What to Drink While Fasting: The Definitive Guide

What can you drink while fasting? Water (still or sparkling), black coffee, plain tea (green, black, or herbal), yerba mate brewed plain, and unflavored electrolytes don't break a fast. Anything with calories, sugar, protein, or most sweeteners does — including juice, milk, cream, broth, and alcohol. Match the strictness to your goal: weight loss, insulin sensitivity, or autophagy.

If you've ever stood in front of your fridge at 9am wondering whether a splash of almond milk is going to ruin everything, this guide is for you. The question of what to drink while fasting is one of the most-asked in the community — and the answer is more nuanced than "just drink water." Here's the definitive breakdown, including the drinks that actively support your fast.

The gold standard: water

Water is the foundation of every fast. It's what your body actually needs during the fasting hours — and most people don't drink enough of it. When you stop eating, you also stop absorbing the water that comes packaged in food (which is roughly 20–30% of most people's daily intake). Combined with the sodium loss that fasting triggers, dehydration is the source of most "fasting headaches" and fatigue.

Still water, sparkling water, mineral water, seltzer — all are equally fasting-safe. Sparkling water can be especially helpful because the carbonation provides a sense of fullness that plain water doesn't. Add a slice of cucumber, a sprig of mint, or a thin wheel of lemon, and you're still well within the fasting zone.

Black coffee — the fasting classic

Black coffee is the second pillar of fasting. A cup of plain black coffee has about 2–5 calories and triggers no meaningful insulin response, so it does not break a fast. Caffeine blunts appetite, sharpens focus, and — preliminary laboratory research suggests — may even support the AMPK activation that fasting switches on for autophagy.

The moment you add cream, milk, sugar, sweetener, or flavor syrup, the fast is over. The defining rule is plainness: nothing in the cup but water and coffee. Espresso, cold brew, pour-over, instant, French press — all fasting-safe, provided nothing is added.

Most people do well with 1–3 cups during a fasting window. Beyond that, watch for jitters, reflux, and disrupted sleep. Caffeine has a 5–6 hour half-life, so a 2pm cup still has half its caffeine in your system at 8pm. If your fasting window pushes coffee late, switch to decaf or tea in the afternoon.

Plain tea — green, black, herbal

Plain tea is one of the most underappreciated fasting drinks. Green, black, white, oolong, and herbal infusions all contain effectively zero calories and trigger no insulin response, provided nothing is added. Tea is fasting-friendly in every tradition — from the Benedictine monks to the Sufi dervishes, hot infusions have always accompanied the contemplative, emptied life.

• Green tea: ~30–50 mg caffeine per 8 oz, rich in catechins (especially EGCG) that may support autophagy. Under 2 calories.
• Black tea: ~40–70 mg caffeine per 8 oz, the most oxidized and robust of the traditional teas.
• Oolong and white tea: moderate caffeine, complex polyphenol profile.
• Herbal tea (peppermint, chamomile, rooibos, hibiscus): caffeine-free, zero calories. Excellent for evening fasting hours when you want warmth without disrupting sleep.

A practical rotation many fasters use: green tea or yerba mate in the morning, black or oolong tea mid-morning, herbal tea in the evening. The warmth and ritual of tea can carry you through the hunger dips that coffee alone might not.

Yerba mate — the premium fasting drink

If coffee is the classic and tea is the contemplative, yerba mate is the premium fasting drink — and it deserves a featured place in your fasting practice. Yerba mate is a naturally caffeinated South American herb, brewed from the leaves of Ilex paraguariensis. Brewed plain, it has no sugar and effectively no calories, making it fast-friendly in the strictest sense.

What makes yerba mate particularly well-suited to fasting is the quality of the energy it provides. Mate contains caffeine plus two related compounds — theobromine (also found in cacao) and theophylline — that smooth out the spike and crash typical of coffee. Most fasters report a steadier, more grounded alertness from mate than from coffee, with less jitters and less of an afternoon crash. For a 16-hour fast that spans the entire morning, that sustained energy matters.

• Naturally caffeinated: ~70–85 mg caffeine per 8 oz (similar to coffee, less jittery)
• Zero calories and zero sugar when brewed plain — does not break a fast
• Rich in polyphenols and chlorogenic acids that may support the cellular pathways fasting activates
• Appetite-supportive: many fasters find mate blunts hunger more gently than coffee
• Mild, earthy flavor that doesn't require sweetener

Traditionally, yerba mate is prepared in a gourd and sipped through a metal bombilla, with the same leaves steeped multiple times throughout the morning. You can also brew it in a French press or tea infuser. Either way: plain. No sugar, no honey, no sweetener, no milk. The fast is in the plainness.

Electrolytes — essential for longer fasts

For fasts under 16 hours, plain water is usually sufficient. But once you go longer — 18 hours, 24 hours, or beyond — electrolytes become non-negotiable. When insulin drops during a fast, your kidneys excrete more sodium, and that sodium loss pulls potassium and magnesium out with it. The result is the classic fasting trio: headache, fatigue, and muscle cramps.

Unflavored electrolytes — sodium (salt), potassium, and magnesium — dissolved in water are fasting-safe and essential. Avoid electrolyte drinks with sugar, dextrose, or amino acids (most sports drinks and many " electrolyte powders" on the market). A pinch of high-quality salt in your water, a magnesium glycinate capsule, and a potassium-rich meal in your eating window cover most needs.

For a 24-hour fast, a working target is 3–5 grams of sodium, 1–3.5 grams of potassium, and 300–400 mg of magnesium over the course of the day. Your exact needs depend on body size, activity, climate, and how long you're fasting. (See our full guide to electrolytes and fasting for the detailed protocol.)

What NOT to drink while fasting

These drinks break a fast — meaningfully raising insulin, triggering digestive enzymes, and ending the metabolic state you're working to maintain. If you consume any of these, the fast is over. That's not a failure; it's information.

• Juice — even fresh-pressed, even green juice. Sugar is sugar.
• Milk and plant milks (oat, almond, soy, coconut) — all contain carbs and/or protein.
• Cream, half-and-half, and heavy cream in coffee or tea.
• Sugar, honey, maple syrup, agave, coconut sugar — pure carbohydrate.
• Bone broth and any protein-containing beverage (collagen, protein powder, BCAAs).
• Alcohol — your liver will prioritize metabolizing it over everything else.
• Most artificial sweeteners — for a clean fast, skip them.
• Smoothies, protein shakes, and meal-replacement drinks.

Borderline items, explained

Some items sit in the gray zone. The answer depends on your goal:

• Lemon water: A few drops or a thin slice in a large glass is trivial — fasting-safe. Half a lemon juiced into a small glass is borderline; skip it for strict autophagy.
• Apple cider vinegar (ACV): 1–2 tablespoons in water has about 3 calories and a negligible insulin effect. Most experts consider it fasting-safe; preliminary research suggests it may even support insulin sensitivity.
• MCT oil or coconut oil: Pure fat, minimal insulin impact. Won't ruin weight-loss fasting, but will blunt strict autophagy signals. Decide based on your goal.
• Cinnamon or a pinch of cocoa in coffee: Negligible calories. Generally considered safe.
• Sugar-free gum: A few calories and artificial sweeteners. For a clean fast, skip it.

How much and when to drink

A practical rhythm during a 16-hour fast:

• On waking: 16 oz of water with a pinch of sea salt.
• Mid-morning: a cup of black coffee, green tea, or yerba mate.
• Through the morning: continue water — aim for a glass per hour.
• Late morning: a second cup of coffee, tea, or mate if needed.
• 30 minutes before breaking the fast: a final glass of water with electrolytes.

Don't wait until you're thirsty — by then you're already mildly dehydrated. Front-load water in the morning, sip steadily through the day, and let caffeine carry you when hunger dips. And remember: the goal isn't purity for its own sake. The goal is to give your body what it needs to fast well — water, electrolytes, and a clean cup of something warm.

If you have reflux, anxiety disorders, heart conditions, or are pregnant or breastfeeding, talk to your healthcare provider about caffeine intake during a fast. This article is general information, not medical advice.