Dr. Pradeep Gadge writes that when educating patients on glycaemic index it is important to not focus on the whole picture, but the factors affecting the GI of Indian food. It is also necessary to inform them that a low glycaemic index doesn't make a food healthy, or mean that one should eat a lot of it.

Food we eat provide fuel to our body in the form of carbohydrates, fat, and protein. Carbohydrates are found in breads, cereals, fruits, vegetables, and dairy products, and they are an essential part of a healthy diet. When we eat any type of carbohydrate, our digestive system breaks it down into simple sugars that enter the bloodstream. But while carbohydrate is an essential part of our diets, not all carbohydrate foods are equal.

What is Glycaemic Index?

The Glycaemic Index (GI) is a relative ranking of carbohydrate in foods according to how they affect blood glucose levels. The glycaemic index, or GI, measures how a carbohydrate-containing food raises blood glucose. A food with a high GI raises blood glucose more than a food with a medium or low GI. A low GI rating of a food does not mean one can eat a larger serving of that food. The total amount of carbohydrate and calories consumed is still important.

The GI of Indian foods

Carbohydrate-containing foods are compared with glucose or white bread as a reference food, which is given a GI score of 100. The GI compares foods that have the same amount of carbohydrate, gram for gram. Carbohydrates that break down quickly during digestion have a higher glycaemic index (GI more than 70).

Low GI foods are also rich in fibre which takes the longest to digest, makes you feel fuller for a longer time and helps control appetite. Some examples of the GI rating of various foods include:

• Low GI Foods: less than 55, examples are unrefined grains, pulses, vegetables, milk and milk products, oats, apple, pear, orange etc.
• Medium GI Foods: those with GI between 56 and 69, examples brown rice, basmati rice etc.
• High GI Foods: GI more than 70; examples include potato, rice, refined cereals like white bread, candies, fried foods, fruit juices etc.

Factors that affect GI of food

The GI of a food or meal is influenced by a number of factors, including the type of sugar, structure of the starch, level of ripeness and cooking method. Factors such as the size, texture, viscosity (internal friction or ‘thickness’) and ripeness of a food affect its GI.

Both fat and acid slow down the rate at which food is digested and absorbed, resulting in a lower GI. Adding fats or acids, such as avocado or lemon juice, will lower the GI of a meal.

Preparation and cooking techniques can change the GI too

1. Food form: Consumption of ground rice raises the blood sugar level to a greater extent than of unground rice.
2. Food components: Fat, fibre, protein and type of starches influence glycaemic index as they affect the rapidity of absorption.

Rate of ingestion is another factor. Sipping 50g of glucose slowly over a several hour period produces a much smaller increase in blood glucose than rapid intake of the same amount.

Foods rich in fat and protein like ice cream, groundnuts, and milk have low glycaemic index. But they are not recommended for diabetics because they have high calorific value. Pulses which have high protein are low in glycaemic index compared to cereals.

Foods with soluble fibre such as beans, have low glycaemic index. Some starches are more slowly digested either because they are protected in structure or because the molecule is unbranched (amylose). Phytic acid, usually contained in cereals and pulses may have a more dominant role in decreasing the blood sugar rise than fibre.

Cooking, processing, and physiological effects can be contributory factors too

1. Method of cooking and processing: Chapattis which need chewing have lower glycaemic index compared to 'wheat congee'. Glycaemic response is higher with cooked than raw food.
2. Physiological effects:
   1. Digestion of dietary carbohydrate in the upper gastrointestinal tract provides glucose, fructose, and galactose for intestinal absorption. The presence of non-absorbable oligosaccharides and viscous dietary fibres such as pectins, B-glucose and gums in fruits, vegetables, and cereals reduces the efficiency of enzyme hydrolysis and slows the rate at which glucose enters the blood stream.
   2. The GI of a food is different when eaten alone than it is when combined with other foods. When eating a high GI food, it can be combined with other low GI foods to balance out the effect on blood glucose levels.

This article was originally published on July 22, 2019.

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.