The Fatometer

Peter says…

Why Your Body Makes You Hungry

fatometerMany, many years ago, long before you and I came to be – before the invention of the internet, the telephone, pizza delivery services, before mopeds, and the wheels that make them possible – before anyone had even thought of taking a slab of pizza dough, smothering it in tomato paste and putting cheese on top – food was generally hard to come by. The only meal options available were fruit, nuts and berries – or catching something and killing it. Which could be a tad treacherous and usually involved a joint effort. Times were tough.

This being the case, it didn’t really make a lot of sense to evolve a hunger mechanism that made your tummy rumble just because you hadn’t eaten. Not when there just wasn’t any food available, and the first pizza delivery company wouldn’t be around for several thousand years.

On the other hand, when food was plentiful – say, when your old pal Ug had managed to trap a woolly mammoth – it made a LOT of sense for your body to encourage you to eat as much as you could from the all-you-can-eat mammoth buffet, because tomorrow that woolly mammoth might be past its ‘best slaughtered by’ date and you’d be back foraging amongst the bushes. In those days, life was quite often a case of ‘survival of the fattest.’

Of course, back in the 21st century every day is ‘woolly mammoth day’. Figuratively speaking. Food is plentiful, and quite a lot of it is packed with calories. And whilst we might eventually evolve a new hunger mechanism that takes all this into account, right now your body and mine are operating on the assumption that the local pizza delivery place might run out of pizza at any moment, and that it’s best to fill up whilst we can.

Put simply, your body is designed to make you fatter.

Let’s have a closer look at how it does that.

You Are Not A Car

If you’re like me then you’ve probably gone through most of your life assuming that hunger is like the fuel warning light that some posh cars have – you’re low on fuel, so you get hungry. Right?


Being ‘low on fuel’ does indeed make you hungry, but how hungry you feel, and how often, is far from simple. You, dear reader, are quite a lot more sophisticated than even the poshest of posh road vehicles, and the mechanism that human beings have evolved to control hunger is really quite ingenious.

In 2005, Dr Seth Roberts (PhD) published a paper entitled “What Makes Food Fattening? A Pavlovian Theory of Weight Control”. In it Dr Roberts cites a number of hitherto unconnected studies (mainly on rats) that led him to make several surprising conclusions, most of which run completely counter to what you and I ‘know’ – or think we know – about how our body works. Let’s break them down:

Surprising conclusion number 1: “the body-fat set point”

To begin with Dr Roberts claims that the human body, yours and mine, has a built in “body-fat set-point” – a weight your body wants to be. I like to think of it as a ‘fatometer’.

Your fatometer is a little like the central heating system in your house. Just as the heating goes on and off depending on how you’ve set your thermostat, your body will turn on hunger, or turn it off, make you feel full, or not, depending on whether you’re lighter or heavier than the weight your fatometer is trying to achieve.

This sounds far-fetched, but in the last decade or so scientists have indeed discovered several hormones (Peptide Tyrosine Tyrosine (PYY), Ghrelin, Leptin… there are others) that control our hunger, appetite, and how quickly we feel satiated after eating. You’ve probably assumed you felt stuffed because there literally wasn’t any room left in your stomach, and those hunger pangs were like the sound an empty oil drum makes when you beat it with a stick. Turns out those feelings are just feelings – they’re ‘chemical’.

Surprising conclusion number 2: what you eat changes your fatometer

The second intriguing element of Dr Roberts’ paper is that just as your central heating’s thermostat dial isn’t fixed, neither is your body’s fatometer. The body turns your fatometer up and down in direct response to what you eat, or don’t eat. The more calories the body registers, the higher it sets your fatometer, and the more hungry you’ll feel later.

So eat something really calorific – say, a slice of cake – and your body turns your fatometer way up, which kicks your overall appetite through the roof.

“How can that be?” you might be asking yourself. How can the body possibly know how many calories are in a slice of cake?

Surprising conclusion number 3: the body ‘learns’ how many calories your food has

Though we’re totally unaware of it, each time we sit down to a meal our minds are busy consulting with our stomachs and associating the flavour of that meal with the calories it contains. Over time your body actually figures out which flavours have the most calories so that it can adjust your fatometer accordingly.

Of course this doesn’t happen overnight, but as you might expect, foods that taste identical each and every time – such as a burger from a burger chain, or a pizza from a pizza delivery company, or your favourite chocolate bar – create very strong associations very quickly indeed.

Surprising conclusion number 4: Some foods turn down the fatometer

Finally, some good news. According to Doctor Roberts, if a food has calories, but your body hasn’t created an association with its flavour, your body will actually turn down your fatometer, thereby lowering your appetite and causing you to feel more full when you eat.

So, for example, were you to sit down to a lovely plate of calorie-laden Ruurgh, which I’m reasonably certain you’ve never had before in your life (mainly because it’s a dish I just made up), your body would turn down your fatometer in response, which will lower your appetite for subsequent meals.

Now all this sciencey fatometer stuff can be, if you’ll forgive the pun, a little hard to stomach. It’s enough to make your head spin. So let me try and summarise it in one sentence.

The more calories you eat,
and the more familiar your food,
the hungrier you’ll become
and the more you’ll have to eat to feel full.

Turns out you are not a car.

You are much, much more complex.

Of course, this is all very interesting but what you really want to know is whether we can use this information to eat loads and stay slim? Is that possible?


Then above is an extract from “How To Eat Loads And Stay Slim” – available now from amazon 

Dr Roberts’ paper (‘What Makes Food Fattening’) is available here and also published on his website

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