Not much. When you go below 800 calories a day you body says "oh! oh! we need food and there's no food here." So it goes into "starvation mode and keeps all of the fat to sustain life." It uses just the bare minimum to keep your vital organs alive. So, it's not a good way to lose weight and you know you could die. It's a better idea to eat at least 800 calories a day. The smart way to lose weight is to take the number of pounds you want to weigh and multiply that number by ten. Like if you wanted to weigh 125 - you would eat 1250 calories each day.

Cortisone as an oral drug is another common culprit (e.g. Prednisolone). Cortisone often causes weight gain in the long run, especially at higher doses (e.g. more than 5 mg Prednisolone per day). Unfortunately, cortisone is often an essential medication for those who are prescribed it, but the dose should be adjusted frequently so you don’t take more than you need. Asthma inhalers and other local cortisone treatments, like creams or nose sprays, hardly affect weight.

We often think that if we can just discover the “right” combination of foods, we’ll magically lose weight or maintain what we’ve lost. There are low-fat diets, low-carb diets, low glycemic diets, Paleo diets, and a lot of iterations of all of these. Jensen points out that in fact there doesn’t seem to be any “right” diet, and there doesn’t seem to be any evidence that one particular diet will work better with an individual’s specific metabolism. “The big myth out there,” he says, “is that there’s a magical combination of foods – be it protein, vegetarian, and what have you – that’s going to be unique because of its unique interaction with your metabolism. We know pretty much that any diet will help you lose weight if you follow it. There’s no magic diet. The truth is that ALL Diets will work if you follow them.”
The sad truth is that conventional ideas – eat less, run more – do not work long term. Counting calories, exercising for hours every day and trying to ignore your hunger? That’s needless suffering and it wastes your time and precious willpower. It’s weight loss for masochists. Eventually almost everyone gives up. That’s why we have an obesity epidemic. Fortunately there’s a better way.