Why Low-Carb Diets Can Wreck Your Performance and Health (Especially If You’re Active)

Ah, carbs. The poor, misunderstood macronutrient. Over the years, they've been villainized more than a comic book supervillain—blamed for everything from weight gain to global warming (okay, maybe not that last one… yet). But here’s the thing: if you’re active, regularly training, or just someone who enjoys not feeling like a sluggish zombie, restricting carbohydrates can do more harm than good.

And if you’re a woman? The risks are even higher.

So, let’s break it all down—why low-carb diets and fasting can sabotage your health and performance, what Relative Energy Deficiency in Sport (RED-S) is, and why you absolutely need carbs if you want to train hard, recover well, and not feel like a human-sized raisin.

Low Energy Availability (LEA) & RED-S: What Happens When You Don’t Eat Enough

Your body isn’t just about lifting weights, running, or doing whatever training you enjoy. It has an entire operating system running in the background—your hormones, metabolism, immune function, reproductive health, and brainpower. And all of that requires energy.

Now, imagine you’re spending more energy than you’re taking in (whether by training a lot, eating too little, or both). Your body starts panicking and making budget cuts like a company in a financial crisis. And guess what’s the first thing on the chopping block? All the "non-essential" processes that keep you thriving, not just surviving.

This state of energy imbalance is called Low Energy Availability (LEA). If it goes on for too long, it turns into Relative Energy Deficiency in Sport (RED-S)—which, let’s be real, is just your body waving a white flag and saying, "Mate, we need to talk."

RED-S can mess up pretty much everything, including:

🔥 Metabolism: Your body slows down to conserve energy—meaning more fatigue and less fat-burning potential. (Yes, restricting carbs and calories too much can actually make weight loss harder.)

⚡ Performance & Recovery: You’ll feel weak, slow, and struggle to build muscle or recover properly. Imagine training with a phone that’s always stuck at 5% battery.

🦴 Bone Health: With low energy and low estrogen (in women), bones become weaker, increasing the risk of stress fractures and osteoporosis.

🩸 Hormonal & Reproductive Health: Women might lose their period (not a badge of honour—it’s a sign your body is in survival mode). Men can experience lower testosterone levels, leading to low energy, poor recovery, and mood swings.

🧠 Brain Function & Mood: Ever feel like a cranky gremlin when you don’t eat enough? Now imagine that all the time. Anxiety, depression, brain fog, and irritability are all common symptoms of RED-S.

🛡️ Immune System: Your body can’t fight off illness as well, so you’re more likely to get sick or feel constantly run down.

Carbs: Your Body’s Favourite Energy Source (Seriously, It Loves Them)

Let’s talk about the big one—carbohydrates. They’re not the enemy. They’re literally your body’s preferred source of energy. When you eat carbs, your body stores them as glycogen in your muscles and liver. This glycogen is then used to fuel your workouts, daily activities, and—yes—your brain function.

Restricting carbs is like trying to run a car without petrol. Sure, you can push it down the road, but wouldn’t it be a lot easier if you just gave it some fuel?

What happens when you don’t eat enough carbs?

❌ Your workouts suffer. Low glycogen = poor endurance, strength, and power. It’s like training with the brakes on.

❌ You feel exhausted all the time. Ever feel like you’re wading through wet cement? That’s what happens when your body has to rely on inefficient energy sources.

❌ You risk muscle breakdown. If your body doesn’t have carbs, it starts breaking down protein (a.k.a. your hard-earned muscle) for fuel. Bad times.

❌ You increase stress hormones. Chronically low carbs can increase cortisol (the stress hormone), making fat loss harder and recovery slower.

In short: cutting carbs is a terrible strategy if you care about performance, recovery, or just feeling good.

How to Avoid LEA & RED-S While Keeping Your Training on Point

You don’t have to go all-in on pasta and doughnuts (although, what a dream). But you do need a balanced approach to fueling your body properly.

Here’s what to do:

✅ Eat enough carbs. If you’re training, aim for at least 3-5g of carbs per kg of body weight (more if you’re doing high-intensity workouts). Whole grains, fruits, potatoes, rice—get them in.

✅ Match energy intake to training demands. On high-training days, eat more. On rest days, adjust accordingly.

✅ Don’t fear pre- and post-workout nutrition. Your body needs fuel before a workout and carbs/protein after to recover properly.

✅ Track your menstrual health (if applicable). Losing your period is a red flag—not a sign you’re "lean." It’s a sign your body is under stress.

✅ Monitor energy levels & mood. Constant fatigue, mood swings, or feeling like an irritable gremlin? Check your nutrition.

✅ Work with a pro if needed. A nutritionist or coach (cough, me, cough) can help you fine-tune things so you’re fueling your body properly while still meeting your goals.

Final Thoughts: Food is Fuel, Not the Enemy

Look, you can technically survive on low-carb diets, but if you actually want to feel strong, energetic, and healthy (instead of just barely functioning), carbs are your friend.

Restricting them won’t just tank your training—it can lead to serious health consequences like RED-S, hormonal dysfunction, and long-term metabolic issues. And that’s just not worth it.

So, eat the damn carbs. Your body (and your performance) will thank you for it.

👉 Want help figuring out exactly how to fuel your training without restrictive dieting? Let’s chat! I work with people just like you to create realistic, sustainable nutrition strategies that support your goals and your health.

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💬 Let me know in the comments—have you ever struggled with low energy from restrictive dieting? What changes made the biggest difference for you?