Is fasting good or bad?

It’s a big question right now, with plenty of so-called experts sitting on both sides of the fence. And like most things in health and fitness, it depends.

Let’s look at this through a female lens, because that’s where a lot of the current debate sits online. If you spend any time on social media, you’ve probably come across two very strong voices in this space.

On one side, you’ve got Stacy Sims, a researcher and coach who has done an incredible job bringing attention to peri-menopause and menopause, and the importance of strength training for women. She’s right on a lot of things too: strength training is hugely beneficial for women, with knock-on benefits for muscle, bone density, hormones, mental health, and longevity. One of her key messages is around getting protein in earlier in the day, and steering most women away from fasted training.

On the other side, you’ve got Mindy Pelz, author of Fast Like a Girl, who takes a different approach, suggesting that fasting can actually be powerful for women when it’s aligned with their hormonal cycle.

Two very smart women with two very different viewpoints. So who’s right?

This is where things get interesting, because the problem with social media is that nuance doesn’t perform well. To build an audience, you need strong opinions, clear statements, and black-and-white answers. There’s no place for “it depends.” But in the real world, especially in coaching, it almost always does depend. Squats might be one of the best exercises on the planet, but for someone in a wheelchair, not so much. Context matters.

So when it comes to fasting, the first question I always ask is simple: why are you doing it, and what are you actually trying to achieve?

Take fat loss as an example. Yes, fasting can be a genuinely effective strategy, because for many people, skipping breakfast naturally reduces calorie intake without having to overthink food choices all day. And despite what you might hear online, the reality at a basic level is simple: most people are eating too much and moving too little.

What about hormones like cortisol? There’s a lot of noise around this, but the reality is that cortisol is supposed to be higher in the morning, since that’s part of what helps you wake up, feel alert, and get moving. It should then gradually lower across the day so you can wind down and sleep at night. So fasting in the morning doesn’t automatically “mess up your hormones” in most healthy people.

What about muscle loss? Fasting itself doesn’t cause muscle loss, but it can make it harder for some people, especially women, to consistently hit their protein requirements across the day. And that’s where the trade-off begins, because many women already struggle to eat enough protein as it is. Add fasting on top of that, and it can become even more challenging.

So you end up with two competing truths: fasting can help reduce calories and support fat loss, but it can also make proper nutrition harder to achieve. Both can be true at the same time.

There’s also something else worth mentioning. We live in a world of constant eating, snacking, grazing, and food available everywhere we look. Our ancestors didn’t live like that. They had periods of eating and periods of not eating, not by design but by necessity. In that sense, fasting isn’t new, it’s just less common now. And there may be some value in occasionally stepping away from constant eating, giving the digestive system a break, and bringing a bit more rhythm back to when we eat.

But here’s the key point: too much of anything becomes a problem. If you’ve never fasted before, experimenting with it might be useful, so pay attention to how your body responds. Energy, mood, training, hunger, all of it is feedback worth listening to. But if you’ve been fasting for a long time and it’s become rigid, stressful, or obsessive, it might be worth experimenting in the other direction instead, adding breakfast back in, prioritising protein earlier in the day, and seeing how that feels, because your body responds to change.

The goal isn’t to follow a perfect rule. It’s to find what actually works for you, in your life, with your goals. Not Instagram’s version of you.