Glucose is a monosaccharide that is part of food (primarily sweets and fruits), as well as obtained from carbohydrate foods during digestion. The hormone insulin is needed to absorb glucose – if not enough, blood sugar levels can rise dangerously.
In turn, fructose is also a monosaccharide found in fruits. The key difference is the mechanism of processing and assimilation (fructose is transformed mainly in the liver, glucose – throughout the body). This ultimately determines the effect on metabolism.
What is glucose?
Glucose is the main source of energy for the nervous system (in particular, it is necessary for neurons to communicate successfully), as well as a structural element for the formation of muscle glycogen stores. Recall that glycogen is the main fuel necessary for the work of muscles.
Normally, glucose is formed during digestion. During the passage of food through the esophagus and stomach, enzymes and an acidic environment turn carbohydrate food into small pieces with the formation of glucose molecules. They are then absorbed in the intestine (or liver) and used as an energy source.
Glucose absorption is impossible without insulin – in fact, this hormone opens up the cells to store energy. Chronically high blood glucose interferes with normal insulin production, causing type 2 diabetes – and an even higher rise in sugar levels.
How is it different from fructose?
Most often, fructose requires a significantly smaller amount of insulin for absorption (or does not require it at all) – in the body, it is absorbed in the large intestine and then transferred to the liver, where it accumulates. The reason is the simpler structure of the molecule.
Since the liver regulates carbohydrate and fat metabolism, excess fructose in the diet (and, therefore, its excessive accumulation in the liver) may be associated with an increase in unwanted fat – as well as an increase in the level of “bad” cholesterol in the blood.
Modern researchers believe that even the body of a completely healthy person is able to absorb no more than 25-50 g of fructose at a time without harm to metabolism.
Which products contain it?
In natural foods, glucose is always found together with fructose and sucrose (first of all, we are talking about fruits and sweet fruits – grapes, watermelon, melon, etc.). The more glucose is contained in the fruit, the sweeter it tastes.
Glucose was first obtained from grape juice in 1747. 100 g of grapes contain 18 g of carbohydrates, of which 15.5 g of sugars (8.1 g of fructose, 7.2 g of glucose, and 0.2 g of sucrose) and 2.5 g of fiber. At the same time, table sugar is an equivalent mixture of glucose and fructose, and honey contains about 40% fructose and 30% glucose.
How is it formed in nature?
Plants form glucose from carbon dioxide and water during photosynthesis (that is, under the action of sunlight) with the formation of oxygen. The type and structure of the plant affect how much glucose, fructose, starch, and fiber are formed.
However, even complex carbohydrates in the process of digestion are converted mainly into glucose – this is how the human body processes and absorbs starch. If carbohydrates have the most complex structure, they are not digested at all – we are talking about fiber.
The more simple carbohydrates (that is, glucose and fructose) a food contains, the higher its glycemic index – and the faster the energy is converted into blood sugar.
The benefits and harms of glucose
On the one hand, glucose is the main source of energy for the body, necessary for the proper functioning of metabolism and maintenance of life. On the other hand, excess glucose is unequivocally detrimental to health and metabolism.
In the course of evolution, the human body was rarely exposed to large amounts of glucose – sweet fruits were available in limited quantities and only in the warm season, and the mass production of sugar and sugar sweets began no more than 100 years ago.
Glucose (and fructose) molecules are able to bind to the proteins and fats of the human body, causing structural damage to them. In particular, excess glucose intake can accelerate the aging process of the skin and internal organs.
Recommended intake for adults and children
Current nutritionist recommendations boil down to the fact that exceeding 10% of the share of simple carbohydrates in the daily calorie intake in the long term leads to the development of a number of serious chronic diseases (obesity, diabetes, hypertension).
In practice, we are talking about 30-50 g of glucose and fructose in its pure form (that is, in the form of sugar and fruits). Among children, due to sweets, snacks, and sugary drinks, the figure can reach 200-250 g of sugar per day.
As for the total amount of carbohydrates in a proper diet, the World Health Organization recommends limiting carbohydrates to 55% of daily calories (approximately 250-300 g), including at least 18-25 g of fiber in the diet.
The total reserves of glucose in the body of an adult weighing 70 kg are about 500 g – about 100 g of processed glucose in the liver, 400 g in the muscles, and only 4 g in the blood.
Glucose is the main source of energy for the human body, necessary to maintain the performance of muscles and the nervous system. However, an excess of glucose (and other simple carbohydrates) can negatively affect metabolism, increasing the level of micro-inflammation and accelerating the aging process.