Unfortunately one of the biggest roadblocks to making any sort of significant change in your life is the people that form your support system. Your friends and family are the people you turn to looking for a boost or some assistance, but they may not be nearly as enthusiastic about your changes as you are.
It's quite possible that neither your friends or family see any reason for you to make the changes you're trying to make. They liked you just fine as you were. If you want there help (and you'll probably need it at some point) then you're going to have to find a way to explain the why to them or they may sabotage your efforts.
In most cases your friends aren't going to deliberately sabotage your efforts, but if they're not on board with what you're trying to do they can seriously hamper them. Whether it's bugging you to go out and drink with them when you're trying to finish your project or buying you chocolate when you're on a diet their actions will expose you to additional temptations and further challenge your will power.
In some cases, particularly with loved ones, they may feel threatened enough by the changes you are making to take more direct action to discourage what you are doing. It is extremely difficult to make major life changes with your wife or close family actively opposing you.
So it all comes down to communication. If you get these people on side they will be your biggest helpers. Otherwise they will create the biggest stumbling blocks to your progress. It's important to first figure out not what you are trying to achieve, but why you are trying to achieve it.
If you can explain why you want to achieve your goal, your friends and family will likely rally round you. At least the ones worth keeping will.
Lack of Support
As I think I've mentioned before I have a very small circle of people around me. Outside of family I have maybe two people I would consider friends and one of those I work with. Quite honestly that's a completely inadequate support system. However, it's not likely to change any time soon. For a variety of reasons, some of which I've touched on already, I'm not particularly comfortable or in a position to expand my social circle.
On the plus side, this means that I don't have to worry about my friends sabotaging my plans. Less positively I can't rely on them for much support either.