Macronutrients

Macronutrients

Definition

        Macronutrients (carbohydrates, fats, proteins, water) are chemical substances primarily used to generate energy or to incorporate into tissues for growth and repair and are required in large quantities in diet.

Introduction

The chemical elements humans consume as diet in the largest quantities are 

·        Carbon

·        Hydrogen 

·        Nitrogen

·        Oxygen 

·        Phosphorus 

·        Sulphur

These are called as CHNOPS. The chemical compounds that humans consume in the largest quantities and provide bulk energy are- 

·        Carbohydrates 

·        Proteins 

·        Fats

Water must be also consumed in large quantities but does not provide caloric value. All macronutrients provide energy. Proteins and fats make the cellular structures.

Carbohydrates are compounds made up of different types of sugars which provide body the energy necessary to run various body functions. Carbohydrates are classified according to their number of sugar units: 

·        monosaccharides (such as glucose and fructose) 

·        disaccharides (such as sucrose and lactose) 

·        oligosaccharides 

·        polysaccharides (such as starch,  glycogen, and cellulose)

Proteins are organic compounds that consist of amino acids joined by peptide bonds. Since the body cannot manufacture some of the amino acids (termed essential amino acids), the diet must supply them. Through digestion, proteins are broken down by proteases back into free amino acids which act as building blocks of cells as well as various secretions like hormones and enzymes. Certain amino acids are synthesized in the body while certain others are not so these should be made available through diet.

Fats consist of a glycerin molecule with three fatty acids attached. Fatty acid molecules contain a -COOH group attached to unbranched hydrocarbon chains connected by single bonds alone (saturated fatty acids) or by both double and single bonds (unsaturated fatty acids). Fats are needed for construction and maintenance of cell membranes, to maintain a stable body temperature, and to sustain the health of skin and hair. As body does not manufacture certain fatty acids (termed essential fatty acids), they must be obtained through one's diet.

List of macro nutrients

Carbohydrates

Monosaccharides

·        Glucose

·        Galactose

·        Fructose

·        Xylose

Disaccharides

·        Sucrose

·        Lactose

·        Maltose

·        Isomaltose

·        Trehalos

Polyols

·        Sorbitol

·        Mannitol

Oligosaccharides

·        Maltodextrins

·        Raffinose

·        Stachyose

·        Fructo oligosaccharides

Polysaccharides

Starch

·        Amylose

·        Amylopectin

·        Modified starches

 

Non starch polysaccharides

·        Glycogen

·        Cellulose

·        Hemicellulose

·        Pectins

·        Hydrocolloids

Protein

Essential amino acids

·        Phenylalanine

·        Valine

·        Threonine

·        Tryptophan 

·        Methionine

·        Leucine 

·        Isoleucine 

·        Lysine

^·         Histidine

 Semi essential amino acids

·         Arginine 

·        Cysteine 

·        Glycine

·        Glutamine

·        Proline 

·        Tyrosine

Non essential amino acids

·         Alanine

·        Aspartic Acid 

·        Asparagine 

·        Glutamic Acid

·        Serine 

·        Selenocysteine

Fats

Saturated (i.e., stable) fatty acids

·         Acetic acid (C2)

·         Propionic acid (C3)

·         Butyric acid (C4)

·         Valeric acid (C5)

·         Caproic acid (C6)

·         Caprylic acid (C8)

·         Capric acid (C10)

·         Lauric acid (C12)

·         Myristic acid (C14)

·         Pentadecanoic acid (C15)

·         Palmitic acid (C16)

·         Margaric acid (C17)

·         Stearic acid (C18)

·         Arachidic acid (C20)

·         Behenic acid (C22)

·         Lignoceric acid (C24)

·         Cerotic acid (C26)

Monounsaturated (i.e., semi-stable) fatty acids

·         Myristoleic acid

·         Oleic acid

·         Eicosenoic acids

·         Erucic acid

·         Nervonic acid

Polyunsaturated (i.e., unstable) fatty acids

·         Linoleic acid (LA) - an essential fatty acid

·         α-Linolenic acid (ALA) - an essential fatty acid

·         Stearidonic acid (SDA)

·         Gamma-Linolenic acid (GLA)

·         Arachidonic acid (AA)

·         Eicosatetraenoic acid (ETA)

·         Timnodonic acid (EPA)

·         Clupanodonic acid (DPA)

·         Cervonic acid (DHA)

Essential fatty acids

·         α-Linolenic acid ALA (18:3) omega-3 fatty acid

·         Linoleic acid LA (18:2) omega-6 fatty acid

Requirement of macronutrients in the diet

Protein requirement

The protein requirement must be carefully maintained. A minimal amount of protein is indispensable in the diet to provide for the replacement of tissue proteins which undergo wear and tear. If the protein content of diet is in excess, the remainder is utilized to produce energy.

The requirement of protein is not only quantitative, but also qualitative, since metabolic aspect of protein is intimately connected with its amino acid composition. The essential amino acids must be supplied in the dietary protein which is the basis of the qualitative aspect of protein material. First class proteins contain more essential amino acids than others.

For adults the adequate maintenance dose is 1 gm of protein per Kg of body weight per day. To provide enough margin of safety 100 gm per day is advocated. One half of it must be given in the form of first class' proteins or proteins of high biological value.

For infants and growing children 3-4 grams of proteins per Kg of body weight per day; for school boys and girls, pregnancy, lactation, etc., 2-3 gm per kg of body weight per day. To provide for the specific dynamic action of proteins, which is approximately 5-10% of B.M.R., proportionate amount of carbohydrates and fats must be added.

Fat requirement

Fat produces high energy and serves as a vehicle for the fat-soluble vitamins A, D, E and K. It also contains essential fatty acids, i.e., linoleic, linolenic and arachidonic acids. Out of the total energy requirement 20-30% should come from fats of the diet. The daily intake of fat should be between 50-100 gm per day.

Carbohydrate requirement

There should be sufficient carbohydrate in the diet to provide energy for daily activities. Out of the total energy requirement 60-70% should come from carbohydrates mostly polysaccharides.

Sources for proteins

Animal sources

·        First class proteins or proteins of high biological value-

·        Meats

·        fish

·        animal milk

·        milk products

·        cheese

·        eggs

Plant sources

·        Second class proteins or proteins of low biological value-

·        pulses

·        grains

·        soybeans

·        tofu

·        quinoa

·        some mushrooms

Sources for fats

Animal sources

·        Milk and dairy products like ghee, butter and cheese

Plant sources

·        Vegetable oils are the chief sources.

Sources for carbohydrates

Animal sources

·        Generally poor, milk provides lactose.

Plant sources

·        Grains like corn, rice and wheat

·        Root vegetables like potatoes

·        Fruits 

·        Vegetables

·        Honey

·        sugarcane