What Will Ruin Intermittent Fasting? The Surprising Fast-Breakers

October 2, 2025 •

5 min read

According to nutrition experts, even a single calorie can disrupt the metabolic state achieved during a fast. It's a common misconception that fasting only involves avoiding large meals, but many seemingly harmless foods, drinks, and supplements will ruin intermittent fasting efforts if consumed at the wrong time.

Quick Summary

Intermittent fasting can be ruined by consuming any caloric substance, even in small amounts, during the fasting window. Common mistakes include sweetened beverages, certain supplements, and forgetting to stay properly hydrated.

Key Points

Any Calories Break a Fast: Consuming any amount of calories, especially from carbs and protein, will trigger an insulin response and technically end the fasting state.
Beware of Hidden Calories: Many drinks, like specialty coffees, fruit juices, and even some bone broths, contain enough calories to break your fast, even if they seem minor.
Supplements Aren't Always Safe: Gummy vitamins, protein powders, collagen, and BCAAs all contain calories or active ingredients that will ruin a true fast.
Artificial Sweeteners Are a Risk: While non-caloric, some artificial sweeteners can still cause an insulin response or increase cravings, undermining fasting goals.
Hydration is Key: Water, black coffee, and unsweetened tea are safe and essential for staying hydrated and managing hunger during a fast.
Focus on Nutrient-Dense Food: During your eating window, prioritize whole, nutritious foods to maximize health benefits and avoid negating your fasting efforts.
Don't Over-exercise While Fasting: Intense workouts on an empty stomach can lead to fatigue and should be scheduled during your eating window.

Understanding the Fasting State

Intermittent fasting (IF) is an eating pattern that cycles between periods of voluntary fasting and non-fasting over a set timeframe. The primary goal, beyond calorie restriction, is to allow your body's insulin levels to drop and stay low for an extended period. When insulin is low, your body switches from burning glucose (sugar) for energy to burning stored fat in a process called ketosis. This metabolic switch is the core mechanism behind many of IF's benefits, including weight loss and improved insulin sensitivity.

Any food or drink that contains calories—specifically carbohydrates or protein—can trigger an insulin response, effectively 'breaking' your fast and pulling your body out of this fat-burning state. Therefore, maintaining a true fasted state requires vigilance not only with food but with seemingly innocent beverages and supplements.

The Common Culprits: What Actively Ruin Intermittent Fasting?

Sugary and Caloric Beverages

While plain water, black coffee, and unsweetened tea are generally safe, most other drinks can immediately break a fast due to their caloric content.

Sodas and Juices: Even 'diet' sodas are a grey area. While calorie-free, some artificial sweeteners can still trigger an insulin response in certain individuals, or increase cravings for sweets later on. All fruit juices are loaded with sugar and will instantly end a fast.
Milk and Cream: Adding milk, cream, or any caloric creamer to your coffee or tea will break your fast. Though some people may allow for a tiny splash, a true fast means avoiding all caloric additions.
Bone Broth: Despite being a popular fasting-friendly item for some, bone broth contains protein and calories (about 15 calories per half-cup), meaning it will technically break a fast. It's best reserved for the eating window or for people following a modified fast.
Flavored Waters: Many flavored waters contain hidden sugars or artificial sweeteners that can disrupt your fast. Always check the label carefully.

The Treachery of Tiny Tastes

It's not just full meals that matter. Even tiny sips or bites can be enough to disrupt your fast.

Gummy Vitamins and Supplements: Most gummy vitamins are essentially candy, packed with sugar and gelatin that will break your fast immediately. Always choose non-chewable tablet or capsule supplements during your fasting window.
Protein Powders and Collagen: Both of these are sources of protein and contain calories. Consuming them will activate your body's digestive processes and end your fast. This is especially important for those fasting for autophagy (cellular repair), as protein triggers the mTOR pathway, which inhibits this process.
Branch-Chain Amino Acids (BCAAs): Though popular in fitness circles, BCAAs contain amino acids that can trigger an insulin response and inhibit autophagy, completely negating key fasting benefits.
Chewing Gum (with calories): Chewing gum can stimulate your digestive system even if you don't swallow it. If it contains any form of sugar or calories, it's a fast-breaker. Stick to sugar-free gum with no calories or sweeteners, though even then some find it triggers hunger.

What About Artificial Sweeteners?

The debate around artificial sweeteners during a fast is ongoing.

Some research suggests certain non-caloric sweeteners like sucralose or saccharin can still trigger an insulin response in some people, or negatively impact gut microbiota.
For those strictly adhering to fasting for metabolic health or autophagy, it's often recommended to avoid all sweeteners, natural or artificial, to eliminate any risk.
Zero-calorie natural sweeteners like pure stevia or monk fruit extract may be a safer bet, but they can still increase cravings for sweet tastes, making fasting more difficult.

A Simple Comparison: What to Have vs. What to Avoid


Item	Fast-Friendly?	Fast-Breaking?	Why?
Water	✅	❌	Zero calories, essential for hydration.
Black Coffee	✅	❌	Negligible calories, can suppress appetite.
Herbal Tea	✅	❌	Calorie-free, unsweetened is best.
Diet Soda	🤔 (Depends)	❌ (Often)	Artificial sweeteners can affect insulin response or trigger cravings.
Cream or Milk	❌	✅	Adds calories and fat, immediately breaking the fast.
Fruit Juice	❌	✅	High in sugar and calories.
Bone Broth	❌ (Strictly)	✅	Contains protein and calories; acceptable for 'dirty' fasts but not a true fast.
Gummy Vitamins	❌	✅	Full of sugar and gelatin.
Protein Powder	❌	✅	Protein contains calories and triggers insulin.
BCAAs	❌	✅	Amino acids can trigger insulin and inhibit autophagy.
Electrolyte Supplements	✅ (Pure)	❌	Help prevent fatigue without breaking the fast, crucial for longer fasts.

Crucial Mistakes That Negate the Benefits of Fasting

Poor Diet Quality During Your Eating Window

Intermittent fasting isn't a license to overeat junk food. If you spend your eating window gorging on processed foods, refined carbs, and sugary snacks, you may negate all the health benefits gained from fasting. A healthy, balanced diet of whole foods, lean protein, and healthy fats is crucial to maximizing results.

Neglecting Hydration

Dehydration is a surefire way to feel miserable and quit your fasting journey. Drink plenty of water throughout the day, especially during your fasting period, to stay hydrated and curb hunger. For longer fasts, electrolytes can be essential.

Exercising Too Intensely

While moderate exercise during a fast is generally fine, intense, prolonged workouts on an empty stomach can deplete your glycogen stores and lead to severe fatigue or dizziness. If you plan a hard workout, schedule it during your eating window to ensure you have fuel.

Breaking Your Fast with a Calorie Bomb

After a long fast, it can be tempting to break it with a large, high-sugar, or high-fat meal. This can cause a dramatic blood sugar spike and digestive upset. Instead, break your fast gently with easily digestible foods like nuts, eggs, or vegetables, easing back into your regular eating.

Conclusion: Fasting Success Relies on Knowledge

Succeeding with intermittent fasting isn't just about the clock; it's about what you put into your body during both your fasting and eating windows. Knowing precisely what will ruin intermittent fasting is the key to avoiding common pitfalls and ensuring you get the most out of your efforts. Stick to zero-calorie drinks during your fast and nutrient-dense, whole foods when you break it. Your body will thank you with improved metabolic health and better energy levels. Understanding these rules transforms fasting from a struggle into a sustainable lifestyle. For more information on what to eat and avoid, authoritative sources like Healthline offer detailed guidelines.

Frequently Asked Questions

Yes, a splash of milk or cream contains calories from carbohydrates and fat, which will cause an insulin response and technically break your fast.

While calorie-free, many artificial sweeteners can still trigger an insulin response or increase cravings for sweets in some individuals, potentially undermining your fasting goals. For the strictest approach, it's best to avoid them.

Bone broth contains calories and protein, which will break a true fast focused on metabolic switching or autophagy. It is only permissible for those following a less strict or 'dirty' fast.

It depends on the vitamin. Fat-soluble vitamins (A, D, E, K) need food for absorption, and most gummy or liquid vitamins contain sugar. Water-soluble vitamins and pure mineral capsules are generally fine, but always check the label.

Dirty fasting is a less strict approach where individuals consume a very small number of calories (usually under 50) during their fasting window. Items like bone broth or coffee with a small amount of fat are examples, but they still technically break a true fast.

The most common indicator is consuming any food, drink, or supplement with calories, which stimulates an insulin response and ends the fasted state. Feeling an increase in hunger or digestive activity is also a sign.

Break your fast gently with easily digestible foods that are high in protein and healthy fats, such as eggs, avocado, or nuts. Avoid large meals and high-sugar foods, which can cause a blood sugar spike.