Plain water, plain sparkling water, black coffee, and unsweetened tea are the simplest zero-calorie drinks during intermittent fasting. Diet soda and other zero-calorie sweetened drinks are more of a personal-rule decision: they may not add calories, but they can keep cravings or digestive discomfort in the picture for some people.
If you want the cleanest fasting window, keep it unsweetened. If your goal is mainly to avoid calories, check the label and pay attention to how the drink affects your appetite and comfort.
Key takeaways
- Plain water is the easiest fasting-window drink.
- Black coffee and unsweetened tea are commonly allowed in fasting windows [1].
- Sparkling water is usually fine if it has no sugar and no calories.
- Diet soda may fit a calorie-free rule, but it is not the best hydration default.
- FDA-authorized sweeteners are considered safe under approved conditions of use, but "zero calorie" does not automatically mean the drink helps your routine [2].
- If fasting causes dizziness, headaches, unusual fatigue, or mood changes, shorten the fast or talk with a healthcare professional [3].
The simplest fasting-window drink list
Most people do best with a short list:
- water
- plain sparkling water
- black coffee
- unsweetened black tea
- unsweetened green tea
- unsweetened herbal tea
Johns Hopkins Medicine lists water and zero-calorie beverages such as black coffee and tea as options while fasting [1]. The CDC also lists water, plain coffee, tea, sparkling water, seltzers, and flavored waters among low- or no-calorie drink options [4].
The practical rule: if the drink has no sugar, no milk, no cream, no protein, and no meaningful calories, it is more likely to fit a calorie-free fasting window.
Drinks that usually break a calorie-free fast
Avoid these during the fasting window if your goal is to stay calorie-free:
- coffee with milk, cream, or sweetened creamer
- lattes and cappuccinos
- sweetened tea
- regular soda
- juice
- smoothies
- protein shakes
- sports drinks with sugar
- alcohol
- bone broth, unless your specific plan includes it
These drinks may fit during an eating window, but they make the fasting window less clear.
What about diet soda?
Diet soda is usually low- or zero-calorie, so some people include it in a fasting window. Others avoid it because the sweet taste can make cravings stronger or make the fast feel less clean.
There is no single rule that fits every fasting style. Use this decision:
- If you want a strict, simple fasting window, skip diet soda.
- If your goal is calorie control, an occasional zero-calorie soda may fit.
- If it makes you hungrier, bloated, or more focused on sweet foods, move it to the eating window or replace it.
Water, sparkling water, black coffee, and unsweetened tea are better defaults.
Are zero-calorie sweeteners safe?
The FDA says sweeteners such as aspartame, sucralose, and stevia-derived substances are used to sweeten foods and may contribute few or no calories. It also says FDA-authorized sweeteners are safe for the general population under certain conditions of use [2].
That does not mean every person feels good using them, or that sweetened drinks are automatically useful during fasting. Some people prefer to avoid sweet taste during the fasting window because it keeps them thinking about food.
Also, people with phenylketonuria, a rare genetic disorder, should avoid or restrict aspartame because it contains phenylalanine [2].
What about flavored water?
Flavored water can fit if it has no sugar and no calories. Check the label for:
- calories per serving
- added sugar
- juice
- milk ingredients
- protein
- sweeteners, if you are avoiding them
If it is unsweetened and calorie-free, it is usually a reasonable option. If it tastes very sweet, treat it like diet soda: possibly okay by calorie rules, but not always helpful for cravings.
What about electrolyte drinks?
Electrolyte drinks vary. Some contain sugar or calories; others are calorie-free.
A calorie-free electrolyte drink may fit some fasting routines, especially if you sweat heavily, exercise, or live in hot weather. But do not use electrolyte supplements to push through symptoms that need attention.
If you feel dizzy, weak, unusually tired, nauseated, or confused, stop the fast and consider medical guidance. If you have a medical condition, take blood pressure medication, have kidney disease, or have been told to manage sodium or potassium intake, ask a clinician before using electrolyte products.
Caffeine can help or hurt
Black coffee and unsweetened tea can fit a fasting window, but caffeine is not a substitute for food or hydration.
Consider reducing caffeine during the fast if it causes:
- jitters
- nausea
- reflux
- anxiety
- sleep disruption
- headaches when you skip it
If coffee only works when you add cream and sugar, move it to the eating window or switch to plain tea during the fast.
How GoFasting can support drink choices
GoFasting can help you log fasting windows and water intake, then review patterns as you adjust your routine.
Use tracking as feedback. If a fasting window with only water feels easier than one with diet soda, that is useful. If a longer fast leads to low water intake or repeated symptoms, that is also useful. The app can support consistency, but it does not decide whether fasting is medically appropriate.
FAQ
Do zero-calorie drinks break a fast?
Plain zero-calorie drinks such as water, black coffee, and unsweetened tea usually fit a calorie-free fasting window. Sweetened zero-calorie drinks depend on your fasting rules and personal tolerance.
Can I drink Coke Zero while intermittent fasting?
If your rule is strictly calorie-based, it may fit. If your rule is to avoid sweet taste or sweeteners during the fast, save it for the eating window.
Can I drink coffee while fasting?
Black coffee is commonly allowed. Coffee with milk, cream, sugar, or sweetened creamer belongs in the eating window.
Can I drink tea while fasting?
Unsweetened tea is usually fine. Sweet tea, milk tea, and bottled teas with sugar do not fit a calorie-free fasting window.
Is lemon water okay while fasting?
A small squeeze of lemon adds very few calories, but strict fasting styles may avoid it. If you want the simplest rule, choose plain water.
Bottom line
For intermittent fasting, the best zero-calorie drinks are simple: water, plain sparkling water, black coffee, and unsweetened tea. Diet soda and sweetened zero-calorie drinks are optional, not essential. If they make fasting harder, keep them out of the fasting window.
Medical disclaimer
This article is for general educational purposes only and is not medical advice. Talk with a qualified healthcare professional before changing your eating or drinking routine if you have a medical condition, take medication, are pregnant or breastfeeding, or develop concerning symptoms.
References
- Johns Hopkins Medicine. Intermittent Fasting: What Is It, And How Does It Work? https://www.hopkinsmedicine.org/health/expert-qa/intermittent-fasting-what-is-it-and-how-does-it-work
- U.S. Food and Drug Administration. Aspartame and Other Sweeteners in Food https://www.fda.gov/food/food-additives-petitions/aspartame-and-other-sweeteners-food
- Mayo Clinic. Intermittent fasting: What are the benefits? https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/intermittent-fasting/faq-20441303
- CDC. About Water and Healthier Drinks https://www.cdc.gov/healthy-weight-growth/water-healthy-drinks/index.html