Supplements to Take While Fasting

Intermittent or extended fasting as part of a ketogenic diet can yield some incredible health benefits in the form of mental clarity, heightened focus, improved cognitive function, increased insulin sensitivity, and reduced inflammation. Regular fasting has even been shown to improve health on a cellular level, since fasting kickstarts a process known as autophagy, where the body repairs and eliminates damaged cells (including cancerous or precancerous cells).

During a fast--whether 14 hours or 7 days--the goal is to completely eliminate carbohydrates and protein from the diet for a specified period of time. And while some fasters still choose to consume limited calories from fat, for instance “bulletproof” coffee with MCT or coconut oil, many fasters choose to completely eliminate any caloric intake--leaving some lingering questions about which supplements and vitamins to take while fasting, if any.

The Importance of Supplementation While Fasting

Even for fasters who choose to refrain from eating at all during a fast, it’s vital to include certain supplements in a fast. While fasting, the body relies completely on stored fat for energy, making the production of ketones in the liver to effectively process that fat more vital than ever. However, many of the vitamins and nutrients required to sustain ketosis are depleted rapidly over the course of a day, or even a few hours.

Whether you fast intermittently or for extended periods of time, and whether you cut all caloric intake during a fast or allow for fat calories, the supplements required to sustain ketosis are the same. However, the longer you fast and the more limited your caloric intake, the more important supplementation becomes for gaining the max amount of benefit from your fast.

Intermittent Fasting Supplements Vs. Extended Fasting Supplements

Intermittent fasting supplements

Intermittent fasting involves shorter periods of food restriction. Some keto dieters choose to fast intermittently by dedicating an “eating window” of 4-7 hours each day during which they consume calories. Others regularly skip a particular meal. And still others eliminate caloric intake completely for one or two days.

During these shorter fasting windows, you’re unlikely to deplete your levels of most vital vitamins and nutrients, as long as you’re typically eating a nutrient-dense diet. However, some nutrients are depleted very quickly as the body’s ketone levels rise, so supplementation with those nutrients in particular is ideal for an optimal fast.

An extended fast of up to 7 days will rely on the same supplements needed during intermittent fasting, as well as a few others:

Supplements Vital to Intermittent and Extended Fasting:

Sodium and Potassium (Electrolytes):

As ketone levels rise during a fast, insulin levels drop--signaling the body to flush electrolytes like sodium and potassium. These minerals are vital for ketogenesis (the process of turning fat into energy), and low electrolyte levels are a quick recipe for fatigue, lightheadedness, and low energy as the body struggles to access fat stores.


Magnesium regulates several bodily processes, including nerve function and blood pressure. Unfortunately, it’s also quickly and easily depleted as ketone levels rise. You’re likely to notice a “brain fog” or muscle cramps during a fast if your magnesium levels are depleted.

B-Complex Vitamins:

B-complex vitamins like riboflavin, niacin, biotin, and thiamine help the body absorb nutrients. While B-complex vitamins aren’t flushed from the body during ketosis the same way magnesium and electrolytes are, many people are chronically deficient in B-vitamins. Taking a supplement regularly can help ensure proper absorption of magnesium and potassium.

Supplements Vital to Extended Fasting

Best supplements for extended fasting

If you plan to fast longer than two days, the supplements above become even more vital to sustaining a healthy, productive fast that delivers optimal health benefits and minimizes any potential risks. Maintaining proper electrolyte and magnesium levels is particularly important to avoid refeeding syndrome, a potentially fatal condition that results from eating after a period of extended, dangerously low electrolyte levels.

If you will be fasting for more than two days, you’ll want to maintain a focus on electrolyte levels, magnesium, and B-complex vitamins, as well as adding the following supplements to your fast:


The top question for many people on an extended fast is, “Can I take a multivitamin during a fast?” The answer is “yes!” with an important caveat: A multivitamin can be an effective way to shore up your levels of a broad variety of important vitamins during an extended fast; however, it’s important to avoid multivitamins that contain dextrose or maltodextrin (aka, sugar and calories).

Vitamin D:

Many people are vitamin D deficient, since this critical vitamin is difficult to find in food sources. Not only is it vital to bone density and immune health, but like B-complex vitamins, it helps the body absorb and functionally use critical nutrients including magnesium.


Chromium isn’t found in all multivitamins, but it has been shown to mitigate hunger cravings that might lead to ending a fast before you’re ready.

BHB Supplementation While Fasting

In addition to maintaining levels of vital minerals and nutrients during an intermittent or extended fast, many fasters choose to incorporate BHB supplements, or exogenous ketones (ketones that come from outside the body).

Beta Hydroxybutyrate, or BHB is one of the three “ketone bodies,” produced naturally in the liver as your body enters ketosis.

On a cellular level, the body requires BHB (either in natural or supplemented form) to use stored fat for energy through the Krebs cycle. Supplementing with BHB during a fast ensures that your body will have adequate levels of BHB in the bloodstream to metabolize your fat as energy. BHB supplements (also known as BHB salts) are combined with sodium and potassium, to maintain necessary electrolyte levels.

Some people question whether supplementing with BHB/exogenous ketones will disrupt a fast; however, increasing the amount of exogenous ketones in the body won’t disrupt your fast any more than increasing the amount of electrolytes will. These supplements simply increase the body’s ability to process stored fat as energy for the brain and body.

BCAA Supplementation While Fasting

Branched Chain Amino Acids, or BCAA supplements, are another popular choice for intermittent or extended fasts, especially for individuals who want to build muscle mass.

BCAA supplements provide the same vital amino acids found in protein, which allow the body to sustain and build muscle; however, it’s important to recognize that these diet supplements do contain calories (about six calories per gram) and, taken in significant doses, do have the potential to disrupt a fast to some degree.

If maintaining a strict calorie-free fast is important to you (there is a significant debate between experts as to whether a calorie-free fast is superior to an extremely limited calorie fast), you may want to avoid this supplement. However, many people enjoy positive results with BCAA supplements and don’t notice any negative impact to their fast.

H2O: The Most Important Supplement to Your Fast

Most important supplement for fasting

No matter what form your intermittent or extended fast takes, it’s vitally important that you drink plenty of water to keep your body hydrated.

Your body tissue and internal organs (including your brain) depend on water to function properly and maintain adequate levels of minerals and nutrients. Water also helps the body eliminate toxins and wastes properly.

Dehydration during a fast can quickly lead to fatigue, dizziness, fatigue, cravings, confusion, irritability, and headaches. Keep a water supply with you at all times, and hydrate your body consistently throughout the day.

With the proper support from water, vitamins, and minerals your intermittent or extended fast can be a healthful and pleasant experience. Listen to your body, prepare for your fast thoughtfully, and enjoy the many benefits that fasting has to offer!

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