Glucose: The Body's Fuel Sugar, Blood Glucose Tests, ORS and Indian Foods

Glucose is a simple sugar, a single molecule that needs no digestion, and it is the form in which carbohydrate travels in your blood. ICMR-NIN's Nutrient Requirements for Indians, 2020, asks that everyone aged one year and above eat at least 100 to 130 g of carbohydrate a day, and gives the reason in one line: that is the minimum the brain needs as glucose. Rice, roti, dal, fruit and milk all end up supplying it. This entry belongs to the carbohydrates section of the handbook, and it covers the sugar itself, the blood tests that measure it, and its two special uses in ORS and in sport.

What is glucose, and what does it do?

It is the body's working fuel. ICMR-NIN's Dietary Guidelines for Indians, 2024, lists glucose and fructose as the simple carbohydrates of fruits, vegetables and honey, and counts carbohydrate at 4 kcal per gram. Starch, the main carbohydrate of cereals, millets, pulses and tubers, is built from glucose units and is broken back down to glucose in the gut. On a food label the same sugar may be printed as dextrose: the guidelines name glucose and dextrose side by side in their list of added sugars.

The brain is the largest single user. A review in Trends in Neurosciences puts the human brain at about 2 per cent of body weight and about 20 per cent of the body's glucose-derived energy use, and describes its supply from the blood as continuous. Only about 4 g of glucose circulates in the blood at any moment, and the liver keeps topping it up from its store of glycogen, which a review in Nutrition Reviews puts at about 80 g on average.

How does the body keep blood glucose steady?

Two things work together: a hormone and a store. After a meal, glucose enters the blood, the pancreas releases insulin, and muscle, fat and liver cells take glucose in. Between meals the liver releases glucose at about the rate the tissues remove it. The Nutrition Reviews paper describes the result as a blood glucose held between 4.0 and 5.5 mmol/L, or 70 to 100 mg/dl, in a healthy person at rest. The handbook entry on insulin and insulin resistance explains what happens when that response weakens.

When no carbohydrate has been eaten for many hours, the liver also makes new glucose from amino acids and glycerol. This is why blood glucose does not run out overnight or on a fasting day, and why the Indian minimum of 100 to 130 g of carbohydrate is described as a floor for good health, not as the amount below which the brain stops working.

How much glucose do you need in India?

ICMR-NIN sets no separate requirement for glucose. Its 2020 report sets a minimum for all carbohydrate, 100 to 130 g a day from the age of one, and an acceptable range of 45 to 65 per cent of energy for adults. Nearly all of that is meant to arrive as starch from cereals, millets and pulses, which the body turns into glucose itself. For glucose bought as a powder, a syrup or a sweet drink, the limit that applies is the one for added sugar.

The same guidelines tell new mothers not to give honey, glucose, water or diluted milk to a newborn before breastfeeding begins. For adults, a spoon of glucose powder stirred into water is added sugar like any other, and counts towards the 25 g. The article on how much sugar a day is reasonable works through that allowance in teaspoons.

Glucose in Indian foods: mostly eaten as starch

Very little of the glucose you absorb is eaten as glucose. The Indian Food Composition Tables 2017 measured free sugars food by food, and raw milled rice has 75.70 g of starch per 100 g against 0.54 g of free glucose; whole-wheat atta has 56.82 g of starch and 0.78 g of glucose. Free glucose is found mainly in fruit, dried fruit, sugarcane juice and jaggery, usually alongside fructose and sucrose.

Read the starch column as glucose waiting to be released: the 80 g of raw rice in one meal carries about 60 g of starch. That is why the cereal on the plate matters far more to blood glucose than the free glucose in a fruit. NNWA's table of carbohydrate in Indian foods ranks every food in the database, and the page on grapes as a fruit gives the full panel for one of the richer sources.

Which blood glucose tests does a doctor order?

Four tests are in routine use, and ICMR's Guidelines for Management of Type 2 Diabetes, 2018, names them all: fasting plasma glucose, the oral glucose tolerance test, a random plasma glucose, and glycated haemoglobin, written HbA1c. The first three measure glucose in the blood at one moment. HbA1c measures glucose attached to haemoglobin, and the guideline notes that its use in India has some limitations.

The table is there so that you can read a report, not so that you can diagnose yourself. The guideline says a result in the diabetes range should be confirmed with another test, and the American Diabetes Association draws the fasting line for prediabetes lower, at 100 mg/dl. Home glucometers read capillary blood, laboratories differ, and illness, medicines and pregnancy all shift the picture. What a number means for you is the doctor's call. NNWA's guide to prediabetes covers the eating side once that conversation has happened.

High blood glucose: the Indian picture

The ICMR-INDIAB study, which examined more than 1,13,000 adults across the country between 2008 and 2020, put the weighted prevalence of diabetes at 11.4 per cent and of prediabetes at 15.3 per cent. NFHS-5, using a single random finger-prick reading, found 12 per cent of women and 14 per cent of men aged 15 and over above 140 mg/dl. ICMR's guideline adds that more than half of all people with diabetes have no symptoms at all, which is the case for testing on a doctor's schedule. The diabetes risk calculator gives a first estimate of where you stand.

Why is there glucose in ORS?

Not for energy. ORS was built on the finding that glucose and sodium are carried across the gut wall together, and that water follows them, so the sugar in a sachet is there to pull salt and water in. The formula WHO and UNICEF recommended from 2002, reprinted that year in the journal of India's child specialists, holds 13.5 g of anhydrous glucose and 2.6 g of sodium chloride per litre, giving 75 mmol/l each of glucose and sodium and a total osmolarity of 245 mOsm/l. The earlier formula was stronger, at 311 mOsm/l.

The proportions are the point. WHO's criteria ask that glucose at least equal sodium and not exceed 111 mmol/l. In the trials reviewed for the change, children with non-cholera diarrhoea given the weaker solution needed unscheduled intravenous fluid 33 per cent less often, with stool output about 20 per cent lower. In NFHS-5, 61 per cent of Indian children with diarrhoea were given ORS from a packet. Mix a sachet in the exact volume of clean water printed on it; a drink such as nimbu pani is not a measured substitute.

What does the evidence say about glucose in sport?

It supports carbohydrate during long, hard sessions and offers little for short ones. The International Society of Sports Nutrition's 2017 position stand advises about 30 to 60 g of carbohydrate an hour, as a 6 to 8 per cent solution, for high-intensity bouts longer than 60 minutes, and notes that a consistent benefit appears only once exercise reaches about 90 minutes. A 2011 consensus paper in the Journal of Sports Sciences gives the same 30 to 60 g an hour and allows up to 90 g an hour for events beyond two and a half hours.

Glucose alone has a ceiling. A 2010 review by Jeukendrup reports that the gut's transporters limit how fast swallowed glucose can be used, to about 1 g a minute, and that mixing glucose with fructose raised the rate to as much as 1.75 g a minute. These are findings in trained athletes working for hours. They are no argument for a glucose drink on a 40-minute walk.

A worked example: ORS is not a sports drink

This is an illustrative case, not a real person. A 31-year-old club cyclist in Pune plans a three-hour Sunday ride and wonders whether the ORS sachets at home will fuel it. Taking the lower end of the 30 to 60 g range, she wants 30 g of carbohydrate an hour. ORS holds 13.5 g of glucose a litre, so 30 g would mean about 2.2 litres every hour, which nobody can drink on a bicycle.

A 6 per cent drink holds 60 g a litre, so 500 ml an hour supplies the 30 g. In food, by IFCT 2017, a 100 g ripe robusta banana carries about 19 g of available carbohydrate and 20 g of black raisins about 13 g, so one of each in an hour comes to about 32 g. The arithmetic shows the two drinks do different jobs: ORS replaces salt and water lost in illness, and a sports drink or a banana supplies fuel.

Common myths and mistakes about glucose

The first mistake is to treat glucose as a harmful substance in itself. It is the fuel every cell uses, and ICMR-NIN sets a minimum for the carbohydrate that supplies it. The concern in India is the form and the amount: the 2024 guidelines warn that foods high in sugar or refined cereals are absorbed fast and bring a sharp rise in insulin.

A second mistake is to rank foods only by glycaemic index, the scale on which glucose is the reference food. ICMR-NIN's 2024 annexure gives indicative values of about 78 for rice, 66 for wheat chapatti and 38 for Bengal gram, each from ten volunteers, and warns that they shift with ingredients and cooking. The article on the glycaemic index of Indian foods explains how to use the scale sensibly.

Too much, too little, and when to see a doctor

Persistently high blood glucose is diabetes, and ICMR's guideline lists its usual signs: passing urine often, thirst, weight loss despite eating well, tiredness, itching, repeated urinary or genital infections and wounds that heal slowly. Low blood glucose is mostly a side effect of diabetes medicines; the guideline calls it the commonest side effect of one widely used class of tablets. Neither is managed by food alone, and nothing in this entry is a reason to change or stop a prescription.

Learning this subject at NNWA

Carbohydrate digestion, blood glucose and the reading of food tables are taught at NNWA, a private skill academy in Kolkata that teaches online in English and Hindi. Its courses, among them Diabetes Nutrition, train people to coach healthy clients on food and to refer medical cases to a doctor. None of them is a degree or a dietitian qualification.