Fasting has become increasingly popular as a therapeutic strategy for managing chronic ailments and increasing fat oxidation and sporting performance. But fasting is not for everyone, with particular considerations for women, who might be harming their health when training in a fasted state.

The Benefits of Fasting

Intermittent fasting and time-restricted feeding have left a long-term impression on the way we eat, Ian Craig, founder of the Centre for Integrative Sports Nutrition, told the Epoch Times. Fasting is a popular strategy for addressing various health concerns, such as optimizing blood lipid profiles, reducing oxidative stress and inflammation, facilitating cellular detoxification, promoting gut rest, managing weight, and stabilizing insulin levels. According to Mr. Craig, there has been a notable surge in the adoption of fasted training among athletic communities, underscoring its relevance in the realm of sports performance.

A 2016 study published in The Journal of Translational Medicine, might have added to the surge in its popularity. The researchers investigated the effects of time-restricted feeding on 34 resistance-trained men. Participants were divided into two groups: one consumed food within an eight-hour window (the fasting group), while the other followed a standard 12-hour eating window (the normal eating group). Importantly, both groups maintained similar caloric intake throughout the study period. After eight weeks, results indicated that the fasting group experienced a significant reduction in fat mass while preserving muscle mass compared to the normal eating group.

Fasted training has gained further traction due to a  2009 study published in the Journal of Strength and Conditioning Research. This study highlighted that restricting calorie intake by up to 40% over a three-week period, coupled with overnight fasting, could enhance a cyclist’s power-to-weight ratio without compromising their endurance cycling performance.

Additionally, research published in The British Journal of Nutrition sought to elucidate the impact of aerobic exercise performed in fed versus fasted states, particularly focusing on carbohydrate and fat metabolism. The findings underscored a significant increase in fat oxidation during exercise in a fasted state compared to a fed state.

Indeed, it’s no surprise that training in a fasted state has skyrocketed in popularity, and rightfully so. With a growing body of research highlighting its potential benefits for fat oxidation, metabolic flexibility, and performance enhancement, fasted training has gained widespread attention among athletes and fitness enthusiasts alike.

The Downside of Fasting

Mr Craig elucidated that while restricting fuel before and during exercise can induce a state of cellular stress, which may yield benefits, it also has the potential to compromise an athlete’s recovery capabilities and performance. He highlighted that exercising in a fasted state may place increased strain on the adrenal glands, potentially impairing the function of thyroid hormones and other anabolic processes. Importantly, he emphasized that the majority of studies on fasting have been conducted on young, active males, who possess a degree of physiological resilience and can adapt relatively easily to short-term challenges.

It’s crucial to recognize that each athlete is unique and may not derive the same benefits from fasted training. Mr. Craig emphasized that when working with clients, especially an “over-enthusiastic amateur or elite athlete,” the risk of adrenal fatigue must be taken seriously. Such individuals may already experience compromised endocrine function, including the pituitary, adrenal, gonadal, and thyroid systems, which could be further exacerbated by a fasting regimen, leading to increased cortisol release in the absence of sufficient nourishment.

Mr. Craig warns that intermittent fasting could further weaken the adrenals, particularly in individuals who are already overtrained or under significant stress, rendering it an unsuitable approach that could prove detrimental.

He further underscores the importance of recognizing that while many studies and fasting regimens tout short-term physiological benefits such as enhanced insulin sensitivity and weight management, the long-term implications may vary considerably.

A study conducted in 2008 indicated that training while in a glycogen-depleted state, such as during fasting, could serve as a beneficial strategy for endurance athletes early in the season. This is because metabolic capacity holds greater significance than muscle strength for these athletes. The study suggests that the adverse effects of the altered hormonal environment on muscle mass are likely to have minimal impact on their long-term performance. However, as training intensity increases, replenishing glycogen stores becomes essential. For motor endurance athletes, the potential negative effects of glycogen-depletion on muscle mass should be taken into consideration. Elevated cortisol levels may restrict skeletal muscle hypertrophy.

Another study conducted in 2016 highlighted that adequate glycogen levels or food intake before exercise could hinder post-exercise muscle protein synthesis. The recommendation suggests that athletes should “fuel for the work required.” Carbohydrate availability could be deliberately reduced before training to promote a ‘work-efficient approach to training.’ However, if the objective of training sessions is to ‘accomplish the highest workload possible over extended durations,’ then sufficient carbohydrates should be consumed within the 24-hour period prior to and during the specific training session.

Why Fasted Training Might Harm Women’s Health

Candace Vermaak, a respected lecturer at the University of Stellenbosch’s Department of Exercise, Sport, and Lifestyle Medicine, underscores a critical point: fasted training isn’t universally suitable, especially for women. She told the Epoch Times that cortisol levels naturally peak in the morning, potentially exacerbated by intense fasted workouts. This heightened cortisol release, particularly impactful for women, can lead to chronic elevation, disrupting the delicate balance of sex hormone production. Such disruption may impede not only athletic performance but also overall well-being by interfering with the regulation of estrogen and testosterone levels.

When embarking on fasted training, it’s crucial to understand the delicate balance between utilizing fat stores for energy and the potential risk of tapping into muscle reserves, particularly if fat levels are low or hormonal fluctuations come into play. Vermaak highlights that excessive or high-intensity exercise in a fasted state can exacerbate this risk, placing undue stress on sex hormones and inhibiting their release. This disruption can detrimentally affect women’s overall function and performance.

How to Make Your Training Work for You

Drawing from his extensive experience working with clients, Mr Craig often recommends reintroducing a nourishing breakfast to those who were following a strict fasting regime to support morning training sessions. This approach often helps them to optimize body composition, enhance training performance, and facilitate better recovery dynamics between exercise sessions.

He further explains that what is often missing in the interpretation of the term ‘intermittent fasting’ is the word intermittent. These approaches must be used intermittently (not all the time) depending on the context of an individual’s current state of health, training patterns, stress levels and genetic predispositions.

Vermaak advocates for a measured approach, recommending no more than two to three fasted training sessions per week or limiting such sessions to low-intensity activities. A 2020 review of the literature published in the Open Access Journal of Sports Medicine suggests that endurance athletes avoid high-intensity training while fasting. When fasting, only low-intensity training is recommended to ensure athletes recover properly to increase performance.

It’s an individualized endeavor, requiring careful consideration of factors such as blood sugar levels, stress levels, sleep quality, and metabolic profile before delving into fasted training, Vermaak says. Prioritizing these assessments ensures optimal performance and well-being while mitigating the potential risks associated with training in a fasted state.

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