There’s one question that comes up more than almost any other when people start 16:8 intermittent fasting: can I drink this?
It happens at 7 a.m. when you’re reaching for your coffee. It happens at 10 a.m. when a coworker offers you a sparkling water. It happens at noon when you’re wondering if that green tea with a dash of honey is really going to ruin everything. The question seems simple, but the answer has some nuance to it — and getting it wrong can unknowingly stall your results.
Here’s the honest answer upfront: during your fasting window on 16:8, the goal is to consume nothing that triggers a meaningful insulin response or delivers calories your body can use for energy. Anything that does those two things breaks your fast. Anything that doesn’t is generally fair game. The rest of this guide breaks that down drink by drink, so you know exactly what to reach for and what to avoid.
Why What You Drink During the Fasting Window Actually Matters
Before getting into the list, it’s worth understanding why this question matters so much. The benefits of 16:8 intermittent fasting — fat burning, improved insulin sensitivity, reduced hunger, better metabolic markers — rely on your body remaining in a fasted metabolic state during those 16 hours. That state is characterized by low circulating insulin, depleted liver glycogen, and the shift toward using stored fat for fuel.
The moment your body receives calories — particularly carbohydrates or protein — insulin rises, the fat-burning signal is interrupted, and the fasted state ends. So the practical test for any drink during the fasting window is: does it contain meaningful calories? Does it trigger an insulin response? If the answer to either is yes, it breaks your fast.
A randomized controlled trial published in the Journal of Nursing Research (2022) involving 101 overweight and obese adults with prediabetes found that 16:8 time-restricted fasting produced significant reductions in body weight, waist circumference, and blood glucose compared to controls — confirming that the physiological state preserved during the fasting window is doing real metabolic work worth protecting. (Source: PubMed / Journal of Nursing Research, 2022)
With that context in place, here’s what you can and can’t drink.
The Safe List: What You Can Drink During Your 16:8 Fasting Window
1. Water — The Obvious Foundation
Plain water is the foundation of any fasting window and should be your primary drink throughout the 16 hours. It has zero calories, zero insulin response, and supports virtually every function your body is performing during the fast — including the cellular repair processes (autophagy) that fasting is known to promote.
Aim for a minimum of 8–10 cups across the full 24-hour period, and more if you’re exercising. Many people feel fatigue, brain fog, or hunger during a fast that they attribute to the fasting itself when it’s actually mild dehydration. Staying well-hydrated is one of the simplest things you can do to make the fasting window feel more manageable.
Sparkling water and plain mineral water are equally safe. Carbonation does not break a fast. The only caveat is flavored sparkling waters — check the label and make sure there are no added sugars, sweeteners, or calories. Most plain sparkling waters (plain LaCroix, plain Perrier, plain club soda) are completely fast-safe.
2. Black Coffee — The Fasting Window’s Best Ally
Black coffee is the most important fasting-friendly drink to know about, because for most people it transforms the fasting window from a miserable 16-hour countdown into something genuinely sustainable.
A clinical trial published in BMC Nutrition and referenced by the National Institutes of Health (NCT02199483 registry) specifically permitted black coffee and calorie-free beverages during fasting windows, a protocol consistent with the clinical consensus that plain black coffee — at roughly 2–5 calories per cup — does not meaningfully trigger insulin release or interrupt fat-burning in healthy adults. The appetite-suppressing and mild thermogenic effects of caffeine also make the fasting window easier to hold for most people. (Source: NIH Clinical Trials / PMC Fasting Study)
What makes black coffee fast-safe:
- Approximately 2–5 calories per cup — far below any meaningful metabolic threshold
- No carbohydrates, which means no insulin spike
- Contains chlorogenic acids and polyphenols that may actually support the same autophagy pathways fasting activates
- Caffeine suppresses ghrelin (hunger hormone), making it easier to push through the fasting window
What breaks it: milk, cream, sugar, flavored syrups, MCT oil, butter, or any other additive that adds meaningful calories or protein. A splash of whole milk adds roughly 20–30 calories, including lactose and protein — enough to trigger a small insulin response. Heavy cream in small amounts (under one tablespoon) is a gray area that most fasting practitioners tolerate; a full pour is not. Black is the only reliably fast-safe coffee.
For those who love coffee but want a cleaner, more mindful fasting experience, a Fellow Stagg Pour-Over Coffee Set elevates black coffee into something genuinely enjoyable rather than utilitarian. Properly brewed black coffee at the right temperature is a completely different drink from a rushed drip brew — and when that’s your primary fasting companion for 16 hours, making it excellent is worth the investment.
3. Green Tea, Black Tea, and Herbal Teas
Plain teas — unsweetened and without milk — are entirely fast-safe and offer some additional benefits beyond simple hydration. Green tea in particular contains EGCG (epigallocatechin gallate), a polyphenol that has been shown in multiple studies to support fat oxidation and enhance the metabolic effects of fasting. It also contains a modest amount of caffeine alongside L-theanine, which produces a calm, focused energy without the edge that straight coffee can bring.
Black tea is equally safe in its plain form and provides a slightly different flavor profile for people who want variety through the fasting window. The tannins in black tea also have a mild appetite-suppressing effect that helps with longer fasting periods.
Herbal teas — peppermint, chamomile, ginger, hibiscus — are all completely safe as long as they contain no added sweeteners or fruit pieces that could add sugar. Most pure loose-leaf and bagged herbal teas are zero-calorie and have no measurable effect on insulin.
The one thing to watch for is chai tea or flavored tea blends that contain dried fruit, honey crystals, or milk powder in the blend itself. Always check the ingredient list.
4. Plain Sparkling Water and Mineral Water
Beyond still water, plain carbonated water is completely safe during the fasting window. Sparkling mineral water like plain Pellegrino or Perrier contains trace minerals (magnesium, calcium, bicarbonate) that are actually beneficial during fasting, when mineral losses can increase due to lower insulin levels.
Flavored sparkling waters with no calories and no sweeteners (like plain LaCroix) are also safe. However, some flavored waters contain citric acid in quantities that could theoretically stimulate digestive activity — while this likely doesn’t break a fast in any meaningful sense, those with sensitive digestion sometimes find plain sparkling water easier on an empty stomach.
5. Electrolyte Drinks (Zero Calorie)
This one catches a lot of people off guard, but electrolyte supplementation during the fasting window is not only allowed — for many people, it’s necessary.
When insulin drops during fasting, the kidneys become less efficient at retaining sodium, which causes increased excretion of sodium — and subsequently potassium and magnesium — through urine. This electrolyte depletion is the primary reason people experience the classic fasting side effects: headaches, fatigue, muscle cramps, and brain fog. Most people who struggle with the 16-hour fasting window aren’t struggling because of hunger; they’re struggling because of electrolyte imbalance that could be easily corrected.
A review of the physiological effects of fasting published in The American Journal of Medicine confirmed that potassium excretion increases significantly in the early stages of fasting and stabilizes at a consistent daily loss — making mineral replenishment an important consideration during regular fasting practice. (Source: The American Journal of Medicine, Fasting and Electrolytes Review)
Pure electrolyte supplements containing sodium, potassium, and magnesium with no calories, no sugar, and no artificial sweeteners do not break a fast. They have no caloric content and don’t trigger an insulin response.
For a clean, no-calorie electrolyte option, the LMNT Electrolyte Drink Mix has become popular in the intermittent fasting community specifically because it contains meaningful sodium (1,000 mg), potassium (200 mg), and magnesium (60 mg) per packet with zero sugar and zero calories. It’s one of the few electrolyte products formulated to actually address fasting-related mineral loss without breaking the fast.
The Gray Zone: Drinks That Need Context
Apple Cider Vinegar (ACV) in Water
A tablespoon of ACV diluted in water is a common fasting addition. It contains roughly 3–5 calories, has no sugar in pure form, and has some evidence behind its effects on blood glucose and satiety. For most weight-loss-focused fasters, it’s unlikely to break a fast meaningfully. For strict autophagy-focused fasting, the acetic acid may have minor effects worth considering. Overall: safe for most purposes.
Diet Sodas and Zero-Calorie Sweetened Drinks
This is where opinions genuinely differ. Technically, zero-calorie diet sodas don’t contain calories and don’t raise blood glucose directly. However, some research suggests that certain artificial sweeteners — particularly sucralose and aspartame — may trigger a cephalic phase insulin response in some individuals, where the brain anticipates calories based on the sweet taste and releases a small amount of insulin preemptively.
The evidence here is mixed and largely depends on individual metabolic sensitivity. For most people trying 16:8 for weight management, an occasional diet soda during the fasting window is unlikely to derail results. For those seeking the deeper metabolic benefits of fasting or who are highly insulin-sensitive, sticking to unsweetened drinks is the safer approach.
Bone Broth
Bone broth contains protein and fat, which technically breaks a fast from a strict physiological standpoint. However, many practitioners use it during extended fasts because it provides electrolytes and minerals that ease fasting symptoms. For 16:8 specifically, it’s unnecessary and should be saved for the eating window.
What Definitely Breaks Your 16:8 Fast
These are the non-negotiables — drinks that contain enough calories, protein, or sugar to interrupt the fasted state regardless of how small the amount seems:
- Milk of any kind — cow’s milk, oat milk, soy milk, almond milk with calories
- Juice — even small amounts of fruit juice contain significant sugar and will spike insulin
- Smoothies — contain fiber, sugar, and often protein; solidly in the eating window
- Coffee with cream, sugar, flavored syrups, or oat milk
- Sports drinks and most commercial electrolyte beverages — most contain sugar
- Alcohol — contains 7 calories per gram and impacts liver metabolism and fat burning significantly
- Protein shakes or collagen peptide drinks — protein triggers an insulin response and breaks the fast
Making the 16:8 Fasting Window Actually Work
The drinks above are your toolkit for a successful fasting window — but how you use them matters. A practical morning-to-noon fasting routine might look like this:
Start the fasting window with a large glass of plain water immediately upon waking. This addresses the mild dehydration from sleep and kicks off the day before coffee. Follow with black coffee or green tea. Around the midpoint of your fasting window, an electrolyte drink or plain sparkling water helps maintain energy and mental clarity. Close out the fasting window with herbal tea or water to avoid arriving at your eating window ravenously hungry.
For people who find the transition to fasting difficult, the right drinks make an enormous difference. Hunger during the fasting window is often a combination of genuine hunger, boredom, habit, and electrolyte depletion — and most of those are addressable without eating. A well-brewed black coffee at 10 a.m. solves most fasting window problems more effectively than willpower alone.
A high-quality electric gooseneck kettle like the Cosori Pour-Over Kettle makes preparing precise-temperature teas and coffees during the fasting window fast and easy. Green tea in particular requires a specific water temperature (around 175°F) to avoid bitterness — variable-temperature kettles solve this instantly and make the fasting window experience meaningfully better without adding any calories to it.
The Bottom Line
What you can drink during 16:8 intermittent fasting comes down to a simple principle: zero calories, zero insulin response, and nothing that signals your body to shift out of its fasted metabolic state.
Plain water, black coffee, unsweetened teas, plain sparkling water, and zero-calorie electrolyte drinks are all fully safe and collectively give you more than enough variety to get through a 16-hour window comfortably. The drinks to avoid are anything with calories, sweeteners, milk, juice, or protein — full stop.
Nail the drinking rules and the fasting window becomes dramatically easier to maintain. Which means the 8-hour eating window becomes more productive, and the results you’re working toward come more consistently.
Now that you know exactly what to drink during your fasting window, the next logical question is what to eat when that window opens. What you put on your plate during your 8-hour eating window determines whether 16:8 actually delivers results or just becomes a complicated way to eat the same things you always have. If you want a done-for-you starting point, this free 7-day meal plan for intermittent fasting takes all the guesswork out of it — with a full week of meals designed to work with your fasting schedule, keep you satisfied, and support real fat loss during the hours your eating window is open
Disclaimer: This article is for informational purposes only and does not constitute medical or nutritional advice. If you have a health condition or take medication, consult your doctor before starting intermittent fasting.
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