Romans 7:9 For I was alive without the law once: but when the commandment came, sin revived, and I died.
The commandment came into your mind to stop eating junk food, sin was activated and you died.
Can I give you a word of advice? The word "Why" should cease immediately from our lips, we will never get the answers for "Whys" while we are complaining. Those answers always come when we are not crying for the reasons why.
The question you should be asking is, "What wisdom, knowledge and/or strength am I lacking that is causing me to fall sway to these destructive habits?"
Hosea 4:6 My people are destroyed for lack of knowledge.
We are perishing in our minds due to lack of information. Once this data is received and acted upon salvation comes to our understanding and we'll find the strength to overcome these temptations.
I know what your going through brother. For two solid months a few years ago I bought boxes of chocolates and spent hours looking online for more delectables to consume and I blew up like good year blimp to 375lbs. God was telling me to stop, my body was telling me to stop, my heart was saying stop. Finally, armed with the knowledge and strength needed to overcome, I cut out all salt and hydrogenated fats from my diet. Since I love sweets, I turned my attention from chocolate which was making me fat to non chocolate items, protein bars, etc.. I'd make my own cookies without the use of egg and fats and use Carob powder in place of chocolate. It's been a few years now since I've entered a fast food joint. When I discovered how much salt and fat that went into each Whopper I nearly keeled over. I am now down to 280lb, still in the obese bracket, but it's coming off. Bread was another hurdle. Bread puts on the pounds, so I had to cut back on that as well and use alternative means like Rice crackers or Rye breads, breads that were low in gluten. The heavier bread the better because you won't eat a lot of it.
You have the power to overcome, the strength is there, it's just waiting on us to see if we are going to use it or not. It's kind of useless to obtain that strength KNOWING that your going to give into the temptation regardless of the consequences. Being a Christian, we know full well what we are doing. We are tempted and we know what we are about to commit is going to harm us so we do it anyway and afterward complain to God as to why He didn't intervene. God will not intervene on our strongwill to do something. He will wait until we fall flat on our faces, totally disgusted with ourselves.
Read the dietary label on each product, if you see hydrogenated fat or modified fat they are saying the same thing, avoid them, they were designed to keep the product on the shelf for a long time and meant to kill you. These companies do not have your health in mind, their mind is on your wallet. Salt and Sugar are two of the major issues surrounding obesity. Salt keeps you eating salt, sugar keeps you eating sugar and hydrogenated fats binds them together to make the perfect death. Once you realize that these are killing you, you will be more mindful of what you are putting into your body.
If you see high fructose corn syrup and/or the first and second ingredient is glucose fructose or sugar, that should tell you right there that the product that your considering to buy is mostly sugar.
Change your prayer from why to "Lord, I need knowledge and I need understanding about how to eat properly." He will help you if your willing to be helped. There will be moments where you'll give in to some whim but start again and each time you start again it gets better.
And whatever you do, don't go on a diet. Just cut back and read the label, make better choices, and if your able to walk, walk a brisk walk every day for 20 minutes. If you can't walk because your obese, you'll need to do some form of exercise to get your lower limbs working so you can walk.
A helpful book that got me started on this was, "Your Diet in Health and Disease" by Harry Benjamin. It was written in 1945 but it reads as if the writer was living in our day with our problems. There are many other books as well, but get your hands on books about herbs and spices, make your own cookies, cakes and low gluten breads. Explore the world of food without excess salt and sugars. Food is meant to be enjoyed.
My suppers usually are some sort of a green salad with basmati rice, veggies and a piece of fish, all steamed baked. I use white balsamic vinegar, with a splash of lemon juice and olive olive oil on my salad. I try to keep snacks on hand like hummus with no salt rice crackers, nuts, raisins, etc.. but you have to check the label on these too, they sometimes use hydrogenated fats to preserve the nut.