Let's talk about lipids

Today I'll present you the lipids, or FATS. Those have, as the insulin does, an undeserved bad reputation.

Lipids are fatty acids, composed by an hydrocarbonated chain (with different lengths) and ended by a carboxyle group


Carbone bonds can either be saturated or unsaturated

We usually distinguish the saturated fatty acids (don't have not any double bond), the monounsaturated fatty acids (only one double bond) and the polyunsaturated fatty acids which have at least two double bonds.

Here are the fatty acids we usually consume :
Saturated fatty acids
Butyric acid
Caproic acid
Caprylic acid
Lauric acid
Myristic acid
Palmitic acid
Stearic acid
Arachidic acid

Monounsaturated fatty acids
- Omega 9 :
Palmitoleic acid
Oleic acid

Polyunsaturated fatty acids
- Omega 6 :
Linoleic acid
Arachidonic acid

- Omega 3:
Alpha-linolenic acid (ALA)
Eicosapentaenoic acid (EPA)
Docosapentaenoic acid (DPA)
Docosahexaenoic acid (DHA)

Fatty acids are usually stored as triglyrecides within the fat cells (adipocytes), which are the main source of fat.
Triglyrecides are called such because they contain three fatty acid molecules bond together by their carboxyle group to the hydroxyles groups of a glycerol molecule :


Every fatty food contains in diffent proportions saturated, unsaturated and polyunsaturated fatty acids.
These very same proportions will likely determine the physico-chemical properties of a fatty food.

These proportions would modulate the mixed melting point : a fat, high in saturated fatty acids will be more resistant to high temperatures than a monounsaturated fatty acid, that last being more resistant to the polyunsaturated fatty acid.
For instance, the butter, high in saturated fatty acid is solid around 20 degrees, while vegetal oils, high in unsaturated fatty acids are liquid at the same temperature.

Lipids transportation
Lipids, being hydrophobic (they do not dissolve into water), are being transported within the blood stream by proteic structures called apolipoproteins - the gathering is called lipoproteins.

Lipoproteins, depending on their density (amount of apolipoproteins, cholesterol and lipids), could be classified in 5 categories :
- Chylomicrons
- Very Low Density Lipoproteins : around 80% or the triglycerides
- Intermediary Density Lipoproteins
- Low Density Lipoproteins : around 75% of the total cholesterol
- High Density Lipoproteins

The more a lipoprotein contains triglycerides the less it is dense, and vice versa, the more it contains apoproteins, the more dense it is.

All the lipoproteins contain :
- a main kernel, made of cholesterol and triglycerides (hydrophobic compound)
- a shell, made of apolipoproteins, phosopholipids and free cholesterol, making the transportation possible within the plasma :


# Chylomicrons
Within the small intestine are formed the chylomicrons, which mainly carry triglycerides (being synthesized from dietary fatty acids) and a small amount of cholesterol.

They first circulate within the lymphatic stream, the blood stream. Once they reach the plasma, the triglycerides are hydrolized by the lipoprotein lipase (enzyme that catalyzes the fats) - making those fatty acids available for the peripherical tissues OR being drained by the adipocytes where they are converted back to triglycerides.
The more the hydrolizes moves on, the more the chylomicrons shrink; while their excess material is being transfered to the High density lipoproteins that move around.
In the end of the process, the only thing that is left are remnant chylomicrons, which contain less triglycerides than cholesterol. Those are destroyed within the liver.
Chylomicrons move into the blood stream around one hour after a meal, and disappear after 8 to 12 hours.

# Cholesterol
The dietary fat bring around one quarter of the moving cholesterol, the rest being synthesized by :
- The liver
- The intestines
- Surrenal glands
- Ovaries/ Testicles
- Skin
- Nervous system (yes! )

Cholesterol is able to regulate itself on both its synthesis and intra-cellulary penetration : an excess limits the inner production, the circulating levels being stables.

Lipids can have an andogenous origin :
From glycerol and from the free fatty acids, being released by the liver or adipose tissues. The liver is able to synthesize fatty acids as triglycerides (Very Low density lipoproteins, with cholesterol). The produced triglycerides are also hydrolized by the lipoprotein lipase, and again, the different tissues drain the circulating fatty acids, the lipoproteins shrink (less triglycerides and more cholesterol), turning them into Intermediary lipoproteins.

Because the cholesterol in excess cannot be degraded by the tissues, the moving HDL drain it from the peripherical cells, in order to constitute what we call "HDL-2" (High Density Lipoproteins, cholesterol rich).
These HDL bond on hepathic receptors, are catabolized and the cholesterol is used for biliary acid synthesis

What lipids are used for ?

# Energy usage
Lipids are a kick-*kitten* and cheap fuel for the body : their oxydation provides around 9,4 kcal per gram. When fat are stored as triglycerides within the adipocytes, the efficiency is amazing - the storage process using around 2 to 3% tops. An average joe is able to carry around 100 000 kcal
Neolipogenesis (fatty acids synthesis from glucose or amino acids) usually doesn't occur - the consumed fatty acid being mostly the one being stored at maintenance.
In excess, a neolipogenesis ~can~ occur, but the process being much costly, that doesn't usually happen (around 20% of the energy is used for the conversion).

Lipidic stores are mainly used by the muscles, the liver and the myocarde (heart tissue), and contrary to glucose, fatty acids oxydation doesn't happen after dietary fat consumption - insuline inhibits lipolysis, and stimulates lipogenesis

# Structural usage
Cellular membranes contain a double phospholipidic layer (bilayer), which itself contains around 40% of saturated fatty acids, 50% of monounsaturated fatty acids/ polyunsaturated fatty acids and 10% of cholesterol :


The polyunsaturated fatty acids are usefull when it comes to cell movements and deformations ; for instance, erythrocytes (red globules) can only penetrate capillaries because of the fluidity of the membrane.
Cholesterol and phospholipids proportions that can be found within the cell membrane, and their composition in fatty acids have a direct influence on the membranal proteins (such as enzymes, transporters, hormonal receptors) but more importantly such composition for the phospholipids is determined by the dietary triglycerides availability.
In other words, the fat you eat modulate the phospholipids composition. For instance, the more polyunsaturated fatty acids you eat, the more insuline receptors you'll have (or a better stimulated activity) - in the opposite, lacking in omega 3 polyunsaturated fatty acids would impair the insuline-receptor complex. By having fatty intakes, high in polyunsaturated omega 3 fatty acids, you could prevent the insulin resistance.

Mitochondrial membranes are also rich in polyunsaturated fatty acids, while the omega 3 seem to play an important role in the proteins involved in the electrons transportations performance - free radicals, made by electrons leaks could happen with defectuous membranes.
The brain is the organ where polyunsaturated fatty acids are the most abundant : 60% of the phospholipids are composed of Arachidonic and Docosahexaenoic acid (DHA).

During the pregnancy period, the child's brain consumes important quantities of Docosahexaenoic acids, the mother would likely suffer from defficiencies of DHA during such period - that would explain the postnatal depression (studies still in progress). The mother's milk should ideally be also high in omega 3 polyunsaturated fatty acids ; this can be done by having dietary fat high in Alpha-linolenic and polyunsaturated fatty acids (EPA and DHA)

DHA remains, for adults, essential for the cerebral functioning - more and more studies show that insufficient polyunsaturated fatty acids consumption are responsible of several things, such as :
- Depression
- Neurodestructives phenomenons
- Mood swings/ Mood decrease

It is recommended to have around 3 grams per day of polyunsaturated fatty acids - which is around 10 grams of omega 3 oils, such as Olive or Colza oil and around 400g per week of fatty fishes (mackerel, tuna, salmon, etc....)

# Lipids and genetic
Some experiments on animals showed that the consumed fatty acids, for instance saturated ones, can modulate some genes, especially proto-oncogenes (genes that turn to oncogenes ; genes which their expression promote cancers development). Some other researches also showed that saturated fatty acids could play a role in the hepathic lipogenesis expression genees :
http://jn.nutrition.org/content/126/4_Suppl/1105S.full.pdf

Other interesting studies have found a link between breast and prostate cancers increase ("crossed cancers") AND an unabalanced omega 3 / polyunsaturated fatty acids omega 6 ratio. From 1950 to 1990, breast cancers went from 18 to 28% for 100 000 women deceases, and for 100 000 men, death by prostate cancers went 15 to 30%.
Omega 3 could prevent breast cancers metastase rate.

#Lipids and alterations
On a daiy basis, men consumne around 20 fatty acids from both animal and vegetal sources, some though are fragile - sun/ light/ air could alterate their composition.
The most exposed being the long-chain polyunsaturated fatty acids. Some of them are also purposely alterated in order to update the thermic resistance of the fatty bodies.
The more an acid is polyunsaturated, the more it is liquid on ambient temperature, but at the same time, the more it sensible to ligth and air oxydation - and the less it resists to high temperature. In the opposite side, saturated and monounsaturated fatty acids resist to oxydation at high temperatures.

You would make sure not to expose polyunsaturated oils to light and air. Olive oil contains chlorophyll, making that last even more sensible to light.
Truth is... every oil oxydates in one or other way. For instance, a closed bottle of oil would have from 50 micro-gramss to 500 micro-grams in six months only !
Not to mention that self-oxydation is increased when the fatty bodies met air/ light - even more when the air volume within the volume increases by its usage.
That wouldn't even surprise me that olive bottles in outdoor restaurants would be unfit for human consumption

When the temperature increases for polyunsaturated fatty acids, some compounds that could provoke cancers develop : ketonic bodies, alcanes, lactones

# Lipids and cooking
Based on the fatty acids repartition, the most resisting to high temperatures fats are :
- The Butter
- The Olive oil
- The arachid oil

The cooking of those fats can be enhanced by adding several foods. For instance, by adding oinions, you prevent lipoperoxydation (thanks to their antioxidant properties).
Nevertheless, it is always a bad idea to cook oils at high temperatures, and both fried and fumed oils are unfit for human consumption. For instance - the oil used for french fries, left to ambient air become unfit after 4 or 5 usages only.
Under 180°, sunflower, soya, and colza oils keep their properties - but even if those oils can be warmed, cannot be fried if you want to prevent their lipoperoxydation.
Nut oil can only be used for uncooked preparations.

# Margarines, Hydrogenated and trans fat
In order to make margarine, a mix of different fatty acids is used : oils, concrete fats (solid at a temperature on which oils are not). The oils being used are :
- Sunflower oil
- Corn oil
- Soya oil
- Colza oil
- Olive oil
- arachid oil

As for the solid fats, they could either come from copra (coconuts), palm oil, and even sometimes animals suet (lard).
The solid state and the resistance to high temperatures would be impossible without some "solidification" process : the hydrogenation the food industry uses.
The hydrogenation is the saturation of the hydrocarbonated chains of the polyunsaturated molecules with hydrogene - making these oils solid (more or less saturation of the multiple double bonds).
In the end, the orignial polyunsaturated chain turn to a more monounsaturated/ saturated chain. The hydrogenation alterates in the end both composition and position of the multiple double bonds that compose a polyunsaturated chain.
If we take for instance some sunflower-made margarin ; you end up with around 30% of polyunsaturated fatty acids, while sunflower oil contains around 65% of polyunsaturated fatty acids. As for the saturated acids ; well you go from 13 to 50% in the end for that same oil !
The only interesting thing about margarin based on sunflower oil thought, is that its consumption is made possible even at high temperature (since it contains more saturated acids) - while in its main form, it is not.

Same approach applies for olive-based margarines - hydrogenation lower the monounsaturated rate from 75 to 35%

The trans fat are fats for which the molecules are converted to solid ones. The trans fat alterate the prostaglandine synthesis
More reading here :
http://www.nahanniriverherbs.com/94,201

And even if the food industry claims that some fat may contain less than 2% of trans fats, some bad-quality margarines can contain up to 20% of trans fat - the very same fat used for chips, biscuits, bakeries, etc...)
Picking the right margarine will end up to be a real sport, due to polyunsaturated/ unsaturated/ saturated alteration and omega3/6 ratio.

# Advices
In oder to sum-up, here are some advices you would give/ apply to yourself (or not...)
- When the frying-pan is used, always better to use olive oil or arachid oil.
- The more you higher temperature, the more an oil turns unfit for human consumption.
- Most of the oils should not be exposed to light/ air, and should be kept in fresh air (I'd avoid the mayonnaise pots open during barbecues periods).
- When it comes to frying oils, after 4 or 5 usage, they become unfit for human consumption (lipoperoxydation).
- Most of the people lack of essential fatty acids.
- Omega 3 prevent cardio-vasculary diseases, enhance cellular exchanges, brain development and functioning.
- Colza oil should never be used above 180°c.
- Nut oil should only be used for cold preparations.
- Eat your omega 3 fatty fishes godamnit (mackerel, tuna, etc..)
- The same principle of cooking applies for fishes, above 180°c, you basically alterate the polyunsaturated chain. (a Tuna steack cooked at 250°c ends up to be useless when it comes to polyunsaturated properties).
- If your regiment prevents fishes consumption, I strongly advices EPA/ DHA supplementation (in fact, even if you eat your fishes)
- Mixing one tsp of colza and olive oil kicks *kitten*
- Avoid trans fats


Sources
http://www.ncbi.nlm.nih.gov/pubmed/12442909?dopt=Abstract
http://en.wikipedia.org/wiki/Trans_fat
http://www.sciencedaily.com/releases/2009/05/090502084827.htm
http://cat.inist.fr/?aModele=afficheN&cpsidt=7292315
http://www.webmd.com/diet/features/what-to-know-about-omega-3s-and-fish
http://www.umm.edu/altmed/articles/omega-3-000316.htm
http://www.ncbi.nlm.nih.gov/pubmed/12728744