Nutritional biochemistry

The branch of science that interprets or explains the relationship of food with the functioning of living system is nutritional biochemistry. Nutrition refers to all kind of nourishment that is helpful for sustainability of life. The study of nutrient requirement and the diet that provides these nutrients is also termed as nutrition. So, the nutrition includes the uptake of food, the chemical composition of nutrients and their metabolism to make them useful for the functioning if living systems of life.

We can say that nutritional biochemistry is the study of nutrition as a science. The nutritional biochemistry specifically focuses on nutrient chemical components, and how they function metabolically, physiologically, biochemically as well as their impact on disease. Nutritional Biochemical research is primarily based  upon defining dietary and nutritional needs in sick and healthy individuals and the reduction of side effects of pharmaceutical drugs.

Basic categories of nutrients

The components of food that sustains the functioning of living systems are termed as nutrition. The nutrients can be classified in two categories depending upon their requirement in body:

  1. Macronutrient
  2. Micronutrients


As the name suggests, the human body requires large amount of these nutrients. Consequently, these provide a bulk of energy. Carbohydrates, fats, proteins are macronutrients.

Water is one of the essential component and the universal solvents for almost all chemical reactions of the cell. But some of the biochemist does not consider it as the nutrient but as a solvent only as food is not the only source of its supply in body. While some other considers it as the essential nutrient because the survival of an individual also depends upon its supply. However , a nutrient or as solvent, direct or indirect  water has its vast role in almost all biochemical reactions of cell. For example, glycolysis occurs in cytosol of cell that contain water in it. So water also provide medium for the reactions. Deficiency of water cause dehydration , hallucination and in severe cases death may occur.

  1. Carbohydrates

A major energy source of the body is carbohydrates that provide 4kcal of energy upon hydrolysis. They are present in all types of sugars and starch so named as saccharides (sugars) also. Carbohydrates can be classified as mono,di and polysaccharides that is because on the monomer sugar components that are present in that compound.

  • Glucose is the simplest carbohydrate and a monosaccharide.
  • Sucrose is disaccharides that upon hydrolysis yield two monosaccharide’s units glucose and fructose.
  • Starch and glycogen are examples of polysaccharide that yield multiple monosaccharide units upon hydrolysis.

Metabolism of Carbohydrates

The digestion of carbohydrates starts in the mouth by the action of saliva and is finally broken down to the simplest units that are later absorbed in the small intestine. Their digestion includes hydrolysis of disaccharide and polysaccharide to simple sugars. The series of reactions involving assimilation, utilization of glucose by body.

Ribose, xylose and arabinose are 5 carbon sugars (Pentoses- monosaccharides) and present in vegetables and fruits and are of significance as are constituent of riboflavin (Vitamin B), RNA and DNA. These are not required in diet as these can be synthesized by all animals.

Dietary fibers are non-digestible carbohydrates – cellulose, hemi cellulose, gums, mucilage, pectin and lignin in plants.They are classified as soluble and insoluble dietary fiber. They do not provide any nutritive value, but are helpful in many ways. Cellulose has a high molecular weight, is non-crystalline, insoluble in water and tasteless.

A normal value for blood glucose is 80-120mg/dl. Depending on the type of carbohydrate it has effect on the blood glucose levels. Glycaemic Index (GI) is the blood glucose response after having a carbohydrate meal. GI is affected by number of factors such as physical characteristics of food (intact or ground form), cooked or uncooked food, fiber content of food, presence of fat and protein in the diet. 

Significance of carbohydrates in cellular metabolism
  • Major source of energy for the body
  • Carbohydrates are utilized for the energy production by the process of glycolysis
  • The products of glycolysis are later utilized as the reactants of the kreb cycle and the electro transport chain that completes the oxidation of the carbohydrates (glucose)
  • Soluble dietary fibers help in lowering of blood cholesterol level and blood glucose levels.
  • Other insoluble dietary fibers are also have role as they stimulate the digestive track contractions
  • For certain foods, starches can be used as thickening agents like corn flour.
  • Helpful for the growth of desirable bacteria eg. lactose;
  • Pentose’s ( 5 carbon sugars) are components of DNA and RNA

About 40 grams of the dietary fibers and 55-60% of the carbohydrates in daily diet are required and recommended for the adults by the nutritionist.

2. Fats

These are triglycerides of fatty acids and glycerol, having the structure of CH3 (CH2 )nCOOH ,and a concentrated source of energy that provide about 9kcal of energy.

They are classified on the basis of bonding present in their carbon atoms. The presence of double bond cause unsaturation of fatty acids while the fatty acids having no double bond are saturated fatty acids. Fatty acids are solid at room temperature and are termed as fats while others are in liquid form and termed as oils.

Metabolism of Fats

The digestion of fats occurs in the small intestine by action of bile. The lipase enzyme converts fats into fatty acids and glycerol. Later, the body absorbs these in blood in the form of lipid droplets- the chylomicrones . These fats are later resynthesized to triglyceride in the intestinal cell.

When the body needs energy (in starvation etc), certain enzymes carry out β-oxidation of fats. This breaks down long-chain fatty acids to yield the reactants of the energy cycle-kreb cycle. This results in production of actyl CoA that the kreb cycle incorporates to provide energy and reducing equivalents NADH and FADH2 to cell.


Β-oxidation of fats yields acetyl Co A that is later undergoes kreb cycle of mitochondria of cell. 

Transport of these triglycerides takes place by lipoproteins by via lymph to blood. From blood, the small chain fatty acids are directly absorbed by the capillaries and cells.

Significance in metabolism

  • Fats are a concentrated source of energy that provide 9kcal/g
  • They have a vital role as building blocks for synthesis of biologically important lipids e.g phospholipids, sphingolipids and cholesterol esters. All of these have several metabolic regulatory roles.
  • Helpful for the absorption of fat-soluble vitamins.
  • Essential fatty acids (that cannot be synthesized in body so their requirement is met by diet) are vital for the function and structure of body cells membranes. Also they are important for the hormones as well. For example, the essential fatty acid linoleic acid and alpha-linolenic acidare vital for body.
  • Mono-unsaturated fatty acids (having a single double bond in their structure) are vital for lowering risk of coronary heart disease,cancer, and other inflammatory disorders.
  • Fats as adipose tissue act as an insulator and also protects the vital organs of body.

3. Proteins

These are polymers of amino acid that are linked together by peptide bonds. the proteins consists carbon, hydrogen oxygen and nitrogen. Some may have sulfur and phosphorous in their structure depending upon the type of their constituent amino acids. These amino acids may be water soluble hydrophilic or water insoluble hydrophobic that are soluble in organic solvents. There are 20 types of amino acids more abundantly present in proteins. They are of two types: essential and nonessential amino acids.

Our body cannot synthesize essential amino acids to meet their requirement. Therefore, we need to take these in diet. For example, valine, histidine etc.

The human body, itself can synthesize non-essential amino acids. For example, cystein and arginine etc. Protein like meat and milk are animal proteins and the body absorbs these much rapidly and easily. On the other hand, the proteins from plant sources such as legume plants are plant proteins. These are a source of essential amino acids for the body.

Metabolism of Proteins

Like the other macronutrients, protein digestion also starts from stomach. It finally completes in small intestine where most of the absorption occurs. The hydrolysis of protein results in their break down to polypeptides and finally into amino acids.

Biological Value (BV) of proteins is the percentage of absorbed protein nitrogen which our body retains after consuming the protein rich diet. A high BV is indicative for a high rate of amino acids utilization in body provided by the proteins. Animal protein foods like meat and milk show higher BV than vegetable protein foods.

Significance in metabolism

  • Proteins are essential for general growth, maintenance & repair of certain body tissues.
  • Have secondary role as energy source.
  • Vital for the synthesis of protoplasm, enzymes e.g. globular proteins and hormones.
  • For production and maintenance of body cells
  • These also have role in supply of the essential amino acids which our body cannot synthesize

Summary of macronutrients metabolism and role biochemical reactions of energy production


  1. Vitamins

These are the group of organic nutrients and the body needs these in small quantities for certain of biochemical functions of the cells. Usually the body cannot synthesize most of these vitamins. Therefore, their supply is maintained by the diet containing these vitamins.

Metabolism of Vitamins

Similar to fats metabolism the vitamins are absorbed in small intestine to the blood in form of chilomicrons. Every vitamin has its own metabolic pathway for use in cellular energy production.

Some vitamins are hydrophobic that these are lipid soluble. The body absorbs these during the normal fat absorption. Transport of these vitamins occurs in blood by the lipoproteins or some carrier proteins. For example, vitamin A,D,E & K.

Some vitamins are water soluble that usually acts as enzymes co-factor. For example, folic acid that acts as carrier molecule. Thiamin, niacin and riboflavin etc.

Recommended diet for each vitamin is highly specific as their deficiency as well as high concentration can cause diseases. High levels of vitamins lead to the condition termed as vitamin toxicity.

2. Minerals

Minerals are inorganic molecules that have a vital role in the body directly or indirectly being a part of some enzymes and other complexes like iron is a part of hemoglobin- an oxygen carrier molecule.

Significance in metabolism

  • Sodium is for electrolytic balance and for transmission of nerve impulse as well
  • Iron is part of heme group of hemoglobin that is oxygen carriers


  • Potassium also involves in nerve impulse conduction
  • Calcium for nerve impulse transmission and in muscle contraction, also for the healthy bones and teeth
  • Phosphorous maintain acid-base balance as buffering agent in blood
  • Magnesium has role in nerve impulses transmission and part of certain enzymes as cofactor
  • Sulfur is part of some of proteins and some amino acids and it helps in formation of sulphide linkages in protein folding.
  • Chromium regulates the blood sugar level and works closely to the insulin hormone
  • Selenium is antioxidant
  • Fluoride is for healthy teeth and bones
  • Iodine is part of thyroid hormone and involved in metabolism
Health issue due to minerals deficiency

Deficiency of minerals results in:

  • Electrolytic imbalance in body
  • Disruption in  nerve impulse conduction which affects brain functioning and coordination
  • The mineral ions that are part of other enzymes will directly affect their activity.

Bottom line

All the nutrients have a vital role in most of the biochemical reaction and pathways of energy production in cells. So these all collectively sustain the life by maintaining  and regulating (as part of enzymes) the biochemical pathways. Deficiency of any of these nutrients may have adverse health effects. Even there excess as in case of vitamins can be toxic. So these nutrients must be present in our daily diet as so as to maintain their healthy and recommended supply to body.

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