Nutrition During Fasting: What is forbidden while fasting?

October 3, 2025 •

4 min read

Recent studies suggest that intermittent fasting can offer metabolic benefits and improve insulin sensitivity. For anyone undertaking this practice, whether for health or spiritual reasons, clearly understanding what is forbidden while fasting is essential for success and safety.

Quick Summary

This article outlines the forbidden items and behaviors associated with different types of fasting, including both religious and health-based methods, to help participants navigate their dietary and lifestyle restrictions.

Key Points

Caloric Intake: For intermittent fasting, any consumption of calories will break the fast, including small amounts from oils or broth.
Religious Abstinence: Religious fasting, like Ramadan, forbids intentional eating, drinking, sexual activity, and immoral behaviors during daylight hours.
Hydration is Key: Water, black coffee, and unsweetened tea are generally permitted and crucial for staying hydrated during any fast.
Medical Exceptions: Individuals with health conditions or those requiring medication have specific exemptions or rules, especially in religious contexts. Consult a doctor before fasting if you have a medical condition.
Non-Caloric Meds: Non-nutritive injections are typically allowed in both religious and health-focused fasting, as they do not provide energy.
Intentional vs. Unintentional: Unintentional or forgetful eating does not break a religious fast, but intentional acts do.
Beware of Misconceptions: Myths about 'allowable' calorie limits or seemingly harmless substances, like bone broth during an intermittent fast, should be avoided.

Fasting, an ancient practice spanning numerous cultures and religions, has seen a modern resurgence in health and wellness circles. While the core principle—abstaining from food or drink for a set period—remains the same, the specific rules for what constitutes a 'broken' fast can vary significantly. This distinction is critical, as the forbidden elements for a religious fast, like Ramadan, are far more encompassing than those for a health-focused intermittent fast. Understanding these nuances is key to achieving your desired physical or spiritual outcomes.

What is Forbidden While Fasting? Understanding the Core Principles

At its heart, fasting involves restraint, but the scope of that restraint is what defines the specific type of fast. In a health context, the primary goal is often to induce metabolic changes, such as shifting the body into a state of ketosis or triggering cellular repair processes (autophagy). Consequently, any intake of calories or items that cause an insulin spike is generally forbidden. In contrast, religious fasting, such as the Islamic fast during Ramadan, is a spiritual discipline that extends beyond mere caloric restriction to encompass a broader abstention from certain actions and thoughts during daylight hours.

What is Forbidden During Intermittent Fasting (for Health)?

For those following intermittent fasting (IF), the rules revolve around avoiding caloric intake during the fasting window. The general consensus is that any consumption of calories will break the fast by providing the body with fuel, thus halting the intended metabolic effects.

Foods and Drinks to Avoid during Fasting Window:

Any caloric food: This includes all solid food, fruit, grains, meat, dairy, and nuts. Even small amounts are enough to disrupt the fasting state.
Sugary beverages: Soda, fruit juice, sports drinks, and sweetened teas or coffees are off-limits, as they spike insulin levels.
Caloric condiments: Cream, milk, and sweeteners in coffee or tea will break your fast.
Broth and oils: While often low-calorie, bone broth and added fats like MCT or coconut oil can contain enough protein or fat to signal your body to exit the fasting state.
Chewing gum (sugared): Sugar in gum provides calories and can trigger an insulin response.

What is Forbidden During Religious Fasting (e.g., Ramadan)?

Religious fasting is more comprehensive, focusing on spiritual purification as well as physical abstinence. The rules of Ramadan, for instance, prohibit a range of activities from dawn until sunset.

Actions and Substances to Avoid:

Intentional eating and drinking: This includes water and any other liquid.
Sexual intercourse: Any sexual activity is forbidden during fasting hours.
Smoking: Ingesting smoke is considered a form of consumption and therefore breaks the fast.
Intentional vomiting: Deliberately inducing vomiting invalidates the fast.
Negative behavior: Beyond physical acts, the spirit of religious fasting requires abstaining from immoral actions like lying, gossip, and anger.

How Exemptions and Medications Fit In

Both religious and health-based fasting have special considerations for certain individuals. Islam, for example, exempts the sick, the elderly, travelers, pregnant or breastfeeding women, and menstruating women. For health fasting, individuals with underlying conditions like diabetes should always consult a healthcare provider before starting. In terms of medications, the rules also diverge significantly.

Religious fasting and medication: Non-nutritive injections, like painkillers or vaccines, generally do not break the fast, while oral medications do. Nutritional IV drips, however, are forbidden.
Health fasting and medication: Since the goal is often to avoid an insulin response, non-caloric medication, including many pills, may not break a fast. However, it's essential to follow your doctor's advice, especially if medications need to be taken with food.

Comparison of Forbidden Items While Fasting


Aspect	Religious Fasting (e.g., Ramadan)	Intermittent Fasting (Health)
Food/Drink	Strictly forbidden, including water, between dawn and sunset.	Any caloric intake is forbidden during the fasting window.
Sexual Activity	Strictly forbidden between spouses during daylight hours.	Not a restriction, but energy levels may affect activity.
Behavioral Sins	Forbidden to foster spiritual purification (e.g., lying, anger).	No specific restrictions, but healthy habits are encouraged.
Nutrient Injections	Forbidden, as they provide nourishment.	Forbidden, as they introduce calories and trigger metabolic processes.
Non-Nutrient Injections	Generally allowed (e.g., vaccines, insulin).	Allowed, as they do not provide calories.
Smoking	Strictly forbidden, as it is considered consumption.	Breaks the fast due to chemical intake; also contrary to health goals.
Alcohol	Forbidden.	Strictly forbidden during the fasting window due to calories.

Conclusion

Ultimately, what is forbidden while fasting is defined by the type of fast being observed and its underlying purpose. For those practicing intermittent fasting for health benefits, the primary rule is a simple, if strict, one: avoid all caloric intake during the fasting window to maintain metabolic rest. In contrast, religious fasting involves a more holistic abstinence, covering not only food and drink but also negative behaviors and other specific acts that compromise the spiritual integrity of the fast. Staying hydrated with non-caloric drinks is a universal recommendation for any type of fast. No matter your motivation, a clear understanding of your fast's rules is crucial for achieving your goals and ensuring safety and success.

For more information on the principles of Islamic fasting, you may find resources like this one helpful: Islamic Legal Rules of Fasting - IslamiCity

Frequently Asked Questions

For intermittent fasting, drinking water is not only permitted but encouraged for hydration. For religious fasting, like in Islam, water is forbidden during the daylight fasting period.

Yes, black coffee is permitted during the fasting window of intermittent fasting. It contains negligible calories and does not typically trigger an insulin response.

For intermittent fasting, any amount of calories will technically break the fast. In religious fasting, however, forgetting and unintentionally consuming food or drink does not invalidate the fast.

Using a miswak or toothbrush is generally permissible during religious fasting, provided you are careful not to swallow any paste or water. It is often better to use it cautiously or leave it for non-fasting hours.

No. Nutritional IV drips are considered a form of nourishment and will break both a religious fast and a health-focused intermittent fast.

Sugared chewing gum contains calories and will break a fast. Some sugar-free gums contain artificial sweeteners that might prompt an insulin response, so many fasters avoid all types of gum during their fasting window.

No, smoking and vaping are considered forbidden during both religious fasting and intermittent fasting, as they involve inhaling substances that affect the body's internal state.