Running on Empty (and Loving It): What Marathons Taught Me About Fasting

I was chatting with a colleague this week about long-distance running. He’s training for the Melbourne Marathon, and casually dropped the term “hitting the wall.”

Apparently this isn’t just a dramatic metaphor — it’s the moment (usually around kilometre 20ish) where your body basically throws up its hands and says, “Nope. We’re done here.” Your glycogen tank hits empty, your legs turn to concrete, and every step feels like wading through wet cement.

Marathoners try to dodge this apocalypse by “carbo loading” beforehand and slurping down energy gels mid-run… which sounds very glamorous. The longest I’ve ever run is 14km — no drinks, no gels, and definitely no cement legs. I’ve never hit the wall. (Maybe I’ll try a half marathon one day just to meet the wall in person.)

But that got me wondering: could you actually run a full marathon without refuelling mid-run?

Turns out: maybe, yes — if you switch fuel tanks.

You see, the body has three fuel tanks: carbs (stored as glycogen), fat, and protein. Glycogen is your fast-access fuel. Fats are slower but nearly endless. Proteins… well, they’re your muscles, and you don’t want to burn those. The trick is getting your body into ketosis — when it taps fat as the main fuel source instead of carbs.

As someone who’s been fasting since my teenage years (weekly church fasts, “fasting and praying” seasons…), this fascinated me. I still fast regularly, partly for spiritual reasons, partly to keep my weight in check, and partly to train my body to be “metabolically flexible.”

And lately, fasting has gone mainstream. Science now links it to longevity, reduced ageing, and boosts in human growth hormone. Intermittent fasts, 24-hour fasts, multi-day water fasts — all seem to spark impressive results.

There is a catch though. A sports scientist friend warned me that when your glycogen runs low — before you fully switch into fat-burning mode — the body often nibbles on your muscles for protein. This risk grows as you get older and naturally lose muscle. So now I’m planning to add some strength training to keep my muscles safe while still fasting.

Back to marathons: it’s apparently possible to run the whole 42.195km while in ketosis — burning fat the entire way. Your body becomes its own fuel tank. No gel packs, no pit stops. Just you, your legs, and the quiet knowledge that you’re powered by discipline, not just carbs.

And honestly… I love that idea. That our bodies can thrive not only on more, but on less. That we don’t always have to be topping up — we can train ourselves to last longer on what we already have.

Your Turn:
Curious to see how this lands for you:
Have you ever tried fasting — even a short one? What surprised you most about the experience?
Do you like the idea of using fasting to build “metabolic flexibility”?
If you could design your own fasting experiment, how would you do it?

👉 Hit reply and share your thoughts — your answers could inspire fellow readers in future issues.

Your Investment Menu

Walk into any restaurant and you'll find the menu organized into categories—appetizers, mains, desserts. The investment world works similarly, with asset classes serving as the main categories on your financial menu. Just like you wouldn't build a meal entirely from desserts, you shouldn't build a portfolio from just one type of investment.

Cash and cash equivalents are your financial vegetables—not exciting, but absolutely essential. This includes bank deposits and money market funds. They're the safest option with the lowest returns, providing instant access when needed. The trade-off? Cash barely keeps up with inflation over time.

Fixed income investments (bonds) are like reliable carbohydrates—steady energy that keeps you going. You're lending money to governments or companies in exchange for regular interest payments. They're less volatile than stocks but offer moderate returns. The catch? Interest rate changes affect bond values.

Equities (stocks) are your investment protein—the muscle-building component. You own pieces of actual businesses that employ people and generate profits. They offer the highest potential returns over long periods but come with significant volatility. Some years they'll be your best performers, other years they'll keep you awake at night.

Real estate rounds out the main categories—your healthy fats, essential but often overlooked. This includes direct property or REITs. Real estate often provides both income and growth, plus it tends to hold value during inflation. The downside? It's typically less liquid than financial investments.

Each asset class responds differently to economic conditions. When inflation rises, real estate and stocks often outperform bonds. During recessions, government bonds typically beat stocks. This is why diversification across asset classes is so powerful.

L-Plate Takeaway: Don't try to master every investment option immediately. Start by understanding the basic asset classes available in your market, then gradually expand your knowledge. The magic happens when different asset classes work together in your portfolio, not when you find the "perfect" single investment.