Should Women Train Fasted?

Fasted training—exercising without eating beforehand, typically after an overnight fast (10+ hours)—has sparked debate in the fitness and nutrition world. Some claim it’s a powerful fat-burning tool, while others warn that it may impair performance or lead to muscle loss.

So, what does the research actually say?

Fasted Cardio: Does It Burn More Fat?

Fasted aerobic exercise has been widely studied for its impact on fat oxidation and endurance performance. A meta-analysis found that while eating before exercise improved longer-duration endurance performance, it had no significant effect on shorter aerobic sessions.

What happens when you train fasted?

✔️ Your body increases circulating free fatty acids, meaning you mobilize more stored fat.

✔️ Fat oxidation improves over time, which may enhance metabolic flexibility.

✔️ Your performance may not suffer in short-duration exercise, but for extended endurance sessions, pre-exercise fueling can be beneficial.

However, here’s where it gets interesting: fasted training doesn’t mean you have to skip protein.

A 2021 study found that pre-exercise protein ingestion did not blunt the metabolic benefits of fasting but did influence muscle acetylation and mitochondrial adaptations. In other words, you can still reap the benefits of fat oxidation while supporting muscle function if you consume protein before training.

In fact, research confirms that protein (up to 40 grams of whey) doesn’t interfere with fat oxidation, whereas carbohydrates do. If your goal is to maximize fat burning and metabolic flexibility, training in a fasted state or with protein only may be an effective approach.

Fasted Resistance Training: Does It Affect Strength and Muscle Growth?

The research on fasted weight training is mixed - and it’s important to emphasize that these studies were conducted in men.

A meta-analysis found that intermittent fasting reduced body weight and fat mass without negatively impacting lean body mass. However, many of these studies involved training during a feeding window, meaning participants weren’t truly fasted.

For example, one of the best RCTs involving resistance-trained men found that training in the evening between meals combined with overnight fasting of 16 hours didn’t negatively affect strength or muscle mass, but did cause some fat loss.

So, what happens when you lift weights on an empty stomach?

✔️ A 2024 study showed no significant differences in strength or total training volume between fasted (16 or 12 hours overnight fasting) and fed (post-breakfast) resistance-trained individuals.

✔️Another study found that skipping breakfast before training resulted in fewer total reps for squats and bench press. However, a follow-up study found that even consuming a zero-calorie breakfast helped restore performance.

The problem with these studies is that they just looked at performance on a few sessions, rather than tracking adaptations over the course of weeks, months, or even years of consistent training. From a research standpoint, it remains unknown if fasted training negatively impacts muscle growth and strength gains over time, especially in women (the above trials all involved men).

That said, these findings suggest that some people tolerate fasted strength training well, while others may struggle with energy and performance. If you find yourself fatiguing quickly or lifting less than usual, consider consuming protein before training to maintain strength and performance.

Does Fasted Training Cause Muscle Loss?

One of the biggest concerns with fasted training is whether it leads to muscle breakdown. The reality? Fasting does increase muscle protein breakdown (MPB), but this doesn’t necessarily mean you’re losing muscle—especially if you refuel properly.

During fasting, your body still requires essential amino acids (EAAs) for organ function. When you’re not consuming protein, about 85% of these EAAs come from muscle tissue. However, this doesn’t mean you’re rapidly wasting away—it’s simply part of normal metabolic turnover.

Both muscle protein synthesis (MPS) and muscle protein breakdown (MPB) increase after fasted training, but net muscle balance remains negative until protein is consumed. 

Muscle is rebuilt only when amino acid availability is increased post-exercise. This means post-workout protein intake is essential to shift muscle balance from breakdown to growth.

Should Women Train Fasted?

Fasted training can be beneficial, but women’s physiology responds differently to fasting compared to men—particularly due to hormonal sensitivity and metabolic regulation. In fact, for some women, it can backfire due to greater sensitivity to energy restriction and hormonal disruptions.

One key player in this process is kisspeptin, a neuropeptide responsible for the regulation of hormones, metabolism, and appetite. Women not only have naturally higher kisspeptin levels and more kisspeptin-producing neurons, but they may also be more sensitive to its effects. Their hormonal cycles create a unique feedback loop that influences metabolism and energy balance. Additionally, other hormones—such as leptin, oxytocin, and dopamine—interact with kisspeptin, further contributing to the complexity of fasting in women.

When fasting, especially without adequate carbohydrate intake, women can experience a reduction in kisspeptin expression. Layering fasting on top of exercise stress can amplify this reduction due to the stress being imposed on the body. This can lead to:

✔ Appetite dysregulation—increased cravings and erratic hunger cues

✔ Disruptions in sex hormones—menstrual irregularities and lower estrogen, progesterone, and testosterone levels

✔ Metabolic slowdown—reduced thyroid function, making fat loss harder

✔Increased stress response—higher cortisol, leading to more belly fat storage

Moreover, women naturally rely more on fat oxidation for fuel compared to men, regardless of training intensity, meaning they may already be efficient at burning fat without needing to train fasted. Estrogen seems to increase the maximal activity of key enzymes in the fat oxidative pathway of skeletal muscle.

To be clear, fat oxidation is not the same as fat loss. Women don’t necessarily lose more fat than men from exercise, they simply rely more on fat for fuel. Men’s higher muscle mass and energy burn often result in equal or greater absolute fat oxidation than women, despite a lower percentage of total energy coming from fat.

One of the biggest concerns with fasted training is its impact on women’s reproductive and neuroendocrine function (the communication between the nervous and endocrine systems).
Fasting before exercise may exacerbate these issues, particularly in women who are already training intensely or restricting calories. Carbohydrate restriction also has a negative effect on the hypothalamic-pituitary axis independent of energy intake.

What this means for women training fasted:

✔ If you feel great training fasted, keep doing it! But if you notice irritability, fatigue, menstrual cycle changes (which won’t always be consciously “felt” or noticed), or performance drops, consider eating before workouts.

✔ Pre-exercise protein intake (instead of complete fasting) can protect muscle and help prevent an exaggerated stress response.

✔ Women with menstrual irregularities (amenorrhea, oligomenorrhea, anovulatory cycles, luteal phase defect, or excessively symptomatic menstrual cycles), high stress, or struggling with recovery should be cautious with frequent fasted training.

For women, fasted training should be used cautiously and strategically, rather than as a routine practice. While it may be viable in limited contexts—such as one low-intensity session per week—chronically training fasted carries more risks than benefits for most women. Given the potential neuroendocrine effects, including disruptions to hormonal balance, thyroid function, and metabolic regulation, it’s important to proceed conservatively.

The best approach is to prioritize metabolic and hormonal resilience first. In the absence of long-term data, err on the side of caution, ensuring adequate fueling around training to support recovery, hormone balance, and long-term health.

How Much Should You Eat Before Training?

A common question we get is: "If I need to eat before training, does it have to be 30–50g of protein like my first meal?"

The short answer? Not necessarily.

The 30–50 gram protein recommendation for your first meal is designed to maximize muscle protein synthesis and maintain muscle mass over time. However, pre-training nutrition serves a different purpose—it’s about fueling your workout while minimizing digestive discomfort.

In other words, the goal isn’t to maximize MPS but instead to give it a little bump while reducing stress hormones going into training. Of course, the meal after training should include ample protein to maximize muscle growth.

✔ If you’re strength training first thing in the morning, consuming 30–50g of protein before training may feel too heavy. In this case, a smaller protein dose (10–20g) is still beneficial, especially in the form of easily digestible sources.

✔ If you train later in the day and you’re eating a full meal beforehand, then yes—aiming for 30–50g of protein makes sense, as it contributes to your total daily protein targets.

✔ If you struggle with early-morning workouts, protein-only options can help preserve muscle while allowing your body to continue oxidizing fat efficiently. Adding carbs may be useful for higher-intensity sessions.

Also keep in mind that pre-exercise feeding is one of the best times to use protein powders due to the ability to get more protein with little digestive discomfort. While the diet as a whole should be based around whole food high-quality protein sources (meat, eggs, dairy, etc.), pre-workout represents a great strategic opportunity for protein powders.

The Takeaway: Should You Train Fasted or NOT?

Fasted training has its pros and cons, and whether it’s right for you depends on your goals, physiology, and how your body responds.

✔ For endurance training, fasted sessions may enhance fat oxidation and metabolic flexibility, but pre-exercise protein intake can protect muscle without negating the fat-burning benefits.

✔ For resistance training, results vary—some people experience no loss in strength, while others feel weaker. If you struggle with energy or performance, having protein before training may help.

✔ Muscle loss isn’t a concern unless fasting is prolonged and post-exercise protein intake is inadequate. Refueling after training ensures muscle repair and recovery.

✔Women should be cautious with fasted training, as they are more sensitive to energy deficits and hormonal disruptions. If fasting leads to irritability, fatigue, cycle irregularities, or performance declines, adjusting meal timing may be necessary.

If you’re set on training fasted, here’s how to do it without compromising performance:

• ✔Hydrate adequately and don’t overdo pre-workout caffeine
  ✔ Keep strength training sessions shorter and more intense
  ✔ Prioritize post-workout protein and refuel properly
  ✔ Consider a small protein-only pre-workout meal (e.g., whey shake, meat, EAA’s, BCAAs)

There’s no single right answer—listen to your body and adjust based on your individual response.

For a full personalized protocol, Contact Tania Atkin

Email: Hello @taniatkin.com

Reference: Dr. Gabrielle Lyon. 2023. Forever Strong: a New Science-Based Strategy For Aging Well.