Grace, and Grace Alone.
I aborted my previous fast at 32 hours. Many of us ( I included) assume that self-control comes from the self. Our mind has been eroded, softened, neutralized by years of the dominion of the flesh. God has set us so our mind would dictate its conduct to our body, but sin has turned that balance upside down. Many people find themselves wanting to fast, to stop smoking, drinking, doing drugs, snoozing, cheating on their diet, procrastinating, and a whole bunch of bad habits that satisfy the flesh but drag our minds and lives down. Unsurprisingly, they keep failing over and over again because their minds are too weak to control their fleshly desires. But, If you're at this point of your life where it seems like you've tried everything but can't quit, just give it to Jesus. When self-control can't come from your weakened mind, pray for the Holy Spirit to give you the strength to overcome. It can only work when you've given up on trying to make it by yourself, on relying on your own fleeting willpower. Any success you may have this way will be very short-lived, and I talk not only from my personal experience but also from other people's experiences. I've seen my own father return to smoking and drinking after 8 years clean, I've seen all sorts of people regain the weight they've lost (myself included). Your only support, your only weapon is the Holy Spirit.
“This is the word of the Lord to Zerubbabel: ‘Not by might nor by power, but by My Spirit,’ Says the Lord of hosts.
Zechariah 4:6, NKJV
For God gave us a spirit not of fear but of power and love and self-control.
2 Timothy 1:7 ESV
No temptation has overtaken you except such as is common to man; but God is faithful, who will not allow you to be tempted beyond what you are able, but with the temptation will also make the way of escape, that you may be able to bear it.
1 Chorinthians 10:13, NKJV