What Is Intermittent Fasting (IF)?
Intermittent fasting is a dietary pattern in which eating and fasting periods alternate throughout the day or week. Unlike traditional diets, IF specifies when to eat, not what. For athletes, it can be an effective tool for improving body composition.
Key Benefits for Athletes:
- Improved Insulin Sensitivity — lower insulin levels improve fat burning
- Increased Growth Hormone — fasting can increase GH secretion 2–5 times
- Autophagy — cellular renewal, reduced inflammation after intense training
- Simplicity — fewer meals = less planning, less calorie counting
📊 Most Popular IF Protocols
| Protocol | Fasting Window | Eating Window | Suitable | Difficulty |
|---|---|---|---|---|
| 16:8 (Leangains) | 16 hr | 8 hr | For most athletes | Lightweight |
| 18:6 | 18 hr | 6 hr | For Fat Loss | Intermediate |
| 20:4 (Warrior Diet) | 20 hr | 4 hr | For Experienced | Hard |
| OMAD | 23 hr | 1 hr (1 meal) | Extreme Fat Loss | Very Difficult |
| 5:2 | 2 days/week (500–600 kcal) | 5 normal days | Flexible Option | Intermediate |
| Alternate Day | Every Other Day | Every Other Day | Aggressive Fat Loss | Hard |
🏋️ Combining Training with IF
This is the most frequently asked question: how to train while fasting? The answer depends on your goals:
🌅 Morning Training (During Fasting)
Suitable for endurance sports and cardio. Fasting increases fat oxidation. Before training—BCAA or black coffee. After training—the first meal within the eating window.
🕐 Training Before the Eating Window
The optimal option. You train at the end of the fasting period (14–15 hr), and immediately after training you open the eating window. This way you take advantage of the anabolic window.
🌙 Training in the Eating Window
Suitable for strength sports. Before training, eat carbohydrates + protein. This will give you more energy for heavy weights.
🧬 BCAA During Fasting
10 g BCAA before training during fasting may reduce muscle catabolism. However, technically this "breaks" the fast—decide based on your priorities.
🍽️ Sample 16:8 Daily Plan
| Time | Activity | Notes |
|---|---|---|
| 07:00 | Wake up, water + black coffee | Allowed during fasting: water, coffee, tea (without sugar) |
| 08:00–09:00 | Training (strength) | Before training: BCAA 10g or black coffee |
| 12:00 | 🚀 First meal (window open) | Largest Meal of the Day: 40–50g Protein + Carbohydrates + Fats |
| 15:00 | Second Meal | Medium: 30–40g Protein + Vegetables |
| 18:00 | Third Meal (Before Closing) | 30–40g protein + healthy fats (for slow absorption overnight) |
| 20:00 | 🔒 Eating window closed | Water only, herbal tea |
📈 IF Effect on Muscle Mass: Myths and Truth
⚠️ Who Is IF Not Suitable For?
🤰 Pregnant and Breastfeeding
IF is categorically not recommended during pregnancy and breastfeeding — a constant supply of nutrients is required.
🍬 People with Diabetes
People with type 1 diabetes should avoid IF without medical supervision. Type 2 — only after consulting an endocrinologist.
🧑🤝🧑 Teenagers
A growing body needs a constant flow of nutrients. IF is not recommended under 18 years of age.
🏋️ Elite Strength Athletes
For professional strength athletes who need ~4000+ kcal per day, IF may be impractical — it is difficult to consume that many calories in 8 hours.
🧪 IF and Sports Performance: What Science Says
| Research Area | Result | Level of Evidence |
|---|---|---|
| Strength Preservation | 16:8 IF for 8 weeks — strength indicators did not change if protein was sufficient | High |
| Muscle mass | Slight decrease in lean mass (0.5–1 kg per 12 weeks) if the deficit is large | Intermediate |
| Endurance | Aerobic endurance does not decrease during fasting; anaerobic may drop 5–10% | Intermediate |
| Fat burning | 3–8% higher fat burning compared with calorie restriction | High |
| Inflammation Reduction | CRP and IL-6 markers decrease noticeably after 4 weeks of IF | High |