Digestion and Absorption of Fats

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Digestion And Absorption Of Fats

 

The digestive system breaks down food into simple components that can be readily

absorbed, and these are then reconstituted into the various components of the

body. Because fats are water-insoluble, their digestion and absorption is

different from that of the other nutrients we eat.

 

Fats must first be emulsified, which means that they must be dispersed in the

aqueous medium of the intestinal contents before they can be broken down by

enzymes. Emulsification is achieved by the addition of bile salts and lecithin

to the gut contents which, together with the churning of the ingested material,

breaks the fat up into droplets.

 

These tiny droplets are then acted upon by enzymes known as lipases which are

released by the pancreas. Lipases break the fat down into fatty acids,

monoglycerides and diglycerides.

 

By the further action of bile, still tinier droplets called micelles are formed

which are polar and consist of bile and bile salts, monoglycerides, fatty acids

and glycerol.

 

Once these products have been absorbed by the absorptive cells of the

intestines, they are again converted to triglycerides which together with

phospholipids from protein-coated droplets known as chylomicrons.

 

About 80% of chylomicrons find their way into the lymphatic system via the lymph

ducts of the gut villi, whilst the other products of digestion, such as the

sugars and amino acids enter the bloodstream via the capillaries.

 

The lymphatic system acts as a filter to remove harmful residues and bacteria

before returning to the fatty acids to the bloodstream. Excessive fat intake

thus places severe demands on the lymphatic system and can lead to increased

susceptibility to disease and common ailments such as fatigue, headaches, colds

and flu.

 

Cholestoral Content of Selected Foods

 

RIND. 1986. Food composition tables. 2nd. ed. South African Medical Research

Council.

 

 

As there are no lipases nor emulsifiers secreted in the saliva or stomach, lipid

digestion does not commence until the ingested food has left the stomach.

 

Excess fat in the diet will also retard the digestive processes in the stomach,

and protein digestion thus takes considerably longer if free fat is present.

 

Moreover, the fat coats the ingested food making it difficult for the

water-soluble enzymes in the stomach to penetrate and commence the process of

digestion.

 

This is particularly true if the protein is of animal origin, as animal proteins

take longer to digest than plant proteins and also require a lower stomach pH

than do plant proteins.

 

Meat, for example, takes some 3-6 hours preparation time in the stomach, but the

presence of free fat will lengthen the digestion time well beyond this point.

A further consequence of this delay is that the products of carbohydrate

digestion will start to ferment under these circumstances and lead to a build up

of acid fermentation products.

 

Protein foods prepared by frying or grilling will give a satisfied after-dinner

feeling, but this is because of the longer time that the food remains in the

stomach, and not because of the better nutrient quality of the food consumed.

 

The presence of fats in the food retards the digestive process in the stomach

cause fat induces the release of hormones known as GIP (gastric inhibitory

peptide) which slows down the gastric activity.

 

Once the food has left the stomach and entered the duodenum, fatty acids in the

duodenum will cause the release of another hormone (known as

cholecystokinin-pancreozymin), which induces the gall-bladder to contract and to

release bile into the small intestine.

 

This same hormone will also induce the pancreas to release sodium bicarbonate

into the duodenum to neutralize the acid in the chyme so that the alkaline

phases of digestion can commence.

The phospholipid lecithin, which is produced in the liver and assists in the

emulsification of fats, is also released into the duodenum.

The presence of these emulsifiers makes it possible for the water-soluble

enzymes in the duodenum to operate optimally, even in the presence of fat.

 

In whole foods the fats are not in a free form (they are still surrounded by the

phospholipid bilayer), and thus remain water-soluble until acted upon the

lipases in the duodenum.

 

Even whole foods that are rich in fats, such as oilseeds, nuts and oil rich

fruits such as avocado pears and olives will thus not interfere with the

digestive process in the stomach.

Only once the fat has been extracted in its free form will it retard the

digestive processes.

 

Lecithin plays a significant role in the metabolism of fats in general, and it

protects against the accumulation of fatty deposits in the arteries.

 

As the liver can only produce a limited amount of lecithin per day, the regular

consumption of fatty foods, particularly animal products, will lead to a

reduction of lecithin reserves and lay the foundation for the development of

arteriosclerosis.

 

A regular supply of whole foods such as fruits, vegetables, grains, seeds, nuts

and legumes will ensure that the body's lecithin needs are met.

 

Legumes ( non-gmo soybeans, lentils, dried beans) in particular are an excellent

source of lecithin, but all whole foods will help the body to produce natural

lecithin and aid in the emulsification of dietary lipids.

 

The above has been excerpted from the book Diet and Health by Professor Walter

J. Veith available through our webstore.

 

http://www.amazingdiet.org/

_________________

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JoAnn Guest

mrsjoguest

DietaryTipsForHBP

http://www.geocities.com/mrsjoguest

 

 

 

 

 

 

 

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