nutrition

Complex Carbohydrates

Complex carbohydrates: what are they?

Synonyms of "carbohydrates": sugars, carbohydrates, carbon hydrates.

Complex carbohydrates are energy macronutrients and provide 3.75 calories (kcal) per gram (g); their molecular structure is polymeric, meaning that each complex carbohydrate consists of the union of more than 10 simple carbohydrates (up to several thousand). The latter are "monomeric units" made up of MONOSACCARIDES, which is the most basic form of glucides: glucose, fructose and galactose (energy complex carbohydrates for humans are based on glucose). Metaphorically speaking, monosaccharides constitute the rings, while the chains deriving from their union are represented by polysaccharides.

All sugars are ternary compounds: hydrogen (H) + oxygen (O) + carbon (C) and their biological function is different between the animal and vegetable kingdoms; in the animal kingdom, carbohydrates are mainly used to produce ATP (Adenosin Tri Phosphate - pure energy) or to build energy reserves (glycogen for about 1% of body weight), while in the plant kingdom (organisms that can synthesize them) "from nothing" - autotrophs) these also have an important STRUCTURAL function (see cellulose).

Complex carbohydrates for humans; what are they

Complex carbohydrates can be divided according to their molecular variety: those containing ONLY ONE TYPE of monosaccharides are called homopolysaccharides, while those containing DIFFERENT types are called heteropolysaccharides :

  • Homopolysaccharides (thousands of molecules): starch, glycogen, cellulose, inulin and chitin.
  • Heteropolysaccharides (thousands of molecules): hemicellulose, mucopolysaccharides, glycoproteins and pectins.

There is also a functional classification of complex carbohydrates, which is based on their biological function in the PLANT kingdom:

  • Nutritional : starch and glycogen.
  • Structural : cellulose, hemicellulose, pectin etc.

Complex carbohydrates: nutritional homopolysaccharides

The human being is able to digest complex carbohydrates thanks to an enzymatic pool that acts from the mouth (salivary amylase), up to the intestine (pancreatic amylase and disaccharidase of the intestinal brush border) to split the α-glycosidic bonds 1, 4 and 1.6 (carbon position linked to the next carbon).

The most common nutritional homopolysaccharide among plant reserves is STARCH; it, chemically composed of amylose chains (20%) and amylopectin (80%), represents the primary energy source of the Mediterranean diet (± 50% of the total kcal).

Amylose is a linear polymer composed of 250-300 units, contains α1.4 glycosidic bonds and is soluble in water; amylopectin is a branched polymer composed of 300-5000 units, contains α-1, 4 bonds and (in branching points) α-1, 6 glycosides. The various types of starch (wheat, rice, barley, corn, etc.) are different for their molecular structure and have a different glycemic index; this means that, although all the starches are glucose polymers, there is a certain structural difference that determines the speed of digestion and absorption.

The other most common nutritional homopolysaccharide MA belonging to the animal kingdom is GLYCOGENO; it has an amylopectin-like structure with 3000-30000 glucose units and contains α-1.4 bonds and (in the branching points) α-1.6 glycosidics. It concentrates in the muscles, in the liver and to a lesser extent in the kidneys (1-2%) of the animals. Glycogen is essential for the maintenance of blood sugar and athletic performance of the athlete; its "recharge" depends on the type of diet but, while for the sedentary it can also be complied with diets with a very low sugar content (thanks to neoglucogenesis), for the sportsman it depends exclusively on the amount of ingested carbohydrates (especially complex).

Complex carbohydrates: importance of structural homopolysaccharides and heteropolysaccharides

Even complex structural vegetable carbohydrates (homo- or heteropolysaccharides), are molecules of great nutritional value, but lacking an energy function for MAN. They, which possess ALSO β-glycosidic bonds, require specific digestive enzymes and ABSENT in our saliva, pancreas and intestines; on the other hand, many other animals and above all different micro-organisms (including those of the intestinal bacterial flora) are able to hydrolyse them by drawing energy with the production of water, acids and gases.

OMO-polysaccharides

CELLULOSE is a homo-structural consisting of long glucose chains (3000-12000) bound by β-1, 4 glycosidic bonds. In human beings it promotes intestinal transit and is the main member of dietary fiber .

In contrast, the INULIN is a homo- formed by FRUCTOSE chains bound by β-2, 1 glycosidic bonds; it is very present in artichokes and chicory where it is a reserve substrate.

CHITIN is a homo- consisting of long chains of a "derivative" of glucose, acetyl-glucosamine ; it is of animal origin and is the carapace of crustaceans and insects.

STRAIGHT-polysaccharides

Among the hetero- the EMICELLULOSE stand out; they are a large group that also contains: xylans, pentosanes, arabinosilanes, galactans, etc. They too, like cellulose, constitute the dietary fiber and represent a substrate for the intestinal bacterial flora that uses them for energy purposes, releasing gas and acids.

MUCOPOLISACCHARIDES are hetero-present in all animal tissues, where they constitute the PRIMARY element of connective tissue. The main ones are: hyaluronic acid, chondroitin and heparin .

GLYCOPROTEINS carry out numerous biological functions within the body; they are molecules conjugated by chains of amino acids and glucides; these molecules include serum albumin, globulin, fibrinogen, collagen, etc.

Among the hetero- of vegetable origin we also remember the PECTINES; long chains of galacturonic acid "partially" combined with methyl alcohol. They combine with cellulose and are amorphous, hydrophobic, NOT fibrous; with presence of acids and sugars they form GELATINE and are used as food additives in jams etc.

Notes on the digestion of complex carbohydrates

The digestion of complex carbohydrates begins in the mouth; during chewing (in which the jaw, tongue and teeth shatter and mix the food) the glands secrete the saliva that kneads and soaks the food bolus. Saliva contains an enzyme, ptyalin or salivary α-amylase, which begins to hydrolyze starch into dextrins and maltose.

In the stomach, complex carbohydrates do NOT undergo other simplification processes, but once placed in the duodenum and mixed with pancreatic juices, they hydrolyze by the action of pancreatic α-amylase, definitively breaking down all the starch-free amylose and amylopectin chains in disaccharides.

The last digestion of the still partially complex chains (disaccharides) occurs SELECTIVELY; in the small intestine the disaccharides are hydrolyzed by the enzymes of the enteric juice; the catalysts responsible are: sucrase for sucrose (with production of glucose and fructose), isomaltases for α-1, 6 bonds of maltose (with production of maltose), maltase for α-1, 6 bonds of maltose (with production of glucose), isomaltase for the α-1, 6 bonds (with production of maltose), lactase [if present] for lactose (with production of glucose and galactose).

Complex carbohydrates: nutritional functions, dietary intake and foods that contain them

Complex carbohydrates are the most important source of energy for rapid use but at low cost in our body. Except cellulose and other non-digestible (quantitatively secondary) molecules, all the carbohydrates we take with the diet are hydrolysed, absorbed, transported to the liver and eventually transformed into glucose. The latter is then poured into the blood, where it "should" be present in concentrations equal to 80-100 mg / dl.

In addition to direct glycemic homeostasis, complex carbohydrates contribute to the maintenance of muscle and hepatic glycogen reserves, the latter responsible for the glycemic support EVEN in the prolonged fasting.

NB . Glycemic homeostasis is essential to maintaining nervous function, but if the carbohydrate intake is excessive, it can be converted into lipids and contribute to the increase of fat deposits and / or fatty liver (fat and glycogen).

The "non-digestible" complex glucides are constituents of dietary fiber; this, not being hydrolysable by the enzymes of the human organism, once it has reached the colon undergoes fermentation (and not putrefaction) of the physiological bacterial flora. Dietary fiber is therefore a prebiotic because it promotes the growth of the healthiest bacterial strains at the expense of harmful ones. It must be introduced for about 30g / day, broken down into soluble and insoluble ; the soluble one (in water) determines the gelation of the faeces, modulates the absorption of the nutrients and consists of: pectins, gums, mucilages and polysaccharides of the algae . Insoluble fiber causes an increase in gas volume by stimulating peristaltic segmentation contractions and includes mainly: cellulose, hemicellulose and lignin .

The total need for carbohydrates is 55-65% of the total kcal (never less than 50%), and of these about 45-55% must be introduced with complex carbohydrates. The protracted lack of sugars can also cause serious side effects, such as: marasmus, weight loss and muscle depletion, growth delays ; on the other hand, excess contributes to weight gain, obesity, favoring the appearance of type 2 diabetes and the pathogenesis of other dysmetabolisms.

The dietary sources of complex carbohydrates are mainly:

  • Cereals and derivatives (pasta, bread, rice, barley, spelled, corn, rye, etc.)
  • Tubers (potatoes)

The dietary sources of fiber are mainly:

  • For the soluble: vegetables and fruit, legumes.
  • For the insoluble: cereals and derivatives, legumes.

NB . Complex carbohydrates are an essential energy source especially for athletes and athletes who, if they excessively alter the balance of nutrients, worsen the effectiveness and efficiency of the metabolism to the detriment of performance. The increase in sugars in an athlete / sportsman who does not introduce enough sugar results in a significantly ergogenic effect.