Lack of willpower

decision fatigue

"Willpower" is basically BS, but it's BS most people believe in. Even people who have been studying these things.
So... what makes me think I know it better than people who have been studying it?
I am one of the people who has problems with "willpower" or the "lack of it", and I have overcome these problems, and I know it has nothing to do with any of that stuff people say. 
It really is just an excuse. You say it and your brain accepts it as a fact and makes your body obey. So you think it is a fact. Now, if you start telling yourself that you have all the willpower ever needed to do ANYTHING, your brain will accept that as a fact and will make your body obey. And suddenly you HAVE all the "willpower". It is because there is no such thing as willpower. It's all an illusion, an idea.
It's like "Do. Or do not. There is no try."
Do, or do not. You have already made the decision. Your brain is already preparing your body and mind to do what you decided.
So to overcome your "lack of willpower", you need to make the decision before you NEED to make the decision, and rob yourself any options.
Yes, you want to lose weight.
Yes, you want to nourish your body with nutritious, delicious food.
Yes, you want to go out for a run.
OK, so you don't want to go out today. You don't need to. After the run.
Because not going for a run is not an option. You don't have that choice. Don't start lying to yourself about that. You don't have that choice. You have already decided you want to go for a run. Sorry, you should have thought that when you made the decision, it's too late to change your mind now. When you have reached your goal, then you can make a new decision, but what is your goal? To get fit? To lose weight? To run every morning? If it's the last one... Oops.
No, you don't want that piece of cake. You have already decided that, when you decided to start eating well. You don't want to eat anything, because you are not hungry.

Now... it's totally OK to change your goals, but if you have decided for the last 20 years to lose that 20 pounds and you just keep changing your decision all the time, until next time you pick the same goal again.... it's time you stop lying to yourself. You don't want to lose that 20 pounds. You want something else. Find out what that is.

Perhaps you want to get nice clothes and they don't exist in your size? Then I suggest you learn to sew clothes. Perhaps you want to get a new bikini and go to a beach? You can. Right now. They make bikinis in many sizes.
You want to look nice? You do. There will always be people thinking you look horrible. But there will also always be people thinking you look nice. (You better be one of them.) And most people won't be thinking about your looks at all.
Besides, it doesn't matter.
It's not a beauty contest.
There are no laws against "ugly people in public", even though some a-holes would like that.
You have the same right to enjoy public places, beaches, restaurants and everything as everyone else.
Your looks are not your best quality any way, nor do they matter much. You have plenty of wonderful qualities, you don't need to look like a photoshopped teenager, too.
If someone says something nasty to you about how you look, you can always answer "If you don't like the look of me, don't look at me." Any further comment is to be brushed away with "not my problem". And then try to remember that yourself. It's not your problem if someone doesn't like the way you - or anyone - looks. You don't get to decide what they look at, and if someone wants to look at ugly things - it's their business. I'd much prefer to look at pretty things, but - who am I to judge? And who are they to judge your looks? If you were participating in some sort of beauty contest, then, yes, but you aren't. You are just participating in life, and looks are not even on the list of qualities to be judged. You don't owe anyone to look nice. You don't owe it to yourself nor to your lover, why would you owe it to a total stranger? On top of that, a stranger with no manners and nasty personality? Does anyone owe ANYTHING to people like that? I don't think so.
Maybe you want to have friends? Your weight is irrelevant.
Maybe you want certain hobbies? Your weight is irrelevant. Unless there is a weight limit. There is no weight limit to most sports or any other hobbies, so are you sure there is one in your chose one?
Maybe you want to not be teased, harassed, called names, bullied? That... unfortunately, no-one can avoid that. We live in a culture with very little compassion and kindness. People think they are entitled to criticize their fellow human beings, of any reason, and they do. It is seen as witty, and people who react are seen as weak and over-sensitive people, who "need to toughen up, get a thicker skin". Yep, more BS. Sensitivity is a beautiful quality. People who expect a silk dress to endure what a heavy-duty overall does, are idiots. Sensitive people are silk dresses or cashmere sweaters, hard people are heavy-duty overalls and firemen rocks. There is time and place for both of these, but they are not the same. Yet, when it comes to people, the culture somehow expects everyone to be Kevlar. And then they wonder why there is so little kindness, consideration, care and love in the society... 

There is only one thing you can do about bullying.
Remember that they don't define you, they define themselves. It is not so that people are kind to you, because you are kind to them. They are kind to you because they are kind people. Bullies bully because they are bullies, not because you deserve to be bullied. You don't get to choose how they react, what they do or say, you don't have that kind of control over them. They are not helpless victims of your magical influence that somehow forces them to bully you. Remember all those dog-owners who reacted on the "men can't help raping" BS? "If my dog won't touch a piece of meat on the floor in front of it, because I said "no", then a man should be able to not touch a woman because she said "no" - or didn't say "yes". A human being should be able to not bully a person they know they can bully. It's not the victim's fault he/she is bullied. It is 100% the bully's fault.
And remember that these people are doing the best they know how. Bullying is a reaction of fear. Yep...  people who bully you are afraid of you. Your mere existence is a threat to their status, their position. Just look at people who bully - there's always some sort of strength, power. Either they are popular, and their victim is not, which gives them the power of numbers and support, or they are physically strong, and their victim is not. The bullied ones, they are either the smart ones, the bookish boys, who aren't that strong and physically able to defend themselves, but everyone knows they are smarter than the bullies, and that is really scary. What if people start to appreciate smartness over muscles? What will these bullies have left? Nothing. Or the bullied ones are those who are different. In a society where the looks are everything, people being different are saying "I don't care about the limitations put on by the society, I look as I please, not to please you". And that is a challenge. These people have to be "put in their place", made to "realize how wrong it is to be different", because "different" people are not sheep. "Different" people are not followers. It's hard to control and manipulate "different" people. And this is also the reason to why so few adults support and protect the bullied ones. They are also just people, and think the same way. The age doesn't really matter, this happens everywhere, from kindergarten to old people's homes.
So - now that you know why these people are saying those nasty things to you, maybe you could have some pity to them. It's really hard to be afraid of someone you pity. It's also really hard to get hurt by what they say. You know their mouths are just moving and they are spouting their own fear and pain and anger, it just doesn't mean anything. They are just trying to deal with all those feelings and they do it the best they can. They haven't been taught to do it in any other way. They are being rewarded for doing it this way. They think it's right. Poor buggers.
And a fat woman comfortable with her weight and looks is really damn scary... she threatens the whole structure of the society! A woman who cannot be controlled, manipulated and diverted by making her ashamed of not looking "right", and focusing all her efforts to that! A woman who thinks she has other qualities than the patriarchal reproductive ones! (healthy, young, fertile, child-bearing hips, nursing breasts...). A person who says "I know what you think of me, but I don't care". That's about as scary as it gets!
I don't know why you want to lose weight. But you do. Find out, and maybe it's THAT what you want, and not the actual weightloss. (Also, you probably will lose weight when you get THAT. People are mysterious creatures...)

Also, if you want to, let's say, try bungee jumping, and there is a weight limit, then you either try to find a way to bungee jump without weight limit, or lose the weight, and if it doesn't matter how to lose weight, I sincerely suggest you stop eating unless you reach your goal weight.

FASTING IS NOT A HEALTHY WAY OF LOSING WEIGHT AND SHOULDN'T BE USED LIGHTLY.

One should not do this unless your BMI is over 30, or longer than a week if it's under 30. 

No need to think about what to eat, just eat nothing. The permanent damage caused by starving will start only after one's body has used all the fat there is, and reaching a normal adult weight limit will not get you there.
Just remember to drink, though. Water is absolutely necessary, but it would be good to drink milk, too. It is very nice package of nutrients body needs, like calcium for bones, lactose to keep your brain in working condition and many minerals and vitamins, but if you have problems with milk, try to replace it with something nutritionally equal.
Gurgle with sugar water (remember to spit it out) when you are hungry. 
You might get problems with your bowels, but this is not permanent. (It's very likely you have problems with your bowels if your BMI is over 30).You will be able to eat so that your bowels get in good shape pretty quickly after you stop your fasting (and I also suggest you do that.).
Also, you need to keep moving, to see that your body doesn't use the muscles to feed itself, but the fat.
Human beings are made to store fat to feed upon during starvation. Let your body do its thing.

But, and I really can't say this too often, THIS IS A DANGEROUS WAY OF LOSING WEIGHT, DON'T DO IT UNLESS YOU REALLY CAN'T DO IT IN ANY OTHER WAY, BUT REALLY NEED TO.
It WILL fuck up your head.
You WILL have to fix the problems caused by it, and it WILL cause problems.

If you want to lose weight in a healthy, sane and permanent manner, there are ways to do that. Basically eat less, move more. If you just skip sugar (and sweeteners) and refined wheat, and add veggies, and take a walk every day, you will lose weight until you reach a healthy weight. You don't need to count calories or think what you eat, where, when, why or how much.