Often food is compared to fuel like petrol for cars. This is a very poor comparison. Burning petrol supplies energy for a car to move. Similarly, food keeps living things supplied with energy to function but food is not only for that.  Cars get tear and wear. Fuels cannot heal them. On the other hand food is used for growth and repair. Machines are not attacked by bugs.  So another function of food is fighting germs and healing. The basic unit of fuel is Hydrocarbon while that of food is Carbohydrates.

Food categories.

A balanced diet for healthy living should include macronutrients and micronutrients.

Macronutrients include:-

1. Carbohydrates
2. Proteins
3. Lipids
4. Fibres
5. Plenty of water

The micronutrients are:-

1. Vitamins
2. Mineral salts
3. Trace elements and
4. Phytochemicals along with antioxidants

Macronutrients

1.Carbohydrates

The staple diet of people all over the world includes carbohydrates. Wheat in the west, rice in the east and yams in Africa are rich sources of starch.

These are compounds containing carbon, and water, synthesized by plants during photosynthesis.  The simplest of these are monosaccharaides which include glucose (dextrose), fructose present in many fruits and honey.

Glucose is an ultimate product of digestion and transported in the body as blood sugar. This is the fuel for cellular respiration.

Disaccharides are formed by the combination of simple sugars. They include sucrose cane sugar) and maltose obtained from malt (dried germinating grains).

While simple sugars and disaccharides easily dissolve in water Polysaccharides are insoluble. This property makes them suitable for storage inside the bodies of plants, as starch and in animals as glycogen.  

Starch is the principle food present in grains, yams and potatoes.   

The main function of carbohydrates is to supply energy. 1 gram of carb gives 16.7 kJ of energy.  Most organisms can build other complex substances necessary for body tissue, hormones etcetera starting from simple sugar.  What they cannot make is acquired from others.

2. Proteins.

These are highly complex compounds containing billions of Carbon, Hydrogen, Oxygen and Nitrogen along with a few Sulphur and Phosphorus here and there.

Amino acids are the simplest units of this group. Complex protein polymers are built by the addition of these monomers. Humans need 22 amino acids, out of which only 13 can be assembled inside the body.  The rest have to be taken from food. These are listed here as essential amino acids…

phenylalanine, valine, threonine, isoleucine, methionine, leucine, histidine, lysine and tryptophan. Vegans often miss the last  two, as they are not commonly present in vegies.

Proteins are mainly used for growth and repair. DNA and RNA, various enzymes, hormones are protein molecules. In times of scarcity they can be used as a fuel to generate energy.

Recommended daily intake of protein is about 50 g for adults. Protein rich food includes eggs, beans, animal flesh and dairy products.  Mushrooms are a good source of proteins for vegetarians.

When a protein food is taken it has to be split up into its basic units, amino acids. These are then re arranged to the type of the protein molecules the body needs.  If one unit necessary for a particular protein polymer is absent the others have to discard. These are delaminated in the liver and used to generate energy. Ammonia, the byproduct formed during his process is poisonous, it is converted urea and expelled in urine. There is no way for stockpiles of protein or amino acids as for fats and carbohydrates. 

The RDA (Recommended Daily Allowance) of protein for an adult is 8g for a kilogram of body weight. The growing children and athletes need more.

3. Lipids

They are also made up of Carbon, Hydrogen and Oxygen just as Carbohydrates but with higher hydrogen to oxygen ratio. They include fats and oils, phospholipids and steroids. They are excellent energy producing molecules.1g of lipid can produce twice as much energy as 1g of carbohydrates.

Excess carbohydrates in the food can be converted to fat and stored in the body as adipose tissue. Fat in the skin prevents heat loss while internal fat cushions some of the vital organs. Some hormones are made from fat. Bile acids are steroid based. Lipids also help in the absorption and transport of insoluble vitamins, such as A, D, E and K, which dissolve in fat.

Too much fat in the diet, especially the animal fats, seems to have adverse effects on health. They can cause high blood pressure, obesity, diabetes and even some forms of cancer. Cholesterol, which is a form of fat, a sterol (steroid-alcohol), cannot be transported in pure form due to insoluble nature. So they are attached to transport molecules called lipoproteins. Just as some vehicles with bad drivers cause accidents on the highway LDL vehicles loaded with cholesterol cause cardiovascular disease.  HDL taking cholesterol clears up congestion in the blood vessels.

Your cholesterol levels can be obtained by a blood test known as a lipid profile test.  If you have 120 to 160 mg. of LDL per a deciliter it would be normal.

The body can synthesize almost all the required fatty acids from carbohydrates except two. They are linoleic acid and linilenic acid.

Saturated Fats

These are of animal origin and found in a solid or semi-solid state below 25°C. They are fully saturated with Hydrogen atoms and contain no double bond between carbon- carbon.  Red meat, Whole milk, Butter and tropical oils contain a high proportion of saturated fat. However Coconut oil seems to be having added benefits due to the presence of Lauric acid. It is advisable to limit for less than 5% of saturated fat in your diet.

Unsaturated Fat

These remain as liquids at a room temperature of 25° C.  Good examples are Olive oil, Their molecules have at least one double bond.

Type of Food	Mono unsaturated	Poly unsaturated	Saturated Fat
1.Butter	30 %	4 %	66 %
2.Margarine	43 %	35 %	22 %
3.Mayonaise	30 %	55 %	15 %
4.Canola oil	64 %	28 %	8 %
5.Olive oil	72 %	14 %	14 %
6.Peanut oil	50 %	32 %	18 %
7.Saflower oil	76 %	15 %	9 %
8.Sesame oil	42 %	15 %	43 %
9.Sunflower oil	42 %	46 %	12 %
10. Coconut oil	6 %	3 %	91 %

Transfat

These are formed during hydrogenation of oils to make margarine.  These are more harmful than the saturated fats. These are generally present in some biscuits and baked food where they use cheap margarines. Generally food labels do not indicate the presence of Trans fatty acid.  It can be obtained by subtracting the values of unsaturated and saturated fat contents from the total fat value.

SUMMARY

Macronutrients

	1.Carbohydrates	2. Proteins.	3. Lipids
Elements	Carbon, Hydrogen and Oxygen.	Carbon, Hydrogen and Oxygen.	Carbon, Hydrogen, Oxygenand Nitrogen.
Formula	Cm(H2O)n	H H3N   C   COOH                  R	CnH2n+1COOH
Basic unit	Glucose	Amino acid	Fatty acid
Types	Monosacharides        eg. glucose (dextrose), fructose p Disacharides              eg. sucrose (cane sugar) and maltose Polysacharides           eg. Starch, Glycogen.	Essential .     phenylanine, valine,threonine,              isoleusine, methionine,leucine, histidine, lysine,tryptophan.	Saturated                       eg. Red meat, Whole milk, Butter and tropical oils  Monosaturated eg. Olive oil. Poly Unsaturated                    Transfat Produced during hydrogenation of oils to make margarine.
Food crops	Wheat, Rice, Yams and tubers.	Eggs, Animal flesh, Dairy products, Legumes and mushroom.	Vegetable oils, Animal flesh, Dairy products, Avacado.
Balance	60%	20-30%	10-20%
RDA		8 g.per kg body wt.
Energy from 1g.	16.7 kJ		32kJ

Dietary Fibre

The word ‘fibre’ is a misnomer and one must not expect them to be in the form of threads. Fibre gives roughage for the undigested part of the food facilitating defecation. There are two forms of fibre called soluble and insoluble.

Soluble fibre.

These come mainly from soft pulp of fruits and vegetables. They form a gelatinous mass in the intestine and promote the growth of healthy bacteria. They also slow down the movement of digested food helping the process of absorption.

Insoluble fibre

These mainly consist of cellulose, from the cell walls in plant matter. Whole grains, the skin in potato and some fruits are rich in insoluble fibre. They also encourage bacterial growth, facilitate the bowel movements and keep the contents moist. One disadvantage of them is the production of gas due to fermentation.

Minerals

A regular diet should also contain the following elements for proper nutrition.

Element or ion	RDA for adults.	Function	Sources
Iron Fe2+	8.0 mg	To make Haemoglobin in red blood cells and myoglobin  in muscles. Excess of Iron is the most frequent cause of poisoning deaths among children in the U.S.	Dried beans Liver Dried fruits  egg yolks Iron-fortified cereals and whole grain. Black Tea can reduce Iron absorption.
Potassium K+	5.0 g	Build proteins. Break down and use carbohydrates Build muscle Maintain normal body growth Control the electrical activity of the heart Control the acid-base balance	Meat, fish, Soybean, broccoli, peas, lima beans, tomatoes, potatoes (especially their skins), sweet potato (Kidney patients should  avoid this element)
Chlorides  Cl-	2.0 g	Flud balance,. For digestive juices.	Usually taken as sodium chloride.(table salt)
1.           Calcium 2.              Ca2+	1.0 g	Growth of bones and teeth., blood clotting, intra cellular signalling, and muscle contraction.                                     18% of bones tissue is calcium.	Cheese, milk, yoghurt. Green vegies.
Chlorides  Cl-	2.0 g	Keeps the proper balance of body fluids. It is an essential part of digestive (stomach) juices.	Usually taken as sodium chloride.(table salt)
Sulphur	1.5 g	The health of your joints, skin, hair, nails and connective tissues. It can function to reduce pain	cruciferae vegetables
Phosperus.	750 mg	Helps the development of bones and teeth.	Whole wheat, cottage cheese, garlic.
Magnesium Mg2+	310 mg.	Contraction and relaxation of muscles Function of enzymes and production of protein.	Green vegies, Fruits Nuts, legumes brown rice,  Soy products
Zinc Zn+	8 mg.	Enhances immunity. Helps to heal wounds.	Meat, nuts, whole grains, legumes, and yeast.
Fluorine F-	4 mg	For tooth enamel. A hardening component of bone and it is present at about 4% as calcium fluoride,  while too much fluoride causes brittleness.	Mostly from water.