Q: I overindulged over the weekend and weighed myself on Monday and have gained 3kg since Friday. How did this happen?!  

A: Firstly, don't freak out!
It's quite unlikely you've actually gained that much in body fat in such a short space of time.

To gain a kilogram of body fat, we know that you'd need to consume around 30,000kJ / 7,200 cal in excess of your daily requirements.

 There are a number of factors which can falsely elevate your weight after a short period of over-eating, such as:

1. Increases in stored glycogen:
When you eat a lot of carbohydrate from either starchy food like bread, pasta, rice, or sugars in sweets or drinks, the resulting blood glucose is stored as glycogen in the liver and muscle. Each gram of glycogen is stored with around 3g of water - so storing 500g of glycogen packs on another 1.5kg of water.

2. High salt intake:
If you overindulged on salty snacks (think potato crisps, take away, processed meats etc) this causes water retention which can easily add kilograms of weight.

To combat this, make sure you drink lots of fluid to flush out the salt (it sounds counterintuitive, but is true), focus on eating lots of fresh fruit and vegetables, cut down on the salt, caffeine containing drinks (tea, coffee, diet soft drinks) and alcohol, and do some exercise to get things moving.

3. Alcohol:
If your weekend binge also included some serious volumes of alcohol, this can cause you to retain water. As alcohol is dehydrating, your body goes into overdrive to retain water so to not become dehydrated.

4. Genetics:
Depending on your genes, there is a wide variation in an individual's propensity to store excess energy from over-eating as body fat.

It's just the way it is - some people are better at dissipating excess energy as heat, whereas in other people, the excess energy is very efficiently stored as fat. Thanks mum!

5. Chronic under-eating:
If you've been under-eating (i.e. less energy than your body needs to sustain itself), this can slow the metabolism to such an extent that when you do eventually eat more, your body holds onto the excess energy in fear of the next 'famine'.

Thanks to Metabolic Jumpstart for this great information.
http://www.metabolicjumpstart.com/