The human body needs a number of nutrients every day. In fact, we need to ingest  more or less  40 different nutrients in order to keep our body healthy. No single food contains all these nutrients. So the best way is to eat a variety of different foods.

And what is considered a healthy diet is to obtain the necessary nutrients in necessary quantities required by the body.

The two most important factors that affect the value of food are: its nutritional value and its bioavailability. The nutritional value depends on its composition (proteins, carbohydrates, lipids, mineral salts, vitamins…), the manner in which it is prepared

 ( boiling, steaming, etc…).The amount of a nutrient that gets into the bloodstream determines its bioavailability.

A. Bioavailability

1. Bioavailability depends on several factors,

-The chemical form or the composition of food, food combining, the amount of food, etc…

-Age, sex, the physical state of the person, etc…

2. The bioavailability of, carbohydrates, proteins and fats is usually very high at more than 90% of the amount ingested. Bioavailability of vitamins, minerals, is subject to a complex set of influences

3. Many nutrients interactions affect the bioavailability. The major effects of the nutrient interaction can be illustrated with:

    a. Magnesium, manganese, selenium, iron are involved in the metabolism of vitamins.

Calcium, copper , magnesium and  zinc help the easy absorption of vitamins  A, D, K and C. Magnesium, for example, is involved in the metabolism of calcium and the vitamin C.

   b. Vitamin C also improves the absorption of iron from food of vegetable origin

   c. Phytic acid is a compound found in many plant-based foods, and contains a high proportion of phosphorus.and found in the fiber of legumes and seeds.

     - Phytic acid blocks the absorption of minerals, such as calcium, magnesium, iron and zinc.

     - Phytic acid, also reduces the absorption of valuable vitamins such as vitamin B3

    On the other hand, these interactions of the phytic acid with minerals can be beneficial. For example,   the reaction with toxic metals as the cadmium or the aluminium is valuable. Toxic metals may cause nervous system damage, affect digestive tract, and may also cause fertility problems.

Avidin is a substance, present in raw egg white and stops vitamin B8 absorption. but when avidin is fully cooked then loses its ability to bind vitamin B8.

And here are some factors which affect the stability of some vitamins,

             Factors which affect the stability of some vitamins

This means that if for example, we want to consume an orange juice, it is not recommendable to squeeze the orange hours in advance When it comes into contact with the air, the vitamin C oxidation process begins and it loses properties.

 B. Preparation of food

Foods must be processed to improve their digestibility.

How people prepare food is determined by a variety of factors, and according to learned habits, own preferences, economic circumstances, cultural norms, etc..

However, ensuring an adequate food preparation is essential to ensure that food is properly assimilated .And by eating foods that are easier to digest it is possible to provide our bodies with the necessary nutrients.

With that said, let's now explore some of the methods for food preparation,

1. The frying process adds calories and fat to meals, this only can be reduced if a proper frying technique is used

2. Sautéing is the cooking of food in a small amount of oil in a pan over direct heat. The idea is to brown the surface of the food, creating additional flavour. This process is less unhealthy than other preparation methods.

But it's also used to fully cook whole dishes. Whether it's meat or vegetables, time in the pan is brief, if we cut vegetables into thin, bite-sized pieces, and meat  into portions sized and then we just add  a little water, or a little stock and  cook for a few minutes till done.

3. Roasted or grilled vegetables are very delicious, but lose considerably its vitamins.

Nearly any vegetable can be grilled, eggplant, zucchini, eggplant, onions, potatoes…

 For a healthier choice, brush any vegetable with a little olive oil, wrap it in aluminum foil. So this way, the vegetable will be cooked in its own juices and preserve the nutrients content.

4.Avoid cutting vegetables before you're ready to use them, to minimize nutrient loss.

5.It's best to bring the water to boil before adding the vegetables. Using the minimum amount of water retains water-soluble nutrients.

6. When finished cooking, vegetables must be removed from boiling water if we prefer eating only vegetables. This broth can be used as the liquid part of a soup, or for other dishes. We increase the levels of nutrients by substituting vegetable broth instead of water when making dishes.

7. High-temperature cooking of some foods for short periods retains more vitamins than those which are cooked lightly for a longer.

8. Steaming vegetables is a very effective method that helps to preserve minerals and is a better option than boiling as vitamins do not leach into the water and get thrown away. Foods are generally more nutritious and delicious when steamed.

  9. Before freezing vegetables, enzymes that oxidize vitamins must be destroyed. Blanching vegetables before freezing inactivates the enzymes. The vegetable is exposed to boiling water for 3 minutes and then is rapidly cooled in ice water for 5 seconds.

10. Sometimes we can find different textures and a different hardness in the same vegetable. Obviously the tender parts of the vegetable do not have the same requirements as the hard parts. The key here is to add the vegetables in order of their hardness. This includes cabbage and broccoli as well as chard and celery. Cooking chard leaves requires less than 2 minutes, but the stalk needs 10 minutes to be tender. And also time of cooking is different if we cut the vegetable into pieces.It takes at least 20 minutes to cook a whole cauliflower, and less than 10 minutes if is cut into florets. A good option is to check food regularly while cooking, every 10 minutes at the beginning, and every minute at the end.

11. When you turn off the heat, the high temperature inside the food causes it to carry on cooking until it cools down.

12. Thicker liquid takes longer to boil. Carrots take about 20 minutes to boil in water, but it may take longer to cook with lentils,

13. Here is a list of  some vegetable cooking times

Cooking times(minutes) for some boiled vegetables. The times start after the water has come to a boil and the heat is off.