What Not to Eat During Intermittent Fasting

November 24, 2025 •

4 min read

According to a study published in The BMJ, intermittent fasting can be just as effective for weight loss as traditional calorie restriction, but your food choices are critical for success. Knowing what not to eat during intermittent fasting is crucial to prevent blood sugar spikes, curb cravings, and support your health goals. This guide will help you navigate your eating windows wisely.

Quick Summary

Intermittent fasting requires strategic food choices during eating windows to maximize benefits and avoid setbacks. Avoid processed foods, sugary items, high-fat meals, and alcohol to prevent blood sugar spikes, digestive discomfort, and sabotaging your progress. Focus on nutrient-dense, whole foods to support sustained energy and overall health.

Key Points

Avoid Sugary Beverages: Sugary drinks and sweetened coffees cause insulin spikes that disrupt your fasted state and can trigger cravings.
Limit Processed Foods: Highly processed foods with added sugars and unhealthy fats offer little nutrition and can increase hunger.
Skip Fried and High-Fat Meals: Heavy, greasy foods can shock your digestive system after fasting, leading to discomfort and bloating.
Stay Clear of Alcohol: Alcoholic beverages contain calories and interfere with fasting benefits, often increasing appetite.
Break Your Fast Gently: When ending a fast, choose small portions of easily digestible foods like broth, eggs, or steamed vegetables to avoid digestive upset.
Focus on Whole, Nutrient-Dense Foods: During your eating window, prioritize lean proteins, vegetables, fruits, and whole grains to support overall health and energy levels.
Hydrate with Calorie-Free Drinks: Stick to water, black coffee, and unsweetened teas during your fasting periods to stay hydrated without breaking your fast.

The Perils of Processed and Sugary Foods

One of the most common mistakes people make while intermittent fasting is viewing the eating window as a free-for-all. This mindset can quickly derail progress, as the body is more sensitive to what it consumes after a period of fasting. Processed and sugary foods are at the top of the 'avoid' list for several reasons:

Blood Sugar Rollercoaster: Consuming high amounts of sugar after a fast leads to a rapid spike in blood glucose, followed by a crash. This not only negates the insulin-regulating benefits of fasting but also triggers intense cravings, making it difficult to adhere to your fasting schedule.
Empty Calories: Items like candy, cookies, sugary cereals, and sodas offer little to no nutritional value. They provide empty calories that won't keep you full, leading to increased hunger and overeating.
Inflammation and Fatigue: High sugar and processed food intake can cause inflammation and lead to energy crashes and fatigue, which are counterproductive to the improved energy levels and mental clarity many seek from intermittent fasting.

Why High-Fat and Fried Foods Are a Problem

While some healthy fats are essential, a fast should not be broken with excessively high-fat or fried foods. Your digestive system has been at rest and can be overwhelmed by a sudden influx of heavy, greasy meals.

Digestive Distress: Digesting fried foods and high-fat items puts a significant load on your digestive enzymes, which may be less active after fasting. This can cause indigestion, bloating, and stomach pain. It is especially important to be gentle with your digestive system when breaking a prolonged fast, and heavy fats can trigger discomfort.
Counteracts Benefits: The purpose of intermittent fasting is often to improve metabolic health, including fat burning. Consuming an abundance of unhealthy fats, particularly trans fats found in fried foods, undermines this process and can contribute to weight gain.

Alcohol and Caloric Beverages

Any beverage containing calories will technically break a fast. This includes fruit juice, sugary teas, and, most importantly, alcohol. Even low-calorie alcoholic beverages contribute to your daily intake and can negatively impact your intermittent fasting results.

Disrupts Fasting State: Alcohol, soda, and sweetened beverages contain calories and can spike insulin levels, which immediately breaks your fast. For those on a strict fasting protocol, this defeats the purpose entirely.
Appetite Stimulation: Alcohol can stimulate your appetite, making it harder to stick to your eating window and increasing the likelihood of making poor food choices.
Empty Calories and Hydration: Like sugary foods, alcoholic drinks contain empty calories and can lead to dehydration. Stay hydrated with water, herbal tea, or black coffee instead.

A Comparison of What to Avoid vs. What to Prioritize


Food Category	What Not to Eat	What to Prioritize
Processed Foods	Packaged snacks, chips, frozen meals, fast food	Whole, unprocessed foods like fruits, vegetables, and lean proteins
Sugary Items	Soda, candy, cookies, sweetened drinks, pastries	Berries, apples, and other fruits with natural sugars and fiber
Fats	Deep-fried foods, fatty meats, cream-based desserts	Healthy fats from avocados, nuts, seeds, and olive oil
Grains	White bread, refined pasta, sugary cereals	Whole grains like oats, quinoa, and brown rice
Beverages	Alcoholic drinks, soda, sweetened coffee/tea	Water, black coffee, and unsweetened herbal tea

The Proper Way to Break a Fast

After a period of fasting, it's wise to ease your digestive system back into work. This is especially true for longer fasts. Starting with a heavy meal can cause discomfort and undo some of the benefits of fasting.

Best practices for breaking a fast:

Start with something light and easily digestible: Think bone broth, a small salad, or a protein shake.
Opt for nutrient-dense foods: Prioritize foods rich in protein, healthy fats, and vitamins to refuel your body efficiently. Good options include eggs, fish, and cooked vegetables.
Stay hydrated: Continue to drink plenty of water throughout your eating window to aid digestion and stay hydrated.
Eat slowly and mindfully: Pay attention to your body's signals and stop eating when you feel satisfied, not stuffed.

The Critical Role of Whole Foods

Eating a balanced diet consisting of whole foods during your eating window is the cornerstone of successful intermittent fasting. Whole foods are rich in the vitamins, minerals, and fiber that your body needs to function optimally. This approach not only provides sustained energy but also helps to curb cravings and keeps you feeling full for longer, making the next fasting period more manageable. A diet based on whole foods, including fruits, vegetables, whole grains, and lean proteins, ensures you are getting the most out of your intermittent fasting regimen. For more comprehensive guidance, resources like the Diet Doctor offer extensive information on low-carb, whole-food diets that complement intermittent fasting perfectly.

Conclusion: Quality Over Quantity

While intermittent fasting focuses on when you eat, the ultimate success and long-term health benefits depend heavily on what you eat. Avoiding processed foods, sugary drinks, fried items, and excessive unhealthy fats is crucial for optimizing your results. By prioritizing nutrient-dense, whole foods, you can prevent metabolic setbacks, reduce cravings, and support your overall well-being. The eating window is not a license for unhealthy indulgence but an opportunity to nourish your body with wholesome fuel. Making smart, intentional food choices is the key to harnessing the full potential of intermittent fasting for better health.

Frequently Asked Questions

If you accidentally consume a small, low-calorie item, it will likely not ruin your progress. However, if you consume something with substantial calories, it will technically break your fast. Don't stress; simply return to your fasting schedule at the next interval.

Yes, adding milk or creamer, which contain calories, will break your fast. To maintain a strict fast, stick to black coffee or unsweetened tea. For a modified approach, some people tolerate very minimal amounts of milk, but it depends on your specific goals.

While diet soda contains zero calories and won't technically break a fast, the artificial sweeteners can still trigger an insulin response in some people. This can potentially stimulate hunger and make fasting more difficult. Water, black coffee, and herbal tea are safer choices.

After a fast of 24 hours or more, it's best to ease back into eating with easily digestible foods. Start with liquids like bone broth or a simple smoothie, then move to soft, cooked foods like eggs or steamed vegetables. Avoid large, heavy meals initially.

While intermittent fasting doesn't restrict specific macronutrients, consuming high-carb, sugary meals can cause blood sugar spikes and energy crashes. To maximize benefits, focus on balanced meals with protein, healthy fats, and fiber to promote stable energy.

Staying well-hydrated with water, black coffee, or herbal tea can often help. Keeping busy during fasting periods and eating balanced, nutrient-dense meals during your eating window will also help manage cravings by keeping you full and satisfied.

The success of intermittent fasting depends on both the timing and the quality of your food. While you may see some results, consistently eating junk food and processed items during your eating window can negate the metabolic benefits and hinder weight loss.