Carbohydrates

Beginner · 10 min

The body's practical fuel

During digestion, carbohydrates are largely converted into glucose, and glucose is the fuel cells use most readily. Under normal conditions the brain draws a significant share of its energy from glucose. Muscles and the liver store part of the glucose as glycogen and use it when needed. Carbohydrate carries about 4 kcal of energy per gram. The body can produce energy without carbohydrate too; but that does not make carbohydrate unnecessary, it only shows that the body is flexible.

The limited size of glycogen stores is one reason performance drops during prolonged fasting or intense exercise; in that situation the body shifts its weight to other fuels.

Simple and complex carbohydrates

Simple carbohydrates are short-structured sugars: table sugar, honey, fruit sugar and milk sugar belong to this group. Complex carbohydrates are long-chained starches: grains, legumes, potatoes. In general, simple sugars are digested faster and complex structures more slowly; but that speed also depends on the food as a whole. Carbohydrate taken together with fibre, fat and protein is absorbed more slowly. That is why taking the same amount of sugar in a piece of fruit and in a fizzy drink is not the same experience for the body; fruit brings fibre and water along with its sugar.

So when you look at the sugars line on a label, think about the whole food too: the same 15 grams of sugar is absorbed at different speeds in a fibre-rich food and in a sugary drink.

Whole grains and refined grains

A grain kernel has three parts: the fibrous outer layer (bran), the nutrient-rich core (germ) and the starchy body. Whole grain products keep all three parts; in refined products the bran and germ are removed, leaving mostly starch. The refined product lasts longer and gives a softer texture, but loses part of its fibre, vitamins and minerals. Checking for wording like whole wheat or whole grain, and checking the order of the ingredient list, is the practical way to apply this distinction at the supermarket.

A brown appearance alone is not proof of whole grain; colour can also come from molasses or similar ingredients. The reliable markers are the whole-grain share stated on the package and the order of the ingredient list.

The trap of looking for a culprit

In recent years carbohydrate has repeatedly been declared the sole culprit of weight gain. The available evidence tells a plainer story: what matters is the overall energy balance and the whole of the eating pattern. The quality difference between types of carbohydrate is real; a pattern built on vegetables, fruit, legumes and whole grains is not the same as one built on refined sugar. But declaring a single macronutrient the enemy is the quickest way to miss that detail.

For your own table, the practical question is this: which group do my carbohydrates mostly come from? If the answer is weighted towards vegetables, legumes and whole grains, the noise of the popular debates is largely beside the point for you.