Should a competing athlete explore intermittent fasting?

The human body is well suited to regular short periods of fasting, and a daily overnight fast of 8-10 hours or even longer is standard for most people.

The warrior diet involves eating one meal a day and restricting intake of macronutrients and calories for the rest of the day. For example, begin your day with water and vegetable juices.   -  Getty Images

The lockdown has allowed for great experimentation in athletes’ eating plans. Many have lost weight by fasting, an approach that is characterised by the absence of energy intake for a sustained period of time, which can range from several hours to days. Fasting is speculated to have various health benefits for the general populations as well as athletes. Studies have hypothesised that exercising in a fasted state forces the body to rely on fat as a fuel substrate instead of carbohydrates, thus inducing fat oxidation. The human body is well suited to regular short periods of fasting, and a daily overnight fast of 8-10 hours or even longer is standard for most people.

One diet, called the warrior diet, is based on one master biological principle: survival. It is based on a book by Ori Hofmekler, published in 2001. The author claims this lifestyle gives high energy, explosive strength and a leaner body. This diet aims to create a lifestyle that mimics how we were predestined to live, i.e., by triggering our survival instincts. The warrior diet requires 20 hours of underfeeding (which includes your sleep) followed by four hours of overfeeding at night. This causes nutritional stress not by restricting calories, but by cycling periods of under-eating and overeating to trigger stress response agents. The warrior diet involves eating one meal a day and restricting the intake of calories and macronutrients for the rest of the day. For example, start your day with water and vegetable juices. As the day continues, have light snacks like whey protein, berries, yogurts, fruits and veggies. Finally, at night, have large, dense, home-cooked meals.

This diet has a three-phase plan based on an individual’s fat loss goals:

Week 1: Detox. This improves the body’s capacity to remove toxins, thus helping the liver to neutralise substances that cause fat gain.

Week 2: Adaptation to fat fuel. Here, the body’s ability to utilise fat for energy is improved.

Week 3: Adaptation to carbohydrates. Slowly introducing carbs can improve the body’s ability to utilise they for energy.

Further stated benefits include:

  • Exercising on an empty stomach supports our sympathetic nervous system and promotes more fat loss.
  • It helps in weight loss, as the body uses the stored fat cell for energy.
  • It can reduce insulin resistance.

Reduction in hunger and mindful eating. The early stages of fasting last for about 24 hours after the last meal is eaten as the body adjusts to the absence of the nutrients that would normally be ingested during this time. Blood glucose is well maintained during this time as the liver glycogen store is progressively hydrolysed and released as glucose into the circulation. It is well established that the rate of carbohydrate utilisation is decreased in the fasted state and that an increased rate of fat oxidation meets the energy demand.

How fasting affects an endurance athlete

Training, as well as competition, for an athlete may be affected by prolonged periods of dietary restraint. While there may be some metabolic advantage to endurance training in the fasted state, in terms of an increased capacity for fat oxidation in the trained muscles, other evidence supports a potential benefit from the intake of nutrients before, during and after each training session. Fasting before exercise may result in more significant mobilisation of liver glycogen, increased gluconeogenesis and increased use of free fatty acids for fuel during exercise.

These adjustments may act against a potential reduction in performance by maintaining sufficient blood glucose for intense aerobic muscular activity. The results of the few well-controlled studies in athletes suggest that there is an increased rate of protein breakdown and fat oxidation during fasting.

The fasted state has different effects based on the type of exercise or training. Augmenting fat oxidation is a primary goal of fitness enthusiasts and individuals looking to improve their body composition. Performing aerobic exercises while in a fasted state continues to be a popular strategy to achieve this outcome.

Lipolysis is blunted during performance of higher- but not lower-intensity exercise when carried out in the fed state. However, this ignores the dynamic nature of the human body, which continually adjusts its use of substrate for fuel. There is evidence that greater utilisation of fat for fuel during a given time period is compensated by greater carbohydrate utilisation later in the day.

Need for high carbohydrate intake by endurance athletes

Carbohydrate requirements for endurance athletes is a debatable topic. The joint position of various organisations is that moderate exercise (one hour per day) requires 5-7gm per kilogramme of bodyweight per day (g/kg/day) of CHO, while moderate- to high-intensity exercise (one-three hours per day) mandates 6-10 g/kg/day. Ultra-endurance athletes with extreme levels of commitment to daily activity (four-five hours of moderate- to high-intensity exercise every day) may need up to 8-12 g/kg/day.

It is rather clear that increasing the availability of carbohydrate substrate will increase the rate of carbohydrate oxidation and decrease the rate of lipid oxidation at rest and during exercise. Ingestion of carbohydrates prior to exercise will stimulate insulin release, inhibiting fatty acid mobilisation from adipose tissue and thereby reducing the oxidation of plasma-derived fatty acids. In contrast, when carbohydrates are consumed after exercise has begun, lipolysis is not suppressed.

As a sports nutritionist, these are my observations for endurance athletes following intermittent fasting or the warrior diet:

  • Lowered energy in training
  • Slower recovery
  • Drain on energy as the week progresses
  • Higher DOMS (delayed onset muscle soreness)
  • Lowered body fat but lowered performance
  • Fatigue
  • Sleep issues
  • Irritation and anger
  • Weekend food rewards not allowed
  • Alcohol not allowed
  • Lowered immunity
  • Iron and bone metabolism issues in women

As an athlete, when you train with very low carbs (fasted states), your muscle glycogen reserves are subsequently lowered. Fatigue sets in faster, and a compromise in your speed, endurance and recovery will be visible. Fatigue, dizziness, lightheadedness, anxiety, insomnia, extreme eating disorder, constipation, irritability and hormonal imbalance are some of the issues you will face. You can lose muscle mass and hence power. You will require extreme willpower to push in training lasting over 40 minutes. With more sessions per week, you will be susceptible to chronic fatigue as well as lowered immunity.

Key areas of nutrition to think about for endurance athletes include:

  • How much do I need to eat and when? You need to think about periodising your diet in the same way as you do your training load. Don’t be swayed by weight loss alone.
  • Does it matter where I get my energy from? Should I be eating more protein, fat or carbohydrates?
  • What is my optimal body composition? Where is the sweet spot between being lean, eating enough to adapt to your training, avoiding illness or injury, and having enough power to make yourself go faster?
  • How do I travel and eat? What are some of the things I need to think about? Are there differences in my nutrition when I travel to cold or hot environments? What difference does altitude make?
  • As a female athlete, is there anything specific I need to consider to stay healthy?
  • Do I need supplements? What are the risks? What are the alternatives?

Athletes are constantly messaging me about fad diets or concepts that got their friends results. Sports and sports nutrition are serious sciences. Every athlete needs to invest in the science of eating right for their body. Getting into the warrior diet or intermittent fasting should be done with the guidance of a nutritionist, and data of body assessments and performance outputs should be made weekly if one attempts such diets. This is the only way to experiment if you set on trying out a new fad. Never attempt a diet plan if you are on medication or have lifestyle disorders. A blood test is advisable to warn of any potential issues due to a fad diet.