Hazrath Ali (R.A) Said that these 4 habits has an ability to weaken your brain power.

1- Speaking loud and listening to loud music:
Speaking loudly and laughing loudly and engaging in crap good for nothing conversation not only steals away your precious time but also has an ability to weak your brain power and listening to loud music does the same.
2- Eating too much especially fried non-veg:
Eating too much is the cause of obesity, diabetes, BP, and many problems. Prophet Mohammed (SAW) ate very less, always ate in company, ate slowly and he ate non-veg only on special occasions and mostly he ate vegetables, porridge and dates. And it is sunnah to follow him. Eating too much is a sin and it is called gluttony and it harms you and weakens your brain power and intelligence.
3- Not giving exercise to body and sitting at one place for long time:
Hard work is the key to success and hard work is also the key to good health. If you want to be healthy then you have got to give exercise to your body, just do it and do whatever it is follow your passions and give all your heart to one task a day.
4- Not listening and learning from people:
When a person feels he or she has learnt enough and do not give room to listen and learn from people then they are in a big illusion. Life is all about learning and it is an endless ocean you are always learning till death.
So learn and learn from people around you.
It is easy when you are strongly determined to quit your bad habits and adopt success habits in place of it.
This ebook is a great master piece in helping you quit bad habits and replace it with good ones The Power of Success habits by Michael Winicott.