When a new year comes around, I often get asked the same question in a variety of different ways, but they all pretty much mean - how can someone lose 'x' amount of weight as quickly as possible. I can understand why people are asking that, but I'm afraid you're asking the wrong question...
During Christmas and New Year celebrations, it is extremely common to put on some extra body fat - the alcohol, the chocolate, the savory foods etc etc. Just by cutting those foods and drinks out in the New Year, will drop a certain amount of fat on its own. However, if a 'body transformation' is what you're after, then other changes need to be made.
If you're aiming for the fastest possible 'weight loss', then it's simply going to come back. To drop weight fast (won't be just body fat - muscle and fluid too) then you'll have to go into an extreme diet - something that is not sustainable. So, once you get to the weight that you're happy with, you will go back to a 'normal' diet, and you'll start to see the fat come back.
To make REAL changes to your physique, then you need to make REAL changes in your lifestyle - your nutrition routine, your exercise routine, your sleep, your snacking habits, your alcohol consumption, your regular 'boozing sessions' etc etc. Unless you change the reasons why you have gained body fat (and not just a few pounds over xmas) then you'll never have the body that you want.
The real answer to the title of this post, is there is no answer - if you want to actually have a fit and healthy physique. I never recommend rapid 'weight loss', as it takes away more muscle tissue and fluid than fat - leaving you weak, hungry, a shapeless body and moody. Do it the right way - make small changes, real lifestyle changes, put in the hard work, and you'll be rewarded with the body that you're happy with.
Lee Gregory Fitness