Fasted Workouts - Tips for Men and Women

Introduction

Fasted workouts, alongside intermittent fasting, have risen in prominence over the last few years. This is primarily due to the amount of high profile athletes and fitness influencers divulging their individual routines on popular podcasts and social media. 

But does fasting before you workout affect both men and women's bodies the same?

In this article we’ll discuss the differences and whether it’s something for you to implement into your training regime.

At a glance

• Fasted workouts are more effective for men as they tend to have higher testosterone levels, making them more resilient to the stress that a lack of food alongside exercising can have on the body.

• Fasted workouts can negatively impact a woman's reproductive hormones and cause menstrual irregularities.

• Avoid fasted workouts when pregnant, breastfeeding, or if you have a history of disordered eating or certain medical conditions (diabetes, adrenal issues).

• Consume electrolytes before, during, and after workouts to prevent dizziness and fatigue.

What is a fasted workout?

A fasted workout is simply the act of working out on an empty stomach, typically after 8-12 hours without food. It’s claimed that fasted workouts enhance fat burning and improve your metabolic flexibility (the body’s ability to switch between different fuel sources). However, the science is nuanced, and effectiveness varies significantly between men and women due to physiological differences.

The Science Behind Fasted Workouts

How Your Body Responds to Fasting

When we exercise, our bodies use carbohydrates (glycogen) and fats for fuel, with a preference for carbohydrates if exercising after eating (in a fed state).

However, when we fast we have lower glycogen levels in our bodies and this forces the body to rely more heavily on fat oxidation (where the body breaks down fatty acids to produce energy). When our glycogen levels are too low our bodies produce a hormone called glucagon, which raises blood glucose levels, and promotes fat breakdown (lipolysis) turning it into usable fatty acids.

Medical Research: Benefits and Risks

Studies have shown that fasted aerobic exercise can improve body composition and reduce fat mass, especially in overweight individuals. This is due to the increase in glucagon as mentioned above. However, research indicates that while fat burning during exercise is higher when fasted, this doesn't always translate to greater 24-hour fat loss compared to fed exercise.

There are some potential downsides to training whilst fasting to be aware of. 

Because your body's glycogen levels are depleted it can lead to muscle protein breakdown (where your muscle proteins are degraded). You can also experience a decline in your performance, especially during high-intensity workouts due to fatigue and the increase in cortisol which is created by the body as a stress response. Women primarily can also experience hormonal disruption and reproductive health issues.

Gender Differences in Fasted Workouts

Why Men and Women Respond Differently

The fluctuations of estrogen and progesterone in women significantly influence their response to fasted exercise. 

Prolonged fasting causes stress to our bodies and elevates cortisol, a natural stress response. For women, the impact of this is more pronounced as their bodies are more sensitive to stress, as well as energy deficits, a by-product of not eating for a lengthy period of time.

All this can negatively impact a woman's reproductive hormones and cause menstrual irregularities.

Something to consider is that women are naturally more efficient at fat burning even when fed, meaning additional benefits from fasted training may be less pronounced or potentially counterproductive.

Fasting and working out seems to have more benefits for men as they tend to have higher testosterone levels which makes them more resilient to the stress that fasting places on their bodies. It means they are likely to experience improved fat metabolism and endurance without the same degree of hormonal disruption seen in women. 

Specific Considerations

How Long Should You Fast?

Our bodies enter into a fasting state when we have not eaten for 10-12 hours. This is why working out in the morning on an empty stomach has become so popular for a lot of people as it is easier to fast overnight whilst sleeping. Even longer periods of fasting (16-24 hours) can enhance fat oxidation but may impair performance during intense exercise.

It’s best to listen to your body. If you choose to start fasted workouts, take it slow. Start with shorter fasting windows and lower intensity training, gradually increasing as you adapt. If you start to feel fatigued or nauseous then you should look to tweak the time you fast for, or the intensity of your training.

5 Optimal Fasted Workouts for Men and Women

Tips for Safe and Effective Fasted Workouts

Hydration and Electrolytes

The need to stay hydrated is even more important when you have fasted, make sure that before, during, and after workouts you consume electrolytes, especially for longer or intense sessions. This will go a long way to preventing dizziness and fatigue.

Timing Your Workouts

Experiment with different timings. Early morning after overnight fasting is common, but find what works for your body and schedule.

Nutrition Post-Workout

When it’s time to break your fast, make sure you have a nutrient-dense meal at the ready. Get plenty of protein for muscle repair, complex carbohydrates for glycogen replenishment, and healthy fats for overall health.

When to Avoid Fasted Workouts

Fasted workouts can be hard, and can place a lot of stress on your body. Avoid if you're pregnant, breastfeeding, have a history of disordered eating, certain medical conditions (diabetes, adrenal issues), experience persistent fatigue or hormonal imbalances, or are new to exercise/fasting.

Conclusion

Fasted workouts can help with fat burning and metabolic health, but just how effective it will prove will depend on the individual. 

The science would suggest that men would have more to gain as their bodies generally tolerate fasted training better, while women need to be more mindful of the hormonal balances that could occur and their overall bodies stress response. Making sure to stay safe is a key priority when thinking about a fasted workout. Listen to your body, prioritize hydration and post-workout nutrition, and seek professional guidance when needed. 

As with all training regimes, consistency is key in order for you to see any real progress. Good luck out there, and remember to stay safe.

FAQs About Fasted Workouts

• Is it good to do fasted workouts? If you exercise when your body is fasted, it will stimulate peripheral fat oxidation, resulting in increased fat utilization and weight loss.

• Do you burn more fat if you workout on an empty stomach? Exercising in a fasted state can increase the percentage of fuel utilized from fat, but it’s not been proven to have long-term effects on stored body fat.

• How long should a fasted workout be? The optimal time for a fasted cardio session should be around 30 - 45 minutes. Longer sessions can feel very fatiguing due to the large calorie deficit.

• Can you build muscle if you workout fasted? Fasting won't enhance your strength training, but strength training will help preserve your muscles if you fast.