What shouldn't you do when fasting? Avoid these critical mistakes

November 14, 2025 •

4 min read

According to a 2024 study, up to 14% of adults worldwide practice some form of intermittent fasting. To achieve the best results, it's crucial to understand what shouldn't be done when fasting and avoid common pitfalls like improper hydration and diet.

Quick Summary

Learn the most common and critical errors to avoid while fasting. Get expert guidance on proper hydration, nutrition, and exercise to ensure a safe and successful fast.

Key Points

Avoid Dehydration: Drink plenty of water and calorie-free fluids, especially during non-fasting periods, to prevent headaches and fatigue.
Break Fast Gently: Don't feast on heavy, fatty, or sugary foods immediately. Start with small, easily digestible options like broth or dates to prevent digestive upset.
Limit Intense Exercise: Strenuous workouts on an empty stomach can lead to dizziness and low energy. Opt for light activities like walking during fasting windows.
Choose Nutrient-Dense Foods: During your eating window, prioritize whole, unprocessed foods. Avoid sugary drinks and processed snacks to maximize health benefits.
Listen to Your Body: Never ignore signs of severe discomfort, such as dizziness, nausea, or extreme weakness. Stop fasting if you feel unwell.
Manage Expectations: Understand that fasting is not a quick fix. Be consistent and patient with results, rather than giving up prematurely due to unrealistic expectations.
Plan Your Meals: Prepare nutritious, balanced meals in advance to avoid impulsive, unhealthy food choices when a fast ends.

Ignoring Hydration and Electrolytes

One of the most critical and common mistakes people make while fasting is neglecting proper hydration. The body loses fluids throughout the day, and when food is not being consumed, the water content found in fruits, vegetables, and other meals is also being missed out on. This can quickly lead to dehydration, which can cause headaches, fatigue, dizziness, and intense thirst. Many mistakenly believe that a few large glasses of water during the eating window are sufficient, but consistent sipping is key. Furthermore, the loss of electrolytes—essential minerals like sodium, potassium, and magnesium—is a frequent issue, especially with prolonged fasts.

How to Avoid Dehydration During a Fast

Hydrate Strategically: Instead of chugging water all at once, sip water regularly throughout non-fasting periods. For religious fasts, like Ramadan, make sure to drink plenty of fluids between Iftar and Suhoor.
Add Electrolytes: Consider adding a pinch of salt or drinking electrolyte-enhanced water to replenish lost minerals. This can be particularly helpful during longer fasts.
Avoid Diuretics: Limit or avoid beverages with a diuretic effect, such as excessive caffeine and sugary drinks, as these can increase urination and fluid loss.

The Wrong Way to Break a Fast

After a period of abstaining from food, the digestive system slows down, and enzyme production decreases. Suddenly overloading the system with a large, heavy, or unhealthy meal can cause significant digestive distress, including bloating, cramping, and even diarrhea. This is especially true for foods that are high in sugar, fat, or refined carbohydrates.

The Mindful Refeeding Comparison


Practice	Mindful Refeeding	Overconsumption
First Meal	Small, easily digestible options like broth or small pieces of fruit.	Large, heavy meal with processed foods, sugar, and excess fat.
Speed of Eating	Eating slowly and chewing thoroughly to aid digestion.	Eating quickly due to intense hunger, often without savoring the food.
Food Quality	Nutrient-dense, whole foods like lean protein, fruits, and vegetables.	High-calorie, low-nutrient foods like fried items, sugary drinks, and desserts.
Body Reaction	Smooth transition, gentle digestion, and steady energy replenishment.	Bloating, cramping, fatigue, and potential for discomfort.

Making Poor Food and Drink Choices

What is consumed during an eating period is just as important as when it is consumed. Using the eating window as an excuse to binge on unhealthy foods can negate the health benefits of fasting and hinder weight loss goals. In particular, avoiding certain food and drink categories is vital.

Less Ideal Food and Drink Choices

Foods High in Sugar and Refined Carbs: Sweets, pastries, white bread, and sugary cereals can cause blood sugar spikes and crashes, making it harder to control hunger. Many processed foods contain hidden sugars that can disrupt metabolic benefits.
Fatty and Fried Foods: Oily and fried foods can be difficult for a fasting-rested digestive system to handle and may cause significant discomfort.
Unhealthy Beverages: High-sugar drinks like soda, sweetened fruit juices, and energy drinks are a major culprit. Even diet or zero-calorie drinks with artificial sweeteners may trigger a response in some individuals and should be limited. Excessive alcohol consumption is also strongly discouraged.

Overexertion and Inappropriate Exercise

While staying physically active is beneficial, pushing the body too hard while fasted can be uncomfortable. Fasting can lower energy levels, and intense exercise in a fasted state can lead to dizziness, nausea, and weakness. The body needs fuel to perform at a high level and to recover afterward.

Recommendations for Fasting and Exercise

Stick to Low-Intensity: Opt for moderate activities like walking, yoga, or light stretching during a fasting window. Save more strenuous workouts for when food has been eaten.
Time Your Workouts: Ideally, exercise either before a fast begins (when fueled and hydrated) or after a fast has been broken and energy stores replenished.
Listen to Your Body: Pay close attention to how the body feels. If excessive fatigue, dizziness, or light-headedness is experienced, stop exercising immediately.

Dismissing Your Body's Warning Signs

The body provides constant feedback, and during a fast, these signals can be amplified. Ignoring extreme hunger, intense headaches, or feelings of faintness is a serious mistake. These are indicators that the body may need nourishment or hydration. Fasting is a tool for wellness, not a test of endurance at the cost of health. It is particularly important for individuals with pre-existing conditions to consult a doctor before fasting, as some health issues can be exacerbated by the practice. Ignoring the body's clear signals is counterproductive to any health goals. Learn more about safe fasting practices from experts at Healthline.

Conclusion: Fast Smart, Not Hard

In conclusion, fasting can offer significant benefits, but these rewards are only realized by avoiding common pitfalls. The most effective fasting practices are those that prioritize safety, mindfulness, and a healthy relationship with food. Neglecting hydration, breaking the fast improperly, and making poor dietary choices can all hinder progress and cause discomfort. By listening to the body, planning eating and activity, and choosing nutrient-dense whole foods, a fasting journey can be both safe and successful. It’s not about how long or how strictly to fast, but how mindfully and healthily the process is approached.

Frequently Asked Questions

Intense exercise is not recommended while fasting, as it can lead to low energy, dizziness, and muscle breakdown. Stick to light to moderate activities like walking or yoga, and schedule more strenuous workouts for after your eating window.

Plain water is the best choice for hydration during a fast. Unsweetened black coffee and herbal teas are also acceptable. It's crucial to avoid sugary drinks, including diet sodas with artificial sweeteners, to prevent metabolic disruption.

Many zero-calorie drinks with artificial sweeteners like aspartame or sucralose are best avoided during a fast, as they may trigger a response in some individuals. It's best to stick to water, plain tea, or black coffee to be safe.

Break a fast with small portions of easily digestible foods. Examples include bone broth, dates, steamed vegetables, or a simple smoothie. Avoid heavy, fatty, sugary, or spicy foods to prevent stomach upset.

Overeating after a fast can cause bloating, cramping, and digestive distress because the system has slowed down. It can also cause sharp blood sugar spikes and hinder weight loss efforts.

Staying well-hydrated is one of the best strategies to manage hunger. Keeping busy with light activities like walking or meditation can also serve as a distraction. Additionally, consuming nutrient-dense, fiber-rich foods during an eating window can help feel fuller for longer.

If feeling unwell, experiencing extreme weakness, persistent dizziness, or nausea, a fast should be stopped immediately. Listen to the body and prioritize safety over sticking rigidly to a fasting schedule.