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Carbohydrates and blood sugar

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The main products deriving from the digestion and intestinal absorption of carbohydrates are glucose, galactose and fructose. Through the mesenteric vein and the portal vein these sugars reach the hepatic capillaries, where they are retained in large quantities.

It is precisely at the liver level that galactose and fructose are converted into glucose, which practically represents the only sugar present in the bloodstream. The term glycemia is used to indicate its concentration in the blood. In a healthy person this parameter fluctuates, on an empty stomach, between 80 and 100 mg/dl. For the individual to be healthy it is essential that blood sugar levels remain relatively constant throughout the 24 hours.

At the end of a meal, glycemic values ​​of around 130-150 mg/100 ml are considered physiological. However, it is normal that during prolonged fasting, or in response to intense physical effort, blood sugar levels drop to 60-70 mg/dl. When the glucose concentration drops further, we speak of hypoglycemia, a condition that is accompanied by symptoms such as tremors, palpitations, intense hunger, paleness, drooling and convulsions. When blood sugar levels fall below 20 mg/dl there is even a risk of coma and death.

The importance of glucose circulating in the blood is linked to the inability of neurons to draw energy from other energy substrates, such as fats and amino acids. Signs of cerebral suffering already appear for glycemic values ​​below 60 mg/dl and are responsible for the typical symptoms previously illustrated.

When blood sugar increases excessively, reaching the threshold value of 180 mg/dl, the body begins to lose glucose in the urine (glycosuria). This, which at first glance might seem like an effective defense mechanism, is actually a dangerous phenomenon, since due to osmotic issues, urine containing glucose attracts a lot of water, resulting in body dehydration.

In physiological conditions glycosuria is equal to 0.

When sugars absorbed from the intestine enter the liver through the portal vein, they can undergo different fates.

First of all, they can be degraded by liver cells to obtain the energy necessary to satisfy the metabolic demands of hepatocytes.

Glucose can also be converted into glycogen, which represents our body's sugar reserve. A certain amount can also be transformed into triglycerides.

The fate of sugars is heavily influenced by the nutritional status of the subject.

In response to a meal particularly rich in carbohydrates, the liver tries to bring blood sugar levels back to normal:

  1. converting its metabolism, normally based on the oxidation of fats, with the aim of consuming mainly sugars
  2. increasing glycogen stores in hepatocytes
  3. favoring the conversion of glucose into fatty acids

Note: glycogen, which is reduced into individual glucose monomers during fasting, can be stored at most in quantities equal to 5-6% of the liver mass (approximately 100 grams). Once these reserves are saturated, the liver is forced to convert the excess sugar into reserve adipose tissue. For this reason, a diet low in fat and rich in carbohydrates (pasta, bread, cereals and derivatives, sweets, etc.) is not effective in promoting body weight reduction.

The liver also regulates blood sugar through the intervention of various hormones; the best known and most influential are called insulin and glucagon respectively.

The regulatory action on glycemic values ​​is not entrusted only to the liver; similarly, insulin does not act only on hepatocytes but influences the metabolism of various tissues. In the muscle, for example, this hormone promotes the entry of glucose which, in addition to being degraded through glycolysis, is transformed into storage glycogen.

Insulin also acts at the level of adipose tissue, increasing the uptake of glucose and stimulating its storage in the form of triglycerides.

Keep reading:
Carbohydrates and hypoglycemia

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