What to Eat and Drink During Intermittent Fasting
Complete guide to what you can eat and drink during intermittent fasting — what breaks a fast, best foods for your eating window, supplements, electrolytes, and more.
Quick Answer: During your fasting window, stick to zero-calorie or near-zero-calorie drinks: water, black coffee, plain tea, and sparkling water. During your eating window, prioritize protein, healthy fats, fiber-rich vegetables, and complex carbohydrates. What you eat matters as much as when you eat — intermittent fasting amplifies good nutrition but doesn't compensate for a poor diet.
Intermittent fasting tells you when to eat. It says almost nothing about what to eat. That's both its strength (simplicity) and its weakness (people assume timing alone does the heavy lifting).
The reality is that your food choices during the eating window determine whether you feel energized or drained, whether you preserve muscle or lose it, and whether you actually see the metabolic benefits that fasting promises. This guide covers both sides — what to consume during fasting hours and how to optimize your eating window.
What Won't Break Your Fast
The definition of "breaking a fast" depends on your goal. Here's a practical framework:
For weight loss: Anything that triggers a significant insulin response or provides meaningful calories breaks your fast. Small amounts (under 10 calories) are generally fine.
For autophagy: Stricter. Even small amounts of protein or carbohydrates can activate mTOR and suppress autophagy. Stick to water, plain tea, and black coffee.
For gut rest: Only water. Even coffee stimulates digestive processes.
Most people fast for metabolic and weight management benefits, so the moderate definition applies. Here's what's generally considered safe during a fast:
- Water (plain, sparkling, or mineral). Add a pinch of salt if needed for electrolytes.
- Black coffee. No sugar, no cream. Caffeine slightly enhances fat oxidation during fasting (Acheson et al., 1980).
- Plain tea. Green, black, herbal — all fine without sweeteners or milk.
- Apple cider vinegar diluted in water (1-2 tablespoons). Negligible calories and may support insulin sensitivity (Johnston et al., 2004).
For the full breakdown on beverages, see what to drink while fasting.
Common "Does This Break My Fast?" Questions
These come up constantly, so let's address them directly.
Lemon water: A squeeze of lemon in water adds roughly 1-3 calories. This will not break your fast for any practical purpose. The vitamin C and flavor may actually help you stay hydrated. Full analysis in does lemon water break a fast.
Bone broth: This one is more complex. A cup of bone broth contains 30-50 calories, including amino acids that can stimulate mTOR and insulin. For strict fasting, it breaks your fast. For a more relaxed approach focused on weight loss, some people use it as a bridge during longer fasts. Details in does bone broth break a fast.
Apple cider vinegar: At about 3 calories per tablespoon, ACV does not meaningfully break a fast. Some research suggests it may even enhance fasting benefits by improving insulin sensitivity. More in apple cider vinegar and fasting.
Artificial sweeteners: This is debated. While zero-calorie sweeteners don't provide energy, some research suggests they may trigger cephalic phase insulin responses — your body releases a small amount of insulin in anticipation of incoming sugar (Just et al., 2008). The effect appears to be small and varies by sweetener type. If you're concerned, skip them during fasting hours.
Electrolytes: The Overlooked Essential
One of the most common reasons people feel terrible while fasting isn't hunger — it's electrolyte imbalance. During fasting, insulin levels drop, which causes the kidneys to excrete more sodium. This can lead to headaches, fatigue, dizziness, and muscle cramps — symptoms often misattributed to "not eating."
The primary electrolytes to watch:
- Sodium. A pinch of salt in water or taking salt directly can resolve fasting headaches within minutes. Aim for 1-2g of sodium during extended fasting periods.
- Potassium. Important for heart and muscle function. Low-calorie sources during fasting are limited, so ensure adequate intake during your eating window through foods like avocado, spinach, and potatoes.
- Magnesium. Involved in over 300 enzymatic reactions. Magnesium deficiency is common even in non-fasters. Supplementation (200-400mg magnesium glycinate) is reasonable.
Deep dive in electrolytes during fasting.
Supplements During Fasting
Whether supplements break your fast depends on the supplement. Fat-soluble vitamins (A, D, E, K) need food for absorption and should be taken during your eating window. Water-soluble vitamins (B-complex, C) can technically be taken during fasting but may cause nausea on an empty stomach.
General guidelines:
- During fasting: Electrolytes, black coffee, plain tea. Most other supplements are better with food.
- During eating window: Multivitamins, fish oil, fat-soluble vitamins, protein supplements, creatine.
- Timing note: If you take medications that require food, this sets a boundary on your fasting window. Your health comes before your fasting protocol.
Full supplement guide in supplements during fasting.
What to Eat: Breaking Your Fast
How you break your fast matters more than most people realize. After 16+ hours without food, your digestive system has been resting. Hitting it with a large, complex meal can cause bloating, discomfort, and blood sugar spikes.
The ideal fast-breaking approach:
Start small. Begin with something easily digestible — a handful of nuts, a small portion of protein, or some cooked vegetables. Give your digestive system 15-30 minutes to wake up before eating a full meal.
Prioritize protein. Protein is the most satiating macronutrient and the most important for preserving muscle mass during intermittent fasting. A 2015 study in the American Journal of Clinical Nutrition found that higher protein intake (1.2-1.6 g/kg/day) significantly improved body composition during caloric restriction (Leidy et al., 2015).
Include healthy fats. Fats slow gastric emptying, keeping you satisfied longer and providing steady energy. Avocado, olive oil, nuts, and fatty fish are excellent choices.
Add fiber. Vegetables, legumes, and whole grains provide fiber that supports gut health and satiety. After a fasting period, fiber-rich foods help stabilize blood sugar as you begin eating.
Specific meal ideas and strategies in best foods to break a fast.
Optimizing Your Eating Window
Your eating window is where nutrition happens. Treat it with intention.
Protein distribution. Research from the University of Texas found that distributing protein evenly across meals (25-40g per meal) maximizes muscle protein synthesis compared to loading it all into one meal (Mamerow et al., 2014). If you eat two meals in your window, aim for substantial protein at each.
Nutrient density over calorie counting. Intermittent fasting naturally reduces calorie intake for most people. Rather than counting calories obsessively, focus on eating nutrient-dense whole foods. If every meal includes protein, vegetables, healthy fat, and some complex carbs, you're covering your bases.
Avoid the junk food trap. One common mistake: people assume that a restricted eating window gives them license to eat anything. It doesn't. A 2020 study in JAMA Internal Medicine found that time-restricted eating without attention to food quality produced modest weight loss but minimal metabolic improvement (Lowe et al., 2020).
For detailed eating window meal plans, see best foods for eating window.
Protein and Fasting
Protein deserves special attention because it's the macronutrient most people under-eat during intermittent fasting. When you compress your eating into 6-8 hours, it's easy to fill up on carbs and fats and fall short on protein.
The consequences are real: inadequate protein during fasting leads to muscle loss, which lowers metabolic rate and undermines long-term body composition goals. The International Society of Sports Nutrition recommends 1.4-2.0 g/kg/day for active individuals, and even sedentary adults benefit from at least 1.0-1.2 g/kg/day.
Practical protein strategies for fasters: prioritize protein at your first meal, use protein-rich snacks (Greek yogurt, jerky, eggs), and consider a protein supplement if whole food intake falls short.
Complete guide in protein and intermittent fasting.
Keto and Intermittent Fasting
Combining a ketogenic diet with intermittent fasting is popular because they share a metabolic pathway: both shift the body toward fat oxidation and ketone production. During fasting, you enter a mild ketogenic state naturally. A keto diet extends that state into the eating window.
The potential synergy is real but so are the risks of overdoing restriction. Combining two restrictive approaches can make adherence difficult and increase the risk of nutrient deficiencies. If you're considering this combination, start with intermittent fasting first, establish the habit, then experiment with macronutrient changes.
Full analysis in keto and intermittent fasting.
How Fasted Helps
Tracking what you eat is just as important as tracking when you eat. Fasted's meal logging feature lets you record meals during your eating window so you can spot patterns — are you getting enough protein? Are you eating too close to your next fast? The app's combination of fasting timer and meal log gives you a complete picture of your daily nutrition timing. Multiple schedule options (16:8, 18:6, OMAD, and custom) let you match your fasting protocol to your nutritional needs.
New to intermittent fasting? Start with our getting started guide. Looking for weight loss strategies specifically? Visit our weight loss pillar.
Frequently Asked Questions
Does black coffee break a fast?
No. Black coffee contains negligible calories (about 2-5 per cup) and does not trigger a meaningful insulin response. It may actually support fasting by increasing fat oxidation and suppressing appetite. However, adding sugar, cream, or milk does break a fast.
How much protein do I need during intermittent fasting?
Aim for at least 1.2-1.6 g of protein per kilogram of body weight daily, distributed across your eating window meals. Active individuals and those over 50 should aim for the higher end. For a 70kg person, that's 84-112g of protein per day.
What should I eat first when breaking a fast?
Start with something easily digestible and protein-rich — eggs, a small portion of fish or chicken, or a handful of nuts. Avoid large, greasy, or very sugary meals as your first food after fasting. Give your digestive system 15-30 minutes before eating a larger meal.
Do I need to take electrolytes while fasting?
Many people benefit from electrolyte supplementation during fasting, particularly sodium and magnesium. If you experience headaches, dizziness, fatigue, or muscle cramps during fasting, electrolyte deficiency is the most likely cause. A pinch of salt in water is the simplest first step.
Can I drink diet soda during my fast?
Technically, diet soda has zero calories. However, artificial sweeteners may trigger small insulin responses in some people, and carbonated sweetened drinks can increase hunger and cravings. If your goal is strict fasting for autophagy, skip it. For weight loss purposes, occasional diet soda is unlikely to significantly impact results.