• Moloya G.

Carbohydrates: Understanding the basics

What are carbohydrates?

Carbohydrates are components of foods containing carbon (C), hydrogen (H), and oxygen (O), usually with a hydrogen: oxygen atom ratio of 2:1.

They are one of the major sources of fuel in our body.

All carbohydrates are made up of sugar molecules and can be classified into monosaccharides, disaccharides, oligosaccharides and poly-saccharides.

Monosaccharides are one-unit-only sugars like glucose, fructose and galactose.

They are simple carbohydrates that cannot be hydrolyzed further into polyhydroxy aldehydes or ketone unit.

Sugars having aldehyde group are called aldoses and sugars with keto group are called ketoses.

Depending on the number of carbon atoms monosaccharides are named as triose (C3), tetrose (C4), pentose (C5), hexose (C6), heptose (C7) and so on.

Disaccharides- When two monosaccharides are combined together with elimination of a water molecule it is called disaccharide.

These are a combination of two individual one-unit-only sugars .

Oligosaccharides - According to World Health Organization (WHO), oligosaccharides are carbohydrates with 3-9 sugar units.

The most well-known are medium chains of single unit sugars and include mannose , fibres such as short-chain inulin and fructo-oligosaccharides which consist of up to 9 fructose units .

Fructo-oligosaccharides or oligofructans naturally occur in low sweetness vegetables such as artichokes and onions.

Raffinose and stachyose are two other examples of oligosaccharides found in some pulses, grains, vegetables, and honey.

Poly-saccharides are long single-unit sugar chains and include starches like those found in potatoes, onions and carrots.

Polysaccharides are polymerized products of many monosaccharide units. They may be homo or hetero polysaccharides. Starch is the major form of stored polysaccharide in plants.

This means that carbohydrates are constituents of foods that get converted into glucose, or sugar, in our bodies during digestion.

Glucose comes either directly from carbohydrate-containing foods and drinks, or is produced by the body from non-carbohydrate sources.

Why do we need carbohydrates?

Most importantly, carbohydrates provide the energy for body metabolism and also play an important role in the structure and function of our cells, tissues and organs.

Depending on the type, a gram of carbohydrates provides different amounts of energy: Starches and sugars are the main energy-providing carbohydrates, and supply 4 kilocalories (17 kilojoules) per gram

Polyols provide 2.4 kilocalories (10 kilojoules) (erythritol is not digested at all, and thus gives 0 calories)

Dietary fibre 2 kilocalories (8 kilojoules)

They are especially important for the brain, which relies on glucose for fuel. Studies show that administering glucose can enhance many aspects of cognitive function and positively impact attention, memory and learning.

Therefore, it may be especially important to keep blood glucose levels at an optimum level for good cognitive function.

During digestion, carbohydrates are broken down into their monosaccharides by digestive enzymes which are then absorbed causing a glycaemic response.

Some of the carbohydrates (eg.,dietary fibre ) cannot be broken down and they get either fermented by our gut bacteria or they transit through the gut without being changed. Examples, cellulose, pectins, hemicellulose, and gum.

What are the required and recommended daily intake of Carbohydrates?

  • Adults should get 45% to 65% of their total daily calories from carbohydrates, 20% to 35% from fat, and 10% to 35% from protein.

  • Carbohydrates derived from cereals form the chief source in our diets. The Dietary Guidelines for Americans( 2015–2020) recommend consuming 6 ounce-equivalents per day of grains on a 2,000 calorie diet.

  • The Estimated Average Requirements for Indians - 2020 for CHO has been set at 100 g/day for ages 1 year and above with a RDA of 130 g/day, assuming a coefficient of variance (CV) of 15% based on variation in brain glucose utilization. Plant foods such as fruits and vegetables are quality carbohydrates that are loaded with fibre.

  • Studies show an increased risk of heart diseases with low-fibre diets. Lack of adequate dietary fibre in diets containing refine foods, lead to weight gain, constipation and even colon cancer.

  • World Health Organization (WHO) suggests an intake of >25g of fibre per day (76). Various food and health related organizations encourage meeting the recommendations through a diet rich in vegetables, fruit and whole-grain cereals. Majority of countries recommend an intake of 25-35 g/day of dietary fibre for adults and the recommendation range from 18-38g/day .

  • The Indian Council of Medical Research recommends that the daily diet of an adult should contain at least 40g of dietary fibre (based on 2000 Kcal diet) . As per the British Nutrition Foundation, the government published guidelines (2015) recommends a dietary fibre intake of 30g a day for adults (aged 17 years and over).

What happens when we eat too much refined carbohydrates or sugars?

Eating too much refined carbohydrates or sugars may cause -

  • Premature ageing. Excessive sugar consumption can cause long-term damage to skin proteins, collagen and elastin, leading to premature wrinkles and ageing.

  • Sleeplessness.

  • Low energy.

  • Unexplained bloating.

  • Weakened immune system.

  • Constant cravings.

  • Weight gain.

  • Dental caries

  • Pre diabetes

  • Type 2 diabetes

What is Glycaemic Response?

When we eat starchy, sugary, carbohydrate - containing foods, blood glucose level in our body rises and then decreases - a process known as the glycaemic response. Glycaemic response reflects the rate of digestion and absorption of glucose, as well as the effects of insulin in normalising the blood glucose level.

What factors affect the Glycaemic Response?

A number of factors influence the rate and duration of the glycaemic response:

The food itself:

  • The type of the sugar(s) that form(s) the carbohydrate; e.g. fructose has a lower glycaemic response than glucose, and sucrose has a lower glycaemic response than maltose

  • The structure of the molecule; e.g. a starch with more branches is more easily broken down by enzymes and therefore more readily digestible than others

  • The cooking and processing methods used

  • The amount of other nutrients in the food, such as fat, protein, and fibre

  • The metabolic responses in every individual:

  • The extent of chewing

  • The rate of gastric emptying

  • Transit time through the small intestine (which is partly influenced by the food)

  • Metabolism itself

  • The time of day the food is ingested

What is Glycaemic Index(GI)?

The Glycaemic Index(GI) is a number that tells you how fast or how slow your body converts carbohydrates in a food into blood sugar. It provides information about how the body digests carbohydrates using a scoring system of zero to 100.

The GI concept was used in the management of diabetes before being used in other clinical situations.

It helps you pick foods that will not cause dramatic changes in your blood sugar levels.

GI and Diabetes

The scale ranges from 1 to 100; for a prediabetes diet, the lower the number, the better:

· < 56 = Low

· 56 - 69 = Medium

· >69 = High

Low-GI foods (GI < 56) contain carbohydrates that take the body longer to break down than high-GI foods. It means that low GI foods raise a person's blood sugar levels more slowly than moderate- or high-GI foods.

Research suggests that focusing on foods with low-glycaemic index carbohydrates and high fibre may protect against diabetes and cardiovascular disease.

You can use food labels to estimate the Glycaemic Index value of a particular food.

GI and balanced eating

Scientists(Jenkins et al., 1983) originally planned GI for people with diabetes as a guide to food selection, advice being given to select foods with a low GI.

Lower GI foods were considered to confer benefit as a result of the relatively low glycaemic response following ingestion compared with high GI foods.

Research suggests that it is the amount of carbohydrates that you eat rather than its GI that has the largest impact on the increase in blood sugar levels after a meal. Hence, it is important to eat sensible portion sizes of carbs and include low GI foods in our daily meals.

A common misinterpretation is that low GI food means low carbs. In fact, low carbs indicate the quantity whereas low GI indicates the quality of carbohydrate and your body’s response to it.

Similarly not all low GI foods are healthy for example ice creams and chocolate have medium to low GI, but they have higher fat and calorie content.

So rather than focusing only on the GI number of the foods, GI should be used in the context of balanced eating.

Example of Low GI carbs are

Conclusion - Carbs - good or bad?

In conclusion, with carbs being condemned as the major cause of weight gain and people going in for keto diets, we have to realize, carbs are not all bad .

It is essential for healthy brain functioning and provide fuel to different body functions and metabolism.

However, it's the type and quantity of the carbs you eat that one has to watch out for— not carbohydrates themselves.


1. World Health Organization (2003) Diet, Nutrition and the Prevention of Chronic Diseases. Geneva: WHO

2. Gopalan C, Rama Sastri BV, Balasubramanian SC (2016). Nutritive value of Indian Foods, National Institute of Nutrition. Indian Council of Medical Research, 2016.

3. Stephen MA, Champ MJM, Cloran SJ, Fleith M, Lieshout LV, Mejborn H, Burley VJ(2017). Dietary Fibre in Europe: Current state of knowledge on definitions, sources, recommendations, intake and relationships to health. Nut Research Reviews; 30: 149-190

4. Longvah T, Ananthan R, Bhaskarachary K, Venkaiah K. Indian Food Composition Tables. National Institute of Nutrition. Indian Council of Medical Research,2017.

6. ICMR. Nutrient requirements and recommended dietary allowances for Indians. A report of the expert group of the Indian Council of Medical Research, New Delhi, 2010.

7.Slavin, J., & Carlson, J. (2014). Carbohydrates. Advances in nutrition (Bethesda, Md.), 5(6), 760–761.

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