What are the benefits of fasted training?
Joel Enoch explains all you need to know about fasted workouts, including their pros and cons, and whether they are suitable for Ironman athletes
What is a fasted workout?
Fasted training usually refers to training with low carbohydrate availability. This can be achieved in several ways, including: not eating carbs after a first session, then training again; training after sleep; long sessions where carb stores are drained in the initial part of the session; or a diet low in carbs.
Carbs are easy for the body to access if intensity is high and energy is needed quickly, but you store little; fat’s the preferred option when not too out of breath (as it takes oxygen and time to produce energy from fat) as even lean triathletes store lots of energy as fat.
What are the benefits of fasted training?
There’s good evidence that if you train in a carb-depleted state, you encourage your body to burn fat as fuel at increasingly higher intensities. This may be useful for ultra-endurance, low-intensity exercise; the reduction of unwanted body fat (5-7% over a season); or to re-programme the system for athletes looking to go long, who have a power-sport background and burn carbs preferentially at a very low level of effort.
What are the disadvantages of fasted training?
However, our bodies have been shown to perform best when given the combination of fat and carbohydrate as fuel. Plus, fat burning reduces our ability to use carbohydrate – typically meaning no improvement in performance in an Ironman race and also reductions in training intensity. Neither of which are ideal.
What is the best practice?
Best practice is to train the body to be able to burn fats efficiently, but still utilise carbs for harder efforts, recovery and race day. This can be done in the following ways:
Longer (2-3hrs), low-intensity pre-season rides with low carbohydrate availability.
Daytime carbs followed by hard evening sessions, low carb-recovery, sleep and then low-intensity am training before
high carb breakfast.
Middle three days of recovery weeks eating low-carb diet.
Increase carbohydrate for races and hard training sessions.
Race-specific training fuelled same as event.
Some triathletes insist the body can be retrained to burn fat while maintaining maximal performance. However, research suggests this is simply reinventing the wheel, as our bodies are already designed to utilise both carbohydrate and fat for best performance.
Joel Enoch is a sports scientist and triathlon coach who’s helped athletes of all abilities reach their multisport goals.
- Are raw vegetables always better for you than cooked ones?
- What are the most important nutrients endurance athletes need in their diet?
- Do female athletes need to carb-load more, or less, than male ones before a race?
- What is a detox and is it necessary?
- Body composition testing: what’s the best and most accurate test?
- Should you maintain your racing weight over winter?
Joel Enoch
Triathlon coach and performance lifestyle advisor 
