Last reviewed: July 2026

Carbs explained: sugars, starches and fiber

Carbohydrates come in three forms: sugars, starches and fiber. Sugars and starches are digested for energy at about 4 kcal per gram, while fiber passes through largely undigested and contributes little usable energy. On a nutrition label, "carbohydrate" is the umbrella figure, with "of which sugars" and often fiber listed underneath. The useful takeaway is that treating all carbs as one thing makes no sense: the same 40 grams can be fiber-rich oats or pure table sugar.

The three members of the carbohydrate family

Sugars are the simplest carbohydrates: glucose, fructose and the pairs they form like sucrose (table sugar) and lactose (milk sugar). Starches are long chains of glucose that your body breaks down into those simple sugars during digestion. Fiber is also a chain, but one that human enzymes cannot dismantle, so it moves through the gut mostly intact. That single difference, digestible versus not, is why fiber is counted as carbohydrate on the label yet barely adds calories.

How the label groups them

The main "carbohydrate" line is the total. In the EU, fiber is listed separately and is not included in the carbohydrate figure, while in the US the carbohydrate total includes fiber and you subtract it yourself. "Of which sugars" tells you how much of the total is sugar, whether natural or added, though the label rarely separates those two. Reading per 100 grams rather than per serving is the honest way to compare products, because serving sizes are chosen by the manufacturer.

Same gram count, very different foods

This is the point that dissolves the "carbs are bad" idea. Look at what an identical carbohydrate load looks like across real products.

The fiber and the food structure are doing the real work. A whole apple and a spoon of sugar can carry similar sugar grams, but the apple arrives with fiber and water that slow everything down. The same logic explains why fruit is not too high in sugar despite the number on the label.

Simple vs complex, and why it is not the whole story

You will hear carbs split into "simple" (sugars) and "complex" (starches), with complex framed as always better. It is a decent rule of thumb but leaky: refined white starch digests quickly, and some sugary whole foods digest slowly because of their fiber. A better question than simple-versus-complex is how much fiber the food has and how processed it is. That predicts fullness and blood-sugar response more reliably than the simple label.

So how many carbs should you eat?

There is no universal number. Carbohydrate is not an essential nutrient in the strict sense, but it is the body's convenient fuel, especially for higher-intensity activity. For most people, the practical target is not a gram count but a quality shift: favour fiber-rich whole starches and fruit, keep an eye on added sugars, and fit the total into your overall calories. If a specific choice is unclear, put two labels next to each other with the comparison tool and look at fiber and sugar, not just the carb line.

Bottom line

Carbohydrate is a family, not a single villain: sugars and starches for energy, fiber for the gut and fullness. The grams on a label tell you very little on their own. What matters is the company those grams keep, mainly fiber and how much the food has been processed.