A carbohydrate is a class of organic compounds. There are two types of carbohydrates: simple carbohydrates and complex carbohydrates. Simple carbohydrates include glucose, fructose, and galactose which in turn can form sucrose (= table sugar), lactose, or maltose. Complex carbohydrates include starch, glycogen as well as fiber

Characteristics of carbohydrates:

  • Preferred energy substrates of cells
  • A distinction is made between simple carbohydrates and complex carbohydrates.
  • Stored in the body as glycogen
  • Found mainly in sweet products, starchy foods, and fruits
  • Excess carbs can lead to hyperinsulinism and long-term type 2 diabetes

Why eat carbohydrate-rich foods?

Carbohydrates: definition and benefits

Energy role

The main role of carbohydrates is to provide energy to the cells of the human body (1g of carbohydrates provides 4 calories). When we eat them, they are transformed more or less quickly into glucose, which is the fuel for certain cells in the body. 

This is the case with brain cells. Note that glucose is the exclusive fuel of the brain, which needs about 140 g per day.

Appetite regulation

Complex carbohydrates, and especially fiber, play an important role in regulating appetite. They make it possible to reach satiety more quickly and to be satiated more durably. They are therefore essential for a balanced diet.


All carbohydrates have their own hyperglycemic power, that glucose being one of the highest. Simple sugars, which are more quickly assimilated, therefore make it possible to quickly raise blood sugar and re-sweet the body. 

This characteristic is particularly appreciated and used in high-level athletes or even in diabetics in the event of hypoglycemia.

Promotes good sleep

The assimilation of carbohydrates induces an increase in the availability of tryptophan in the body. Tryptophan is an amino acid precursor, among others, of serotonin and melatonin. These two substances act favorably on falling asleep.

Constitution of glycogen stock

Glucose is either used immediately by the body, as it constantly needs energy, or stored as glycogen in the liver and muscles for later use. This is why athletes, before a competition, seek to increase their glycogen reserves by eating foods rich in carbohydrates.

What is the difference between carbohydrates and sugar?

Simple sugar is the smallest link in the carbohydrate family. It is he who is responsible for the sweet taste of food. Fructose, galactose, and glucose are made up of a single molecule. Associated, they form more complex molecules. 

For example, sucrose (white sugar) contains fructose and glucose and lactose (milk sugar) contains galactose and glucose.

Carbohydrate-rich foods

The main sources of carbohydrates are cereal products, fruits, certain vegetables, and legumes. In general:

  • 1 serving of grain products contains: 15 g of carbohydrates
  • 1 serving of fruit contains: 15 g of carbohydrates
  • 1 serving of vegetables contains: 5 g of carbohydrates
  • 1 serving of dairy products provides: 12 to 15 g of carbohydrates
  • 1 serving of legumes provides: 15 g of carbohydrates
  • 1 serving of added sugar contains: 15 g of carbohydrates

It should be noted that these foods have been classified only according to the criterion of the number of carbohydrates. It is therefore important to understand that the type of carbohydrates as well as the amount of fiber can vary from one food to another.

The different types of carbohydrates

Intrinsic simple sugars are found naturally in foods, such as fructose from fruit and lactose from milk. Simple added or extrinsic sugars are added to foods and beverages by manufacturers, cooks, or consumers themselves: white or brown sugar, honey, maple syrup, fruit juice concentrate, corn syrup, glucose, etc

Simple sugars provide four calories per gram. Whether intrinsic or extrinsic, purified or not, refined or not, all of them, with the exception of fructose, have the same effect on blood sugar levels by causing them to rise rapidly: they have a high glycemic index. 

To learn more about the glycemic index, see our text on this subject.

Used by the World Health Organization, the term “free sugars” includes added sugars AND sugars in fruit juices. Note that this classification is specific to the WHO and that most public health authorities do not make this amalgam (see box below).

Starch is a complex carbohydrate because it is made up of a chain of sugars. It is notably present in potatoes, certain vegetables, bread, pasta, and cereals. Starch also provides four calories per gram. 

It does not taste sweet. It is absorbed more slowly than simple carbohydrates and therefore does not raise blood sugar levels as quickly: its glycemic index is lower than that of simple sugars. To learn more about the glycemic index, see our text on this subject.

Fiber is also a complex carbohydrate. In fact, as they are made up of a very complex chain of sugars, they are not absorbed by the body. 

They do not provide calories. In addition, they slow down the absorption of other carbohydrates: this is why eating fruit increases blood sugar levels less rapidly than drinking fruit juice. Only foods of plant origin provide fiber: whole grains, fruits, vegetables, etc. They don’t taste sweet.

How to properly use carbohydrates?

Utilization of carbohydrates

How many carbohydrates should you consume per day?

Carbohydrate requirements are based on the average minimum amount used by the brain. There is no tolerable upper intake level for carbohydrates because the scientific data are insufficient. 

On the other hand, it is advisable to limit the intake of added sugars to less than 15g per day because, beyond this quantity, individuals tend to consume fewer essential nutrients. In addition, the consumption of added sugar promotes overweight and civilization diseases such as diabetes. 

Soft drinks, sweets, cakes, cookies, fruit drinks, sweetened dairy products, and breakfast cereals are the main sources of added sugars in the population.

Babies 0-6 months            ND*** ND***
Babies 7-12 monthsND***ND***
Babies 1-3 years old100130
Children 4-8 years old100130
Boys 9-13 years old100130
Girls 9-13 years old100130
Boys 14-18 years old100130
Girls 14-18 years old100130
Men 19-50 years old100130
Women 19-50 years old100130
Men 50 and over100130
Women 50 and over100130
Pregnant women135175
Nursing women160210

*EAR: estimated average requirement which represents the average daily intake of nutrients sufficient to meet the requirements of half of the healthy subjects.

** ANC: recommended nutrient intake which represents the average daily nutrient intake to meet the nutrient needs of 97 to 98% of healthy individuals.

***ND: not defined

In addition, it is known that carbohydrates should provide between 45 and 55% of the total calories for the day. Fibre, on the other hand, should represent 25 to 30 g per day in healthy adults.

low carb diet

The glycemic index (GI) is a scale that ranks foods rich in carbohydrates according to the increase in blood sugar compared to a reference food, either glucose or white bread. The higher the index, the more the consumption of this food causes an increase in the level of sugar in the blood. 

There are several benefits to consuming foods with a low glycemic index including controlling blood sugar and blood cholesterol levels, controlling appetite, and reducing cardiovascular risk. 

Low glycemic index diets, compared to low-fat diets, have also been shown to have better weight loss success rates.

What are low-carbohydrate foods?

Foods low in carbohydrates are green vegetables, lean meats and fish, dairy products, oilseeds, and vegetable oils. As a general rule, all non-industrial preparations allow the amount of added carbohydrates to be controlled and are therefore generally healthier.

Adverse effects of carbohydrates

Carbohydrate deficiency

A diet very low in carbohydrates (below the minimum amount required for the brain) can lead to increased production of ketones and therefore, loss of bone mineral density, hypercholesterolemia, increased risk of stones urine, and even harm to the development and functioning of the nervous system. Very low carbohydrate intakes can also alter the feeling of well-being (malaise, fatigue).

Excess carbohydrates

Excess intake of carbohydrates (especially refined sugars) has been shown to have adverse effects including increasing the risk of dental cavities, certain types of cancer, overweight and obesity, and high blood triglyceride levels. In the long term, excess sugar can cause hyperinsulinism and then type 2 diabetes.

Interactions with other nutrients

Many elements influence the speed of carbohydrate absorption and therefore the glycemic index of foods. For example, the presence of proteins, lipids, or fibers in the food reduces the rate of absorption of the sugar it contains. Similarly, methods of preparation or cooking have influenced the glycemic index.

Chemical properties

The term carbohydrate includes a class of organic compounds that differs from others by their structure. Carbohydrates contain a ketone or aldehyde carbonyl group and at least two -OH functions. Their chemical formulas all derive from the formula Cn(H2O)n.

In the body, they play a major role in energy and energy storage. Indeed, in plants, they are stored in the form of starch, and in animals in the form of glycogen.


Nutrient history

Sugar, long reserved for certain privileged people, saw its consumption explode in the 19th century. Indeed, the consumption of sugar in the world has been multiplied by 8, we consume today nearly 35 kg per year and per inhabitant. 

Faced with this rise in sugar, many scientific studies have emerged and firmly demonstrated the dangers of sugar on health. In recent years, we have therefore noticed the emergence of new sweeteners which aim to preserve the sweet pleasure without having the disadvantages: aspartame, stevia, etc.

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