Types of sugar explained, from glucose to maltose

Food contains six types of sugar in meaningful amounts: three single sugars — glucose, fructose, and galactose — plus three double sugars built from them: sucrose, lactose, and maltose. All six deliver 4 calories per gram. What separates them nutritionally isn't the molecule, it's whether it was added or came packaged inside a whole food.

Single sugars and double sugars

Every sugar in food is either a monosaccharide (one ring) or a disaccharide (two rings joined). Digestion has one job here: cut every disaccharide back into monosaccharides, because only single sugars cross the wall of the small intestine. Enzymes on the intestinal lining handle it — sucrase for sucrose, lactase for lactose, maltase for maltose.

Starch sits one level above: long glucose chains that amylase breaks into maltose (and shorter fragments), which maltase then finishes converting to glucose. That's why the sugars line and the total carbohydrate line can tell different stories about the same food.

The three monosaccharides

Glucose

The body's default fuel, and the thing "blood sugar" refers to. On ingredient lists it usually appears as dextrose, the same molecule. Little of what you eat is free glucose — most arrives bound into starch or sucrose — but honey, grapes, corn syrup, and glucose syrup supply it directly. It's noticeably less sweet than table sugar.

Fructose

Fruit sugar, and the sweetest of the common sugars. It's free in fruit, honey, agave syrup, and high-fructose corn syrup. Absorption is slower than glucose and uses a different transporter, and the liver does most of the metabolic work, which is why fructose and glucose behave differently in the body despite identical calories.

Galactose

The one nobody buys in a bag. Galactose is almost never eaten free — it arrives attached to glucose as lactose, and the liver converts it to glucose afterward. For practical purposes, galactose means milk.

The three disaccharides on an ingredient list

Sucrose: glucose + fructose

Sucrose is table sugar; cane and beet sugar are the same molecule and behave identically in a recipe. It's also naturally abundant in mango, pineapple, carrots, sweet potato, and maple syrup — maple is mostly sucrose, not the fructose people assume. Once sucrase splits it, you have equal parts glucose and fructose.

Lactose: glucose + galactose

Milk sugar, and the only sugar eaten in quantity that comes from animals. Cow's milk carries roughly 5 grams per 100 mL, so a cup lands near 12 grams — all of it naturally occurring, none of it added. Lactose is barely sweet, near a fifth of sucrose, which is why milk with 12 grams of sugar in it doesn't taste like a soft drink.

Lactase production drops after early childhood in most of the world's adults, which is what lactose intolerance describes. Aged hard cheeses hold very little lactose — whey is drained off and bacteria consume much of the rest — and yogurt sits below milk.

Maltose: glucose + glucose

Malt sugar. It forms whenever amylase cuts starch, so you meet it in malted barley, malt extract and syrup, malted milk powder, and beer wort. Slow-roasting a sweet potato converts a share of its starch to maltose, which is where the extra sweetness over boiling comes from.

Types of sugar compared

Sugar	Family	Built from	Typical sources	Sweetness (sucrose = 100)
Glucose	Monosaccharide	—	Honey, grapes, corn syrup, starch digestion	~70–75
Fructose	Monosaccharide	—	Fruit, honey, agave, high-fructose corn syrup	~120–170
Galactose	Monosaccharide	—	Only as half of lactose	~30
Sucrose	Disaccharide	Glucose + fructose	Cane and beet sugar, maple syrup, fruit	100
Lactose	Disaccharide	Glucose + galactose	Milk, yogurt, soft cheese, whey ingredients	~15–20
Maltose	Disaccharide	Glucose + glucose	Malt syrup, malted barley, malted milk	~30–50

Sweetness figures are approximate; perception shifts with temperature and concentration.

Sucrose vs glucose: what actually differs

Sweetness, the speed of the blood-sugar rise, and where the fructose half goes. Pure glucose raises blood glucose faster than an equal weight of sucrose, since half of sucrose is fructose taking a slower, liver-first route. Sucrose tastes sweeter, so a recipe needs less of it.

None of that changes the label: both are 4 calories per gram, and both count as added sugars once a manufacturer puts them in a product.

What the label does with all six

US Nutrition Facts panels report Total Sugars — every mono- and disaccharide in the food, natural or not — then a line reading "Includes X g Added Sugars," which covers sugars added during processing plus sugars from syrups, honey, and fruit juice concentrate. The FDA's Daily Value for added sugars is 50 grams on a 2,000-calorie diet. The World Health Organization recommends keeping free sugars under 10% of daily energy, with a conditional recommendation of under 5%, and the American Heart Association suggests a ceiling near 25 grams a day for women and 36 grams for men. Knowing how the added sugars line is calculated is worth more than knowing which -ose is in the jar.

That's the honest answer to which sugar is "worst," too. The molecules are close to interchangeable, and the split that carries nutritional weight is added versus naturally occurring — a gram of sucrose in a cookie and a gram in a mango arrive with entirely different company.

Because every -ose collapses into the same number, tracking tools don't ask you to tell them apart. Sugar Tracker, an added-sugar tracking app for iPhone, rolls sucrose, dextrose, maltose, and the syrups on a panel into a single added-sugar total for the day.

Sugar names that skip the -ose

Most sweeteners on a panel are mixtures rather than single sugars. High-fructose corn syrup blends glucose and fructose, near 55% fructose for soft drinks and 42% for baked goods. Plain corn syrup is mostly glucose, invert sugar is sucrose already split into its halves, and honey is largely free fructose and glucose with fructose slightly ahead. Brown sugar, turbinado, demerara, and muscovado are sucrose carrying different amounts of molasses.

Two lookalikes aren't sugars under label rules: maltodextrin, a short glucose chain counted as starch even though digestion turns it into glucose, and sugar alcohols, which end in -ol and supply fewer calories per gram.

FAQ

What is sucrose, and is it the same as table sugar?

Sucrose is a disaccharide of glucose and fructose, and yes, it's table sugar. Cane and beet sugar are chemically identical, and plain "sugar" on an ingredient list means sucrose.

What is lactose, and does it count as added sugar?

Lactose is milk sugar, a disaccharide of glucose and galactose. The lactose naturally present in milk and plain yogurt is not an added sugar and doesn't appear on that line. Lactose added as an ingredient — in a protein powder, say — does count.

What is maltose used for?

Maltose is the sugar of malted grain: malt syrup and malt extract, malted milk powder, beer brewing, and some Chinese and Japanese syrups. Manufacturers use it where they want body and mild sweetness rather than the punch of sucrose.

Which type of sugar is sweetest?

Fructose, by a clear margin — roughly 1.2 to 1.7 times as sweet as sucrose depending on conditions. Glucose sits below sucrose, and lactose is the least sweet of the six at roughly a fifth of table sugar.

Do all types of sugar have the same calories?

Yes: 4 calories per gram across every mono- and disaccharide, lactose and maltose included. What differs is sweetness, absorption speed, and metabolic route, not energy.