Best Supplements to Take While Intermittent Fasting (2025)

Practical Guide · 7 min read

Supplements and Intermittent Fasting: What Breaks the Fast?

The key question when combining supplements with intermittent fasting (IF) is: does this supplement trigger an insulin response or disrupt the metabolic benefits of fasting? Here is a clear breakdown by fasting goal.

Safe During the Fasted Window

NMN / NR (sublingual): Does NOT break a fast. Sublingual absorption bypasses digestion, and these molecules have no caloric content and don’t trigger insulin. In fact, fasting and NMN work synergistically — fasting activates AMPK while NMN provides NAD+ for SIRT1 to operate optimally.

Magnesium glycinate: Safe while fasted. Zero calories, doesn’t trigger insulin. Some people find taking magnesium on an empty stomach causes mild GI discomfort — if so, move to eating window.

Caffeine: Does not break a fast. May enhance autophagy and fat oxidation during the fasted period. Plain black coffee or caffeine tablets are fine.

Electrolytes (without calories): Sodium, potassium, and magnesium in plain form are fine and recommended for extended fasts (16h+) to prevent electrolyte depletion.

Take With Your Eating Window

Vitamin D3+K2, omega-3, creatine, collagen: All fat-soluble or protein-based — take with your first or largest meal. No benefit to taking fasted, and some (like D3) absorb significantly better with fat.

Ashwagandha: Take with food to reduce GI irritation. Doesn’t affect fasting benefits but better tolerated with meals.

The Best IF Supplement Stack

During fast: NMN 250mg sublingual on waking + black coffee/caffeine + electrolytes if extended fast.

Breaking fast (first meal): Collagen 10g + vitamin C + vitamin D3 5000IU + K2 + omega-3 3g + creatine 5g.

Evening: Magnesium glycinate 400mg + ashwagandha 300mg + apigenin 50mg (30-60 min before bed).

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