Introduction to Food Macromolecules (Updated)

A macromolecule refers to a large molecule formed by the aggregation of smaller particles known as monomers. Macromolecules occur in many spheres of life, including in food. Food avails nutrients the body needs for survival. Biological macromolecules make up most of these crucial nutrients required to sustain life. Macromolecules are necessary for the body in large amounts and essential for the normal functioning of the body.

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Biological macromolecules include carbohydrates, lipids, nucleic acids, and proteins. All macromolecules named above are polymers, apart from lipids. The biological macromolecules are each essential constituent of the cell and perform many functions. When put together, these molecules form the most considerable fraction of the cell’s dry mass.


Carbohydrates, at the chemical level, are composed of carbon, hydrogen, and oxygen.  Carbohydrates occur abundantly as sugars, fibres and starches found in grains, milk products, fruits, and vegetables. Foods rich in carbohydrates are crucial for a balanced diet. Carbohydrates are the primary source of glucose in the body. Glucose is oxidized in mitochondria to release energy, which supports various vital body functions.

Classification of Carbohydrates

Carbohydrates are grouped based on the level of polymerization. They are classified into monosaccharides, disaccharides, polysaccharides and oligosaccharides. Monosaccharides are made up of one simple sugar and are common in fruits. The three most important simple sugars are glucose, also known as grape sugar, fructose, and galactose. The three sugars are isomers. Slight alterations in the structure of these sugars influence their biological significance. For instance, the arrangement of a specific hydroxyl group in different isomers causes a difference in taste. Galactose rarely occurs alone in as a simple sugar; it is usually found in combination with other simple sugars.

Disaccharides are double sugars; they occur as a result of linkage between two simple sugars. Sucrose is made up of glucose and fructose, one molecule each. Sucrose is found in cane sugar. Other disaccharides include lactose, found in milk, and maltose. Oligosaccharides are made up of between three and six units of simple sugars (monosaccharides). Polysaccharides are made of many units of simple sugars, in tens, hundreds or thousands. Polysaccharides are the main form of the occurrence of carbohydrates in nature. Cellulose, the most commonly found polysaccharide, is a key structural component in plants and is made up of multiple units of glucose linked to each other. Starch, found in plants and glycogen, found in animals are other examples of glucose polysaccharides.

Functions of carbohydrates

The primary roles of carbohydrates in the body are the production of energy, energy storage, ensuring that the body’s reserve of proteins is spared, assembly of macromolecules, and aiding in lipids’ metabolism.

Carbohydrates supply energy to all body cells. Most cells prefer glucose to fatty acids as their chief energy source. Other cells, such as red blood cells and the brain, produce energy only from glucose. Body cells break down the chemical bonds of glucose to release energy in a controlled manner.

If the body amasses enough energy for proper functioning, the excess glucose is stored, majorly in liver and muscle cells in the form of glycogen. Glycogen is widely branched to allow for rapid breakdown whenever the cell requires energy.

Some of the glucose absorbed into the body forms ribose and deoxyribose. The two sugars are essential building blocks of ATP, RNA, and DNA. Glucose is also utilized in NADPH manufacturing, which acts as a cofactor in chemical reactions and cushions the body against reactive oxygen species (ROS).

The availability of adequate glucose levels prevents protein breakdown as a means of generating energy by body cells.  An increase in glucose levels in the blood also limits the use of lipids as a source of energy. High glucose levels stimulate insulin release, which signals the body cells to use glucose to produce energy.

Good carbs and bad carbs

Good carbohydrate refers to foods containing high amounts of fibres; their breakdown takes a longer time and is, therefore, a good energy source. Examples of good carbohydrates include fruits, vegetables, and whole-grain cereals. Bad carbohydrates contain low amounts of fibres; foods containing bad carbohydrates include sugar, white flour, white bread, and rice.


Proteins are polymers made up of many amino acid units linked together; they form long chains. There are 20 naturally occurring amino acids in proteins. A protein molecule is usually larger in comparison to a sugar or salt molecule. Human bodies can produce amino acids, but others must be obtained from food. The amino acids that cannot be produced by the human body are known as essential amino acids and include lysine, histidine, threonine, isoleucine, leucine, methionine, valine, phenylalanine, and tryptophan.

The amount of protein required in the body varies with health, weight, how much physical activity the person engages in, age, and gender. A protein’s nutritional value is determined by the number of essential amino acids it has. Humans source proteins mainly from animals and animal products; plants contain very low amounts of protein content. Food rich in proteins includes fish, eggs, dairy products, lean meats, poultry, and plant proteins (nuts, legumes, whole grains, and lentils). Animal products, chia seeds, quinoa, and hemp seeds contain every essential amino acid and are hence referred to as the ideal proteins (complete proteins).  Soy products are also complete proteins. Plant proteins lack one or more essential amino acids and are hence regarded as incomplete proteins.  People who eat a compulsory vegan diet should combine various complementary plant proteins to ensure they obtain all the nine essential amino acids. Examples of these combinations are macaroni and cheese and rice and beans.

Functions of proteins.

Transport of oxygen; hemoglobin, a protein in red blood cells, plays a significant role in the transport of oxygen by acting as its carrier from the lungs to the tissues.

Proteins act as enzymes. Enzymes catalyze specific biochemical reactions and increase the rate at which they occur. Each enzyme has its particular binding site, which binds to a particular substrate, like a key to its lock.

Proteins also act as antibodies. Antibodies are the critical components of humoral immunity. They recognize and bind to specific foreign antigens and, by so doing, tag them for destruction by other immune cells.

 Proteins form part of body structures, such as collagen in ligaments and keratin in hair cells.

Contractile proteins facilitate the contraction of muscle cells and movement inside single cells.

Proteins also form receptors, which are key components of the signal transduction pathway.


  Lipids are a group of nonpolar organic compounds. They are hydrophobic. The chemical constituents of lipids are carbon, hydrogen, and oxygen. Lipids are grouped into three main categories, namely, triacylglycerols, phospholipids, and sterols. Triacylglycerols make up the largest fraction of the lipids obtained through diet and are found in vegetable oil, some meats, whole milk, cheese, butter, and naturally in nuts, olives, corn, and avocados. At room temperature, fats are solid while oils are in liquid form. Phospholipids are found in tiny amounts in the diet. Phospholipids are also synthesized inside the body to form vesicles for the transport of fat and to form the membranes of organelles and the cell membrane. Cholesterol is a well-known sterol; most of it is produced within the body.

Functions of lipids

Lipids serve as the primary reserve of energy. The extra energy after the food we have eaten is digested and stored in the adipose tissue. Fats can pack together without water in between their molecules and store more energy per unit than carbohydrates.

Lipids play a key role in the regulation of body functions and signalling. Triacylglycerols maintain body temperature even with changes in the temperature outside. Triacylglycerols also help in the production and regulation of hormones. For instance, adipose tissue produces leptin, which controls appetite. Fats sustain the generation of nerve impulses, help in the formation of neural cell membranes, and enable the transmission of electrical impulses in the brain.

Lipids improve the absorption of fat-soluble molecules—improved absorption results in increased bioavailability. Fat-soluble vitamins, A, D, E, and K and some phytochemicals such as lycopene require fat for them to be absorbed effectively.

Glycerophospholipids form the main part of the structure of cell and organelle membranes. Phospholipids enhance the fluidity of cell membranes. Lipids also regulate the permeability of the cell membrane.

Essential fatty acids, such as linoleic acid and linolenic acid, form eicosanoids, which include thromboxanes and prostaglandins. These play a significant role in fever, pain, and blood clotting.   Lipids also form part of some enzyme complexes.

Nucleic acids

Nucleic acids are macromolecules made up of many nucleotides. Nucleotides are building blocks of DNA and RNA. Each nucleotide contains an aromatic base (nitrogen-containing) and five-carbon sugars linked to a phosphate group. Nucleic acids contain four of the five nitrogen-containing aromatic bases each: adenine, guanine, cytosine, thymine, and uracil, denoted as A, G, C, T, and U, respectively. A and G are classified as purines. C, T, and U are categorized as pyrimidines. A, C and G are found in all the nucleic acids; T however, occurs in DNA alone while U is present in RNA only. They contain the genetic information of the cell and instructions that direct protein synthesis. They are the key determinants of characteristics an organism is going to inherit. Nucleic acids occur naturally, and their components include organic bases, sugars, and phosphoric acid.

The two types of nucleic acids are ribonucleic acid (RNA) and deoxyribonucleic acids (DNA). DNA molecules are double-stranded, while RNA molecules are single-stranded.  In RNA, the pentose sugar has a hydroxyl group on the second carbon, while in DNA, the pentose sugar lacks a hydroxyl group in the same position. In the absence of a phosphate group, the sugar linked to any of the bases is called a nucleoside. DNA contains genetic material for all organisms (free-living) and the majority of viruses. RNA carries genetic material for specific viruses; it also occurs in living cells which it is essential for protein synthesis.

Nucleic acid can be sourced from foods such as seafood (chlorella algae, sardines, and fish), nuts, and vegetables (broccoli, cabbage, spinach, and cauliflower), mushrooms, meat (chicken, beef, and pork), and yeast.

Functions of nucleic acids

Nucleotides are polymers of nucleotide units. Most biological processes require nucleotides. Nucleotides aid in the repair of the gut, enhance the growth of cells and boost the immune system.  Nucleotides also encourage the growth of muscles and detoxification. They also help to maintain regular metabolism in the cell. Besides boosting antioxidants’ function, nucleotides prevent the body from being damaged by reactive oxygen species(ROS).

DNA codes for proteins; it is decoded by messengers and broken into single strands copied on RNA.  Replication of DNA assists in functions such as the growth and maintenance of cells and tissues. During replication, the DNA strands unwind, and several bases are left without partners along the molecule. Unpaired bases then attach to the free bases forming a new strand, which complements the original strand. This results in a strand that is similar to the original one before unzipping. Two pairs of coiled DNA strands are obtained as a result. DNA passes genetic information from one generation to the next (heredity); this is based on the fact that chromosomes are made from genes, and genes are made from DNA.

Messenger RNA is responsible for transcribing the DNA code to a form that can be read and used for protein synthesis. Ribosomal RNA consists of two subunits, the smaller subunit which decodes the genetic information on mRNA, and the larger subunit, which facilitates a polypeptide chain formation by linking amino acids. Ribosomal RNA also combines with cytoplasmic proteins resulting in ribosomes, where protein synthesis occurs. Ribosomal RNA, therefore, guides the translation of mRNA. Transfer RNA pairs up the anticodon to codons in mRNA and carries the amino acid encoded for by the messenger RNA.  Apart from its role in protein synthesis, RNA also enhances the regulation of body temperature, improves cognition, and has antiviral, anti-anoxia, and anti-aging properties.

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