Intermittent fasting (IF)

Intermittent Fasting (IF) is a nutritional approach that alternates periods of eating and abstaining, using flexible time windows.

For a more in-depth review, see the complete guide to proper nutrition — a foundational guide from the expert team at Sport Zona.

What it is

Intermittent fasting (IF), also known as periodic fasting, is a dietary regimen that focuses on alternating periods of food intake with periods of abstaining from food. It is not a diet in the traditional sense, as it does not restrict specific types of food or calories, but rather dictates the time frames within which a person can eat. The goal is to create a metabolic switch where the body depletes its glycogen stores and begins to use fat as its primary energy source.

There are various protocols for implementing intermittent fasting, with the most popular including the 16/8 method (16 hours of fasting, 8-hour eating window), 5:2 (two days of restricted calorie intake per week), and Eat-Stop-Eat (24-hour fast once or twice a week). The choice of protocol often depends on individual preferences, goals, and lifestyle. During fasting periods, it is generally permissible to consume water, black coffee, and unsweetened tea to maintain hydration and alleviate hunger.

How it works

The mechanism of intermittent fasting is related to changes in the body's hormonal balance and metabolism. In the absence of a constant influx of food, especially carbohydrates, insulin levels drop significantly. This low insulin level signals the body to switch from burning glucose to burning fat for energy – a process called metabolic switching. This transition leads to the mobilization of stored fat reserves and the release of fatty acids, which can be converted into ketone bodies and used by the brain and muscles.

Key physiological changes include:

• Lowered insulin levels, which aids in fat burning.
• Increased Growth Hormone (GH) levels, critical for muscle growth and repair.
• Pronounced lipolytic effect, leading to the breakdown of fat stores.
• Activation of autophagy, a cellular cleansing process.

These adaptations help with weight management while also offering potential benefits for cellular health and recovery.

Why it's important for athletes

For athletes, intermittent fasting can offer several advantages, particularly in terms of body composition control and improved metabolic flexibility. Shifting to a mode where the body is more efficient at burning fat can be beneficial for athletes aiming to reduce body fat while preserving muscle mass. Studies suggest that training in a fasted state can increase fat burning during physical activity.

However, it is important to note that intermittent fasting must be carefully adapted to the training regimen. To avoid muscle mass loss, adequate protein intake is essential. Protein intake recommendations for active individuals are around 1.6-2.2 g/kg of body weight, distributed within the eating window. Sports federations and the ISSN (International Society of Sports Nutrition) emphasize the importance of an individual approach and monitoring performance and recovery. While some athletes may benefit from IF for improving endurance training metabolism, strength athletes must be particularly cautious to ensure sufficient energy and nutrients for anabolic processes and optimal recovery after high-intensity training.

Related terms

• Autophagy — A cellular self-cleaning process that is enhanced during fasting periods, improving cellular health and recovery.
• OMAD (One Meal A Day) — An extreme form of intermittent fasting where the entire daily food intake is consumed in a single meal, often practiced for weight management.
• Ketosis — A metabolic state where the body uses fat and ketone bodies for energy, which can be induced through prolonged fasting or a ketogenic diet.
• Anabolism — The process of building tissues, such as muscles, which is the opposite of catabolism and is critical for muscle recovery and growth, requiring adequate nutrient intake.