The Prophet (salallaahu `alaihi wassallam) said:
“The human being can fill no container worse than his belly. Sufficient for the son of Adam are so many morsels of food as will keep his spine upright. But if he must eat more, then a third for his food, a third for his drink and a third for his breath.”
At-Tibb An-Nabawī p.20. Hadīth reported by Imām Ahmad in Al-Musnad (4/132), At-Tirmidhī (2499), Ibn Mājah (3349), and it was authenticated by Al-Albānī in Sahīh Sunan At-Tirmidhī (1939).
So the Sunnah encourages with moderate eating and not constantly indulging oneself because that eventually leads to poor health and illnesses.
“Material illnesses arise from an increase of matter which comes to a point of excess in the body whereby it harms its natural functions – and these are the most common illnesses. They are caused by consuming more food before the previous meal has been properly digested; by eating in excess of the amount needed by the body; by consuming food which is of little nutritional value and is slow to digest; and by eating different foods which are complex in their composition. So when a person fills his belly with these foods and it becomes a habit, they cause him various diseases…”
At-Tibb An-Nabawī p.20; Medicine of the Prophet, ITS, p13.
So here we see this great scholar highlighting that which has been known throughout the ages till this very day of ours by the experts in the field of nutritional and holistic medicine – and that is the harm that comes to the body due to overeating, to the point of excess, beyond what the body needs even before the previous meal has been digested. People today are no longer in the habit of feeling hungry as our ancestors were – they desire to be satiated constantly throughout the day and night. This constant filling of the stomach to excess leads to illnesses that have become widespread in societies today. This is where fasting is an excellent habit to get into at least twice a week (as the Prophet recommended) or even once a week, as it curtails the desires, it is a spiritual nearness to the Lord, a cleanser of the digestive tract and helps in weight loss. And when you break the fast, you do so with simple healthy foods.
Another important point mentioned by Ibnul-Qayyim is the harms of consuming food of low nutritional value that is complex in nature and therefore slow to digest. Today we hear of cases where people may be morbidly obese, yet malnourished at the same time because they’re not getting the right type of nutrition-rich food. The modern diet of complex processed foods that has become a norm in many households leads to illnesses and diseases that were unheard of by our forefathers (or were at least extremely rare). The less processes your food goes through before you consume it, the better. The closer it is to nature, the better. The simpler it is, the better. So organic raw (fresh) milk is better than pasteurised and homogenised milk; butter is better than margarine; raw vegetables are better than fried; a baked potato is better than fried chips or french fries; steamed vegetable are better than boiled; home cooked food is better than fast food from a takeaway restaurant; organic fruit and vegetables are better than those sprayed with chemicals; organic and free-range meat and chicken is better than those injected with antibiotics and hormones and fed with “food pellets”; organic free-range eggs are better than eggs from caged chickens; butter, ghee (clarified butter) and coconut oil is better than vegetable oils; grilling and baking is better than frying (deep frying is bad for health); a homemade cake using good and natural ingredients is better than a supermarket one; non-GM (non genetically modified) is by far better than GM; all sugary foods and drinks are bad for health (even the concentrated juice drinks). Watch out for packaged foods and meals with long lists of ingredients and chemicals; try as much as you can to cook at home with simple basic ingredients involving simple processes (steaming, grilling, baking, boiling, etc) – remember, the closer to nature the food is, the better. Eat plenty of leafy green salads and colourful vegetables (organic whenever possible) – use butter, olive oil, avocado, vinegar to add flavour. Organic may not be affordable for everyone, in which case think about buying from your local farmer or visit farmers’ markets, or consider growing you own – and if all of that is not possible, then buy the non-organic greens and wash them thoroughly! Beware of refined carbohydrates – refined carbohydrates are rapidly absorbed into the bloodstream, causing risky spikes in blood sugar and insulin levels. Most common chronic diseases of Western Civilisation have been tied to these types of (deliciously addictive) carbohydrates, therefore it is wise to keep them to a minimum. Examples of foods that are refined starches include white flour, white bread, white pasta, white rice and cereals that contain little to no fibre. Carbs that have been refined digest very quickly, which can lead to surges in your blood sugar level. You may find that after a blood sugar surge, your energy drops. You may also experience food cravings, which, if you’re trying to lose weight, can hinder your success. Generally, anything that comes in a box or bag (think chips/crisps, crackers, biscuits and pretzels) has been refined. Learn which carbs are refined and scratch them off your grocery list forever.
“When a person is moderate in his eating and takes only so much of it as he needs, keeping a balance of quantity and quality, the body benefits more from this than it does from a large amount of food. There are three degrees of eating: (1) out of need; (2) in moderation; and (3) in excess…”
At-Tibb An-Nabawī p.20; Medicine of the Prophet, ITS, p13.
“The Prophet (salallaahu’alaihi wassallam) has made it known that he found sufficient such morsels as would keep his spine upright, with which his strength would not be lowered or weakened; but if one goes beyond that, then let him eat to fill a third of his belly, and leave another third for water and a third for breath. This is most useful for body and heart. For if the belly is filled with food, it does not have enough space for drink, and when drink is added to it, this leaves little space for breath. Thus it is afflicted by distress and fatigue, and it bears this like one carrying a heavy burden – and this state will lead to corruption of the heart; and the limbs become too lazy to perform the obligations, and instead they move swiftly in submission to desires brought about by fullness of the belly.”
At-Tibb An-Nabawī p.21; Medicine of the Prophet, ITS, p13.