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What Breaks a Fast? Drinks, Gum and Medicines

What breaks a fast? Trials allowed water, black coffee and tea, but no calories. Gum is untested; never change a medicine to keep fasting.

Written by
Blimbi Editorial
Editorial review
Reading time
5 min

Editorial review against cited sources, not medical review. Educational, not medical advice.

In 30 seconds

In the trials cited here, no calories were allowed during the fasting window; water, black coffee and tea were. Sugar, fat and protein end that fast, while sugar-free gum remains unclear because the studies did not test it or set a calorie threshold. Medicines have their own instructions, so never skip or change a dose to keep fasting.

  • The fasting trials cited here defined the fasting window as no caloric intake.
  • Water, black coffee, tea and, in one trial, up to two diet sodas a day were allowed during the fast.
  • Sugar, milk, cream, juice and anything with protein or fat end a zero-calorie fast.
  • A 'safe' calorie allowance is a convention, not an evidence-based threshold, and the trials did not address gum.
  • Do not skip, delay or change a medicine to protect a fast; ask your clinician or pharmacist how it fits your window.

What counts as breaking a fast?

Confusion about what breaks a fast often comes from mixing the fasting window as researchers defined it with online claims about insulin, autophagy or ketones. The trials behind this guide used the simpler definition: no energy intake during the fast. Drink-by-drink detail is in coffee during intermittent fasting, water and lemon water and diet soda while fasting.

In the 12-week TREAT trial, the time-restricted group was told to eat from noon to 8 p.m. and to completely abstain from caloric intake for the rest of the day.

In a 12-month randomized trial of eating only between noon and 8 p.m., participants were encouraged to drink plenty of water during the 16-hour fast and were allowed energy-free drinks such as black tea, coffee and diet sodas, up to two diet sodas a day.

Whether common foods, drinks and products end a zero-calorie fast
ItemBreaks the fast?Context
Water, still or sparklingNoNo energy; a 12-month trial encouraged plenty of it during the fast.
Black coffee or plain teaNoEnergy-free drinks were allowed during the fast.
Diet or zero-sugar drinksNoLittle or no energy; one trial allowed up to two diet sodas a day, but WHO advises against sweeteners for weight control.
Milk, cream or plant milkYesDairy contains fat and protein, and cream is high in fat, so even a splash adds energy.
Sugar, honey, juice or regular sodaYesSugars provide energy, which breaks the trials' no-calorie rule.
Sugar-free gum or mintsIt dependsNot addressed by the trials. They are sweetened with lower- or no-calorie sweeteners, and polyols can have a laxative effect in large amounts.
Prescribed medicinesIt dependsA separate question from the fast. Some are taken with food, some on an empty stomach and some lower blood sugar; do not change a dose or its timing without your clinician.

Is there a proven calorie cut-off?

You will often read that anything under a certain number of calories keeps you fasted. The sources here do not support a specific number. Sweeteners show the grey zone: little or no energy, yet guidance on them is about safety and weight control, not fasting.

NHS guidance considers approved sweeteners safe within acceptable daily intakes and notes that polyols such as sorbitol and xylitol can have a laxative effect in large amounts, while WHO advises against using non-sugar sweeteners for weight control.

What about medicines?

Whether a tablet ‘breaks’ a fast matters less than taking it correctly. Food instructions differ, and even black coffee can matter for some medicines.

NHS guidance says levothyroxine should be taken on an empty stomach 30 to 60 minutes before the first meal of the day or any drink with caffeine, such as tea or coffee, while naproxen should ideally be taken with or after food.

An NIDDK diabetes specialist notes that intermittent fasting restricts calories, not fluids, so people with diabetes can drink water, diet soda, tea or black coffee; NHS guidance advises people on insulin or some other diabetes medicines not to skip or delay meals.

What did the trials actually test?

Early evidence

Trial rules, not biochemical thresholds

Here, what breaks a fast is defined by trial rules: no caloric intake, with water and energy-free drinks allowed. The trials did not test small calorie allowances, gum or supplements, so other rules are conventions, not findings.

Why do medicines come first?

Talk to a qualified health professional before fasting if you are pregnant or breastfeeding, under 18, living with or recovering from an eating disorder, have diabetes, take insulin or a medicine affected by meal timing, are an older adult, or are acutely ill. Do not change the dose or timing of any medicine without your clinician. See Blimbi’s safety guide.

Frequently asked questions

Does sugar-free gum break a fast?

The trials cited here did not say, so under a strict no-calorie rule it is a grey area and a personal choice. According to NHS guidance, gum with polyols such as sorbitol or xylitol can have a laxative effect in large amounts.

Do I have to skip my morning medication while fasting?

No, and do not move it either without advice. Ask your clinician or pharmacist how your medicines fit your eating window: some must be taken with food, and some, such as levothyroxine, on an empty stomach before coffee. If you have diabetes, never adjust doses on your own to fast.

Sources

  1. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical TrialDylan A. Lowe et al. American Medical Association (AMA), November 1, 2020.DOI: 10.1001/jamainternmed.2020.4153 · PMID: 32986097Human randomized trial

  2. Time-Restricted Eating Without Calorie Counting for Weight Loss in a Racially Diverse Population: A Randomized Controlled TrialShuhao Lin et al. American College of Physicians, July 1, 2023.DOI: 10.7326/M23-0052 · PMID: 37364268Human randomized trial

  3. Water, drinks and hydrationNHS. NHS, May 17, 2023.Official guidance

  4. Use of non-sugar sweeteners: WHO guidelineWorld Health Organization. World Health Organization, May 15, 2023.Official guidance

  5. Dairy and alternatives in your dietNHS. NHS, December 11, 2023.Official guidance

  6. The truth about sweetenersNHS. NHS, February 20, 2023.Official guidance

  7. Fasting Safely with DiabetesMartin M. Grajower. National Institute of Diabetes and Digestive and Kidney Diseases, August 26, 2020.Official guidance

  8. LevothyroxineNHS. NHS, July 6, 2026.Official guidance

  9. NaproxenNHS. NHS, June 25, 2026.Official guidance

  10. Low blood sugar (hypoglycaemia)NHS. NHS, August 3, 2023.Official guidance

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