Willy Trolove: All we need is a few African predators

The average New Zealander is getter larger. We're already the seventh-fattest country in the OECD. If we keep piling on the kilos, the whole nation will look like a never-ending balloon festival.

Luckily, the Government is on the case and in the Budget Dr Cullen set aside $76 million to throw at obesity.

With a target that big you'd think he couldn't possibly miss. But he will. No matter how many resources the Government puts into healthy eating programmes, food advertising regulations, and obesity-fighting bureaucrats, we will keep piling on the weight. And there's one simple reason for this: Africa.

Humans spent the vast majority of their existence wandering the African savannah, hunting and gathering. Our digestive system was developed for a world without supermarkets.

That is why diets seldom work. As Professor Robert Winston writes in his book Human Instinct, if you reduce the amount of food you eat, your body believes it's in a savannah famine.

It tries to keep your weight constant by slowing your metabolic rate. This makes it even harder for you to lose weight, and when you eat normally again, you'll put on weight faster than before you started dieting.

This explains why one moment Oprah Winfrey is thin and banging on about her latest diet, and the next she's the size of the Michelin man.

And it explains why the dieting industry isn't making much impression on our enlarging population: our bodies are more efficient at resisting weight loss than most diets are at promoting it.

If Oprah can't get thin and stay that way, there's not much hope for the average Kiwi, who, let's face it, has apathy as their middle name.

Humans on the savannah stayed slim because they burned the excess energy they consumed. Our ancestors had to catch wild game, kill it, carry it home and barbecue it without condiments.

Just getting a square meal involved a lot of running, jumping, and tearing around in the kind of energetic manner that is frowned on now, when we're not even allowed to stub a toe in the workplace. That's why obesity is booming.

We're not growing fatter because we're eating too much or have lost the willpower to resist cream doughnuts. We're growing fatter because we get our food without exercise.

A few decades ago we spent our days digging ditches, shearing sheep, planting trees and running to the pub before it closed at 6pm. Now, the most energetic thing we do at work is waddle to the snack box.

We need drastic measures. We need to make people exercise for their food. Food retailers already help out. Some supermarkets are as big as Belgium, and the weekly shop involves a good stroll. But supermarkets need to be re-designed.

Car parks should be banned. Shoppers should have to lug their food home as if it were a wildebeest they'd felled with a spear.

Travelators should be installed in every aisle and set in reverse to work like treadmills, so shoppers have to jog to stand still. In treat aisles, the travelators should be set at high speeds so that if you want a bar of chocolate you have to burn the equivalent amount of energy just to grab it from the shelf.

Chips, biscuits and peanuts should be stationed at the far end of an obstacle course, so that shoppers have to run, climb, jump, swim, and crawl under barbed-wire.

And finally, African predators should be released in the store to encourage shopping to be carried out at calorie-burning speeds.

A leopard crouching above the tinned goods, a crocodile dozing in the delicatessen, and a pride of lions loitering among the chilled meats will bring the savannah into our daily lives - and thin down the population a lot more effectively than the Government can.