Over the past 20 years portion sizes have grown bigger and bigger. Nutritionists are convinced they've been a major contributor to our obesity problem. They've even coined a name for it - "portion creep". Look at these familiar examples of supersized portions. See how the larger serve of fizzy drink, juice, muffins and popcorn will stack on the kilojoules and add another layer to your midriff.

When Coca Cola was first created in 1915, a "single serve" was the iconic 250ml waist bottle. Just enough to quench your thirst and add a little refreshment to your day. It came in at 450kJ. Now we sip the 600ml buddy-size bottle. It too is regarded as a "single serve". But it slugs you a hefty 1080kJ plus a lot of sugar. Not that good for you.

Juice used to come in a smallish 200ml glass. With 285kJ, that's the equivalent to one whole piece of fruit if you're sticking to a low-kilojoule diet. Not a lot. Today, at those trendy juice bars, a 600ml tumbler is the smallest size you can order - equal to 4 pieces of whole fruit. And yes even though it's healthy, there's still 855kJ in that bucket of juice. If you don't burn it off, it will go where all the excess goes to - to bulk out those love handles!

Muffins once were small cup cakes weighing around 55g and leaving us with 810kJ. They were a home-made treat, but a small one so didn't do damage to your diet. Now muffins balloon out of their paper case and weigh a hefty 175g. At this weight, you get landed with 2580kJ with your morning coffee. It's value for money but not for our waists!

When you popped the popping corn at home in a pan, a serve was a cup full. With a knob of butter melted in, you got a reasonable 1265kJ. These days, popcorn at the movies comes in a huge "Maxi box" and adds 3455kJ. Here's the bad news. For only $2 more, you can upsize from a "Maxi" box to a "Super Mega" box. You get double the weight of popcorn - AND double the fat and kilojoules!

So be portion wise and save kilojoules and girth.

* Catherine Saxelby is a nutritionist and the author of Nutrition for Life. Find more healthy eating tips at www.foodwatch.com.au