Monosaccharide - Simple Sugars | Carbohydrates

Monosaccharides, are simple sugars and the most basic units of carbohydrates. They are fundamental units of carbohydrates and cannot be further hydrolyzed to simpler compounds. They are usually colorless, water-soluble, and crystalline solids. Examples of monosaccharides include; glucose (dextrose), fructose (laevulose), and galactose.


Monosaccharides, are simple sugars and the most basic units of carbohydrates. They are fundamental units of carbohydrates and cannot be further hydrolyzed to simpler compounds. They are usually colorless, water-soluble, and crystalline solids. Examples of monosaccharides include; glucose (dextrose), fructose (laevulose), and galactose.

Simple sugars.


Glucose, dextrose or grape sugar, occurs naturally in fruits and plant juices and is the primary product of photosynthesis. Most ingested carbohydrates are converted into glucose during digestion and it is the form of sugar that is transported around the bodies of animals in the bloodstream. It can be manufactured from starch by the addition of enzymes or in the presence of acids. Glucose syrup is a liquid form of glucose that is widely used in the manufacture of foodstuffs. It can be manufactured from starch by enzymatic hydrolysis.

Fructose, or fruit sugar, occurs naturally in fruits, some root vegetables, cane sugar and honey and is the sweetest of the sugars. It is one of the components of sucrose or table sugar. It is used as a high-fructose syrup, which is manufactured from hydrolyzed corn starch that has been processed to yield corn syrup, with enzymes then added to convert part of the glucose into fructose.

In general, galactose does not occur in the free-state but is a constituent with glucose of the disaccharide lactose or milk sugar. It is less sweet than glucose. It is a component of the antigens found on the surface of red blood cells that determine blood groups.

Fuel metabolism.

Vital elements of RNA and DNA.


Fuel Metabolism:
One major function of a monosaccharide is its use for energy within a living organism. Glucose is a commonly known carbohydrate that is metabolized within cells to create fuel. In the presence of oxygen, glucose breaks down into carbon dioxide and water, and energy is released as a byproduct. Glucose is a product of photosynthesis, and plants obtain energy from glucose through respiration. Humans acquire glucose from food, and the body transforms this monosaccharide into energy.

Energy Storage:
When monosaccharides are not immediately needed by many cells they are often converted to more space-efficient forms, often polysaccharides. In many animals, including humans, this storage form is glycogen, especially in liver and muscle cells.

Building Blocks:
Monosaccharides are also the foundation for more complex carbohydrates, or they serve as components to amino acids. The ribose and deoxyribose monosaccharides are vital elements of RNA and DNA, which are the building blocks of life. While monosaccharides cannot be broken down into smaller sugars, disaccharides and polysaccharides are broken down into monosaccharides in processes like digestion. For example, the disaccharide lactose is degraded into monosaccharides, which can be absorbed into the human body.

Fruits are a good source of simple sugars.

Milk is especially a rich source of the simple sugar galactose which is a component of lactose.


Aside from lactose found in milk and small amounts of specific sugars in red meat, almost all dietary carbohydrates come from plant foods. Dietary sources of monosaccharides therefore are mostly fruit, vegetables, honey, dairy products, processed foods and from the digestion and conversion of other carbohydrates (disaccharides, oligosaccharides and polysaccharides). Below is an overview of the most common sources of monosaccharides:

Whole foods that act as natural sweeteners are the richest sources of the monosaccharides fructose and glucose, usually in combination. In addition to table sugar, which is made from either sugar cane or sugar beets, natural sweeteners such as honey and molasses are high in simple sugars. Honey is mostly fructose, while corn syrup and maple syrup are mostly glucose. Agave nectar, often touted as a more healthful alternative to table sugar, contains a high ratio of fructose to glucose.

Fruits, especially apples, cherries, grapes, guavas, lychees, honeydew melon, watermelon, mangoes, papayas, pears, persimmons and pineapple, are the richest whole-food sources of the monosaccharide fructose. Unless you have a fructose intolerance, health professionals generally recommend getting most of your simple sugars from whole fruits, which contain fiber that slows down your body’s absorption of sugars, as well as healthful vitamins, minerals and antioxidants. Dried fruits and fruit juices are more concentrated sources of fructose.

Diary Products and Meat: Dairy products are the richest food sources of galactose. Milk, butter, sour cream, ice cream, yogurt and other dairy products don’t contain actual galactose, but they do have a sugar called lactose, which the body breaks down into glucose and galactose. Ingredients derived from dairy products, such as whey protein, dry milk solids and casein, can also contribute galactose. Fermented and aged dairy products such as cheddar cheese and yogurt generally contain less sugar. While meats generally contribute little in the way of sugars, organ meats such as liver are the exception. They’re rich in galactose.

Vegetables and Legumes: Generally, vegetables contain much less sugar than fruits, and don’t contribute many simple sugars to the diet. Vegetables that tend to contain more fructose include artichokes, asparagus, beans, broccoli, cabbage, chicory, onions and leeks, peanuts, tomatoes and zucchini. Beans, lentils, chickpeas and sugar beets also provide galactose.

Early symptoms of low blood sugar include weakness, lightheadedness, and dizziness.

Severe low blood sugar can result in seizures, loss of consciousness, or death.


When your blood sugar (glucose) levels fall below the normal range, it’s called hypoglycemia, or insulin shock. Low blood sugar can happen when you skip a meal or are malnutrition. It can also happen if your pancreas releases more insulin than it should after you’ve eaten.

Another possible cause of low blood sugar is drinking too much alcohol, especially on an empty stomach. This can interfere with the liver’s ability to release stored glucose into your bloodstream. Hepatitis and other problems with your liver can also lead to low blood sugar. Other causes include kidney disorders, anorexia nervosa, a pancreatic tumor, or adrenal gland disorders.

Insufficient blood sugar levels can cause a rapid heartbeat and heart palpitations. However, even if you have diabetes, you may not always have obvious symptoms of low blood sugar. It’s a condition called “hypoglycemia unawareness.” This happens when you experience low blood sugar so often that it changes your body’s response to it. Normally, low blood sugar causes your body to release stress hormones, such as epinephrine. Epinephrine is responsible for those early warning signs, like hunger and shakiness. When low blood sugar happens too frequently, your body may stop releasing stress hormones (hypoglycemia-associated autonomic failure, or HAAF). That’s why it’s so important to check your blood sugar levels often.

Every cell in your body needs sugar to work properly. It’s your body’s main source of energy. Low blood sugar levels can cause a variety of problems within your central nervous system. Early symptoms include weakness, lightheadedness, and dizziness. You may feel nervous, anxious, or irritable, and you’ll probably be hungry. Lack of coordination, chills, clammy skin, and sweating are common. Tingling or numbness of the mouth may be a sign of low blood sugar. Other symptoms include blurred vision, headache, and confusion. You may have difficulty performing simple tasks. When blood sugar levels drop during the night, you may have nightmares, cry out during sleep, or other unusual behaviors.

Severe low blood sugar is sometimes called insulin shock. Untreated, it can be very dangerous, resulting in seizures, loss of consciousness, or death.

World Health Organization's independent meta-studies specifically distinguish free sugars from sugars occurring naturally in food.


The negative health effects of monosaccharides or sugars are mostly a result of over consumption. Studies have suggested that chronic consumption of refined sugars can contribute to metabolic and cardiovascular dysfunction. Some experts have suggested that refined fructose is more damaging than refined glucose in terms of cardiovascular risk.

Controlled trials have also shown unequivocally that consumption of refined sugar (also called “free sugar”) increases body weight and body fat, and that replacement of sugar by artificial sweeteners reduces weight. This found that "SSBs (sugar-sweetened beverages) may increase the risk of metabolic syndrome and type 2 diabetes not only through obesity but also by increasing dietary glycemic load, leading to insulin resistance, β-cell dysfunction, and inflammation".

As an overview to consumption related to chronic disease and obesity, the World Health Organization's independent meta-studies specifically distinguish free sugars ("all monosaccharides and disaccharides added to foods by the manufacturer, cook or consumer, plus sugars naturally present in honey, syrups and fruit juices") from sugars occurring naturally in food.

In regard to contributions to tooth decay, the role of free sugars is also recommended to be below an absolute maximum of 10% of energy intake, with a minimum of zero. There is "convincing evidence from human intervention studies, epidemiological studies, animal studies and experimental studies, for an association between the amount and frequency of free sugars intake and dental caries" while other sugars (complex carbohydrate) consumption is normally associated with a lower rate of dental caries. Lower rates of tooth decay have been seen in individuals with hereditary fructose intolerance. Also, studies have shown that the consumption of sugar and starch have different impacts on oral health with the ingestion of starchy foods and fresh fruit being associated with low levels of dental caries.


The World Health Organization recommends that both adults and children reduce the intake of free sugars to less than 10% of total energy intake. A reduction to below 5% of total energy intake brings additional health benefits, especially in what regards dental caries (cavities in the teeth).

Sugar found naturally in milk, fruit and vegetables doesn't count as free sugars. We don't need to cut down on these sugars, but remember that they are included in the "total sugar" count.

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