In Imam al-Ghazali's fantastic book, The Forty Foundations of the Religion, he divided the forty foundations into four chapters. The first chapter relates to matters of Belief, the second matters of Practice, and the last two chapters are about the diseases and beautification of the heart. Each chapter contains ten foundations.
When it comes to the first foundation in chapter three — diseases of the heart — the Imam listed gluttony or excessive eating as the mother of all diseases of the spiritual heart. This is because excessive eating leads to evil desires such as haram sexual lust, love of this world, etc. In short, excessive eating hardens the spiritual heart.
The Imam and many great spiritual masters advocate fasting as the path to a healthy spiritual heart (qalbun saleem). Getting our food under control is the first step to getting our lower self (nafs) under control.
Interestingly, medical doctors tell us that excessive eating can also lead to calcification of the physical heart — which is the hardening of the physical heart.
There seems to be a link between the health of the spiritual and physical hearts. Therefore, excessive eating is terrible for both hearts.
Rasulullah advocates fasting at least three days each month — the 13, 14 and 15th of each lunar month, a.k.a the White Days. If you want to do more than add Mondays and Thursdays every week.
But going hungry is not just about fasting in the day and later on feasting at night. Rasulullah taught us that a few morsels of food are sufficient for a person. And if that is too little, we should fill one-third of our stomach with food, one-third water, and one-third air.
Today we live in an age of abundance — probably the first time in human history. In the past, most humans eat to live. But today, many live to eat and are proud to call themselves a foodie.
May Allah help us all in getting our food intake under control. When we reduce our food intake, we decrease the pathways of shaitan in us, for Rasulullah told us that, "Shaitan runs through the blood vessels of human, so constrict their pathways by going hungry and thirsty."
Controlling our desire for food is the first step to controlling our nafs, which is also the first step to purifying our hearts.