What Can You Drink While Intermittent Fasting?

One of the first questions people ask when starting intermittent fasting is: what can I actually drink during my fasting window? The answer matters — the wrong drink at the wrong time can break your fast; the right one makes the fasting hours significantly easier.

The short version: water, black coffee, and plain tea are all safe. Almost everything else needs evaluation. This guide covers every common drink category, explains the science behind which ones break a fast and which don’t, and gives you a quick-reference table you can use before reaching for anything during your fasting window.

Why Some Drinks Break a Fast and Others Don’t

A fast is broken when you consume something that triggers an insulin response or delivers significant calories. Understanding what fasting actually is — specifically the metabolic states your body cycles through — helps explain why some drinks are safe and others aren’t.

The two main mechanisms that break a fast:

1. Insulin response. When insulin rises, fat oxidation stops. Your body switches back to glucose as its primary fuel. Anything that raises blood glucose (carbohydrates, some amino acids) or triggers insulin through other pathways (some artificial sweeteners via cephalic phase response) can pull you out of the fasted metabolic state.

2. Caloric intake. The general threshold is around 50 calories, though the type of calories matters — carbohydrate and protein calories raise insulin more than fat calories. Keeping drinks under 5 calories per serving is the safest approach during a strict fast.

For a comprehensive breakdown of what breaks a fast beyond drinks — including foods, supplements, and medications — see our complete guide on what breaks a fast.

What You Can Drink While Fasting: Quick Reference

Drink	Fasting-Safe?	Notes
Water (still)	✅ Yes	Zero calories, zero insulin impact
Sparkling water (plain)	✅ Yes	Safe if zero calories and no sweeteners
Black coffee	✅ Yes	2–5 kcal, no insulin spike
Decaf coffee (black)	✅ Yes	Same as regular — no insulin impact
Green tea (plain)	✅ Yes	Trace calories, may enhance fat oxidation
Black tea (plain)	✅ Yes	Trace calories, safe during fast
Herbal tea (unsweetened)	✅ Yes	Most varieties are fasting-safe
Electrolyte supplements (zero-cal)	✅ Yes	Sodium, potassium, magnesium — check for sugar
Apple cider vinegar (diluted)	✅ Generally	Trace calories, may improve insulin sensitivity
Coffee with cream	⚠️ Gray zone	~50 cal/tbsp — may end autophagy for some
Bulletproof coffee	⚠️ Gray zone	Fat doesn’t spike insulin but ends autophagy
Diet soda	⚠️ Gray zone	Artificial sweeteners may trigger cephalic insulin response
Milk (any type)	❌ No	Protein + carbs = insulin spike
Oat milk	❌ No	High in carbs
Juice (fruit or vegetable)	❌ No	Concentrated sugar
Sports drinks	❌ No	Sugar + carbs
Sweetened coffee or tea	❌ No	Sugar spikes insulin
Protein shakes	❌ No	Protein raises insulin significantly
Alcohol	❌ No	Calories + metabolic disruption

---

Water

Water is the gold standard of fasting drinks. It has zero calories, zero insulin impact, and actively supports the fasting process in several ways:

• Reduces perceived hunger. Mild dehydration is often misinterpreted as hunger. Drinking water when you feel a hunger pang during your fast frequently eliminates the sensation within 10–15 minutes.
• Supports kidney function during fat metabolism — your kidneys process the byproducts of fat oxidation and need adequate water to function efficiently.
• Maintains electrolyte balance. During a fast, kidneys excrete more sodium (lower insulin = less sodium retention). Drinking enough water — ideally with added electrolytes — prevents the “fasting headache” that many beginners experience.

How much: aim for 2–3 liters (8–12 cups) of water per day during fasting. More if you exercise.

Sparkling Water

Plain sparkling water — carbonated water with no added flavors, sweeteners, or sugars — is completely fasting-safe. The carbonation has no effect on blood glucose or insulin.

Check the label carefully. Many products sold as “sparkling water” or “sparkling mineral water” contain:

• Added fruit juice (breaks fast)
• Natural flavors that include sugars (may break fast)
• Sweeteners like sucralose or stevia (gray zone — see below)

Safe options: plain sparkling water (Perrier, San Pellegrino, unflavored LaCroix), or any product showing 0 calories and 0g carbohydrates on the nutrition label.

Black Coffee

Black coffee is the most widely used drink during intermittent fasting — for good reason. It’s essentially calorie-free, doesn’t trigger insulin, and actively supports fasting through multiple mechanisms.

What black coffee does during a fast:

• Enhances fat oxidation — caffeine increases fat mobilization from adipose tissue
• Suppresses appetite — reduces ghrelin and blunts hunger signals
• Improves cognitive function — helpful when energy dips during the early part of a fast
• May support autophagy — coffee’s polyphenols activate AMPK, the same pathway that drives cellular cleanup during fasting

For the full science on black coffee and fasting — including the cortisol timing question and exactly what additives break your fast — see Black Coffee While Fasting: Does It Break Your Fast?.

And for the comprehensive hub on all coffee + fasting questions, see Can You Drink Coffee While Fasting?.

Timing tip: wait 60–90 minutes after waking before your first cup. This lets the natural morning cortisol spike (cortisol awakening response) peak and begin declining before caffeine adds to it.

Tea

Plain tea — green, black, white, oolong, or herbal — is fasting-safe. The trace calories (2–5 kcal per cup) have no meaningful effect on insulin or fat metabolism.

Green tea deserves special mention for fasting:

• Contains EGCG (epigallocatechin gallate), a catechin that has been shown to enhance fat oxidation and modestly boost metabolic rate
• Contains L-theanine, an amino acid that promotes calm focus and reduces the jitteriness that caffeine can cause — helpful during fasting hours when stress response may already be slightly elevated
• Multiple studies have found that green tea catechins enhance the fat-burning effects of fasting

Herbal teas (peppermint, chamomile, ginger, rooibos): all fasting-safe. Make sure they’re unsweetened — most pre-packaged herbal teas contain no added sugar, but always check.

What to avoid with tea: adding milk, cream, or sugar immediately breaks the fast (protein + carbs in milk, instant insulin spike from sugar).

Electrolyte Drinks

Electrolyte supplementation during fasting is often necessary, not just optional. Here’s why:

When insulin is low (as it is during fasting), your kidneys excrete more sodium. Sodium loss pulls magnesium and potassium with it. This depletion is responsible for most of the negative symptoms beginners associate with fasting: headaches, muscle cramps, fatigue, irritability, and brain fog.

What to look for in a fasting-safe electrolyte drink:

• Sodium: 300–500 mg per serving
• Potassium: 100–300 mg per serving
• Magnesium: 50–100 mg per serving
• Sugar/carbohydrates: 0g
• Calories: 0 kcal

What to avoid:

• Sports drinks (Gatorade, Powerade, Lucozade): contain 25–35g of sugar per serving — completely off-limits during a fast
• “Healthy” electrolyte drinks with added coconut water or fruit juice: contain carbohydrates that break your fast
• Electrolyte products sweetened with honey or cane sugar

Safe options include LMNT (unflavored), Ultima Replenisher, Key Nutrients, or simply adding a pinch of sea salt to water.

Apple Cider Vinegar

A tablespoon of apple cider vinegar (ACV) diluted in water is generally considered fasting-safe. ACV contains:

• Roughly 3–4 calories per tablespoon
• Zero sugar, zero protein
• Acetic acid, which research has shown to improve insulin sensitivity and slow gastric emptying

Some intermittent fasting practitioners use ACV specifically to blunt post-fast insulin spikes by drinking it 15–30 minutes before their first meal. The evidence here is modest but directionally positive.

One caution: undiluted ACV can damage tooth enamel and irritate the esophagus. Always dilute in at least 250ml of water.

The Gray Zone: Artificial Sweeteners

Diet soda and artificially sweetened drinks occupy the most contested territory in fasting science. The calorie count is effectively zero — but that doesn’t mean they have zero metabolic effect.

Some research suggests that artificial sweeteners (aspartame, sucralose, saccharin) can trigger a cephalic phase insulin response — essentially, your body releases a small amount of insulin in anticipation of calories, based on the taste of sweetness alone. This response varies by individual and by sweetener.

The practical guidance:

• If your primary goal is weight loss, diet sodas are unlikely to significantly impair your results
• If your goal is autophagy or strict insulin minimization, avoid artificial sweeteners during your fasting window
• Stevia has the least evidence of cephalic insulin response and is the safest sweetener choice for strict fasting

What Definitely Breaks Your Fast

To be clear about the other end of the spectrum:

• Milk, cream, oat milk, almond milk (with protein): Protein triggers insulin; carbs in most plant milks raise blood glucose
• Juice (any kind): Concentrated sugar, immediate blood glucose and insulin spike
• Smoothies: Even “healthy” smoothies with fruit and yogurt contain significant protein and carbs
• Protein shakes: Protein is the most potent insulin trigger after carbohydrates
• Sports drinks and energy drinks: Sugar + carbs
• Alcohol: Significant calories, and your liver prioritizes metabolizing alcohol over fat — it pulls you immediately out of fat-burning mode

Building Your Fasting Drink Routine

Here’s a practical daily drink routine for someone doing 16:8 fasting (eating window: noon–8 PM):

7:00 AM (wake): Water immediately — 500ml with a pinch of sea salt 8:00–8:30 AM: First cup of black coffee or green tea (after cortisol peak begins declining) 10:00 AM: Second cup of black coffee or herbal tea if needed 11:30 AM: Zero-calorie electrolyte drink before breaking the fast at noon 12:00 PM: Break the fast — now all drinks including milk, juice, etc. are permitted

This routine covers hydration, electrolytes, caffeine, and hunger management across the entire fasting window without breaking the fast.

---

Drinks are one of the most practical levers in intermittent fasting — the right choices make the fasting window easier; the wrong ones undo the work of the hours you’ve already put in. Keep it simple: water, black coffee, and plain tea during the fast, and hydrate aggressively to prevent the dehydration that most beginners mistake for hunger or fatigue.

EasyFasting is an iOS fasting timer that tracks your fasting phase in real time, shows which metabolic state you’re in, and logs your streaks automatically. Download it free on the App Store.