The Most Effective Way to Lose Fat and Build Lean Muscle as a Woman

Fasted cardio is one of those fitness trends that sounds like it should work, right? You wake up, skip breakfast, work out on an empty stomach, and your body burns stored fat for fuel. But I can tell you—as a nutrition consultant and someone who did this religiously—the answer is a lot more nuanced than the internet makes it seem. I break the whole thing down in my latest podcast episode, including the research and the hormone piece that nobody talks about. Plus, I’m sharing what I did differently after my second pregnancy that led to losing 7% body fat.

What Is Fasted Cardio?

Fasted cardio is exactly what it sounds like: performing cardiovascular exercise (running, cycling, walking, etc.) after an overnight fast, typically first thing in the morning before eating anything. The idea is that because your glycogen stores are partially depleted from sleeping all night and your insulin levels are low, your body will tap into stored fat for energy instead of using carbohydrates. And here’s the thing: that part is technically true. Your body does oxidize more fat during a fasted workout. A meta-analysis of 27 studies involving 273 participants confirmed that aerobic exercise performed in a fasted state does increase fat oxidation compared to exercising in a fed state. So the theory isn’t completely made up.

But fat oxidation during a single workout and actual fat loss over time? Those are two very different things. And that distinction is where fasted cardio falls apart as a strategy, especially for women.

Does Fasted Cardio Lead to More Fat Loss?

No, and the research is solid on this. A landmark study published in the Journal of the International Society of Sports Nutrition looked at this exact question in 20 healthy young women. The women were randomly assigned to either a fasted or fed group. Both groups performed one hour of steady-state cardio, three times per week, for four weeks while following a calorie-controlled diet.

The result? Both groups lost weight and fat mass. But there was no significant difference between the fasted and fed groups. None.

Why I Want You to Stop Skipping Breakfast

So yes, your body burns more fat during a fasted workout. But it compensates later in the day by burning more carbohydrates and less fat. Your body is dynamic. It adjusts. Over 24 hours, the net effect on fat loss is essentially the same whether you ate before your workout or not. This is what I talk about in the podcast episode, and it’s one of those findings that I think every woman needs to hear before she skips another breakfast in the name of “maximizing fat burn.”

Why Fasted Cardio Can Be Particularly Problematic for Women

Here’s where it gets really important, and this is the piece that most fitness content leaves out entirely. Our hormonal systems respond differently to fasting and exercise stress than men’s do. When you exercise in a fasted state, your body perceives it as a stressor. Cortisol rises. And when cortisol stays elevated chronically (which happens when you combine fasted training with under-eating, poor sleep, or a stressful life), it can disrupt your menstrual cycle, impair thyroid function, increase fat storage around your midsection, and break down muscle tissue.

And if your goal is body recomposition (losing fat while building muscle), that’s the exact opposite of what you want.

The Approach That Backfired

This is something I experienced firsthand. After my first son, Wilson, I did fasted cycling classes multiple times a week. I was barely eating. I thought I was doing everything right. But my body looked puffy, I felt inflamed, and I wasn’t getting stronger. My body wasn’t reflecting the work I was putting in. In the podcast episode, I go much deeper into what was happening hormonally and why that approach backfired.

The Muscle Problem Nobody Talks About

Beyond the hormonal impact, fasted cardio has another issue that doesn’t get nearly enough attention: it’s not great for preserving muscle mass.

When you train in a fasted state, especially if you’re also in a caloric deficit, your body can break down amino acids from muscle tissue for energy. That means you could be losing the very thing that changes your body composition. Muscle is metabolically active tissue. The more muscle you carry, the more calories you burn at rest. It takes up less space than fat. It’s what gives your body shape and definition! It’s truly magic.

If you’re spending your mornings doing fasted cardio and then wondering why your body isn’t changing despite all the effort, this could be a big piece of the puzzle. You’re burning calories, sure. But you may also be burning through the muscle you need to actually look and feel different.

What to Do Instead If Your Goal Is Body Recomposition

First and foremost, get my Stronger Body Blueprint! It outlines everything you need to know, step by step, to lose body fat and build muscle. Additionally, in the podcast episode, I walk through exactly what I changed between my first and second postpartum experience. The short version: I stopped chasing fat burn and started building muscle. Here’s what that looked like:

1. I started eating before training. Nothing super filling or elaborate. Sometimes it was a protein coffee or half a banana with a small handful of walnuts or Greek yogurt with honey. The point was giving my body fuel to actually perform and recover. Pre-workout nutrition doesn’t need to be complicated, but it does need to exist!
2. I prioritized strength training over cardio. I shifted from cycling classes and long cardio sessions to lifting 3-4 times per week, 30-45 minutes max per session. I started focusingb on compound movements with progressive overload. This is what actually builds muscle and changes your shape.
3. I ate enough. This is the one I talk about constantly because it’s the one most women get wrong. You can’not ‘tbuild muscle in a body that’s chronically underfueled. Carbohydrates are part of the equation, too. Protein at every meal (at least 25 grams) is a non-negotiable. And eating enough to support your training is what allows your body to actually do the work of recomposition.

15 months later, I had gained 9 pounds of muscle and dropped 7% body fat. Same scale weight as my first postpartum body, completely different composition.

But What If You Like Working Out on an Empty Stomach?

I want to be clear about something: if you genuinely feel better training without food in your stomach, that’s okay! Some people don’t tolerate eating before exercise. Some people feel nauseous or sluggish. Pre-workout fuel is ultimately a personal preference, and I talk about this in the episode too. The issue isn’t occasionally training fasted. The issue is building a whole fat loss strategy around it, especially if you’re also under-eating, over-exercising, or dealing with hormonal stress. That combination is where fasted cardio stops being neutral and starts working against you.

What to Take Away

Fasted cardio does increase fat oxidation during exercise, but it does not lead to greater fat loss over time. The research on women specifically found no difference in body composition between fasted and fed groups when calories were equated. For women, chronic fasted training can elevate cortisol, disrupt hormones, and break down muscle tissue, all of which work against body recomposition goals.

If you want to change your body composition, the most effective approach is to fuel your workouts rather than fast through them. The full step-by-step framework is in my 56-page guide, The Strong(er) Body Blueprint. It covers all of it: the nutrition, the training, progressive overload, and how to make it work with a busy life. I built it for the woman with her hands full who wants to change her body composition in the most sustainable way possible!