NUTRIENTS

OBJECTIVES Define nutrients Classify nutrients Comprehend structure and functions of nutrients

NUTRIENTS Nutrients have been defined as “chemical substances found in food that cannot be synthesized at all or in sufficient amounts in the body, and are necessary for life, growth and tissue repair”. or “Nutrient “or “food factor” are organic and inorganic complexes contained in food, which are responsible for the functions of foods and protect the body from disorders”.

NUTRIENTS Nutrients include; Proteins Carbohydrates Lipids Vitamins Minerals Water

CLASSIFICATION OF NUTRIENTS Classification on Basis of Requirement: Macronutrients: Carbohydrates (65 – 80%) Fats and oils (10-30%) Proteins (7-15%) These ore often called “proximate principles” because they form the main bulk of food.

CLASSIFICATION OF NUTRIENTS 2. Micronutrients: Minerals Vitamins Require in small amounts i.e milligram to micrgram

NUTRIENTS

CARBOHYDRATES (CARBS) Carbohydrates (from 'hydrates of carbon') or saccharides (Greek σάκχαρον, sákcharon, meaning "sugar") are the most abundant of the four major classes of biomolecules. Carbohydrates provide the largest single source of energy in the diet; providing 4 kcal per gram and satisfy our instinctual desire for sweetness. Carbohydrates are substances having the empirical formula Cx(H2O)y , e.g C6(H2O)6 = glucose (Fig. 2.1).

Fig. 2.1 :The structure of glucose, fructose & sucrose

CLASSIFICATION OF CARBOHYDRATES The basic building block of carbohydrates is a monosaccharide, often glucose itself. Carbohydrates are classified depending on the number of monomer (sugar) units they contain.

CLASSIFICATION OF CARBOHYDERATES COMPLEX CARBOHYDERATES SIMPLE CARBOHYDERATES MONOSACCHARIDE (Glucose, Fructose, Galactose) DISACCHARIDE (Sucrose, Lactose, Maltose) OLIGOSACCHARIDE (Human milk oligosaccharide) POLYSACCHARIDE (Starch, glycogen, dietary fibers)

SIMPLE CARBOHYDRATES: MONOSACCHARIDES The simplest carbohydrates are the monosaccharides, or simple sugars. The three most common monosaccharides are; Glucose Fructose Galactose

SIMPLE CARBOHYDRATES: DISACCHARIDES Disaccharides are double sugars which contain two monosaccharide units linked together. Examples of disaccharides are: Sucrose (Glucose + Fructose) Lactose (Glucose + Galactose) Maltose (Glucose+ Glucose)

SOURCES OF CARBOHYDRATES

COMPLEX CARBOHYDERATES: POLYSACCHARIDES Oligosaccharides contain between 3 and 11 monosaccharide residues. Polysaccharides are those with longer chains of monosaccharides. The polysaccharides tend to be insoluble in water, and only some can be used by human beings to produce energy.

COMPLEX CARBOHYDERATES: POLYSACCHARIDES Polysaccharides are classified as: Starch Polysaccharide Non-starch Polysaccharide

STARCH POLYSACCHARIDES Glycogen is made in the human body and is sometimes known as “animal starch”. Surplus monosaccharides that are not used to produce energy are converted to glycogen which is stored in liver and skeletal muscles for later use as an energy source. The body’s glycogen stores are relatively small (250–500 g in a 50–70 kg adult human); Most of the stored glycogen is released and oxidized within 12 hrs.

STARCH POLYSACCHARIDES Starch is an important source of energy for humans. Starch molecules in plants occur as granules in the form of amylose and amylopectin. Starch is liberated during cooking when the starch granules rupture because of heating. As much as 10–20% of dietary starch in individual foods and mixed meals is not digested to glucose; It is referred to as ‘Resistant Starch’.

STARCH Foods containing large amounts of starch include; Cereals (e.g. wheat, rice, maize), Root vegetables (e.g. potato) and Legumes (e.g. kidney beans, baked beans) There is little starch in most fruits and vegetables, apart from bananas, roots and tubers.

NON-STARCH POLYSACCHRIDE Some plant polysaccharides in foods are resistant to hydrolysis by human digestive enzymes and are referred to as. “Non-starch Polysaccharide”. They form the main part of dietary fiber. Cellulose, hemicellulose, lignin, pectin and gums are mainly non-starch polysaccharide, present in plants.

SOURCES

FUNCTIONS OF CARBOHYDERATES Carbohydrate provides 4 KCal per gram. The body can obtain all its energy from protein and fats. However, the neurons generally cannot burn fat and need glucose for energy; Carbohydrates and their derivatives play major roles in the working process of the immune system, fertilization, blood clotting, and development.

FUNCTIONS OF CARBOHYDERATES Diets high in carbohydrate are usually associated with lower prevalence of obesity, heart disease, non-insulin-dependent diabetes. Carbohydrates (dietary fiber) helps in digestion and in preventing constipation, mainly by absorbing water, and increasing the bulk of the diet & stool. Because it facilitates the rapid passage of materials through the intestine, fibre may be a factor in the control of diverticulitis, appendicitis, haemorrhoids.

BENEFICIAL EFFECTS OF CARBOHYDRATES The bulk in high-fibre diets may contribute a feeling of fullness or satiety which may lead to less consumption of energy, and this may help reduce the likelihood of obesity. High intakes of dietary fibers may also reduce the risk of large bowel cancer. Fibre may bind the carcinogenic substances and speed their transit through the gut. Fiber also increases the amount of water in the faeces, thereby diluting the effect of any carcinogens.

RECOMMENDED INTAKE OF CARBOHYDRATE The Food and Agriculture Organization and World Health Organization jointly recommend that 55-75% of total energy intake should be from carbohydrates, but only 10% directly from sugars (simple carbohydrates). Most Pakistani diet, contains excessive amount of carbohydrate, providing as much as 90% of total energy intake.

DIETARY PROTEINS

DIETARY PROTEINS The word protein means “that which is of first importance”. Proteins are complex organic nitrogenous compounds containing nitrogen and often sulphur in addition to carbon, hydrogen, oxygen. For an adult man who weighs 70 kg, about 16% of body weight is made by protein (i.e. about 11 kg); with 43% in muscles, 16% in blood and 15% in skin.

AMINO ACIDS Amino acids are the building blocks of protein. The amino acids are linked in chains through peptide bonds. There are 20 amino acids required for protein synthesis and are divided in two groups: Essential Amino Acids (cannot be synthesized by the body) Non-essential Amino Acids (can be synthesized by the body)

AMINO ACIDS There are 9 EAA including; Leucine, Isoleucine, Lysine, Methonine, Threonine, Valine, Tryptophane, Phenylalanine and Histidine.

FUNCTIONS OF PROTEIN Functions of proteins include: Growth and development of the body; Maintenance, repair & replacement of damaged tissues; Part of metabolic & digestive enzymes and hormones; Maintenance of osmotic pressure; Protein are essential for immunity; Protein can also supply energy (4 kcal per gram)

CLASSIFICATION OF DIETARY PROTEINS “Biologically Complete Protein” contains all the amino acids needed to build new proteins. Animal sources of protein tend to be complete. “Biologically Incomplete Proteins” lack one or more amino acids that the body can't make at all or create by modifying another amino acid. These usually come from fruits, vegetables, grains, and nuts. Adults need a minimum of 0.8 to 1 gram of protein per kilogram of body weight per day.

SOURCES OF PROTEIN Humans obtain protein from two main dietary sources: Animal Sources, also called “First Class Proteins” as they are biologically of higher value. Animal Sources include milk, eggs, meat, cheese, fish, poultry, butter, yougart. Plant sources are pulses, cereals, beans, nuts, oil seed.

SOURCES OF PROTEIN

FATS AND OILS: DIETARY FATS

LIPIDS Lipids are a group of compounds that contain carbon, hydrogen and oxygen like carbohydrates. Lipids dissolve in organic solvents such as petrol or chloroform, but are usually insoluble in water. The word "oil" is used to refer to those lipids that are liquid at room temperature such as groundnut or cottonseed oil , while those that are solid are called “fats” such as butter. Fats which become liquid at body temperature, like ghee and butter are digested and absorbed more readily than beef fat, which has a higher melting point.

CLASSIFICATION OF LIPIDS Fats (also referred to as lipids) in the body are divided into two groups: Storage fat - provides a reserve storehouse of fuel for the body Structural fats - are part of the essential structure of the cells, occurring in cell membranes, mitochondria and intracellular organelles.

CLASSIFICATION OF FATS Fats are classified as; Simple Lipids – Triglycerides Compound Lipids – Phospholipids Derived Lipids – Cholestrol Triglycerides make up about 95% of dietary lipids. Lipids yield fatty acids and glycerol on hydrolysis.

Fig 3.1: Formation of a Triglyceride Molecule

FATTY ACIDS Fatty acid consist of a chain of carbon atoms with hydrogens attached, a methyl group at one end and a carboxylic acid group at the other (Fig. 3.2). Fatty acids are classified as; Essential Fatty Acids (Can’t be synthesized by body) Non Essential Fatty Acids ((Can be synthesized by body) The most important EFA is Linoleic Acid which serve as the basis for the production of other essential fatty acids (e.g linolenic acid & Arachidonic acid).

Fig. 3.2: Structure of A Fatty Acid

CLASSIFICATION OF LIPIDS Lipids may be classified as Saturated or Unsaturated depending on the detailed structure of the fatty acids involved. Saturated fatty acids are those in which carbon–carbon bonds are fully saturated with hydrogen atoms (i.e. 4 hydrogens per carbon–carbon bond). Unsaturated fatty acids are formed when 2 hydrogens are absent, the carbons form double bonds with each other.

CLASSIFICATION OF LIPIDS Unsaturated fats may be further classified as on the basis of number of double bonds: Monounsaturated (one double-bond) Polyunsaturated (two or more double-bonds)

FUNCTIONS OF LIPIDS In addition to enhancing the flavour and palatability of food, lipids make an important contribution to adequate nutrition. Lipids are required for a range of metabolic and physiological processes and to maintain the structural and functional integrity of all cell membranes. They are major sources of energy; – 1 gram of fat gives 9 kcal of energy. Lipids are also the only form in which the body can store energy for a prolonged period of time.

FUNCTIONS OF LIPIDS These stored lipids in adipose tissue also serve to provide insulation, help to control body temperature, and afford some physical protection to internal organs. Fats in the body support viscera such as heart, kidney, and intestine. Lipids are also required for the absorption of fat soluble vitamins.

RECOMMENDED LIPID INTAKE For the adults, dietary fat should provide at least 15 - 20% total energy. At least 50% of fat intake should consists of vegetable oils rich in essential fatty acids. Saturated fat intake should be less than 7-10 % of total daily caloric intake. For infants and young children, dietary fat are equally important. At least until the age of two years, a child’s diet should contain about 40% of energy from fat.

SOURCES OF LIPIDS Naturally occurring dietary lipids are derived from a wide variety of animal and plant sources including Animal sources: Animal adipose tissue (the visible fat on meat); Eggs; fish oil; Milk and products derived from milk fat (cream, butter, cheese, and yoghurt); Plant Sources: Vegetable seeds and nuts and plant leaves. The saturated fatty acids are mostly found in animal fats and unsaturated fatty acids in vegetable oil.

SOURCES OF FATS

HEALTH EFFECTS OF DIETARY LIPIDS Among adults the major health issues concerning intake of fat centre around the role of excessive dietary fat in; Coronary heart disease, Obesity and Certain cancers.

WATER Water constitutes 60-70% of body weight. Water serves as the body’s transportation system; distributing nutrients and essential elements throughout the body. Water also works as the transport for body waste removal. Water regulates body temperature. Daily recommendation for water intake varies in individuals, related to climate, physical activity, age, body size, and state of health.

MICRONUTRIENTS: MINERALS AND VITAMINS

VITAMINS Vitamins are a class of organic compounds categorized as essential nutrients. Vitamins belong to the category of Protective foods. Body needs vitamins in very small amounts, but they are absolutely essential for normal metabolism. Most of the vitamins are discovered during the period of 1890 -1940.

CLASSIFICATION OF VITAMINS Vitamins are classified as: Water soluble vitamins Fat-soluble vitamins

WATER-SOLUBLE VITAMINS Water-soluble vitamins are easily absorbed by human body. Water-soluble vitamins dissolve easily in water, and in general, are readily excreted from the body, to the degree that urinary output is a strong predictor of vitamin consumption Body doesn’t store large amounts of water-soluble vitamins, and they need to be taken regularly. Many types of water-soluble vitamins are synthesized by bacteria.

WATER-SOLUBLE VITAMINS Water-soluble vitamins include: B complex vitamins (Thiamine, Riboflavin, Niacin, Pantothenic Acid, Vitamin B-6, Vitamin B-12, Biotin) Folic Acid Vitamin C

FAT-SOLUBLE VITAMINS Fat-soluble vitamins are absorbed through the intestinal tract with the help of lipids (fats). Fat-soluble Vitamins require bile acids to absorb fat-soluble vitamins. Once these vitamins are absorbed, body stores them in body fat, and used when body need them. Because they are more likely to accumulate in the body, they are more likely to lead to hypervitaminosis than are water-soluble vitamins. Fat-soluble vitamins include vitamins A, D, E, K.

SOURCES OF VITAMINS Vitamins are produced mainly in plants. Vitamins can be obtained directly from the foods and indirectly by animal food to man. Human body can also make vitamins in the intestine by so called “friendly bacteria”.

MINERALS Minerals are organic and inorganic substances categorized as essential nutrients. Minerals belong to the category of Protective foods. Body needs minerals in very small amounts, but they are absolutely essential for normal metabolism. Minerals make up about 4-5% of the body weight. Minerals are required for growth, repair and regulation of vital body functions.

CLASSIFICATION OF MINERALS There are two kinds of minerals: Major or Macrominerals Trace minerals or elements

CLASSIFICATION OF MINERALS Major or Macrominerals are minerals your body needs in larger amounts. They include calcium, phosphorus, magnesium, sodium, potassium, chloride and sulfur. Trace minerals are required in small amounts. These include iron, manganese, copper, iodine, zinc, cobalt, fluoride and selenium.

FUNCTIONS OF MINERALS Micronutrients perform structural and catalytic role including activation of enzymes and hormones. They also regulate metabolic processes and participate in antioxidant enzyme system. Body needs a small but continuous intake of the minerals to maintain its structure and functions. If metabolic needs of these salts are not met, deficiency occurs causing symptoms which vary with the mineral element involve.

SOURCES OF VITAMINS AND MINERALS

CONCLUSION

TEXT BOOKS Textbook of Community Medicine. By Prof. H.A Siddique.(2nd Edition). Parks Textbook of Preventive and Social Medicine. K.Park.

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