Astringent foods

Astringent capacity by precipitation of colloidal proteins

The astringent effect is exerted above all thanks to the combination of high and low molecular weight phenols , and to tannins in the presence of proanthocyanidins (other polyphenols characterized by the oligometric repetition of flavonoids ). It is a fairly complex topic, full of technicalities, which however can be summarized and interpreted by the reader as follows:

“the plant compounds that exert the astringent function are those that lap in the mouth (as occurs with unripe persimmons), which color foods (for example the red of grapes and wine) and which , in general, are considered beneficial for health ( antioxidants , cholesterol-lowering agents , etc.)”.

Astringent capacity for water absorption in the faeces

Secondly, thanks to their absorbent capacity, starchy foods that are poor in water and have a very low residual fiber also exert an intestinal astringent action ; some examples are boiled potatoes , refined cereals (such as polished rice ), isolated starches (such as rice , cornstarch , frumina, tapioca ), etc.

Astringent foods

What are astringent foods?

As anticipated, astringent foods are of plant origin. In addition to lapping (sensation felt mainly in the center and behind the tongue), these often have a sweet and/or sour taste .

There are therefore various vegetables , tubers , fruits , aromatic herbs , cereals, legumes (or parts of them) and herbal medicines (barks, roots, etc.) with astringent properties. Examples of astringent foods are given in the table below.

Controversies over astringent foods

An aspect overlooked by many is that many of these foods, in addition to containing astringent nutritional factors, are often also rich in fiber and water (two factors that soften the stools, hindering constipation ).

For example, unripe bananas and persimmons (with the exception of the cacomela variety ) are highly astringent fruits; this function is lost with maturation, during which certain enzymes convert tannins into fructose . However, bananas but especially persimmons are also rich in fiber and water; this means that, while unripe bananas and persimmons are mainly astringent, very ripe ones (or the cacomela variety) can instead prove to be anti-constipating. A medium-ripe persimmon or banana could therefore prove to have a neutral action or emphasize the subjective tendency to constipation or too liquid stools.

Drinks

Astringent drinks: the definitive solution

The most effective astringent drinks are those obtained from the pressing of vegetables with the aforementioned properties, or composed of aqueous solutions of phytotherapeutic active ingredients (or drugs) . A classic example of an extracted and astringent drink is pomegranate or prickly pear juice .

The phytotherapeutic remedies rich in astringent polyphenols, on the other hand, mainly contain fruits, seeds, leaves, roots and bark (depending on the case): bearberry , camellia, eucalyptus , hawthorn , witch hazel , horse chestnut , ratania , guarana , oak , cinnamon , fern , late cherry , eugenia etc.

Action

Mechanism of astringent foods

Astringent mechanism of polyphenols

Polyphenols are therefore responsible for the precipitation of food proteins and the inactivation of digestive enzymes . This precipitation separates the solid from the liquid, making it sink in the form of a precipitate based on phenols and proteins. The reaction begins in the bolus , in the mouth, and continues in the intestine (first in the chyme and then in the faeces) where it hinders protein absorption and also affects the digestive enzymes .
To demonstrate the astringent action of polyphenols we can note:

1. In the mouth: The sensation of lapping, dryness, friction and dough that requires increased salivation to facilitate swallowing .
2. In the large intestine : more compact and less hydrated stools, often accompanied by an increase in malodorous flatulence .

Astringent mechanism of refined starchy foods

As a consequence of the absorbent action of starches instead, only a late effect is noted caused by the reduction of intestinal peristalsis (due to lack of fibres ) and an increase in faecal consistency.

However, it must be remembered that this last astringent mechanism has very subjective effects; in fact, the digestive system reacts spontaneously to the dryness of foods by releasing water into the digestive juices in adequate quantities. Reducing fiber ( low residue diet ) and increasing refined starches should not be considered an immediate remedy, but rather a basic rule of the anti-diarrhea diet.

Benefits

What are astringent foods for?

Astringent foods fight enteritis , the symptom of diarrhea, the inflammatory states of chronic pathologies ( Crohn’s disease , ulcerative colitis ), ulcers and metal poisoning ; the mechanisms of action that regulate these effects are:

• They reduce the water in the stool
• They decrease intestinal peristalsis (due to reduced nerve sensitivity)
• They are anti-inflammatory (as well as for the intestine, also mildly for the esophagus and stomach )
• They precipitate the protein molecules of bacteria and complex the irritating ones
• Mucous secretions decrease (see Mucus in Feces )
• By binding, they protect the surfaces of ulcerative lesions and promote haemostasis by optimizing coagulation
• Chelating on metals such as aluminum , iron, copper , manganese and vanadium (normally the chelating action on dietary iron is considered anti-nutritional but in the pathology of hemochromatosis it is instead therapeutic).

Side effects

Are too many astringent foods bad for you?

• In case of excessive intake of polyphenols and/or reduction of dietary fiber and/or water, the astringent action may be excessive, predisposing to constipation.
• Moreover, the non-absorption of proteins in the small intestine (caused by the binding of polyphenols with food peptides and with digestive enzymes on the mucosa ) tends to increase their concentration up to the colon , where the bacteria elaborate them with consequent onset of meteorism , tension abdominal and flatulence.
• The chelating action of phenols on minerals reduces their absorption, above all favoring iron deficiency . In addition, inhibition of digestive enzymes ( proteases ) decreases the nutritional absorption of peptide amino acids .
• An excess of tannins can be counterproductive in case of severe inflammatory and ulcerative lesions of the digestive tract; moreover, some statistical data indicate a correlation (unclear but present) between excess tannins and gastrointestinal tumors .
• Polyphenol molecules also precipitate alkaloids and decrease the action of drugs containing them.