Can You Take Supplements While Fasting?

You take supplements for a reason. But if you practice intermittent fasting, a new question arises: will that morning multivitamin break your fast? Should you move your fish oil to your eating window? Is creatine okay on an empty stomach?

The answer depends on the specific supplement, its form, and what fasting benefits you are trying to preserve. Some supplements are perfectly fine during a fast. Others will break it. And some work better when taken with food anyway.

Quick Answer: Pure mineral supplements (electrolytes, magnesium), water-soluble vitamins, and creatine generally do not break a fast. Fat-soluble vitamins (A, D, E, K), fish oil, gummy vitamins, protein powders, BCAAs, and any supplement with added sugars or calories will break your fast. Most supplements are better absorbed with food, so your eating window is the ideal time for the majority of your supplement stack.

Supplements That Do NOT Break a Fast

These supplements contain negligible or zero calories and do not trigger a meaningful metabolic response.

Electrolytes (Sodium, Potassium, Magnesium)

Pure electrolyte supplements are not only fasting-safe but actively recommended during fasting. They contain zero calories and do not trigger insulin. Sodium, potassium, and magnesium support hydration, prevent headaches, and reduce muscle cramps.

Water-Soluble Vitamins (B-Complex, Vitamin C)

B vitamins and vitamin C dissolve in water and contain no significant calories. They can be taken during a fast without issue. However, B vitamins on an empty stomach can cause nausea in some people. If this happens, move them to your eating window.

Creatine

Creatine monohydrate is calorie-free and does not stimulate insulin. It can be taken any time, fasted or fed. If you exercise during your fast, taking creatine with water during your fasting window is perfectly acceptable.

Probiotics

Most probiotic capsules contain negligible calories. Some practitioners argue that taking probiotics on an empty stomach actually improves bacterial survival through the stomach acid environment. Either way, they will not break your fast.

Iron

Iron supplements are calorie-free and do not break a fast. In fact, iron is better absorbed on an empty stomach. However, iron can cause nausea and stomach irritation when taken without food. If you tolerate it, fasted iron intake is fine.

Iodine

Iodine supplements, whether as potassium iodide drops or tablets, are calorie-free and fasting-safe.

Caffeine Pills

Pure caffeine tablets contain no calories and do not break a fast, similar to black coffee. They can help with alertness and may enhance fat oxidation during fasting.

Supplements That DO Break a Fast

These supplements contain calories, protein, fats, or sugars that will end your fasted state.

Gummy Vitamins

Gummy vitamins are essentially candy with added vitamins. They contain sugar, gelatin, and typically 10 to 30 calories per serving. They absolutely break a fast. Switch to capsule or tablet forms during your fasting window, or take your gummies during your eating window.

Fish Oil and Omega-3 Capsules

Fish oil contains fat and calories, typically 10 to 15 calories per capsule. Fat-based supplements trigger digestive processes and break a fast. Additionally, fat-soluble supplements are better absorbed when taken with a meal containing dietary fat.

Fat-Soluble Vitamins (A, D, E, K)

These vitamins require dietary fat for proper absorption. Taking them during a fast means poor absorption and wasted money. Take fat-soluble vitamins with a meal that contains healthy fats during your eating window.

Protein Powder and BCAAs

Protein powders and branched-chain amino acids contain calories and directly stimulate mTOR and insulin pathways, which interrupt autophagy and the fasted state. BCAAs are particularly notable because many people assume they are "safe" during fasting. They are not. Amino acids trigger an insulin response and break your fast.

Collagen Peptides

Collagen powder is pure protein, typically containing 35 to 50 calories per scoop. It will break your fast and inhibit autophagy.

MCT Oil

Despite its popularity in fasting circles, MCT oil contains about 100 calories per tablespoon. It will break a strict fast. Some people use it in "fat fasting" protocols, but this is not true fasting.

Multivitamins with Added Fillers

Many multivitamins contain fillers, binders, and sometimes small amounts of sugar or starch. Check the label. If the multivitamin contains any calories or carbohydrates, take it with food.

Apple Cider Vinegar Gummies

Unlike liquid apple cider vinegar (which is negligible calories), ACV gummies contain sugar and calories. They break a fast. Use liquid apple cider vinegar instead.

The Gray Area

Vitamin D

Vitamin D is fat-soluble and absorbs better with food. However, a vitamin D capsule in oil form contains only about 5 to 10 calories. For strict fasting, take it with food. For practical weight-loss fasting, the caloric impact is minimal.

Ashwagandha and Adaptogens

Most adaptogen capsules contain negligible calories. However, they may cause stomach upset when taken without food. If you tolerate them fasted, they are unlikely to break your fast.

Pre-Workout Supplements

Most pre-workout formulas contain some combination of caffeine, beta-alanine, and sometimes BCAAs or sugar. Check the label. If it contains BCAAs, calories, or sugar, it breaks your fast. A caffeine-and-beta-alanine-only product is fasting-safe.

Optimal Supplement Timing

The best approach is to organize your supplements into two categories based on when to take them.

During Your Fasting Window

Electrolytes (sodium, potassium, magnesium)
Water-soluble vitamins (B-complex, vitamin C) if tolerated
Creatine
Probiotics
Iron (if tolerated)
Caffeine pills
Iodine

During Your Eating Window

Fat-soluble vitamins (A, D, E, K)
Fish oil / omega-3
Multivitamins
Collagen
Protein powder
BCAAs (if you use them at all)
Gummy vitamins
Any supplement with calories

With Your First Meal

Taking your eating-window supplements with your first meal is ideal. This ensures they are consumed with dietary fat for absorption and reduces the chance of stomach upset. Plan this into your fast-breaking routine.

Special Considerations

Medications vs. Supplements

Prescription medications should always be taken as directed by your healthcare provider, regardless of your fasting schedule. If your doctor says take a medication with food, do not skip it because you are fasting. Adjust your fasting window to accommodate your medication schedule, not the other way around.

Supplements and Autophagy

If maximizing autophagy is your goal, be stricter about what you take during your fast. Even supplements with minimal calories can theoretically reduce autophagic activity. Stick to electrolytes and water during your fasting window and save everything else for your eating window.

Research published in Nature suggests that amino acids, particularly leucine, are potent inhibitors of autophagy through mTOR activation. This is why BCAAs and protein supplements are particularly problematic for autophagy-focused fasters.

Fasted Exercise and Supplements

If you work out during your fasting window, you may want to take electrolytes and creatine before your workout. Save protein supplementation for your post-workout meal during your eating window. The research on fasted training performance shows that electrolyte status matters more than immediate caloric intake for most workout types.

How Fasted Helps

Fasted helps you plan your supplement timing around your fasting schedule. Set your eating window in the app and use it as a reminder for when to take your fat-soluble vitamins and caloric supplements. The timer ensures you know exactly when your fasting window begins and ends, so you can organize your supplement stack accordingly.

Frequently Asked Questions

Do apple cider vinegar pills break a fast?

Most ACV pills contain negligible calories (1 to 3 per capsule) and are unlikely to break a fast for weight loss purposes. For strict fasting, liquid ACV diluted in water is a safer choice since you can control the amount precisely.

Can I take a multivitamin on an empty stomach?

You can, but it is not ideal. Many multivitamins cause nausea on an empty stomach, and the fat-soluble components (vitamins A, D, E, K) will not absorb well without dietary fat. Take your multivitamin with your first meal.

Will creatine break my fast?

No. Creatine monohydrate is calorie-free and does not trigger an insulin response. You can take it during your fasting window with water without any concern about breaking your fast.

Should I stop taking supplements while fasting?

No. Intermittent fasting does not require you to stop any supplements. You just need to time them appropriately. Move caloric supplements to your eating window and keep calorie-free supplements in your fasting window if needed.

Do collagen supplements break a fast?

Yes. Collagen is protein, containing amino acids that trigger an insulin response and inhibit autophagy. Take collagen during your eating window, ideally with a meal.