Carbohydrates are macronutrients composed of carbon, hydrogen and oxygen. They are the body's main source of energy and play a key role in cellular metabolism. Depending on their structure, there are three main categories of carbohydrates:
Carbohydrates are found in a variety of foods, both natural and processed:
The nutritional value of carbohydrates depends not only on their chemical structure, but also on the nutritional matrix of the food containing them.
Nutritious carbohydrates: present in whole foods, rich in fiber, vitamins, minerals and bioactive compounds. For example, fruits, vegetables, legumes and wholegrain cereals contain carbohydrates associated with a matrix that slows down their digestion, promoting a gradual release of energy and providing essential nutrients.
Less nutritious carbohydrates: These are found in ultra-processed foods where the original matrix is altered or non-existent. For example, refined sugars found in sweetened beverages, pastries and refined cereals are rapidly absorbed by the body, leading to blood sugar spikes and lower nutritional value, as they are often devoid of fiber, minerals and antioxidants.
Carbohydrate digestion begins in the mouth with salivary amylase, an enzyme that initiates the breakdown of starch. Once in the stomach, this enzyme is inactivated by gastric acidity, and digestion resumes in the small intestine under the action of pancreatic amylase. Disaccharides and polysaccharides are then reduced to monosaccharides, which are then absorbed into the bloodstream.
Once absorbed, carbohydrates have several metabolic functions:
In an individual with a balanced diet when carbohydrate intake is moderate and proportionate to energy needs, less than 5% of ingested carbohydrates are converted to lipids via de novo lipogenesis.
In practice, the majority of excess carbohydrates are burned as energy or lead to a reduction in lipid oxidation (thus favoring storage of dietary fat rather than its utilization).
In the case of massive carbohydrate excess (overeating of simple sugars or refined starches)
When an individual consumes large quantities of carbohydrates in excess of energy requirements and glycogen storage capacity, de novo lipogenesis becomes more active.
Studies show that under extreme conditions (excess carbohydrate intake > 500-700 g/day over several days), de novo lipogenesis can convert 10-20% of carbohydrates into triglycerides stored in adipose tissue.
This conversion is particularly amplified when excess carbohydrates come from refined sugars and fructose, as the liver is the main site of fructose conversion to fatty acids.
Quantity and type of carbohydrate: excess calories from simple sugars (glucose, fructose) are more conducive to lipogenesis than complex, fiber-rich carbohydrates.
Level of physical activity: Regular exercise increases carbohydrate oxidation and reduces conversion to fat.
Glycogen storage capacity: If liver and muscle glycogen reserves are full, excess glucose is more likely to be converted into lipids.
In the average person on a normal diet, less than 5% of carbohydrates are converted to lipids via de novo lipogenesis. This figure may rise with excessive carbohydrate consumption (particularly in the form of simple sugars and fructose), but under realistic conditions, lipogenesis remains a minority phenomenon compared to carbohydrate oxidation and glycogen storage.
Carbohydrates play several essential roles in the body:
The consumption of carbohydrates, whether complex or simple, varies significantly across the world depending on dietary habits, food availability, and socio-economic contexts. It is essential to distinguish between complex carbohydrates, primarily derived from cereals, legumes, and tubers, and simple sugars, which are often added to processed foods. This distinction is crucial for understanding the nutritional and health impacts of these different types of carbohydrates.
According to the World Health Organization (WHO), carbohydrate intake ranging from 40% to 70% of total energy intake is associated with a lower risk of mortality compared to lower intakes. This broad range reflects cultural and dietary variations worldwide. Complex carbohydrates, mainly found in staple foods such as cereals, roots, and tubers, constitute a significant portion of the energy intake in many regions.
In contrast, the consumption of simple sugars, often added to processed foods, varies based on dietary habits and the availability of industrial products. The WHO recommends reducing free sugar intake to less than 10% of total energy intake, and ideally to less than 5% (approximately 25 grams per day) to prevent health issues such as obesity and dental cavities.
In the United States, simple sugar consumption is particularly high. Americans consume an average of 126.4 grams of sugar per day per person, significantly exceeding WHO recommendations. This excessive intake is often attributed to the high prevalence of sugary beverages and processed foods in the daily diet.
On the other hand, complex carbohydrate consumption, derived from sources such as whole grains, is often insufficient, which can lead to nutritional imbalances.
In Europe, simple sugar consumption varies between countries. For instance:
These figures reflect a high consumption of sugary products and beverages. However, some European countries are making efforts to reduce sugar intake through awareness campaigns and fiscal policies, such as taxes on sugary drinks.
Complex carbohydrates remain an essential part of the European diet, with bread, pasta, and potatoes being notable components.
In Asia, complex carbohydrates form the foundation of the diet in many countries, with a dominance of rice, noodles, and traditional breads.
For example:
However, with urbanization and rising incomes, simple sugar consumption is increasing, especially through sugary beverages and processed foods.
This dietary shift poses public health challenges, leading to an increase in sugar-related diseases such as diabetes and obesity.
In Africa, traditional diets are rich in complex carbohydrates, primarily from cereals, tubers, and legumes.
However, simple sugar consumption is increasing, particularly in urban areas where processed foods are more accessible.
This trend is concerning as it is associated with a rise in non-communicable diseases, such as diabetes and cardiovascular diseases.
Although located in South Asia, Afghanistan has unique dietary characteristics.
A recent study found that:
These figures suggest a nutritional transition, possibly linked to an increase in simple sugar consumption and processed foods, although specific data on carbohydrate consumption in Afghanistan is limited.
The distinction between complex carbohydrate consumption and simple sugar consumption is crucial for understanding the nutritional and health impacts of dietary patterns worldwide.
While complex carbohydrates are a fundamental energy source and generally beneficial for health, excessive simple sugar intake is associated with various health issues.
Therefore, it is essential to promote balanced eating habits, emphasizing complex carbohydrate sources while limiting added sugar intake, to improve public health globally.
Not all carbohydrates are equal in terms of their impact on health. The nutritional environment in which they are found - their nutritional matrix - plays a key role in their digestion, absorption and metabolic effect. Favoring whole-food sources of carbohydrates, rich in fiber and micronutrients, is essential for maintaining stable energy levels and optimizing long-term health.
