Glucose

Glucose is the sugar your body runs on. It is a simple sugar (a monosaccharide) with the formula C6H12O6, the same as fructose. PubChem, a public chemistry database, files the name dextrose under D-glucose. Grape sugar and corn sugar are among its other names.

Blood sugar is simply glucose in the blood. Glucose is also what starch turns into when your gut digests it. And it is half of table sugar (sucrose), which is a glucose joined to a fructose. It is one of the sugars in food, and no official daily need or limit is set for glucose on its own.

Most readers have not been told where the glucose they absorb comes from, and free glucose in food is the small part. A group of digestion researchers states that starches are the major source of dietary glucose in weaned children and adults. USDA (the US Department of Agriculture) lists only 10.9 g of free glucose in a cup of grapes. A tablespoon of honey has only 7.51 g.

We found no source that splits a day’s glucose by food. But the US figure of 130 g of carbohydrate a day is built on the glucose the brain uses. Your gut makes that glucose mostly from starch and sugars.

Glucose also has jobs that no other sugar has. It is the preferred treatment for low blood sugar. It is the sugar in oral rehydration drinks, which cut deaths from diarrhea. And it is the load in the glucose tolerance test.

This page sets out what 30 studies and reports show. It covers blood sugar and insulin, the glycemic index and its limits, sports drinks, glucose versus fructose and glucose sensors in people without diabetes. Each finding is given at its real evidence level, with funding stated where we found it.

Health effects of glucose

• ★★★Fewer IV drips with a weaker rehydration drinkIn 8 trials, children with diarrhea given a weaker glucose-and-salt rehydration drink had 0.59 times the odds of needing unplanned IV fluids. A review of 157 studies estimated that rehydration solution may prevent 93% of diarrhea deaths in children under 5.
• ★★★Lower blood sugar peak when fructose replaces glucoseIn pooled trials, swapping glucose or sucrose for fructose at equal energy lowered the blood sugar peak after a meal, most with prediabetes or diabetes. Peak insulin fell too.
• ★★★EU-approved claims: carbohydrate drinks and exerciseThe EU allows carbohydrate-electrolyte drinks to claim they help maintain endurance and water absorption, and carbohydrates to claim they help muscle recovery after hard exercise. These are label rules, not trial results.
• ★★★EU-approved claim: carbohydrates and normal brain functionThe EU allows foods with carbohydrates to claim they help maintain normal brain function, tied to 130 g of carbohydrates a day from all sources. It covers carbohydrates as a class, not glucose alone.
• ★★Glucose first for low blood sugar in diabetesThe 2026 American Diabetes Association prefers glucose (15 g for most) for low blood sugar, under 70 mg/dL, in people on insulin or similar drugs. In 41 adults with type 1 diabetes on insulin, glucose or sucrose tablets and drinks worked better than gel or juice.

Foods high in glucose

Free glucose comes mostly from fruit and honey. In our USDA ranking per serving, dates lead with 16.2 g in 2 dates (48 g). Grapes (10.9 g in 1 cup) and cherries (10.1 g in 1 cup) come next. Honey, blueberries, plums, papaya, bananas, pears and apples follow.

Per 100 g the order changes: honey has 35.8 g and dates 33.7 g, then grapes, cherries and plums; cranberries also make the list. Per 100 kcal, dates (12.2 g) and honey (11.8 g) lead, with bell peppers and tomatoes in the top ten. The ranking below shows every amount.

The ranking counts free glucose, which is the smaller share of the glucose you absorb. A study of starch digestion states that starches are the major source of dietary glucose in weaned children and adults. So bread, rice, potatoes and other starchy foods deliver most of their glucose after digestion, and the ranking does not show it.

Fruit sugars come with fructose: the FDA (the US Food and Drug Administration) describes honey as about one fructose to one glucose. Added forms count differently. The FDA calls corn syrup, made by breaking corn starch down, essentially 100% glucose. High-fructose corn syrup is 42% or 55% fructose, and the FDA says the rest is glucose and water.

How the sugars are counted matters. The WHO defines free sugars as sugars added to foods and drinks by the maker, cook or consumer. They include monosaccharides (single sugars) such as glucose and fructose, and disaccharides such as sucrose. Free sugars also include the sugars in honey, syrups, fruit juices and fruit juice concentrates.

The WHO guideline leaves out the sugars in fresh fruit, vegetables and milk, because it found no reported evidence of harm from them. The 2025-2030 Dietary Guidelines for Americans list glucose and dextrose among the names of added sugars on labels. They say the sugars in fruit and plain milk are not added sugars.

How glucose works

The basic biochemistry is well established. Most of it comes from reviews and from mouse and test-tube work; what glucose does in people is tested in the study cards above.

Four ideas cover most of it. Starch and sucrose are split into glucose, which crosses the gut wall by two carriers. Insulin and the liver hold blood glucose in a narrow range.

The body stores about 500 g as glycogen, and the brain is the big user. The gut sets a speed limit on glucose from drinks. Here is each one, and what has been seen in people.

Starch and sucrose become glucose, which crosses the gut wall two ways

Starches are the major source of dietary glucose in weaned children and adults. In lab work on human gut tissue, enzymes bound to the gut lining (sucrase-isomaltase and maltase-glucoamylase) did 85% of the glucose release from starch fragments. Pancreatic amylase alone did under 15%, though it prepared the fragments the other two enzymes work on.

Sucrose, a glucose joined to a fructose, is also split in the gut. Glucose then crosses the gut wall by SGLT1, a carrier that uses sodium to pull glucose in, and by GLUT2. Mice without SGLT1 developed glucose-galactose malabsorption, and the authors conclude that SGLT1 does most glucose absorption whatever the load.

Another group argues that GLUT2, inserted into the gut-facing membrane, is a major route at high sugar levels. So the shares of the two carriers are still debated. In people, the rare inherited defect of SGLT1 is called glucose-galactose malabsorption.

Glucose also helps other sugars across. In 10 healthy adults, 50 g of fructose with 25 g of glucose caused less malabsorption than 50 g of fructose alone. Glucose raised fructose uptake in a dose-dependent way: more glucose, more uptake.

The link between sugar and sodium absorption is the basis of rehydration drinks. In the 1968 cholera study, the authors note that a sugar the gut actively transports enhanced sodium absorption. Glucose in the perfused solution cut stool output, and fructose was absorbed less well than glucose or galactose.

Insulin and the liver hold blood glucose in a narrow range

A network of organs keeps blood glucose tightly controlled. The pancreas releases insulin, the hormone that lowers blood sugar, and its opponent glucagon. The liver stores glucose after meals. During fasting it makes glucose, from gluconeogenesis (building new glucose) and from glycogen breakdown.

The numbers show how narrow the range is. In 153 healthy people with sensors, glucose sat between 70 and 140 mg/dL (milligrams per deciliter) for a median 96% of the time.

The ADA notes that 70 mg/dL is the threshold for the body’s first alarm responses to falling glucose in people without diabetes. Readings under 54 mg/dL (level 2) are where symptoms of too little glucose reaching the brain begin. Level 3 is a severe event that needs another person’s help.

The glycemic index measures how fast a food raises blood glucose compared with glucose itself, which sits at 100 on the scale. The glycemic load multiplies the index by the carbohydrate in a portion.

The cards show its limits. The index of one bread varied by 20% within a person, and responses to identical meals varied by 68% between people. A 2021 review of published values lists over 4,000 foods. Fruits, dairy, legumes and pasta are usually low, while cereal products, breads and rice range widely depending on how they are made.

The body stores about 500 g as glycogen, and the brain is the big user

A review of muscle glycogen puts the body’s carbohydrate store at about 100 g in the liver and about 400 g in muscle. Only 5 g circulates as blood glucose, so that is roughly 500 g in all (our arithmetic). That is why endurance athletes talk about glycogen: liver glycogen running out is a major cause of fatigue in long exercise.

The brain depends on glucose as its main energy source. The US recommended allowance of 130 g of carbohydrate a day rests on the average minimum amount of glucose the brain uses. Red and white blood cells and the kidney medulla (inner kidney) also need glucose, and the brain can meet part of its needs from ketoacids. The idea that a sugary drink restores willpower does not hold up well in the statistical review above.

The gut sets a speed limit on glucose from drinks

During exercise, the limit on how much carbohydrate the body can burn lies in the absorption step, most likely because the carriers saturate. A review of the field reports that a single carbohydrate is burned at up to about 60 g an hour. Ultra-endurance events call for about 90 g an hour. Rates this high need mixed sugars such as glucose with fructose, which use different carriers.

With mixes, the burning of drink carbohydrate reached 1.75 g a minute, where 1 g a minute was once thought the maximum. The reviewer is affiliated with the Gatorade Sports Science Institute. The chart shows the tracer trial behind the idea.

What has been seen in people

Put together, the human studies say three things. Glucose has clear but narrow uses: low blood sugar (the ADA names 15 g for most people), rehydration drinks and fuel for long exercise. In long exercise, glucose with fructose beat glucose alone in two small time-trial studies (8 and 9 cyclists) and in a review of 14 studies.

The glycemic index is a blunt tool. One meta-analysis found a 0.31% HbA1c gain in diabetes, but the OmniCarb trial found no gain in people on a DASH-type diet. The cohorts that link high-index diets to disease are observational.

And blood sugar in healthy people is steady, while the response to the same meal differs widely. So one food’s index or one sensor spike says less than it seems. We found no trial that shows health gains from glucose tablets or glucose drinks in people without low blood sugar or hard exercise.

How much glucose do you need?

No daily amount of glucose itself is set. The US recommended dietary allowance for carbohydrate, 130 g a day for adults and children, is set from the brain’s average minimum glucose use. The liver makes glucose when you fast, so you do not have to eat it as such.

Real intakes run higher: adult men eat 200 to 330 g of carbohydrate a day and adult women 180 to 230 g. The sugars that are limited are free or added sugars, and glucose in syrups, dextrose and honey counts toward them.

Source	Group	Value	Notes
NASEM (Institute of Medicine) DRI report on macronutrients, as summarized by Ryan-Harshman and Aldoori, 2006	Adults and children	Carbohydrate RDA: 130 g a day. AMDR: 45 to 65% of total calories	The RDA rests on the average minimum amount of glucose used by the brain, which can partly use ketoacids. On 2,000 kcal, 45 to 65% is 900 to 1,300 kcal, or 225 to 325 g at 4 kcal per g (our arithmetic).
EFSA scientific opinion, 2010	Adults and children (from age 1 in EFSA’s summary table)	Reference intake range for total carbohydrates: 45 to 60% of energy	Covers starch and sugars. EFSA found insufficient evidence to set an upper limit for sugars, citing links to tooth decay and, for sugar-sweetened drinks, to weight gain.
EU health claim (Regulation (EU) No 1018/2013)	Foods bearing the claim	Consumers told the effect on normal brain function comes with 130 g of carbohydrates a day from all sources	A labeling condition for the claim, not an EU reference intake.
WHO guideline, 2015	Adults and children	Free sugars under 10% of total energy (strong recommendation); below 5%, roughly 25 g a day, for added benefit (conditional)	Free sugars include glucose added to foods and drinks and the sugars in honey, syrups, juices and concentrates. Sugars in fresh fruit, vegetables and milk are not covered.
EFSA scientific opinion, 2022	Adults and children	Added and free sugars as low as possible within a nutritionally adequate diet	EFSA could not set a tolerable upper intake level for dietary sugars. It calls sugar a known cause of dental caries.
Dietary Guidelines for Americans, 2025-2030 (current)	People of all ages; infants and young children	No amount of added sugars is recommended or considered part of a healthy diet; one meal should contain no more than 10 g of added sugars; avoid added sugars in infancy and early childhood	Issued January 2026. Glucose and dextrose are among the label names for added sugars.
Dietary Guidelines for Americans, 2020-2025 (previous edition)	People aged 2 and older; under 2	Added sugars under 10% of calories a day from age 2; avoid added sugars under age 2	About 200 kcal, or 50 g, on 2,000 kcal (our arithmetic).
FDA Nutrition Facts label	Packaged foods	Daily Value: total carbohydrate 275 g; added sugars 50 g	Added sugars on a label include glucose and dextrose added in manufacture; the 2025-2030 guidelines list both as label names.
Any authority we found	Glucose on its own	No daily need and no upper limit	The site’s intake box also shows no FDA or EU reference value for glucose.

We found no diet-caused glucose deficiency, so this page has no deficiency section. Low blood glucose (hypoglycemia) is a medical problem.

The ADA defines it as a reading under 70 mg/dL. It is a risk mainly for people treated with insulin, sulfonylureas or meglitinides, and rare with other diabetes medicines. See the safety section for how it is treated.

Forms of glucose: absorption and effects

Glucose reaches you in many forms. There is free glucose in fruit and honey, dextrose (the same molecule, per PubChem), corn syrup, and the glucose in starch and maltodextrin. It is also half of table sugar, and part of sports drinks, tablets and gels.

The chemistry is the same in every form. So the forms differ in speed, in what comes with them (fructose, fiber, water, other starch) and in how they are used.

The honest bottom line is that the form matters for two jobs. For treating low blood sugar, tablets and solutions worked faster than gel or juice in one trial. For fueling long exercise, glucose with fructose beat glucose alone.

We found no trial that compared dextrose, corn syrup and starch-derived glucose for long-term health. Nor did we find any showing that glucose tablets help people who do not have low blood sugar.

The trials use set doses: 15 g for low blood sugar. The exercise studies used 1.2 to 2.4 g a minute, or 72 to 144 g an hour (our arithmetic). Those amounts are not typical of eating a piece of fruit.

Form	What it is	What studies show	Source
Free glucose in fruit and honey	Glucose with fructose, water and fiber; honey is about one fructose to one glucose	USDA lists 35.8 g of glucose per 100 g of honey and 7.2 g per 100 g of grapes. The WHO counts honey and juice sugars as free sugars and leaves out sugars in fresh fruit. We found no trial of glucose from fruit on its own.	1, 2, 7
Dextrose	D-glucose; the same molecule as glucose	The ADA calls pure glucose the preferred first treatment for low blood sugar. The 75 g glucose tolerance test uses a load of anhydrous glucose dissolved in water.	3, 4, 5
Glucose tablets, solution and gel	Pure glucose, usually 15 g	Tablets and solutions raised blood glucose similarly in 41 adults; gel and orange juice raised it less at 10 minutes. The ADA lists tablets (long shelf life, easy dosing) and gel (easier for children and people without teeth).	4, 8
Corn syrup	Made by breaking corn starch down; essentially 100% glucose per the FDA	Counted as an added sugar. The 2025-2030 US guidelines list corn syrup among added sugar names.	2, 14
High-fructose corn syrup	42% or 55% fructose; the rest is glucose and water	See the fructose page for the trials.	2
Maltodextrin	Chains of D-glucose units, 3 to 20% reducing sugars; made from starch	Its glucose is absorbed rapidly. Swapping unprocessed starch for maltodextrin may raise glycemic load. In the exercise studies it is treated like glucose.	6, 10
Glucose plus fructose drinks	Glucose with fructose, often 2 to 1, for different carriers	In 14 studies they improved power by 1% to 9% over glucose or maltodextrin alone; glucose helps fructose across the gut wall.	10, 12, 13
Starch	Long chains of glucose digested in the gut; the major source of dietary glucose	See the starch page for types and digestion speed.	11
Sucrose (table sugar)	One glucose joined to one fructose	Worked as well as glucose tablets for low blood sugar in 33 children with type 1 diabetes. People on acarbose must use pure glucose.	4, 9, 13

Here are the form-specific studies, strongest evidence first, 6 in all.

Is glucose safe? Low blood sugar, tests and who should watch it

Glucose from food is not a safety concern for most people. No tolerable upper intake level (the most you can take daily without harm) exists for glucose or for dietary sugars as a whole. EFSA could not set one in 2022, and says added and free sugars should be as low as possible.

EFSA adds that sugar is a known cause of dental caries (tooth decay). The WHO limit of free sugars under 10% of energy covers glucose syrups and dextrose added to food. It leaves out fresh fruit, vegetables and milk.

• Low blood sugar. The ADA says to treat a reading under 70 mg/dL with glucose, 15 g for most people. Check again after 15 minutes and repeat if it is still low. Give oral glucose only to an alert person, and call emergency services for someone who is unalert or cannot take carbohydrate by mouth. Added fat slows and prolongs the rise, and protein should not be used for treatment.
• Acarbose and pure glucose. People taking acarbose, a diabetes drug that blocks sucrose breakdown, should treat low blood sugar with pure glucose only, since sucrose may delay the correction.
• Glucose tolerance tests. The 75 g test diagnoses diabetes when the 2-hour reading is 200 mg/dL or more. The ADA advises at least 150 g of carbohydrate a day for 3 days before the test. In pregnancy it screens at 24 to 28 weeks. These are standard thresholds, and your clinician interprets your result.
• Diabetes and high blood sugar. People with diabetes should plan sugar and carbohydrate changes with their care team. The glycemic index gave only small gains in trials, and individual responses vary.
• Rare inherited conditions. Glucose-galactose malabsorption, a defect of the SGLT1 carrier, stops absorption of glucose and galactose. In mice without SGLT1, the animals thrived on a diet free of both sugars.
• Sports drinks. A review of glucose-fructose drinks reports better gut comfort than with single-sugar drinks. Its authors include staff of a consultancy and of Nestlé Research Center. Mixes are for long events, not for everyday drinking.
• Wearing a glucose sensor without diabetes. Sensors give normal-range data for healthy people, and the same meal can give different readings for different people. A 2026 systematic review of 12 studies found low certainty for diet changes. Certainty was very low for mood, activity and device burden. Its authors say large, lasting benefits, or benefit from the sensor on its own, are not established.

How to use glucose wisely

• Treat a low as your care team advised. For most people the ADA names 15 g of carbohydrate, with pure glucose preferred, checked again after 15 minutes. Keep tablets or gel where you can reach them, since the ADA says first aid kits should include oral glucose.
• Count the starch and the free sugars. Most dietary glucose comes from starch. For added glucose, syrups and honey, the limit that matters is free sugars under 10% of energy (WHO). The glycemic index is a weak guide: the OmniCarb trial found no gain from low-index foods on a DASH-type diet.
• Match the drink to the exercise. For about an hour, a mouth rinse or small amounts of carbohydrate worked. From 2 to 3 hours, a single carbohydrate is used at up to about 60 g an hour. Rates up to about 90 g an hour call for glucose with fructose.

History of glucose

In 1811 the chemist Constantin Kirchhoff, working at the Imperial Court Apothecary in St. Petersburg, turned starch into grape sugar (glucose) with sulfuric acid. He showed that a small amount of acid converted all of the starch and was left unchanged at the end. He also made crystalline sugar from potato starch.

A 2026 essay calls this the first recorded homogeneous catalytic reaction in organic chemistry, a quarter century before the word catalysis existed. A catalyst speeds up a reaction without being used up. Breaking starch down into glucose is still how the FDA says corn syrup is made, now with enzymes.

The physiology came next. In Paris in 1845, the young chemist Barreswil set up a way to measure glucose and became Claude Bernard’s collaborator. In 1848 they reported that the liver contained sugar and other tissues did not, and that year Bernard established the liver’s glucose-making function.

In 1855 a delayed measurement led Bernard to see that a washed liver went on forming glucose. In 1857 he isolated glycogen, which he called animal starch. He also introduced the idea that the body keeps its internal environment constant, which we now call homeostasis.

Insulin followed. In 1921 Frederick Banting produced a pancreas extract that lowered blood sugar in diabetic dogs. He worked in J.J.R. Macleod’s laboratory in Toronto with the student Charles Best.

J.B. Collip did much of the purification, and a method to measure blood sugar in small samples helped the work. The Nobel Prize went to Banting and Macleod, which strained relations among the team.

The most lifesaving glucose story is rehydration. In 1968 Hirschhorn and colleagues showed in 8 cholera patients that glucose in a salt solution run through the gut cut stool output. Oral rehydration solution has been recommended since the 1970s. A review of 157 studies later estimated that it may prevent 93% of diarrhea deaths in children under 5.

The research argument around the glycemic index is much younger. Several of its main authors disclose food-industry ties, which this page notes on each card.

Frequently asked questions about glucose

Is glucose the same as dextrose?

Yes. Dextrose is the name for D-glucose: PubChem files “dextrose” under D-glucose (C6H12O6, molecular weight 180.16). The 2025-2030 Dietary Guidelines for Americans list glucose and dextrose among the names of added sugars on labels. Tablets, test drinks and some sports products use it. See our page on sugars.

What foods contain glucose?

Fruit and honey have free glucose; per serving in our USDA ranking, dates lead with 16.2 g in 2 dates. Grapes (10.9 g in 1 cup) and cherries (10.1 g in 1 cup) come next. Honey (7.51 g in 1 tbsp) and blueberries (7.22 g in 1 cup) follow.

Starchy foods hold little free glucose, but a digestion study calls starches the major source of dietary glucose. See starch.

How much glucose does the body need per day?

No amount of glucose itself is set. The US recommended allowance, 130 g of carbohydrate a day for adults and children, rests on the average minimum glucose use of the brain. The brain can partly use ketoacids, and the liver makes glucose during fasting. EFSA’s reference range for total carbohydrates is 45 to 60% of energy.

How much glucose should you take for low blood sugar?

Most people need 15 g of carbohydrate, preferably pure glucose, says the American Diabetes Association; recheck after 15 minutes and repeat if still low. People on automated insulin delivery usually need 5 to 10 g, and people taking acarbose should use pure glucose only. Call emergency services for someone who is unalert. This is guidance for people with diabetes, so ask your care team for your own plan.

What is a normal blood glucose level?

The ADA diagnoses diabetes from a fasting reading of 126 mg/dL or more. A 2-hour reading of 200 mg/dL or more in a 75 g test also counts (confirmed). A fasting 100 to 125 mg/dL is the prediabetes range.

In 153 healthy people wearing sensors, average glucose was 98 to 99 mg/dL. Readings sat between 70 and 140 mg/dL for a median 96% of the time. Your clinician interprets your own tests.

What is the glucose test in pregnancy?

The ADA describes two ways to screen at 24 to 28 weeks, so ask your clinician which test is used. The one-step 75 g test makes the diagnosis at fasting 92, 1-hour 180 or 2-hour 153 mg/dL or higher. The two-step approach uses a nonfasting 50 g screen followed by a 100 g test. The one-step cut points come from the HAPO study of 25,505 women, where risk rose steadily with glucose and no threshold was seen.

Is glucose or fructose worse for you?

The trials give no simple winner. With 25% of energy as drinks for 10 weeks, fructose added visceral fat and cut insulin sensitivity. Glucose did not, but it raised fasting triglycerides by about 10%.

In 32 men given extra calories, liver fat rose alike on both. Fructose lowers the blood glucose peak after a meal compared with glucose. See fructose.

Do sports drinks need glucose and fructose?

For about an hour, a mouth rinse or small amounts of carbohydrate worked in a review of 61 studies, so the sugar type hardly matters. Past 2 to 3 hours, a single carbohydrate is used at up to about 60 g an hour. Mixing glucose with fructose allows about 90 g an hour. In 14 studies, mixes improved mean power by 1% to 9% over glucose or maltodextrin alone.