Does vitamin C break a fast?

Plain vitamin C tablets do not; it is the added sugar in drink mixes that does.

Is there a fasting-safe vitamin C option?

Yes, a plain sugar-free vitamin C capsule or tablet.

Does Emergen-C raise blood sugar?

Yes, its added sugar raises blood sugar and insulin.

Does Emergen-C Break a Fast?

Reviewed by the FastTrack team · Updated June 2026

Short answer: Yes

Emergen-C breaks a fast. Most flavored vitamin C drink mixes contain several grams of sugar and calories, which raise insulin and end a fast.

Calories	~25-35 kcal per packet
Breaks a weight-loss fast?	Yes
Breaks ketosis?	Yes
Breaks autophagy?	Yes
Insulin impact	Yes

Why Emergen-C breaks a fast

Standard Emergen-C and similar flavored vitamin C powders are sweetened with real sugar, typically delivering five to seven grams of sugar and 25 to 35 calories per packet. That is enough carbohydrate to raise blood sugar and insulin and clearly break a fast, regardless of the vitamin content.

Plain vitamin C is different

It is the sugar, not the vitamin C, that breaks the fast. A plain vitamin C tablet or capsule with no added sugar is essentially calorie-free and fast-safe. If you want vitamin C during your fasting window, use a sugar-free supplement instead of a sweetened drink mix.

How much is safe

Skip the sweetened drink mix during a fast; use a plain sugar-free vitamin C tablet instead.

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Frequently asked questions

Does Emergen-C break a fast?: Yes, the sweetened drink mix contains sugar and calories that break a fast.
Does vitamin C break a fast?: Plain vitamin C tablets do not; it is the added sugar in drink mixes that does.
Is there a fasting-safe vitamin C option?: Yes, a plain sugar-free vitamin C capsule or tablet.
Does Emergen-C raise blood sugar?: Yes, its added sugar raises blood sugar and insulin.