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Fats are composed of a three fatty acids attached to a glycerol backbone and are commonly referred to as triglycerides.  Fatty acids are composed of a carbon chain to which hydrogen atoms are attached and they are fully saturated when carbon chain contains the maximum amount of hydrogen.  Carbon atoms have 4 bonds which requires 2 of those bonds to link to other carbon atoms in the chain and leave 2 bonds avaible to bond with hydrogen.  A mono-unsaturated fatty acid contains a single carbon double bond, which means that it is two hydrogen atoms short of being saturated.  A poly-unsaturated fatty acid contains two or more carbon double bonds, which mean that it is then 4, 6, 8, etc hydrogen atoms short of being saturated.  Dietary saturated fat generally has an even number of carbon atoms although there as trace amounts amounts of C15 and C17 facty acids found naturally in ruminant milk.

Since a mono-unsaturated fat contains a single carbon double bond, the fatty acid chain can have a "kink" in its shape due the missing pair of hydrogen atoms and this is known as the "cis" configuration.  Hydrogen may be added to a poly-unsaturated fatty acid and if the hydrogen atoms are attached so that kink straightens out, the fatty acid with then have a "trans" configuration.  Trans-fats do not occur naturally in foods in significant amounts but are much more common in hydrogenated vegetable oils (like shortening).  Trans-fats adversely affect the metabolism and are implicated in insulin resistance and cardiovascular disease.

There are four groups of fatty acids characterized by carbon chain length. Ben Bikman has a series of Facebook videos that explain how fatty acids are metabolized.

Short chain fatty acids are generally produced by microbes, either through fermentation of dietary fibre in the gut or through food fermentation.  Examples of foods containing SCFA are apple cider vinegar, sauerkraut, kimchi, kafir, yoghurt, and kombucha. The SCFA have somewhat of an unpleasant taste and are reason why fermented foods have a tart flavour.  SCFA are absorbed directly primarily absorbed through the portal vein during lipid digestion and are burned the quickest by mitochondria. SCFA aid in mitochondrial biogenesis and Butyric Acid (C4) is particularly useful metabolically as it helps to regulate the levels of metabolites associated with obesity.  SCFA act as an appetite suppressant and lower the insulin response to a meal.  Butyric acid is readily converted to the β-hydroxybutyrate (beta-hydroxybutyrate, BHB) , a ketone body.

Medium chain fatty acids are relatively tasteless and are commonly found in ruminant milk.  Caproic acid (C6), Caprylic acid (C8), Capric acid (C10) are derived from the Latin word for goat: capra, which explain why goat milk is more tart than cow milk.  Another excellent natural source of MCFA is cococnut oil.  MCFA are increasingly ketogenic as the carbon chain become shorter, that is C6 is sgnificantly more ketogenic than C12 and C8 & C10 fatty acids are commonly used in ketogenic supplements.  MCFA consumption results in a higher metabolic rate than LCFA and MCFA has no effect on serum cholesterol levels.  Lauric Acid (C12), the MCFA that gives coconut oil its solidity, has antimicrobial properties

Long chain fatty acids are found in the bulk of a natural whole food diet. and commonly found in animal and fruit fats (eg, beef tallow, avocado). When LCFA are digested, they enter lymphatic capillaries once they are absorbed into chylomicrons and are then transferred to the blood at the subclavian vein.

VLCFAs are generally found in trace amounts in whole foods and are too long to be metabolized in the mitochondria, and must be metabolized via beta-oxidation in peroxisome.

Short and medium chain fatty acids are metabolized immediately in the priority of their chain length.  The body is unable to store SCFA, which is why they have a high metabolic priority.  Dependin upon the body's metabolic state, LCFA will either go to the liver in the fasted state or to adipose tissue in the fed state.  Once the body returns the fasted state and its glycogen stores are depleted, triglycerides will be withdrawn from adipose tissue.  If the Citric Acid (Krebs) Cycle is overwhelmed, the liver will start converting triglycerides to ketones and this allows excess fat to be wasted by the body either to thermogenesis by brown adipose tissue to wasted through respiration or urination.

See Metabolic Health

 

DISCLAIMER: My background is engineering and what I have written here is from my personal interest in staying healthy. If you disagree with any of it, let know what you feel is inaccurate and include some references so I can make corrections. This is a work in progress so check back often for updates as I continue to learn. CONSULT WITH YOUR DOCTOR BEFORE MAKING DIET AND LIFESTYLE CHANGES.

Fatty Acids

There are numerous benefits to being in a fasted state from a the perspective of mitochondrial health and exercise has similar benefits. Having healthy mitochondria is absolutely essential to good health and impaired mitochondrial function is linked to many chronic diseases. Neurons are particularly susepticible to dyfunctional mitochondria. The process by which the body determines whether it is a fasted or fed state is the Randle Cycle. The fasted state is characterized by low insulin and the presence of ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone), which are a produced by the liver from triglycerides.  Most cells with mitochondria readily use ketones for fuel.  The presence of ketones will cause uncoupling of adipose mitochondria so that they generate heat in addition to producing ATP, which increases the body's metabolic rate.  Ketones help the muscle mitochondria become more coupled so that they are more energy efficient in producing ATP. Benefits of being in the fasted state are:

  • Increased mitochondrial biogenenis (more mitochondria)
  • Increased mitochondrial fusion (enhanced ATP production)
  • Favourable mitochondrial function (less oxidative stress, enhanced ATP production, umcoupling of adipose tissue while maintaining coupling of muscle tissue)

It appears that metabolizing longer-chain saturated fats promotes mitochondrial biogenesis though reverse electron transport via Reactive Oxygen Species (signaling molecules) in the mitochondria's electron transport chain. Increased low-level ROS synthesis (see Mitohormesis) causes localized insulin resistance at the cellular level, which prevents the uptake of glucose. Basically, the higher the ratio of FADH2 to NADH (F/N ratio), the greater the amount of reverse electron transport (RET), which in turn encourages the mitochondrial biosynthesis. Reverse electron transport occurs marginally with F/N=0.46 and not at all with F/N<0.46. Fat oxidation generates greater amounts of FADH2 than glucose oxiation and fat metabolism generates ketones. Because ketones deactive the cell's insulin receptor, they also help prevent the glucose uptake in adipose tissue. Since Linoleic Acid has no RET effect, it acts like a supercharged carbohydrate because it contains 9 calories/gram vs 4 for glucose and it is likely a significant contributor to the obesity epidemic. Industrial seed oils (eg, canola/rapeseed, corn, cotton, peanut, safflower, soybean, sunflower) are a key component of processed foods.

Fatty Acid
(found in)
Carbon
Chain
Length
Carbon
Double
Bonds
(Saturation)
F/N
Ratio
Drives
RET?
Lignoceric acid
(peanut oils and most natural fats)
C24 0 0.489 ↑ ↑ ↑ ↑
Behenic acid
(ben tree seed oil)
C22 0 0.488 ↑ ↑ ↑ ↑
Arachidic acid
(durian fruit, cupuaçu butter, corn oil, peanut oil, cocoa butter)
C20 0 0.487 ↑ ↑ ↑ ↑
Stearic acid
(beef tallow & other animal fats, cocoa & shea butter)
C18 0 0.486 ↑ ↑ ↑ ↑
Palmitic acid
(palm oil, butter, cheese, milk, meat, cocoa butter, soybean oil, sunflower oil)
C16 0 0.484 ↑ ↑ ↑
Myristic acid
(nutmeg, palm kernel oil, coconut oil, butterfat, bovine milk, breast milk)
C14 0 0.481 ↑ ↑ ↑
Lauric acid
(goats milk, coconut & palm oil)
C12 0 0.478 ↑ ↑ ↑
Capric acid
(goats milk, coconut & palm oil)
C10 0 0.474 ↑ ↑
Caprylic acid
(goats milk, coconut & palm oil)
C8 0 0.467 ↑ ↑
Erucic acid
(wallflower seed, high erucic acid rapeseed, & mustard oil)
C22 1 0.465
Paullinic acid
(guarana seed oil)
Gadoleic acid
(cod liver oil)
Gondoic acid
(jojoba oil)
C20 1 0.462
Oleic acid
(olive & sunflower oil, poultry fat & lard)
C18 1 0.457
Caproic acid
(goats milk, coconut & palm oil)
C6 0 0.455
Palmitoleic acid
(macadamia oil)
C16 1 0.452
Butyric acid
(butter & other dairy products, human breast milk, sauerkraut & other fermented foods)
C4 0 0.429
Linoleic Acid
(safflower, sunflower, corn, soybean oils, sesame, & almonds )
C18 2 0.429
Alpha-linolenic acid (ALA)
(flaxseed, walnuts, chia, hemp, and many common vegetable oils. )
C18 3 0.400
Glucose C6 (ring) N/A 0.20

Ancel Keys, a  started us down the path of vilifying LDL cholesterol-increasing saturated fat with his Lipid Hypothesis, similar to the Diet-Heart Hypothesis.  He cherry-picked data to suit his hypthosis in his epidemiological Seven Countries Study and this hypothesis was taken as fact even though there was no solid evidence from radomized control trials to back it up.  Eventually the lipid hypthosis was adopted by the medical community and pharmaceutical companies started selling highly profitable LDL cholesterol lowering Statins.  Statins are now the standard of care for preventing cardiovascular disease but some statin side effects that concern me are: insulin resistance and cognitive impairment.

CBC's Marketplace – Food Fact Check Episode raised a concern about coconut oil, which is a saturated fat rich in medium chain fatty acids.  I believe this was a misinformed concern because the evidence suggests that saturated fats are beneficial and the war on LDL cholesterol has been misguided.  The following research papers concern LDL cholesterol: