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 real nuance — 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.
If you’re new to 16:8 and still building out your full approach, pairing the right drink strategy with a structured eating plan makes a significant difference. This free 7-day meal plan for intermittent fasting gives you a complete framework for what to eat inside your window so that the fasting hours you’re protecting actually move the needle.
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 — depend on your body remaining in a fasted metabolic state during those 16 hours. That state is characterized by low circulating insulin, partially depleted liver glycogen, and a meaningful shift toward using stored fat as the primary fuel source. ¹
The moment your body receives calories — particularly carbohydrates or protein — insulin rises, the fat-burning signal is interrupted, and the fasted state ends. 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 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. ²
With that foundation in place, here’s exactly what you can and can’t drink.
The Safe List: What You Can Drink During Your 16:8 Fasting Window
1. Water — The Foundation of Every Fasting Window
Plain water is the non-negotiable baseline of any fasting window. It has zero calories, produces no insulin response, and supports virtually every function your body performs during the fast — including the cellular repair processes (autophagy) that fasting is known to promote.
Aim for a minimum of eight to ten cups across the full 24-hour period, and more on days you exercise. Many people experience fatigue, brain fog, and intensified hunger during a fast that they attribute to the fasting itself — when it’s actually mild dehydration. Staying consistently hydrated is one of the simplest things you can do to make the fasting window more manageable.
Plain sparkling water and mineral water are equally safe. Carbonation does not break a fast. The only caveat is flavored sparkling waters — check the label carefully and confirm there are no added sugars, caloric sweeteners, or juice content. Most plain sparkling waters (plain LaCroix, plain Perrier, plain club soda) are completely fast-safe.
2. Black Coffee — The Fasting Window’s Most Valuable Ally
Black coffee is the single most important fasting-friendly drink to understand, because for most people it transforms the 16-hour fasting window from a difficult test of willpower into something genuinely sustainable. ³
At roughly two to five calories per cup, black coffee sits far below any meaningful metabolic threshold. It contains no carbohydrates, which means no insulin spike. Beyond that, the chlorogenic acids and polyphenols in coffee may actually support some of the same autophagy pathways that fasting activates. Caffeine also suppresses ghrelin — the hunger hormone — making it measurably easier to hold the fasting window through the morning hours.
What makes black coffee fast-safe:
- Two to five calories per cup — negligible metabolic impact
- No carbohydrates, no meaningful insulin response
- Polyphenols that complement the metabolic effects of fasting
- Caffeine reduces perceived hunger during the fast
What breaks it: milk, cream, sugar, flavored syrups, MCT oil, butter, oat milk, or any additive that adds meaningful calories or protein. A splash of whole milk adds 20–30 calories including lactose and protein — enough to trigger a measurable insulin response. Black is the only reliably fast-safe coffee.
For those who spend 16 hours with black coffee as their primary companion, brewing quality matters more than most people expect. A well-made pour-over at the right temperature is a genuinely different drink from a rushed drip machine brew. The Fellow Stagg EKG Electric Pour-Over Kettle is one of the most highly rated precision kettles available with variable temperature control down to the degree, a built-in stopwatch, and a hold mode that keeps water at your target temperature throughout the brew. At the right brewing temperature, black coffee’s natural complexity emerges in a way that makes the fasting window feel like a ritual rather than a restriction.
3. Green Tea, Black Tea, and Herbal Teas
Plain teas — unsweetened and without milk — are entirely fast-safe and offer 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 amplify the metabolic effects of fasting. It also provides a modest amount of caffeine alongside L-theanine, producing calm, sustained focus without the sharper edge that straight coffee can sometimes bring. ⁴
Black tea is equally safe in plain form and offers variety through longer fasting windows. The tannins in black tea have a mild appetite-suppressing effect that many people find helpful during the middle hours of a fast.
Herbal teas — peppermint, chamomile, ginger, hibiscus — are all completely safe as long as they contain no added sweeteners or fruit pieces that introduce 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 blends or flavored tea products that contain dried fruit, honey crystals, or milk powder in the mix itself. Always check the ingredient list before assuming a tea is fast-safe.
For green tea specifically, water temperature matters significantly. Brewing at too high a temperature (above 185°F) releases bitter compounds that overpower the tea’s natural sweetness — which makes unsweetened green tea much harder to drink plain. The Breville Smart Kettle Luxe offers five precise temperature presets including the optimal 175°F for green tea, 185°F for white and oolong, and 212°F for black tea and coffee — all with a hold function that maintains temperature while you brew. It takes the guesswork out of tea preparation during a fast entirely.
4. Plain Sparkling Water and Mineral Water
Beyond still water, plain carbonated water is fully 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 excretion increases as insulin drops.
Flavored sparkling waters with zero calories and no sweeteners are also safe. Those with sensitive digestion sometimes find that strongly flavored carbonated waters cause minor bloating on an empty stomach — plain sparkling water is the easier option in that case.
5. Zero-Calorie Electrolyte Drinks
This one catches many people off guard: electrolyte supplementation during the fasting window is not only permitted — for most regular fasters, it’s necessary.
When insulin falls during fasting, the kidneys become less efficient at retaining sodium, leading to increased excretion of sodium, potassium, and magnesium through urine. This electrolyte depletion is the primary reason people experience the most frustrating fasting side effects: headaches, fatigue, muscle cramps, and brain fog. Research 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 a practical necessity during regular fasting practice. ⁵
Pure electrolyte supplements containing sodium, potassium, and magnesium with zero calories, zero sugar, and no artificial sweeteners do not break a fast. They contain no caloric content and produce no insulin response.
The LMNT Zero-Sugar Electrolyte Drink Mix has become one of the most popular electrolyte products in the intermittent fasting community for a specific reason: it’s formulated with meaningful therapeutic doses — 1,000 mg sodium, 200 mg potassium, 60 mg magnesium per packet — with zero sugar, zero calories, and no artificial sweeteners.
The Gray Zone: Drinks That Need Context
Apple Cider Vinegar in Water
A tablespoon of ACV diluted in water is a common fasting addition. It contains roughly three to five calories, has no sugar in pure form, and has some evidence behind its modest effects on blood glucose regulation and satiety. For most weight-loss-focused fasters, it’s unlikely to break a fast in any meaningful sense. 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
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 sweet taste and releases a small preemptive insulin signal.
The evidence here is mixed and depends significantly on individual metabolic sensitivity. For most people practicing 16:8 for weight management, an occasional diet soda during the fasting window is unlikely to derail results. For those seeking the deeper metabolic and cellular benefits of fasting, sticking to unsweetened drinks is the more conservative and reliable approach.
Bone Broth
Bone broth contains protein and fat, which technically breaks a fast from a strict physiological standpoint. Many practitioners use it during extended multi-day fasts because it provides electrolytes and minerals that ease prolonged fasting symptoms. For 16:8 specifically, it’s unnecessary — save it for the eating window.
What Definitely Breaks Your 16:8 Fast
These are non-negotiable. Each contains 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
- Smoothies — contain fiber, sugar, and often protein
- Coffee with cream, sugar, flavored syrups, or oat milk
- Sports drinks and most commercial electrolytes — most contain meaningful sugar
- Alcohol — provides seven calories per gram and significantly impacts liver metabolism and fat oxidation
- Protein shakes or collagen peptide drinks — protein triggers an insulin response that ends the fasted state
Making the 16:8 Fasting Window Work in Practice
The drinks above are your toolkit — but how you sequence them through the fasting window matters. A practical morning routine might look like this:
Start with a large glass of plain water immediately upon waking, before anything else. This addresses the mild dehydration that accumulates overnight and primes digestion. Follow with black coffee or green tea through the mid-morning hours. Around the midpoint of your fasting window, an electrolyte drink or plain sparkling water helps maintain energy and mental clarity as glycogen continues to deplete. Close the fasting window with herbal tea or water to avoid arriving at your eating window ravenously hungry.
For those who find the fasting window genuinely difficult in the early weeks, the right drinks address the majority of the challenge. Hunger during a fast is usually a combination of genuine hunger, habit cravings, mild boredom, and electrolyte depletion — and most of those are addressable without eating. A well-brewed black coffee or a cold glass of mineral water with electrolytes solves most fasting window problems more effectively than white-knuckling it with willpower alone.
Building a fasting routine that’s genuinely sustainable comes down to removing friction from the habits that support it. High-quality coffee and tea preparation, a reliable electrolyte product, and a structured eating plan for your open window are the three things that most consistently determine whether 16:8 becomes a permanent lifestyle or something you abandon after three weeks.
References
¹ Mattson MP, Longo VD, Harvie M. (2017). Impact of intermittent fasting on health and disease processes. Ageing Research Reviews. 39:46–58. https://pubmed.ncbi.nlm.nih.gov/27810402/
² Chair SY, Cai H, Cao X, Qin Y, Cheng HY, Ng MT. (2022). Intermittent fasting in weight loss and cardiometabolic risk reduction: a randomized controlled trial. Journal of Nursing Research. 30(1):e185. https://doi.org/10.1097/jnr.0000000000000469
³ Greenberg JA, Boozer CN, Geliebter A. (2006). Coffee, diabetes, and weight control. American Journal of Clinical Nutrition. 84(4):682–693. https://pubmed.ncbi.nlm.nih.gov/17023692/
⁴ Hursel R, Viechtbauer W, Westerterp-Plantenga MS. (2009). The effects of green tea on weight loss and weight maintenance: a meta-analysis. International Journal of Obesity. 33(9):956–961. https://doi.org/10.1038/ijo.2009.135
⁵ Drenick EJ, et al. (1971). Fasting — a review with emphasis on the electrolytes. The American Journal of Medicine.50(2):233–240. https://doi.org/10.1016/0002-9343(71)90152-5
This article is intended for general informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Intermittent fasting is not appropriate for everyone. Individuals who are pregnant or breastfeeding, have a history of disordered eating, are managing diabetes or blood sugar regulation issues, take prescription medications — particularly those that must be taken with food — or have any underlying metabolic, cardiovascular, or gastrointestinal condition should consult a qualified healthcare provider before beginning any fasting protocol. Do not use the information in this article as a substitute for professional medical advice.
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