During the fasting window, the simplest answer is water, black coffee, and unsweetened tea.[1] During the eating window, you can have meals, snacks, and calorie-containing drinks. Intermittent fasting is mainly about when you eat, so the key question is whether something adds calories or turns the fasting window into an eating window.
If you want the cleanest fasting window, avoid foods, sweetened drinks, milk, cream, juice, alcohol, and calorie-containing add-ins until your eating window opens.
Key takeaways
- Water is the easiest fasting-window choice because it has no calories.[2]
- Black coffee and unsweetened tea are common fasting-window options.[1]
- Food, milk, cream, sugar, juice, alcohol, and calorie-containing supplements belong in the eating window.
- Diet drinks and sweeteners are more complicated; few or no calories does not make them the strongest default.[3]
- Fasting rules should not override medication, diabetes, pregnancy, breastfeeding, kidney disease, or eating-disorder concerns.[4]
Table of Contents
Quick list: what fits during fasting
A clean fasting window is easiest when the list is short.
| Item | During fasting? | Notes |
|---|---|---|
| Water | Yes | Plain still water is the simplest option |
| Sparkling water or seltzer | Usually | Choose unsweetened versions |
| Black coffee | Usually | Skip sugar, cream, milk, and syrups |
| Unsweetened tea | Usually | Skip honey, sugar, and milk |
| Diet soda | Depends | Low calorie, but not the strongest default |
| Gum or mints | Depends | Check sugar and calories |
| Supplements | Depends | Some contain calories or need food |
| Medication | Follow medical instructions | Do not change medication timing on your own |
For a deeper drink article, read What other drinks can you drink?.
What belongs in the eating window
Anything with meaningful calories belongs in the eating window. That includes:
- Meals and snacks
- Milk, cream, and sweetened coffee drinks
- Juice, smoothies, soda, and sweet tea
- Alcohol
- Protein powder, collagen, MCT oil, butter, and calorie-containing supplements
- Candy, desserts, and packaged snacks
This does not mean those items are all equally helpful. It only means they fit better outside the fasting window. During the eating window, food quality still matters; intermittent fasting does not make large meals or constant snacking irrelevant.[5]
Common gray-area items
Some items do not fit neatly into a yes-or-no rule.
| Item | Practical approach |
|---|---|
| Lemon water | Plain water is the cleanest choice; a small squeeze adds little but strict rules vary |
| Artificial sweeteners | Check labels; they may add few or no calories but may not help adherence |
| Flavored sparkling water | Check calories, sugar, and sweeteners |
| Electrolytes | Check calories and medical context, especially kidney disease or medications |
| Vitamins | Some need food or can upset the stomach; follow the label or clinician advice |
| Medication | Take as prescribed; do not skip food-required medication to preserve a fast |
The safest rule for uncertain items is to keep the fasting window simple and place gray-area products in the eating window unless you have a clear reason not to.
What to have when the eating window opens
The first meal after a normal overnight fast does not need to be extreme or special. A balanced meal is a steadier default.
Good starting choices include:
- Protein foods such as eggs, fish, chicken, tofu, beans, lentils, or Greek yogurt
- Fiber-rich plants such as vegetables, fruit, beans, or lentils
- Whole grains or starchy vegetables such as oats, brown rice, potatoes, or whole-grain bread
- Healthy fats such as olive oil, avocado, nuts, or seeds
- Water, coffee, or tea with little or no sugar
A healthy plate can emphasize vegetables and fruits, whole grains, healthy protein, healthy plant oils, and water, coffee, or tea with little or no sugar.[6]
For food ideas, read What can I eat while intermittent fasting?.
When fasting-window rules should change
Do not let fasting rules interfere with safety or medical care. If medications need food, do not skip food or change medication timing on your own.[4]
Do not treat fasting as self-guided if diabetes, kidney disease, pregnancy, breastfeeding, underweight status, recovery from illness or surgery, or eating-disorder risk are part of the picture.[4]
Side effects can include tiredness, dizziness, headaches, mood changes, constipation, diabetes management issues, and menstrual effects.[7] Persistent or severe symptoms should change the plan.
FAQ
What can I have while intermittent fasting?
During the fasting window, water, black coffee, and unsweetened tea are the simplest choices.[1][2] During the eating window, meals, snacks, and calorie-containing drinks fit.
What can you consume during intermittent fasting?
It depends on the window. In the fasting window, stick with no-calorie drinks if you want a clean fast. In the eating window, choose balanced meals and drinks that support your goals.
Can I have coffee during intermittent fasting?
Black coffee is a common fasting-window option.[1] Coffee with cream, milk, sugar, syrup, butter, or MCT oil belongs in the eating window.
Can I have supplements during intermittent fasting?
It depends on the supplement. Some contain calories, some are easier to tolerate with food, and some may interact with medications or medical conditions. Check the label and ask a clinician when medical issues are involved.
Can I have water during intermittent fasting?
Yes. Water has no calories and is the simplest fasting-window drink.[2]
Bottom line
During intermittent fasting, keep the fasting window simple: water, black coffee, and unsweetened tea. Put food, sweetened drinks, milk, cream, alcohol, and calorie-containing add-ins in the eating window. If medication or medical context conflicts with fasting rules, medical needs come first.
Medical disclaimer
This article is for general educational purposes only and is not medical advice. Speak with a qualified health professional before starting or changing a fasting routine if you have a medical condition, take medications, are pregnant or breastfeeding, are underweight, have eating-disorder history or risk, or develop symptoms that concern you.
References
- Johns Hopkins Medicine. Intermittent Fasting: What Is It, And How Does It Work?
- CDC. About Water and Healthier Drinks
- U.S. Food & Drug Administration. Aspartame and Other Sweeteners in Food
- Cleveland Clinic. 6 Tips for Fasting Safely
- Harvard Health Publishing. Should you try intermittent fasting for weight loss?
- Harvard T.H. Chan School of Public Health, The Nutrition Source. Healthy Eating Plate
- Mayo Clinic. Intermittent fasting: What are the benefits?