Carbohydrates: classification, and functions

What are carbohydrates?

Carbohydrates are biomolecules that contain carbon, hydrogen, and oxygen atoms. These are sugars found in vegetables, fruits, etc.

Carbohydrates belong to a group of nutrients that are known as macronutrients. Macronutrients are those substances that make up the foods we eat. Macronutrients other than carbohydrates are proteins and fats.

The term carbohydrate means hydrate of carbon. The name is given to it because of these molecules contain carbon, hydrogen, and oxygen atoms.

The recommended daily amount of carbohydrates for an adult is 135grams while for pregnant women the amount is 175 grams.

The amount might be increased or decreases by the person depending on their body conditions. For example, people with diabetes should not eat more than 200 grams of carbs daily.


1. Saccharide is also used for these molecules which derived from the Greek word sakkharon meaning sugars.

2.  1 gram of carbohydrates equals about 4 calories.

3. High GI saccharides quickly enter the blood.

4.  Foods which include high carbs are beans, pasta, rice, potatoes etc.

Classification of carbohydrates

There are four main types of carbs which are,

1.  Monosaccharide
2.  Disaccharides
3.  Oligosaccharides
4.  Polysaccharides


These are simple sugars that cannot be hydrolyzed. Monosaccharides are the building blocks of carbs. The smallest monosaccharides are dihydroxyacetone and glyceraldehydes. Polysaccharides on the basis of the carbonyl group are classified into aldoses and ketosis while on the basis of the number of carbon atoms they are classified into trioses(3C), tetroses(4C), pentoses(5C), hexoses(6C) and so on.

However, for better understanding, the system of classification is often combined. For example, glucose is an aldohexose which means that the carbonyl group present in the glucose is aldehyde and contains six carbon atoms.



Disaccharides are molecules which on hydrolysis yields two monosaccharides. Examples of disaccharides are lactose, maltose, and sucrose. The two monosaccharides units present in disaccharides are joined together by a covalent bond which is known as glycosidic linkage. Glycosidic linkage occurs when the monosaccharides unit undergoes a dehydration reaction.


Lactose also is known as milk sugar yield a molecule of glucose and galactose on hydrolysis.

Maltose on hydrolysis gives two molecules of glucose.

Sucrose on hydrolysis gives a molecule of fructose and glucose.


Oligosaccharides are types of molecules which on hydrolysis yields 3 to 9 monosaccharides units. Oligosaccharides are further classified into two subgroups which are maltooligosaccharides and other oligosaccharides.

Examples of oligosaccharides


Polysaccharides are the type of molecules which on hydrolysis yields more than nine monosaccharides units. Polysaccharides are further classified into two subgroups which are starch polysaccharides and non-starch polysaccharides. Polysaccharides are chains of monosaccharides and these chains may be either branched or unbranched.

Examples of polysaccharides
Modified Starches

Functions of carbohydrates

Carbohydrates are the main source of energy for the body. These molecules provide fuel for the central nervous system. These molecules provide energy for working muscles.

Carbs enable fat metabolism and prevent proteins from being used as a source of energy.

Carbohydrates influence mood and memory.

Simple and complex carbohydrates

The 4 classes of carbohydrates are classified into two groups which are simple and complex carbs. Monosaccharides and disaccharides are grouped into simple carbs while polysaccharides are grouped as complex carbs.

Simple carbohydrates

These are simple sugars consist of one or two molecules and are a rapid source of energy.


Complex carbohydrates

These are a long chain of molecules that fill you up for longer. These molecules are more healthful.


Good carbs vs bad carbs

Carbohydrates which are goods are mostly complex carbs while simple carbs are mostly bad and rarely have any nutritional value.

Below is the list of features from which you can easily understand what is good and bad carbs.

Good Carbs are

1.  Moderate in calories
2.  Low in sodium
3.  Low in saturated fats
4.  High in nutrients
5.  Low in cholesterol
6.  Low in trans fats

Bad carbs are

1.  High in calories
2.  Low in nutrients
3.  High in sodium
4.  High in saturated fats
5. High in cholesterol
6.  High in trans fats

carbohydrates and Obesity

Some people’s arguments that the rise in obesity all over the world is linked to a high intake of carbohydrates.

But here is a reason which you must know that the countries which mostly are affected by obesity are China, India, Brazil, etc. If we see the past of these countries the people of these countries eat foods which are carb heavy than now.

The goal of this example is that you cannot blame carbohydrates for it. Carbohydrates might be the minor cause but the major causes of obesity are

1.  Reduction in physical activity
2.  Higher consumption of junk food
3.  Fewer hours of sleep
4.  The rise in living standards
5.  Stress

What is the Glycemic index?

Glycemic index measures how much and how quickly carbohydrates raise the blood sugar level. This means that types of carbohydrates are not important but the glycemic index is important.

High glycemic foods are foods that raise the blood sugar level rapidly and highly while low glycemic foods are the opposite.

However, the benefits of both high and low glycemic foods are in a phase of controversy.

Carbohydrate and diabetes

Diabetes is a condition in which the body is unable to make insulin.

When we consume carbohydrates they are broken down into glucose which then enters the blood.

The level of glucose in the blood is maintained through the homeostatic mechanism by two hormones which are insulin and glucagon.

Insulin lowers the blood glucose level while glucagon raises the blood glucose level. This is a normal process and works great.

But if there is a sudden increase in glucose level the beta cells of the pancreas become activated and start releasing more insulin than normal to overcome the fault. Sometimes the fault exists for many years due to which the beta cells wear out and insulin production drops and eventually stops. This leads to diabetes.

Symptoms of diabetes
1.  Abnormal thirst
2.  Weight loss
3.  Frequent urination
4.   Lack of energy
5.   Blurred vision

Diet foods

The promoters of diet foods promote processed products that contain artificial sweeteners and emulsifiers similar to junk foods.

The consumers of these products may see temporary weight loss but if they remain physically inactive and quite the diet the weight will go back on.


You must keep it in mind that it is important to eat carbs from healthy foods than to a strict diet in which you count the number of grams of carbohydrates consumed.

Carbohydrates benefits

Carbohydrates are important for mental health because many research shows that people who eat high fat and low carb diet are more depressed and anger than peoples who eat low fat and high carb diet.

Many people’s blamed carbohydrates for weight gaining but actually good carbs help you to lose weight.

Some of the good carbs contain a high amount of fibers, energy, and polyunsaturated fats.

Fibers also lower the cholesterols due to which heart health boost.

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