No. More like an existential crisis of the fitness kind. I'm reading the new book Burn: The Misunderstood Science of Metabolism, by Herman Pontzer.

You can read and exercise simultaneously, you know. They have those little shelves on the treadmills. Just bring the book next time.

Maybe there won't be a next time. Pontzer's bombshell is that exercise doesn't affect how many calories you burn each day. I might as well just sit around and read his book instead.

What? That's preposterous. Who is this Pontzer and why would he want us out of our Lulu Lemons and into our loungewear?

He's a professor of evolutionary anthropology at Duke University, North Carolina, who's studied hunter-gatherer communities for over a decade to see if our modern sedentary lifestyle has slowed our metabolism. Pontzer studied the Hadza people of Tanzania, who walk several kilometres a day while foraging for food, and he discovered that they burn exactly the same calories as people in an industrialised society.

Yes, but lots of people in an industrialised society move around. Maybe even more so than the Hadza. Do the Hadza have Tough Mudder or Barry's Bootcamp?

Not Pontzer's point. He's saying we all burn the same calories every day, no matter what we do, and how vigorously. He even put a number on it: 2500 or so calories for men, and around 1900 for women.

Let me get this straight. If I do a spin class while you sit on the sofa, we will still burn the same calories?

Pontzer says yes. His studies indicate that if you burn more of your daily calories on exercise, your body compensates, burning less on its other processes. So it all evens out in the end.

But what if I want to lose some kilos?

It's back to simple maths: eat less than you burn.

And the exercise? Is there any point?

Plenty.

Pontzer adds that exercise ensures our bodies function optimally, helps us age well, and maintains a strong immune system. Absolutely keep it up. I'll be reading the next chapter on the step machine.

Pontzer's book is available from Penguin for $49.99.