Relax. Even if you're doing everything perfectly, there are heaps of reasons why the number on the scale could be up by a kilo or two. According to Dr Melina Jampolis, author of The No-Time-to-Lose Diet, these are some of the usual suspects:

You were thirsty

Downing 500ml of fluid can cause a "gain" of half a kilo.

You're backed up

Constipation can tilt the scale by as much as a kilogram if it's been more than a couple of days since your bowels did their thing.

You're going on holiday

The changes in air pressure can make you retain water on flights longer than four hours, which can show up as an extra 500 grams to two kilos on the scales.

You ate salt & pepper squid

Have a salty dinner and you could wake up more than a kilogram heavier - your body retains water to dilute sodium.

Aunty Flo's on her way

Hormone fluctuations in the three days leading up to your period can make you retain up to two kilograms of water.