What Breaks a Fast? The Definitive List of Foods, Drinks, and Supplements
The simple rule
Anything with calories breaks a fast. If it triggers an insulin response or provides energy for your body to process, your fasted state is interrupted.
In practice, the line is not always obvious. This guide covers the common questions.
Drinks
Does not break a fast
- Water – Plain, sparkling, or mineral. Drink freely.
- Black coffee – No milk, cream, sugar, or flavouring. A small amount of caffeine can actually support fasting.
- Plain tea – Black, green, white, herbal. Nothing added.
Breaks a fast
- Coffee with milk, cream, or sugar
- Juice (any kind)
- Smoothies
- Soft drinks (regular or diet – diet is debated, see below)
- Alcohol
- Bone broth (contains calories, though some fasters allow it)
Grey area
- Diet drinks and zero-calorie sweeteners – These contain no calories, but artificial sweeteners may trigger an insulin response in some people. Strictly speaking, they do not break a caloric fast, but purists avoid them.
- Black coffee with a tiny splash of milk – A tablespoon of milk adds roughly 9 calories. Some practitioners consider this negligible. Others draw a hard line.
If your goal is a clean fast with no metabolic interruption, stick to water, black coffee, and plain tea.
Supplements and vitamins
Usually does not break a fast
- Electrolytes (sodium, potassium, magnesium) without added sugar
- Plain creatine
- Water-soluble vitamins in capsule form (B vitamins, vitamin C)
Breaks a fast
- Gummy vitamins (contain sugar)
- Fish oil capsules (contain fat calories)
- Protein powder
- BCAAs / amino acids (trigger an insulin response)
- Any supplement with added sugars, fillings, or calories
Best practice
Take calorie-containing supplements during your eating window. Save non-caloric supplements for whenever convenient.
Medications
Prescribed medications should be taken as directed by your doctor, regardless of your fasting schedule. Do not skip or delay medication to maintain a fast. If your medication requires food, eat. Your health comes first.
If you fast regularly and take medication, discuss timing with your healthcare provider. They may be able to adjust your schedule to align with your eating window.
Common scenarios
| Scenario | Breaks fast? |
|---|---|
| Black coffee, no sugar | No |
| Coffee with oat milk | Yes |
| Sparkling water with lemon | No |
| Apple cider vinegar in water (1 tbsp) | Technically yes (3 cal), most fasters allow it |
| Chewing gum (sugar-free) | Grey area – minimal calories but may stimulate appetite |
| Toothpaste (spit out) | No |
| Multivitamin capsule | Usually no |
| Gummy vitamins | Yes |
| Protein shake | Yes |
| A single almond | Yes |
Does it matter?
For most people practising 16:8 or similar protocols, the occasional grey-area item will not meaningfully affect results. Consistency over months matters far more than perfection on any single day.
If you are fasting for specific metabolic or autophagy-related goals, a stricter approach to what enters your body during fasting hours makes more sense.
Track your fasts with Fast Tracka regardless of how strict your approach is. The timer and history help you stay consistent, which is what produces results.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult a healthcare professional before starting any fasting regimen.