G-d has however ordained general rules of health that work through nature which should be practiced to keep the body clean and functioning to its best capacity. He set up nature in such a way that for the majority of people ,certain health rules keep our systems clean and functioning well and to prevent illness. The Torah prescribes certain rules for health.
This includes drinking plenty of pure water to keep the system pure, especially first thing upon awakening in the morning. Dehydration is a cause of many ills. I should mention here that many elderly people and people who live in hot climates where they sweat a lot, or hot dry climates where they dry out easily, can suffer from dehydration more easily. But the solution to dehydration is not just drinking more water. In fact , once you are dehydrated, drinking a lot of water can make it worse! You end up flushing good electrolytes out of your body. So you need to consume things with good electrolytes (ie. Banana smoothie, fresh squeezed orange juice, chocolate milk, eat watermelon and grapes etc.) Some people find that cool water is more thirst quenching than room temp water. Some people find that carbonated water helps for hydration.
Overeating is one of the worst things for health: Torah says we should always eat to partial satiation, not total. Our stomachs should NOT be totally full, so we are able to properly digest the food. If the stomach is too full, our digestion is overtaxed and will not work properly to break down the foods. It is also very important to avoid eating anything for two to three hours before sleeping. This will insure better digestion and certainly better sleep. If we eat too close to sleeping, it creates gas that goes up to the head, resulting in strange dreams.
Studies done recently have shown that people who eat breakfast and avoid eating late night snacks and meals (eating no later than about two hours before sleeping), do not gain weight very much and maintain a better weight overall. Breakfast is an important meal each day.
Sleeping on time and sleeping adequately is also linked to better health: the best sleep is before midnight and it is advised to aim for seven hours of sleep a night. If one sleeps too much , or sleeps in too much, it is not considered beneficial. And too little sleep is also detrimental. Some people do function with less sleep but each person is different and their circumstances are different.
Keeping the bowels moving regularly is a must. Maimonides (the Rambam), the greatest doctor known to mankind, said that most diseases result from constipation and bowels that do not work properly. To that end, we need to discover what works for each of us. Some people require a lot of insoluble fiber. Some require more soluble fiber. Some require more fruits or vegetables. We need to discover the cause of our personal bowel irregularities. For someone it could actually be a gluten issue or a symptom of celiac disease. For someone else it can be a lack of adequate fiber. For others a lack of water. For others it can be the consumption of too much damp producing foods such or for others the consumption of too many foods that dry out the system. But in general the Rambam discusses the importance of fiber to keep the bowels regular. He mentions that one should generally not eat bread that has the bran completely sifted out (in other words, white flour products). So we need to incorporate whole grains into our diet (either gluten containing grains such as spelt or whole wheat, or gluten free grains such as oats or brown rice, and preferably organic grains). And we need to incorporate more vegetables into our diet, not just potatoes (which can be constipating). But even with the need for fiber, there are people with conditions such as crohns or colitis who need to be careful with too much fiber. Everyone’s system is different and each person has to get to know how much fiber they need and what is too much.