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Rational Diet – How Should We Eat To Stay Fit And Healthy

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Rational Diet – How Should We Eat To Stay Fit And Healthy

By eating rational means ensuring a optimal intake of  food both qualitatively and quantitatively, which ensures the maintenance of life, growth and development and contributing to health recovery in case of illness. A balanced diet should contain both macronutrients (carbohydrates, proteins and lipids), which provides the energy for normal activities, as well as vitamins and minerals, which are considered micronutrients.



Caloric Necessary (Energetic Necessary)

As defined by the World Health Organization (WHO), caloric necessary is that the best food energy intake, which provides an ideal energy balance necessary to maintain normal body weight and composition, long-term preservation of health, physical and intellectual activity performing and browsing physiological periods (growth, pregnancy, lactation).

To achieve this is advisable that the energy intake to be equal to energy consumed. Energy intake is supplied by food and energy expenditure is necessary for:

  • Ensuring basal metabolism (60% of total energetic consumption);
  • Volunteer activity, physical and psychological (30% of energetic consumption);
  • Dynamic action, which is specific for each aliment separately (10% of energetic consumption);
  • Thermogenesis.

Daily caloric necessary is generally higher in young than in the elderly, men than in women and depends on your ideal weight, physical activity and physiological states mentioned.

In adults, the simplest estimate of caloric needs can be done by multiplying the ideal weight (in kg) by the number of calories expended per kilogram of body weight and day, depending on the activity performed:

  • Bed rest = 25 kcal per kg body weight / day;
  • Mild physical activity = 30-35 kcal per kg body weight / day;
  • Moderate physical activity = 35-40 kcal per kg body weight / day;
  • Heavy physical activity = 40-45 kcal / kilogram body weight / day.

For calculating the ideal weight there are many formulas available, but the most used is the Broca formula:

  • Ideal weight = Height (cm) – 100 ( in men);
  • Ideal weight = Height (cm) – 105 (in women).

Food Principles

Food principles are represented by carbohydrates, proteins, lipids, vitamins, minerals and water.

Optimal amounts indicated for each food principle (meaning those quantities that involve a reduced risk for developing chronic carential diseases and are enough for physical activity and can provided a good energy balance) are provided by the guidelines developed by specialists.


Carbohydrates have an important energetic role, because one gram of carbohydrate provides 4 kcal. They are present in foods in the form of monosaccharides, disaccharides and polysaccharides. According to all recommendations, carbohydrates should represent between 55% and 65% of total caloric intake,because the minimal amount carbohydrates which ensure the glucose needed for the adult nervous system is 130 g / day.

The main sources of carbohydrates are cereals and cereal products (flour, bread, maize, pasta, rice), vegetables, fruit, sugar and sugar products, the last two sources are not obligatory.

  1. Monosaccharides are represented by glucose and fructose, found in fruits, cereals, syrups and honey. Glucose is oxidized into cells and represents its major energy source, on the other hand it is stored in the liver and muscles as glycogen (energy reserve).
  2. Disaccharides are represented by sucrose (glucose + fructose), maltose (glucose + glucose) and lactose (glucose + galactose).
  3. Polysaccharides important for nutrition (starch and glycogen) are formed by polymerization of glucose molecules. The main sources of starch are cereals, cereal products and potatoes, while glycogen is found in some organs (liver, kidney, muscle).
  4. Sugar and sugar products are not indispensable, but when they are consumed, daily amount of sugar should not exceed 10 g-20 g, so about 4% of caloric intake (up to 10%, according to WHO).

To ensuring an adequate intake of vitamins, minerals and dietary fiber, balanced diet should contain 200 g-300 g of fruits and 300 g-500 g of vegetables.

Balanced Diet

Balanced Diet


Lipids are the most powerful energy source of the body, one gram of fat generates 9 kcal. Some of them play an important structural and functional role, entering in the composition of cell membranes, central nervous system, hormones and cellular messengers. A balanced diet should contain fat at a rate of 20% -30% of daily calories (1 g / kg body weight / day). The minimum required, one that provides fat-soluble vitamins is 40 g / day.

Fatty acids are classified as saturated and unsaturated (mono-and polyunsaturated), depending on the presence and number of unsaturated double bonds in the chain of carbon atoms. Transsaturated fatty acids originate from the conversion of unsaturated fatty acids during thermal or industrial preparation.

Saturated fatty acids originate from animal fats: butter, cream, whipped cream, egg yolk, cheese (cottage cheese, cheese),fatty meat.
Oils (vegetable fat) contain polyunsaturated fatty acids and monounsaturated.
The optimal ratio of dietary fat, the animal and vegetal origin is 1 / 1. For a day, diet should contain 10% rational polyunsaturated fatty acids, 10% monounsaturated acids, saturated fatty acids maximum 10% and a amount of 300 mg cholesterol. It is recognized that such a diet does not favor atherogenesis.

Polyunsaturated fatty acids (PUFA) are of essential fatty acids, which means they can not be synthesized by the body. Their presence is necessary both for normal growth and development, as well as heart and nervous system function. Depending on the position of first double bonds to the methyl end of the carbon chain, there are two classes of PUFA: omega 6 and omega 3.

  1. Omega-6 PUFA have the principal representative linoleic acid of which, in the human body is synthesize arachidonic acid. The main sources of omega-6 PUFA are: sunflower oil, pumpkin oil, sprouts corn oil and soybean oil.
  2. Omega-3 PUFA are mainly represented by alpha-linolenic acid and are found in oily fish. Besides their essential role in growth and development, is considered that omoga 3 PUFA has antiatherogenous effects, so the American Heart Association (AHA) recommend, in general, eating fish at least twice a week, and for the people who have risk factors for coronary artery disease indicate omega 3 fatty acids supplementation with 600 mg/day and even with 1-2 g/day in subjects with a family history of sudden cardiac death.

Recommendations on the required daily amount of polyunsaturated fatty acids are for linoleic acid, 5% -10% of daily caloric necessary, and for alpha-linolenic acid, 0.6% -1.2%. In a rational nutrition, optimum ratio of omega-6 PUFA and omega-3 PUFAs should be 4:1.

Polyunsaturated Fatty Acids

Polyunsaturated Fatty Acids


Proteins are nutrients that are essential to life, the main roles are structural and functional. In second way are used as an energy source, one gram of protein provides 4kcal.

As structure and complexity protein are:

  • simple: albumin and globulin, which splits in aminoacids by hydrolysis;
  • conjugated: nucleoproteins (from RNA and DNA), mucoproteine, glycoproteins, lipoprotein, phosphoprotein and metallo-proteins (ferritin).

The basic structure of the protein consists of essential aminoacids and nonessential aminoacids.

  1. Essential aminoacids (threonine, tryptophan, lysine, leucine, isoleucine, methionine, valine and phenylalanine) are considered essential because their endogenous synthesis is insufficient for the metabolic needs and is necessary an additional contribution.
  2. Nonessential aminoacids (alanine, aspartic acid, asparagine, glutamic acid, arginine, glutamine, glycine, proline and serine) are equally important for protein structure, but if are not sufficient quantities for protein structures, they can be produced from the essential aminoacids or from other precursors.

There are certain aminoacids which can be synthesized by the body in normal conditions, insufficient quantity, but in some situations it is necessary to supplement them by exogenous input, they are called conditionally essential aminoacids (histidine, cysteine, tyrosine).

Functionally, food protein are sources for synthesis of tissue protein and are involved in anabolic processes providing aminoacids necessary for the body. Proteins compose the enzymes, hormones, antibodies and are therefore involved in immune system function. Proteins participate in transport of triglycerides, cholesterol, phospholipids and fat-soluble vitamins.

Optimal protein intake is 11% -13% of daily caloric necessary, or 0.8-1g/kg body weight / day. A rational diet should include animal and vegetable protein in a ratio of 1:1.




Vitamins are found in varying amounts in a daily diet and are essential for almost all body functions including growth and cell division. After solubility criterion, vitamins are classified as:

  • liposoluble (A, D, E, K);
  • hydrosoluble (C and B complex).


Minerals are classified in macrominerals and microminerals.

  1. Macrominerals (sodium, potassium, magnesium, chlorine, phosphorus) are essential substances in the body with multiple functions and represent 4%-5% of body weight. The amount of sodium chloride in a rational nutrition is 4 g / day. Calcium and magnesium deficiency is responsible for the appearance of rickets in children and osteomalacia and osteoporosis in adults. Dietary calcium requirement for adults is 1500 mg. Deficiency of magnesium and potassium can be incriminated in the occurrence of arrhythmias. Magnesium needs in adults is 300 mg-400 mg, and potassium at 3500 mg. Phosphorus intake should be 1500 mg.
  2. Oligoelements (iron, zinc, copper, iodine, fluorine, cobalt, selenium, manganese, molybdenum) are found in small amounts in the body, from where the name of the class, but they are essentials for growth, development and maintenance of normal life.


Water is indispensable for life, being the major component of all tissues and cells and metabolic reaction substrate. In the human body is diveded into intracellular and extracellular water.

Fluid balance maintains balance between water intake and endogenus water, on the one hand, and the water removed, on the other hand.

Water Consumption

  • Water and beverages: 1400 ml
  • Food: 700 ml
  • Resulting from metabolism: 200 ml
  • Total: 2300 ml

Water disposal

  • Urine: 1400 ml
  • Faecals: 100 ml
  • Perspiration:  100 ml
  • Insensible losses: 350 ml
  • Elimination through the respiratory tract: 350 ml
  • Total: 2300  ml

Loss of water more than 20% of body weight (by diarrhea, polyuria, vomiting) may lead to death. Recommended daily fluid intake is 1 ml / kcal in adults, as water, teas, juices, milk, soups, to which 600-700 ml of water contained in foods is added.