The Truth About Fasted Workouts and Women’s Health: What You Need to Know

Intermittent fasting and fasted workouts have gained popularity in recent years, often advertised as powerful tools for weight loss and metabolic health. However, while they may offer some benefits to certain populations, they may not be the best strategy for women, especially when hormonal health and metabolic function are considered.

The Appeal of Fasting Workouts

The concept of fasted workouts is simple: By exercising on an empty stomach, typically after an overnight fast, the body is believed to tap into fat stores more efficiently, leading to fat loss. Some women skip breakfast before working out because they’re not hungry, while others believe it will help them burn more fat. Popular culture often presents intermittent fasting as a quick fix for weight loss, comparable to the keto diet or Atkins. However, what works for men may not be ideal for women, and the small amount of research we have on fasted workouts in women suggests there are significant differences in how each gender responds to fasting.

The Impact on Women’s Physiology

Women are biologically different from men, especially when it comes to how they respond to stress. Fasting and fasted exercise introduce stress to the body, triggering a stress response that is useful when balanced but harmful when overdone. Studies on men and animals have shown some benefits of fasting and fasted exercise, such as improved fat metabolism and insulin sensitivity. However, women, due to their fluctuating hormones and reproductive needs, may experience different effects.

One key player in the female body’s response to fasting is kisspeptin, a neuropeptide that regulates reproductive hormones, metabolism, and appetite. Kisspeptin activity is disrupted when the body senses low energy availability, such as from prolonged fasting and fasted exercise, leading to negative effects on hormone balance, reproductive health, and metabolism​.

Hormetic Stress and the Female Body

Fasting and exercise are forms of hormetic stress—mild stress that promotes resilience and health. When applied in small doses, hormetic stress can have benefits like improved metabolism, lower blood pressure, and reduced oxidative stress. But for women, when these stressors are overused, they can have the opposite effect, leading to hormonal imbalances, menstrual irregularities, and even weight gain​. Women’s bodies are much more sensitive to these stressors due to the infradian rhythm, which governs their hormonal cycles throughout the month.

Cortisol and Stress Hormones

When women engage in fasted workouts, they’re often doing so when their cortisol (the stress hormone) is already elevated, particularly in the morning. High cortisol levels, combined with the energy demands of exercise, can disrupt blood sugar balance, decrease thyroid activity, and actually promote fat storage. Additionally, the decrease in kisspeptin further interferes with sex hormones and metabolism​.

The Risks of Fasted Workouts for Women

While men may experience improved fat metabolism and endurance from fasted workouts, many women report symptoms like increased fatigue, anxiety, disrupted menstrual cycles, and fertility challenges. Over time, this chronic stress on the body can lead to conditions such as hypothyroidism, insulin resistance, and an increased risk of injury​.

What to Do Instead: Fueling for Success

Rather than skipping breakfast and working out in a fasted state, women benefit more from eating a balanced snack or meal before exercise. Carbohydrates are particularly important to fuel muscles and prevent that "hitting a wall" feeling mid-workout. Pre-workout nutrition can also preserve muscle mass, balance blood sugar, and enhance performance.

Some pre-workout snack ideas to consider (mainly carbohydrates + small amount of protein):

• Fruit (banana, orange, berries, apple, pear)

• Dried fruit (dates, apricots, cherries)

• Fruit leather

• 2-3 dates + peanut butter

• Whole grain toast + slice of organic cheese

• Unsweetened apple sauce + cinnamon

• ½ medium sweet potato + cinnamon + drizzle of nut butter

• Fruit based bar (such as a Lara bar or Kind Pressed Fruit bar)

In Summary

Fasting workouts may sound appealing, but for women, they are often more harmful than helpful. The small amount of research we have suggests that women’s bodies require a more thoughtful approach, especially when it comes to fueling workouts. Prioritizing balanced nutrition before and after exercise will not only support hormonal and metabolic health but also optimize performance and recovery.

Resources

Hudson, A. D., & Kauffman, A. S. (2022). Metabolic actions of kisspeptin signaling: Effects on body weight, energy expenditure, and feeding. Pharmacology & Therapeutics, 231, 107974. https://doi.org/10.1016/j.pharmthera.2021.107974

Navarro, V. M. (2020). Metabolic regulation of kisspeptin: The link between energy balance and reproduction. Nature Reviews Endocrinology, 16(8), 407–420. https://doi.org/10.1038/s41574-020-0363-7