting food sources as much as possible (like fruits, vegetables, whole grains, healthy fats, calcium-rich foods, and lean plant- and/or animal-based protein), fasting supplements may be a great ally for meeting your body’s nutritional demands if you’re coming across any obstacles with consuming a balanced diet. If you do have any concerns about not meeting nutritional requirements through what you eat alone, we suggest speaking with your healthcare provider before making any significant lifestyle changes, including taking vitamins.

But if you do end up needing to take supplements, how do you know what the best dietary supplements for fasting are or when you can take fasting vitamins to maximize their power while minimizing intermittent fasting side effects? 

Let’s dig into everything you need to know about the what, when, and why of taking supplements while fasting. 

Do you need intermittent fasting supplements?  

While it’s unlikely you’ll run into body-fuel problems if you fill every eating window with nutrient-dense foods, nutrient deficiencies could arise in the following situations [8]:

• your pre-existing eating plan was already low in vitamins and minerals; and
• you prioritize foods high in refined carbohydrates (e.g., pastries, pizza, regular soda) or saturated / trans fats (e.g., fried foods, commercial baked goods, processed meats) over whole foods like fruits, vegetables, healthy fats (e.g., oily fish, Greek yogurt), grains (e.g., quinoa, buckwheat), and lean proteins (e.g., chicken, fish, tofu).

That’s why it’s important to discuss your eating routine with your primary care provider first, especially if you’re considering switching it up or have specific health-related goals you want to achieve. They’re best placed to help you figure out what, if any, intermittent fasting supplements you might need. 

We can also be part of your support squad, especially when it comes to planning nutrient-rich meals and avoiding common intermittent fasting mistakes that may stall your progress or roadblock your well-being. Head to our SIMPLE quiz, and we’ll help you chart your best course to success, whatever that means for you. 

Will supplements break your fast? 

What breaks a fast? Technically, consuming anything with calories breaks a fast.[9] That means anything you eat or drink that contains calories will stop your fast in its tracks. 

But what does that mean for supplements?

Well, you do eat / drink them, but not all supplements contain calories. Sure, some can break your fast, but others can — and should, for maximum absorption — be taken on an empty stomach.

When you take a supplement should ideally be driven by what the manufacturer specifies on their instructions, but we’ve rounded up some general best practice guidelines in the next section. 

When should you take your supplements?

When you consume a supplement during your eating window, it may not break your fast, but it’s still best to check out what the manufacturer has added to the party of ingredients. Plus, there are certain supplements (like fat-soluble vitamins A, D, E, and K) that make more of a splash when taken with food.[7] Others (like iron, magnesium, and B vitamins) may cause extra bumps in the road (like nausea) if they’re taken on an empty stomach. 

However, everybody is different, and your body may interact with supplements differently. If you’re not sure when — and if — you should take supplements, consult your healthcare provider or dietician. They’ll be able to help you figure out what works best for your unique body.  

Think of it like getting a mattress. It can be the best quality in the world, but if it doesn’t suit your body, you’re going to be stuck counting sheep all night.  

If you’re feeling like you keep hitting an “intermittent fasting not working” tailspin, it may be that the timing or type of your supplement intake (or what / when you eat in general) is affecting your progress. Before raising the white flag, revisit your strategy with your healthcare provider.

Supplements to take with food during your eating window 

As a general rule, you want to take any calorie-containing supplements during an eating window so they don’t break your fast. Those include: 

• protein powders
• branched-chain amino acids (BCAAs)
• essential amino acids (EAAs), like l-tyrosine or creatine
• collagen
• fiber supplements 
• sweetened electrolyte drink powders or effervescent tablets
• gummy vitamins or chewable supplements
• any supplements that contain sweeteners or additional ingredients, like fruit juice, cane sugar, or starches. 

General multivitamin

Even if your multivitamin doesn’t contain any caloric additives, some multivitamins contain zinc, which may cause nausea if taken on an empty stomach.[10] So, you may want to take these during your eating window.

Fat-soluble vitamins (A, D, E, and K)

These four vitamins (which are helpful for your vision and bone, cell, liver, and autoimmune health [11]) are better absorbed and transported in your body when eaten with fat. So, if you choose to supplement any of these, it may be wise to take them with your meals to guarantee optimal absorption! 

Magnesium

Magnesium is one of the most prevalent minerals in your body, and it’s crucial for healthy cell functioning.[12] Some people do get an upset stomach when supplementing magnesium tablets on an empty stomach, so in these instances, you may be better off taking them with food. 

Zinc and copper

Zinc and copper are important minerals for regulating metabolism and supporting your immune system.[13,14] It’s important to note that taking zinc supplements may impact your body’s ability to absorb copper.[15] So, make sure to get ongoing support from your healthcare provider to manage any possible risks. Remember: to avoid an upset stomach, it may be best to have them with food.[16] 

Krill oil or omega krill complex

There’s some evidence to suggest krill oil supplementation may benefit triglyceride levels and cardiovascular health.[17] However, we need larger clinical studies on humans to assess the benefits of supplementing krill oil on other cardiometabolic risk factors and outcomes. Krill oil is also absorbed better when consumed with dietary fat [18], so if you do supplement it, it’s best to take this with a meal, too.

Omega-3 fatty acids 

Omega-3s (found naturally in foods like salmon, walnuts, chia seeds, and edamame) are associated with a range of health benefits, especially heart health.[19] If you don’t consume enough oily fish (e.g., salmon or mackerel) or follow a plant-based diet, you may choose to supplement omega-3s to reach your target nutrient levels.[20]  

It’s best to take omega-3 supplements with a meal that contains dietary fats (like olive oil or yogurt) to enhance absorption and minimize potential digestive comfort.[18,21]

Medium-chain triglycerides (MCTS)

Medium-chain triglycerides (found naturally in coconut oil or palm oil) are known for their ability to increase energy levels.[22] They may also support ketosis.[23] While you can take them with or without food, they are usually mixed with various foods and beverages or drizzled over meals. 

Chromium 

Limited studies exist to justify taking additional chromium supplements, and most of the research focuses specifically on its impact on blood glucose levels and lipid profiles in people with type 2 diabetes.[24] There is, however, some evidence that it may improve blood pressure levels [25], but these results have only been reported for people with type 2 diabetes. Therefore, at this stage, we need more research to validate these potential benefits and determine if certain people are more likely to benefit than others. 

It’s also worth mentioning that chromium supplements may interact with some medications [26], so it’s best to check with your healthcare provider if they’re safe for you. If it is, you should always follow their instructions on when it’s best to take them.

Vanadium

Vanadium is a common supplement talked about in the diabetes world. There’s some evidence that this trace mineral may be useful in glycemic control (particularly for people with type 2 diabetes) [27], but there’s not enough data to validate this potential benefit entirely.[28] If you do choose to supplement vanadium, it’s recommended to take it during your eating window to minimize the risk of stomach discomfort.

Supplements to take while fasting

Unlike fat-soluble vitamins and supplements like krill oil or fatty acids, there are some nutrients that are better absorbed on an empty stomach, and most will not break you out of a fast. If you’re taking supplements while fasting or considering which vitamins to take while fasting, just double check that calorie content: anything below 10 kcal is probably okay. 

Water-soluble vitamins (B and C)

Vitamin C and the eight vitamins that fall under the vitamin B complex umbrella are important for everything from your head to your toes. B vitamins have been linked with brain health and metabolic health [29,30] and are found naturally in a wide range of foods, from whole grains, nuts, and seeds to eggs, fish, and dairy. Some people following a more plant-based diet may find getting enough vitamin B12 harder than others.

Vitamin C is important for immune health, skin health, and disease prevention.[31,32,33] Most people don’t need additional vitamin C in supplement form if they consume fruits and vegetables daily. But if you don’t (like if you follow a keto plan or dislike these foods), you could consider it. 

Unlike fat-soluble vitamins, water-soluble vitamins are absorbed better when taken on an empty stomach as they simply dissolve in water. Staying hydrated is also important, especially for these essential nutrients! 

Iron

Getting the right amount of iron (Goldilocks style — not too little, but not too much) is crucial for regulating metabolic processes and blood oxygen levels.[34] Iron supplementation is generally recommended to be taken at least 30 minutes before a meal or 2 hours before taking other medications.[35] However, if you experience any side effects, have a chat with your healthcare provider, as it could be that you may benefit from taking this with a small amount of food instead. You may also wish to consider supplementing vitamin C alongside iron to help with improving its absorption.[36] 

Folic acid

A folic acid supplement is usually associated with pregnancy since it supports healthy DNA replication and neural development.[37] It may also support better glycemic control and diabetes management in adults [38], but more research is needed to explore this potential benefit further. While you can take folic acid with or without food, folate is derived from a water-soluble vitamin (B), so it’s better to have it during your fasting window with water. 

Probiotics

Probiotics (live microorganisms like bacteria / yeasts) may be small, but they can pack a big health-benefiting punch when it comes to both blood sugar regulation and gut health and digestion.[39,40] Always check the label for calories and added ingredients like sugar. For some, though, it’s best to take these on an empty stomach, so they’re great to take while fasting. If you do take them in the form of yogurts or milky drinks, there will be calories in these, so it may be best to take them during your eating window.

Prebiotics 

Prebiotics (basically high-fiber content food sources like onions and garlic that feed your good gut bugs) can support gut health while also benefiting your immune system and curbing your appetite.[41,42,43] Taking prebiotics supplements during your fasting window with a glass of water gives them more time to hang out in your gut, but don’t forget to check the nutrition label: some may have added ingredients, and many will contain calories that, depending on the dose you use, may or may not break your fast. Likewise, if you experience unusual changes to your bowel movements, you may want to take them with food (and consult your healthcare provider to make sure nothing underlying is going on).

Electrolytes

Natural sources of electrolytes, like Himalayan salt or coconut water, can boost hydration while also providing traces of other nutrients (minerals like potassium, iron, and zinc and vitamins like B and C) without breaking your fast, but electrolyte supplements may be particularly helpful for staying hydrated during intensive bouts of exercise.[44] Some are great to take during fasting windows since you’re extra likely to be dehydrated then, but keep in mind that some electrolyte drinks (like Liquid IV or Gatorade) may have enough calories to break your fast. Always remember our general rule: below 10 kcal is okay.

What are the best supplements for intermittent fasting? 

When it comes to supplements for intermittent fasting, there’s no universal magic potion of “the best” supplements. What you take, how much you take, and how often you take them — if you take them at all — depends on your individual body, eating habits, nutritional needs, and goals for fasting. And if you consume food sources with high levels of nutrients, it’s unlikely you’ll need to supplement your eating habits at all. 

If you’re concerned that your eating routine isn’t giving you all the nutritional fuel you need, or if you’re expecting to encounter any major life events, like illness or family planning, speaking with your healthcare provider is a good place to start.

What are the side effects of taking supplements while intermittent fasting?

Another reason you should always speak with your healthcare provider before making any changes to your eating routine (including modifying the what, when, and how much of any supplement you’re taking) is that some supplements can:

• interfere with existing medications (like we highlighted earlier with chromium) [45];
• be less effective depending on when you take them; and
• cause stomach cramping, nausea, diarrhea, bloating, or other digestive issues.[46]

It’s also important to remember that fasting in general should be avoided by those who:

• are pregnant or breastfeeding;
• are under the age of 18, or 80 years old or more;
• have a history of or are currently diagnosed with an eating disorder;
• are underweight (BMI below 18.5); or
• have a medical condition, like type 1 diabetes.

The advice we have provided on supplements here is also not meant to replace medical advice and isn’t intended for those mentioned in the list above.

SIMPLE’s expert opinion and final thoughts 

Ensuring your body is getting all the nutritional fuel it needs can feel like the trickiest of balancing acts — and we know you didn’t sign up for being on a perpetual tightrope. 

If you’re concerned that you may have a nutrient deficiency, or even if something just doesn’t feel quite right, talk to your primary care provider before playing mad scientist with your meal planning or medicine cabinet. There’s no such thing as the “best fasting supplements” because everybody’s needs are different, and your healthcare team is there to help you figure out what your needs are and how best to meet them. 

We can also help spot you by giving you ideas on what to eat during intermittent fasting and help you build recipe ideas from our nutrient-dense intermittent fasting food list. So we can get to know what makes you you and offer tailored recommendations, start by taking our SIMPLE quiz.

Frequently asked questions 

What multivitamin is best for fasting?

What multivitamin is best for fasting depends entirely on you and what your body needs — it’s not a one-pill-to-superpower-them-all situation. Most of the time, if you’re eating nutrient-dense, health-promoting food sources, a vitamin isn’t necessary. If you’re concerned your nutrient levels are off, consult your healthcare provider. 

Does lemon water break a fast?

As long as the lemon is coming from an actual slice of lemon and not a sugary, artificial flavor, lemon water doesn’t break a fast. 

Can I take collagen while fasting?

While you can take collagen while fasting — and it may be useful for skin health [47] — many collagen supplements contain calories, so to avoid breaking your fast, you should take it during your eating window. 

Do vitamins for fasting stop autophagy?

On their own, vitamins don’t stop autophagy. Just watch out for additives and sugars with calories, which would break your fast. So, always check the manufacturer’s label.

Can I take CBD while fasting?

Yes, you can take CBD while fasting, as long as it doesn’t contain any caloric additives or sugar that would break your fast (oils tend to be better than gummies in that regard). However, keep in mind that research on how it affects intermittent fasting is still limited. 

Written by Aly Owen

Medically reviewed by Louise Bula, RD

Published on | Updated on March 28, 2024