Digestion and Absorption Of Fats

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Digestion and Absorption Of Fats

JoAnn Guest

Sep 12, 2004 19:32 PDT

 

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

thepresence 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 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/

_________________

 

JoAnn Guest

mrsjo-

DietaryTi-

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