If you do one thing this week . . . order the smaller pizza

The dark, cold nights of winter are rolling in, and sometimes the temptation to hibernate and order a takeaway can be strong.

If you dial out for dinner, though, bear in mind that it can be easy to underestimate how much portion size makes a difference to the amount of carbohydrates, fat and calories that land in your tummy if you eat the lot.

Take pizza, for example: the nine-inch version doesn’t sound that much bigger than the seven-inch. But do the maths: the area of a circle (your dinner) is “pi times r-squared” – so the radius (r) is key.

When you jump from seven to nine inches you add an inch of radius, and that amounts to a whopping 65 per cent increase in surface area, or the amount that covers your plate.

So if you are watching what you eat, avoid portion distortion and order the small.