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The science of Nutrition is a relatively new science that studies the nature of different foods and the nutrients they contain in addition to what the body needs and the processes of digestion, absorption, transfer, metabolism (anabolism and catabolism), storage and excretion.

This science has developed from biochemistry and physiology.

It began to be taught as an independent specialization and as a core subject in many university specializations, such as medical sciences (medicine, nursing, and clinical nutrition), food sciences, and home economics, as well as an important optional educational subject in some other specializations, to spread the nutritional culture through university students in their families and communities.

The goal is not only to have a healthy, balanced diet, but also to identify the diseases caused by deficiency of certain nutrients, as well as bad eating habits that lead to the aggravation of disease conditions for many chronic diseases of the modern era, such as heart diseases, arteries, kidneys, cancer, diabetes, obesity, gout, and other diseases, some of which cause many deaths at the present time as a result of these unhealthy habits.

Ignorance of the basics of proper nutrition, as well as in the case of genetic diseases such as galactosemia and phenylketonuria, where infants with these diseases require special dietary systems to avoid very serious mental and physical problems that they may suffer as a result of their infection with these diseases.

It is your duty, as students of this science, to educate the people around you to choose good foods and change bad eating habits (as it was said in the past that prevention is better than cure).

The text quotes the wonderful introduction to the book "Chemistry and the Living Organism" by Molly B. Field.

The Field book follows an American family blessed with a healthy baby named Billy, but when he reached the fourth month of his life, his mother began to notice that he was slow to learn to sit by himself, rarely smiled, and became irritable as his skin became scaly and inflamed, and his mother noticed a pungent, foreign odor when he defecated.

When he reached the age of three, he was still not walking, talking, or controllable, so his parents took him to the doctor, who told them that the tests showed that he had a genetic disease called phenylketonuria (PKU).

PKU is a genetic disease that leads to mental retardation as a result of an increase in the levels of phenylalanine (an amino acid that makes up proteins) more than necessary in the bodies of those infected with this disease.

The increase in the rate of phenylalanine in the child's body obstructs the development of the brain and intelligence, causing severe intellectual disability that cannot be treated, due to a defect in the function of the enzyme phenylalanine hydroxylase, which usually converts phenylalanine into the amino acid tyrosine.

The text mentions that in the case of patients with phenylketonuria (PKU), phenylalanine is not converted to tyrosine correctly.

Regarding Billy, the doctor told his parents that they might have other children with this disease, but he did not prevent them from having other children, and he told them that children with this disease can live a normal life if they are diagnosed immediately after birth, where a special diet is set in which the percentage of phenylalanine is reduced.

He advised them to apply this diet to Billy, whose health condition improved greatly after that, as his foul odor disappeared, his skin and hair color improved, and he began to smile.

After five years, Billy's mother gave birth to a daughter named Suzanne, and tests showed that she also had phenylketonuria (PKU), but her parents followed the special diet recommended by the doctor, so she did not suffer from any of the problems that her brother Billy suffered from and grew normally.

Such a diet contains grains, fruits, and vegetables, and milk, dairy products, meat, fish, and other high-protein foods should be avoided.

There is a picture of the difference between the condition of Billy, who suffered from phenylketonuria (PKU) but was not treated early with that special diet, which reduces the proportion of phenylalanine, and his sister Suzanne, who was infected with the same disease but adhered to that special diet.

What do we eat?: Perhaps one of the most common questions we encounter in our daily routine is: What do we eat? Or what will we eat today?

It is stated that this book is dedicated to attempting to answer this question, and the answer may not end satisfactorily until the last lines of this book.

Before starting to answer this question together, we must answer another important question: Why do we eat? Do we really know why we eat?

It is stated that if we ask some people this question (Why do we eat?), the most common answer we get is that we eat to live).

This answer is incorrect because if we build on it the answer to the first question (What do we eat?), the answer here is (anything).

Such an answer does not make us eat correctly because we will eat anything regardless of the body's need for what we eat or not. Why do we eat?

Nutrition experts have summarized the answer to the question (Why do we eat?) in three main goals:

• We eat to provide the body with the energy necessary to carry out its voluntary and involuntary vital activities.
• To provide the body with materials that help it grow and repair damaged tissues.
• To provide the body with substances that help regulate vital processes in the body and provide it with substances that increase its immunity, vitality, and protect it from diseases.

There are times when children are more correct and accurate in answering the question Why do we eat?.

The children answer by saying:

• We eat to become strong (i.e., to provide the body with the energy necessary to carry out its vital activities).
• We eat to grow (i.e., to provide the body with materials that help it grow, regenerate, and compensate).
• We eat so that we do not get sick (i.e., to provide the body with substances that help regulate vital processes, increase its immunity and vitality, and protect it from diseases).

In fact, our knowledge of why we eat makes us, when we sit at the dinner table, look for foods that will achieve those goals that we have talked about, and therefore we can eat food that contains appropriate amounts of nutrients that the body needs to achieve the mentioned goals to reach a balanced diet.

It Provides the body with energy, helps it grow and repair damaged tissues, regulates vital processes in the body, and increases its immunity and vitality.

The text highlights that, to delve deeper into answering the aforementioned question, we must learn about some of the important terms in nutrition science, the most important of which is the term adequate nutrition, which means "eating food that provides the body with all it needs of nutrients and in quantities that are sufficient to meet its needs.

It doesn't cause any deficiency or excess, which gives the person the activity, vitality, and immunity necessary to resist diseases.

Food: It is the substance that a person takes in solid or liquid form and contains the nutrients that the body needs to maintain it alive and enable it to grow and repair, and this substance includes everything that enters the body from food and drinks, whether through the mouth or injection, so that it provides the body with energy and helps it to grow, repair damaged tissues, and regulate vital processes in the body.

Nutrients: They are the chemical substances that a person obtains from his food and needs constantly, and a deficiency of any of them leads to a disease condition, as the body needs them.

Source of energy to carry out building processes, growth, reproduction, and maintenance of tissues, in addition to regulating the body's work, and these substances include all of carbohydrates, proteins, fats, vitamins, and minerals, and water.

Malnutrition: A term describing what happens from a disorder or deterioration in a person's health as a result of eating unbalanced foods in terms of quantity or quality or as a result of a defect in the processes of digestion, absorption, or metabolism of one or more of the basic nutrients, and cases of malnutrition are not limited to under-nutrition.

Under-nutrition is the result of a deficiency in consumed calories or one or more nutrients, as many people think, but also includes over-nutrition, which is the result of an increase in consumed calories or one or more nutrients, which causes health problems.

Junk Food: A general term that has no scientific explanation and is used for foods of low nutritional value or unbalanced in their content of nutrients, as well as foods that pose a danger to human health, such as foods containing high levels of saturated fat, salt, or sugar.

Food definition: Food is defined as a food that humans eat to help the body grow, survive, and renew its tissues.

Food includes the nutrients necessary for the body to perform its various physiological functions.

There are essential nutrients, which the body cannot form for itself in sufficient quantities to perform vital functions, so they must be obtained in food, and the nutrients in food include carbohydrates, fats, proteins, vitamins, minerals, and water.

These elements can be divided into three main sections:

• The first section: includes the basic organic substances, which are carbohydrates, proteinaceous substances, and fatty substances.
• The second section: includes mineral elements, salts, and water.
• The third section: includes vitamins.

The body does not benefit from food in its complex form, and food must pass through certain stages inside the human body so that the body can benefit from it, and these processes include:

• Digestion
• Absorption
• Transport

The last stage includes the transfer of nutrients from the intestine to the blood in a form suitable for use. Through the process of metabolic transformation or metabolism, which is a vital process in which nutrients become part of the tissues, the metabolic transformation includes the processes of building the body's components (anabolism) or breaking down some of the body's components into other materials that are easy for the body to get rid of. The latter is called Catabolism.

Most of the substances that are destroyed leave the body in the urine through the kidneys or through the lungs in the form of carbon dioxide and water.

Signs of proper nutrition:

• Good overall appearance.
• Shiny hair.
• The eye is fresh and clear, with no dark circles around it.
• Natural skin color.
• Pink color of the nails.
• Weight is appropriate for height and age.
• Healthy teeth.
• Lips are pink.
• The tongue is pink and moist.
• The skeleton is harmonious.
• Strong muscles and tissues covered with a layer of fat, with no folds.
• Physical activity and balance in walking.
• Balanced nervous system and normal muscle strength.

Some important definitions in nutrition:

• Nutrition: A study of foods from the aspects of chewing, swallowing, digestion, absorption by the body, and representation within the body, and expulsion of them as waste from the body, i.e., a study of the course of food.
• Nutrients: They are what enter into the building of the body or what are absorbed in the blood, thus reducing the loss of the body's necessary components, and there is no definitive definition between foods and nutrients, or they are known as substances that supply the body with the necessary elements it needs.
• Malnutrition: It is meant to be:
  • The body's inability to obtain enough of all or some nutrients.
  • The body's inability to metabolize and benefit from the ingested foods in its building, renewal, and activity.
• Meal planning: The term meal planning means applying the basics of nutrition science in preparing and presenting meals for individuals in various circumstances that may vary for individuals from a health, economic, professional, gender, and psychological perspective.