The harms of sugary foods are known: excess weight, diabetes, cavities, hypertension, accumulation of fat in the liver... To the point where many want to wean themselves from them. But can we live without sugar? The Rumor Detector takes stock.
If eating is generally a pleasure, it is also a condition for our survival. The body draws the energy it needs to function from the foods we eat. And even while we sleep, it draws this energy from reserves constituted by certain organs.
This energy comes from three main groups of macronutrients: proteins, carbohydrates and lipids.
The role of sugars
The body digests food by mixing it in the stomach with gastric juice, an acidic liquid that contains enzymes. During digestion, carbohydrates – sugars found especially in floury foods such as bread, pasta, rice or cereals, in addition to fruits, vegetables and sweets – break down into another type of sugar, called glucose. This, once it reaches the intestine, is released into the blood to nourish the cells.
As soon as it is present in the blood, glucose can be used as energy or stored in the liver and muscles in the form of glycogen. The amount varies from person to person, but an average-sized man weighing 70 kg stores about 100 grams of glycogen in his liver .
When you stop eating carbohydrates for several hours, liver glycogen is broken down into glucose and released into the bloodstream to prevent blood sugar levels (blood sugar levels) from falling too low. Glycogen stored in muscles, although in greater quantities, remains in the muscles to meet their energy needs and cannot be released into the bloodstream to nourish the cells.
Glucose, the main source of energy
Glucose is the main fuel for the brain, which requires a constant supply of energy to function and carry out vital functions, such as breathing or sending signals to the nervous system. It consumes 20% of our daily energy. When brain cells, neurons, struggle to obtain or use this fuel, they function less well and can die. And when neurons die en masse, there is a loss of brain capacity.
Sugar therefore seems necessary. Except that glucose is not the only fuel the brain can use. In people whose diet does not contain enough carbohydrates to provide the required 110 to 145 grams of daily glucose , or when the body lacks stored carbohydrates, the brain may use ketones to meet many of its needs. energy needs.
Ketone, an alternative to glucose
After 24 to 48 hours without carbohydrates, the body's glycogen level becomes depleted. The liver then intensifies its production of water-soluble compounds called ketones, created by the breakdown of fatty acids. Ketones are made from ingested fat or the body's fat stores. They can then cross the blood-brain barrier to provide energy to the brain .
Researchers have demonstrated that for some people following a strict ketogenic (keto) diet, that is to say low in carbohydrates (sweet foods, bread, pasta, rice, juice, etc.) and high in lipids, or fats, (red meat, fatty fish, cheeses, butter, avocados, nuts and seeds, etc.), ketones can provide up to 50% of the basic energy needs and up to 70% of the brain's energy needs. The body must be starved of carbohydrates for at least three to four weeks before reaching this keto state.
And for the rest of the brain's energy needs, the liver can produce all the glucose needed, through a process called gluconeogenesis, says a literature review published in 2019. The liver uses compounds from protein consumption and breakdown body or dietary fat, to recreate glucose.
In other words, the brain can meet all its energy demands thanks to glucose stored in the liver, gluconeogenesis and the production of ketones, whether or not we ingest carbohydrates.
The 2005 US Food and Nutrition Board manual (Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids) also indicates that “the lower limit of dietary carbohydrates compatible with life is apparently zero, provided that adequate amounts of protein and fat are consumed.
However, people who eat a lot of carbohydrates and decide to cut out sugar must go through a period of adaptation. Since the brain is not used to using ketones, glucose will remain its main fuel source for some time, drawing on the body's reserves. Once the body is adapted to a very low- or no-carb diet, the brain uses ketones to meet much of its energy needs, and the liver should produce as much glucose as needed to cover the rest. , according to a study published in 2017 .
Verdict
The brain needs glucose. However, this glucose does not need to come only from carbohydrates, it can be produced by the liver. Eating sugar to fuel the brain and provide energy to the muscles is an option, not a requirement. Although eliminating all traces of sugar from our diet seems difficult since it is found everywhere, even in certain vegetables!
Author: Agence Science Presse – Catherine Crépeau