Source, Structure, function and metabolism. 

Factors that can lead to excess or deficiency carbohydrates 

Signs and symptoms in  case of excess or deficiency 


Source, structure, function and metabolism 

Factors that can lead to excess or deficiency of proteins 

Signs and symptoms in  case of excess or deficiency 

Fats and lipids 

Source, Structure, function and metabolism 

Factors that can lead to excess or deficiency of fat 

Signs and symptoms in  case of excess or deficiency 8




The molecular, cellular and biochemical functions of the body are also dependent on its nutritive requirements. Nutritive compounds that are essential for healthy growth and maintenance of body have been classified into macronutrients and micronutrients based on their required amount. Macronutrients are needed by the body in larger quantities and include carbohydrates, fat and protein. The macronutrients are also popularly called as energy providing substances and play a crucial role in maintaining the health of an individual (National Health and Medical Research Council, 2014). This report summarizes information on the composition, consumption and utilization of macronutrients in humans and also on the associated effects in case of excess and deficiency. 


Source, Structure, function and metabolism:

Carbohydrates are defined as complex compounds that are chemically neutral and are composed of carbon, hydrogen and oxygen (Holesh & Martin, 2019). The essential sugars that are associated with human diet are glucose and fructose, dimeric sugars or the disaccharides like lactose and sucrose, and complex carbohydrates with numerous monomers like starch that are normally ingested in staple eating regimen in form of cereals and grains. Complex sugars like starch are very common and widely used in diets. Starch is principally made out of the straight-chain glucose polymers that include amylose α-1, 4 glycosidic linkages and an extended glucose polymer, amylopectin that has α-1, 6 glycosidic linkages (Dashty, 2013). 

The digestion of carbohydrates starts from the mouth itself by the activity of salivary α-amylase that is secreted by the tongue. The amylases that digest carbohydrates are present in the mouth and in the pancreas of human digestive system. The amylases are chemically endosaccharidases that act specifically on the internal or the inner α-1, 4 glycosidic bonds of carbohydrates (Holesh & Martin, 2019).  Once, the partially digested food known as bolus reaches the small intestine, the pancreatic juices enter the lumen of the stomach where the amylases are rendered inactive due to the acidic pH of stomach. The high bicarbonate concentrations present in the pancreatic juices neutralize the gastric acid and this allows the amylases to break down complex carbohydrates into simpler forms like maltose, trisaccharides and even in monomers or the monosaccharides (Qi & Tester, 2019). Once the carbohydrate is broken into its simpler molecules or in monosaccharaides, it is readily absorbed in the blood stream by the action of enterocytes through a specific protein channel which facilitate the transport of monosaccharides (Dashty, 2013).

Factors that can lead to excess or deficiency of carbohydrates

People with carbohydrate metabolism disorder may develop carbohydrate deficiency. The most common disorders associated with deficiency of carbohydrate are acquired. Acquired or secondary problems in carbohydrate metabolism include diabetic ketoacidosis, hyperosmolar coma and hypoglycemia (Ramachanndaran, 2017).

Excess of carbohydrate on the other hand can be occurred due to inappropriate intake of carbohydrate by the muscle cells and this leads to increase in the carbohydrate concentration. Excess carbohydrate intake can also contribute to non-insulin dependent diabetes (type 2 diabetes mellitus) (Mantantzis et al., 2019).

Signs and symptoms in case of deficiency or excess

Symptoms associated with deficiency of carbohydrate include headaches, dry mouth and a fruity smell to the breath with constant fatigue and exertion due to lack of energy ((Ramachanndaran, 2017).

On the other hand, excess can lead to obesity simply by enhancing the production of insulin, which signals cells to save the extra glucose as fat and excessive craving and lethargy are also common signs associated (Salvin & Carlson, 2014).


Source, structure, function and metabolism

Proteins are polymers that are composed of monomeric amino acids that constitute of carboxyl and amide groups. In macronutrients, the proteins function as the building blocks of human body (Wu G, 2016). Complete proteins in diet mainly come from animal sources that include milk and milk products, eggs and meat. Plant based high protein compounds like soy and quinoa also act as reliable sources of complete protein. Eating red beans and other legumes are also good sources. All proteins in the body are simultaneously broken down as they are synthesized in the system. This maintains a total protein content of the system. The suggested daily intake of protein for a healthy adult is ranges from 0.9–1.0 g/ kg of body weight (Semba, 2016).

Enzymes that digest proteins are known as proteolytic enzymes and which act on amide bonds and break them into peptides and monomer amino acids.  Protein breaking enzymes are highly specific as different proteins often contain a specific set of bonds. Based on their mode of action, peptidases are broadly classified into endopeptidases that cleave the internal bonds in the proteins and exopeptidases that cleave proteins from the outer ends. The digestion of proteins begins in the stomach by the action of pepsin (Williamson et al., 2019). Precursor molecule of pepsin, pepsinogen or zymogen is secreted by the cells of gastric mucosa. The precursor undergoes cleavage to become active and turns into pepsin under the influence of acidic pH.  Pepsin possesses a higher affinity towards proteins that constitute aromatic amino acids which include tyrosine, phenylalanine, tryptophan, and leucine (Semba, 2016).. Pancreatic proteases like trypsin chymotrypsin, elastase, and carboxypeptidases are also secreted that digest the proteins post release of pancreatic juices that neutralize the gastric pH. Specific transport proteins help in facilitating the uptake of amino acids and polypeptides upon protein digestion across the brush-border membrane of the digestive system (Williamson et al., 2019). 

Factors that can lead to excess or deficiency of proteins

Protein deficiency in a system can arise due to low intake of protein in the diet. The excessive consumption of protein in diet can lead to health problems. Excess of protein in system is largely attributed to protein-rich diet consumption that is unbalanced and unhealthy (Phillips et al., 2016). 

Signs and symptoms in case of excess or deficiency

Symptoms associated with protein consumption in excess can include development of cardiovascular diseases, diabetes, Alzheimer's disease and kidney stones (Phillips et al.,2016). On the other hand, deficiency in proteins is an important cause of malnutrition since protein is essential for both growth and maintenance of muscle mass. Skin, hair and nail problems, loss of muscle mass, higher risk of bone fractures, increased appetite and increased calorie intake are common symptoms of its deficiency. The deficiency can also lead to diseases like Kwashiorkor disease, marasmus, mental health retardation and even organ failure (Semba, 2016).

Fats and lipids

Source, Structure, function and metabolism

Fats belong to the category of hydrophobic compounds and are often ingested in form of oils and triglycerides in diet directly. Fats are composed of long chains of carbon atoms that are bonded with hydrogen atoms. One terminal of the fatty acid constitutes is a carboxyl group (-COOH) (Sobotka, 2017). Fats are high energy source nutritive compounds and thus, the dietary reference intake (DRI) for fat in adults is about 20% of total calories that are ingested (Carreiro et al., 2016).

Processing of lipids starts in the mouth at time of ingestion. This is finished by the assistance of a lingual lipase that is delivered by glands present in the tongue. In stomach the process of digestion is continued by both lingual lipase and the gastric lipase created by chief cells of the gastrointestinal tract (Purdom et al., 2018). The processing of fats and lipids begins in the stomach with gastric lipase that can divide around 15–20% of the unsaturated fats (Carreiro et al., 2016). The procedure of hydrolysis is finished in the duodenum by lipases discharged alongside the pancreatic juices. An emulsion is shaped in this treatment of fat assimilation which stabilized by preventing lipid particles from merging with each other.  This is done by furnishing a coat on these particles. The particles are coated with bile salts discharged by liver, phospholipids, and cholesterol. This results in the formation of micelles. These micelles are made out of bile salts covering blended and mixed lipids including unsaturated fats, monoglycerides, and cholesterol. Micelles are then trans located across the brush-bordered cells of the enterocytes. Lipase discharged unsaturated fats that are again re-esterified and put away in fat cells as triglycerides (Sobotka, 2017).

Factors that can lead to excess or deficiency of fat

When an individual ingests more calories than they burn in their daily routine of the day in form energy, their body will store the extra calories as fat (Schoeler & Ceaser, 2019). Consumption of calorie rich diet Excess of fat in body can lead to obesity and enhance the risk of various allied diseases. Deficiency of fats is rare and occurs mostly only in infants. In adults either excess or deficiency may occur due to unhealthy eating habits and unbalanced diet consumption (Carreiro et al., 2016).

Signs and symptoms in case of excess or deficiency

Signs of fat deficiency include scaly structure of dermatitis, alopecia, thrombocytopenia, and, in children it may even give rise to intellectual disability. In case of excess fat consumption, individual may gain weight, develop nutritional deficiencies and show signs of cardiovascular diseases (Schoeler & Ceaser, 2019).


Macronutrients play a crucial role in human growth and health maintenance and thus constitute important fraction of human diet to lead a healthy life. Energy consumption in the human body is measured in calories and determines the rate of body growth, repair and develop new tissues, conduction of nerve impulses and regulation of other essential life processes. Deficiency or excess of these compounds can cause severe healthcare problems making monitoring even more crucial. Thus, it is essential to monitor the quantity and quality of these compounds for leading a healthy life.


Carreiro, A. L., Dhillon, J., Gordon, S., Higgins, K. A., Jacobs, A. G., McArthur, B. & Mattes, R. D. (2016). The macronutrients, appetite, and energy intake. Annual Review of Nutrition, 36, 73–103.

Dashty, M (2013). A quick look at biochemistry: Carbohydrate metabolism. Clinical Biochemistry, 46(15), 1339-52.

Holesh JE & Martin A (2019). Physiology, Carbohydrates: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing.

Mantantzis K, Schlaghecken F, Sünram-Lea SI, Maylor EA.(2019). Sugar rush or sugar crash? A meta-analysis of carbohydrate effects on mood. Neuroscience Biobehaviour;101,45-67.

National Health and Medical Research Council (2014). Protein. Retrieved from:

Phillips,S.M., Chevalier, S., Leidy H.J. (2016). Protein "requirements" beyond the RDA: implications for optimizing health. Applications of Physiology in Nutrition & Metabolism,41(5),565-572.

Purdom, T., Kravitz, L., Dokladny, K., & Mermier, C. (2018). Understanding the factors that effect maximal fat oxidation. Journal of the International Society of Sports Nutrition, 15, 3. 

Qi, X. &Tester,R.F. (2019). Fructose, galactose and glucose - In health and disease. Clinical Nutrition, 33, 18-28.

Ramachandaran, S.(2017). Disorders of carbohydrate metabolism. Retrieved from:

Schoeler, M. & Caesar, R. (2019). Dietary lipids, gut microbiota and lipid metabolism. Endocrine Metabolism Disorder, 19,512-520.

Semba R. D. (2016). The rise and fall of protein malnutrition in global health. Annals of Nutrition & Metabolism, 69(2), 79–88.

Slavin, J., & Carlson, J. (2014). Carbohydrates. Advances in Nutrition, 5(6), 760–761.

Sobotka, L. (2017). Metabolism of macronutrients. Nutrition in Neurologic Disorders, 1–17.

Williamson, E., Kato, H., Volterman, K.A., Suzuki, K. & Moore, D.R (2019). The Effect of Dietary Protein on Protein Metabolism and Performance in Endurance-trained Males. Medical Science Report,51(2),352-360.

Wu, G. (2016). Dietary protein intake and human health. Food Functioning, 3,1251-1265.

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