If you’re someone who wakes up at 5 a.m. and within 15 to 30 minutes you’re at the pool or on the trainer then it can often be hard to eat something beforehand—but this can prove to be a costly mistake. There are several factors to consider when it comes to fasted training, primarily around sex differences and the type of session you are going to do. If you are a guy, then no, you can skip fueling before your workout, provided your session is low intensity, not over 90 minutes, and you refuel well after to facilitate recovery. If you are trying to hit higher work output (such as intervals, VO2 max efforts, or HIIT), then you need to have some food prior to or during your session to ensure you are able to hit the intensities you need to for optimal training adaptations. If you are a woman, then yes, you need to fuel first. We know exercising in a fasted state can slightly increase fat burning in women (less so than in men), but fasted exercise over the longer term causes dysfunction of the endocrine system, specifically sex hormones.
Your early morning workouts also provide you with a prime opportunity to practice your race morning meal. As I said in my “Ask Stacy” column about What Makes a Good Pre-Race Meal, the pre-race meal should become part of your race ritual: enough to make you feel calm and ready, but not enough to make your stomach turn.
Regardless of gender, the final consideration when thinking about fueling before a workout is your energy availability: You want to avoid being in a low energy availability state. As triathletes, you may have limited recovery time between sessions and fasted training is known to decrease appetite hormones and daily energy intake, so it is critical to really think about fueling for each session and recovering well. Every now and then it’s OK to do a short, low intensity session in a fasted state, but for long-term health and performance, it is best to eat something small beforehand to reduce the overall negative stress on hormone balance and avoid running yourself down.
More from Dr. Stacy Sims
When it comes to sports nutrition, you’ll be hard pressed to find an expert with as much academic and in-the-field experience as Dr. Stacy Sims. A leading nutritionist and exercise physiologist who has worked with hundreds of professional athletes and age-groupers, Sims is a go-to resource on hydration, nutrition, and sex differences. In 2017, she was named as one of the top four individuals changing the landscape in triathlon nutrition.
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