Fat/Fatty Acids/Triglycerides

[reefedjib]

In continuing my knowledge acquisition in the biochemistry of nutrition, I keep running across references to fat, fatty acids and triglycerides.

Dietary Carbohydrates raise the BG level so insulin is released to manage it back down to a normal level. This includes the rapid conversion of Glucose by the Liver into Fatty Acids for storage in Fat Cells -- our longer-term energy stores. BUT this can only occur when Glucose is present as the from it is stored is known as "Tri-Glycerides"... made up of three Fatty Acids molecules bound together with a Glycerol Molecule (from Glucose)... hence the name. High levels of insulin lock the fat away in the fat cells and does not allow its use as an energy source.

So this seems to say that it is Glucose which is converted into Triglycerides. So what happens to the fat we ingest?

Furthermore, this link on lipogenesis (http://en.wikipedia.org/wiki/Lipogenesis) says:

Lipogenesis is the process by which simple sugars such as glucose are converted to fatty acids, which are subsequently esterified with glycerol to form the triacylglycerols that are packaged in VLDL and secreted from the liver.

Lipogenesis encompasses the processes of fatty acid synthesis and subsequent triglyceride synthesis.

Lipogenesis starts with acetyl-CoA and builds up by the addition of two carbons units

So reading between the lines a bit, it seeems that starting with glucose, we convert to acetyl coenzyme A, like we are going to burn the glucose, but instead some of the acetyl coenzyme A is diverted down the Lipogenesis pathway for Triglyceride production and storage.

So:

glucose -> acetyl coenzyme A -> fatty acid -> triglyceride.

Am I getting this close to right?
So, again, what happens to the fat we ingest?

Thanks!!

[fgummett]

Dietary fat can be stored... but the point is it can only happen in the presence of sufficient levels of Insulin and Glucose... without the Glucose we cannot make the "Tri-Glycerides". Higher levels of Insulin and Glucose lead to greater Fat storage -- as in your typical Type 2 D on a high refined/concentrated carb diet.

So a Big Mac plus fries plus OJ or soft drink leads to more Fat storage, than just a double-burger with bacon, cheese but no bun -- even though the latter may have equal calories.

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Fat is the generic term for the macro-nutrient group.

[Free] Fatty Acids are the simpler building blocks which result from the digestion of dietary Fat... in the same way that Protein is digested into Amino Acids so it can then be reconstructed in muscle, hormones, enzymes etc... think of Lego blocks.

Triglycerides are the form in which Fat is locked away in our Fat (adipose) cells -- made up on 3 Free Fatty Acids molecules bound to a Glycerol molecule (from Glucose) -- they are too big to pass through the Fat cell walls.

[reefedjib]

Dietary fat can be stored... but the point is it can only happen in the presence of sufficient levels of Insulin and Glucose... without the Glucose we cannot make the "Tri-Glycerides". Higher levels of Insulin and Glucose lead to greater Fat storage -- as in your typical Type 2 D on a high refined/concentrated carb diet.

So a Big Mac plus fries plus OJ or soft drink leads to more Fat storage, than just a double-burger with bacon, cheese but no bun -- even though the latter may have equal calories.

So are you saying that Dietary Fat is necesary, along with Glucose and Insulin, to produce Triglycerides? Where does Dietary Fat enter the production cycle: (I'll edit it based on what you added...)

dietary fat -> fatty acid ->
glucose -> acetyl coenzyme A -> triglyceride

You just answered this...when producing the triglyceride. thanks!

The dieting point is exactly the point that Dr. Bernstein is currently making. With equal calories, a high-fat, low-carb meal produces less body fat than a low-fat, high-carb meal.

[fgummett]

So are you saying that Dietary Fat is necessary, along with Glucose and Insulin, to produce Triglycerides?No... dietary carbs/Glucose are also converted to Free Fatty Acids so there is no need to eat ANY fat to gain excess fat mass... although being an essential nutrient we do need to eat fat for our health.

You asked "what happens to the fat we ingest?"... I responded "Dietary fat can be stored... but only in the presence of sufficient levels of Insulin and Glucose"

Gary Taubes explains much of the biochemistry in this presentation...
Big Fat Lies with Gary Taubes, 02/06/08 Stevens Institute of Technology (http://video.google.com/videoplay?docid=4362041487661765149)

[reefedjib]

No... dietary carbs/Glucose are also converted to Free Fatty Acids so there is no need to eat ANY fat to gain excess fat mass... although being an essential nutrient we do need to eat fat for our health.

Ahh, I see. So, Glucose can go directly to Triglyceride. Sneaky. But at the same time, dietary fat is an essential nutrient.

I am really upset at myself right now. I don't have sound ability on my desktop, so I can't listen to that presentation. :(

[fgummett]

In this context "essential" means that it contains nutrients which the body cannot manufacture so it must be ingested.

In the Bernstein book and the following link you can read that while there are essential Fats and essential Proteins there do not appear to be any essential Carbohydrates.

I'd probably temper that by suggesting that while we may not necessarily need ANY carbs we may find benefit (fibre, vitamins, minerals etc... or even just aesthetic reasons like taste) in the form that many carbs come wrapped... green veggies for example. That is not to say that we might not also get those same micro-nutrients from eating steak for example... eat higher up the food chain and gain the benefit of what our "food" has eaten

Again, bear in mind that it is rare to find a real whole food that is simply a single macro-nutrient.

Is dietary carbohydrate essential for human nutrition..? (http://www.ajcn.org/cgi/content/full/75/5/951-a)

[MCS]

Maybe this will help:

Lipase and other digestive juices break down the fat molecules into fatty acids and types of glycerol. Absorption of fat into the body, which takes 10-15 minutes, occurs in the villi - the millions of finger-like projections which cover the walls of the small intestine. Inside each villus is a series of lymph vessels (lacteals) and blood vessels (capillaries). The lacteals absorb the fatty acids and glycerol into the lymphatic system which eventually drains into the bloodstream. The fatty acids are transported via the bloodstream to the membranes of adipose cells or muscle cells, where they are either stored or oxidized for energy. Since glucose rather than fat is the body's preferred source of energy, and since only about 5 percent of absorbed fat (the glycerols) can be converted into glucose, a significant proportion of digested fat is typically stored as body fat in the adipose cells. The glycerol part is absorbed by the liver and is either converted into glucose (gluconeogenesis), and/or used to help breakdown glucose into energy (glycolysis).

[fgummett]

Since glucose rather than fat is the body's preferred source of energy...This is misleading: it may be true that when there is plenty of Glucose around the body will use it first BUT that does not necessarily mean it is the body's preferred energy source.
We have limited Glucose stores and once those are used up we turn to our longer-term [and almost unlimited] Fat stores... this is how we have adapted to survive overnight, between meals, during famines etc...

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If we are adapted to run better on Glucose why do we store only a relatively small amount? Why don't we convert Fat into Glucose?

[MCS]

This is misleading: it may be true that when there is plenty of Glucose around the body will use it first BUT that does not necessarily mean it is the body's preferred energy source.
We have limited Glucose stores and once those are used up we turn to our longer-term [and almost unlimited] Fat stores... this is how we have adapted to survive overnight, between meals, during famines etc...

If glucose wasn't the perferred source of energy why would we use it first.

[fgummett]

If a student does their homework on Friday night so they have the weekend free... does that mean they prefer homework?

This is a misleading assumption.

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There is no conscious process driving how the body uses it food: there are several [relatively] simple homeostatic/feedback systems involved such as... higher BGs leads to higher Insulin, which leads to increased Fat storage and uptake of Glucose by the cells... as the BG starts to fall and the Insulin levels follows we switch "modes" to using Fat instead.

--

Think of it like a hybrid car which runs on electricity when it has been charged, but on a longer journey the gasoline engine kicks in. Does that car "prefer" one energy source over the other?

[PERKDOUG]

So, again, what happens to the fat we ingest?
Thanks!!

Diatary fat is mostly processed in the gut. The fats are assembled in the intestine into triglycerides and loaded onto a balloon like lipoprotein structure called a chylomicron. This particle or structure is similar to the very low density lipoprotein (VLDL) structure the liver uses to deliver the fat it manufactures in the liver. The chylomicron and VLDL particle differ in the protein substructure each carries. The protein structures attached to these little balloons might be thought of as differing bar codes so the particles can be processed in a different way by the metabolic machinery of the body. Think of them as little balloons full of triglyceride fat molecules. The chylomicrons travel the circulatory sysem dropping off the triglycerides to the various structures of the body. Note that the chylomicrons handle only the fatty acids that contain more than 10 to 12 carbon atoms in their carbon chain structure. The shorter chain fatty acids are handled more like glucose by being processed by the liver. Chylomicrons do not hang around long in the circulation. They are created slower than glucose is processed but are short lived being taken out of circulation by the liver. When you do a fasting blood test they are gone but the VLDL carrying the glucose created fatty acids are still there. Go read your cholesterol test results and see the VLDL quantified.
Bottom line: The fatty acids with more than 10-12 carbon atoms are loaded onto chylomicrons and taken out for delivery to the body.
I hope this oversimplification helps.

[It Ain't Over]

I hope this oversimplification helps.

Yes, and thank you for making it all so easy to sort out!

[foxl]

[QUOTE=PERKDOUG;489172]Go read your cholesterol test results and see the VLDL quantified.
QUOTE]

Not everyone includes VLDL in their lipid panel, however. I have never seen a value epxressed for it in any of mine (20 years' worth of annuals!)

[PERKDOUG]

QUOTE=foxl;489215]Go read your cholesterol test results and see the VLDL quantified.
QUOTE]

Not everyone includes VLDL in their lipid panel, however. I have never seen a value epxressed for it in any of mine (20 years' worth of annuals!)

I use the VAP test for mine and get quite a nice breakdown including VLDL and LDL size spectrum. My old tests (before VAP) do not contain it either. For the oversimplified generalizations in my post I should have used triglycerides instead. After all, we are focused on triglycerides not lipoproteins. Sorry!

[foxl]

I may have to ask my Endo for that! hmmm ... (heads back to wish list).

[fgummett]

I may have to ask my Endo for that! hmmm ... (heads back to wish list).

You might also ask for the Apo-B to find out how much of your LDL volume is "small and dense" :motz:* as opposed to "large and fluffy" :marchmell

The Role of LDL Particle Size Assessment... (http://www.centerforpreventivemedicine.com/04114med_messenger.pdf)

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* in the absence of a "small and dense" smilie... I went for "small and tense" instead... same difference... kinda looks like me on my drive home!

[foxl]

I might also ask for the moon and stars ... ROFL!

But I will be bringing up my lipid profile ... and perhaps CRP too.

Heaven knows, you do not ASK, you get exactly ... nothing.

[reefedjib]

Gary Taubes explains much of the biochemistry in this presentation...
Big Fat Lies with Gary Taubes, 02/06/08 Stevens Institute of Technology (http://video.google.com/videoplay?docid=4362041487661765149)

I ended up watching this at work. It was excellent, thanks for posting it.

[reefedjib]

Diatary fat is mostly processed in the gut. The fats are assembled in the intestine into triglycerides and loaded onto a balloon like lipoprotein structure called a chylomicron. ...
I hope this oversimplification helps.

Maybe this will help:

Lipase and other digestive juices break down the fat molecules into fatty acids and types of glycerol....The glycerol part is absorbed by the liver and is either converted into glucose (gluconeogenesis), and/or used to help breakdown glucose into energy (glycolysis).

Thanks guys for interesting discussions of processing dietary fat. I'll see if I can add some processes to my list of biochemical processes of metabolism. I don't have lipoprotein processes, nor glycerol processes (which I can add to gluconeogenesis and glycolysis).

[fgummett]

I ended up watching this at work. It was excellent, thanks for posting it.Great! The book is even better although I have had to read it three times as it is so packed with detail :)

[reefedjib]

Great! The book is even better although I have had to read it three times as it is so packed with detail :)

It's next up after I finish Dr. Bernstein. :)

[Grunch]

So a Big Mac plus fries plus OJ or soft drink leads to more Fat storage, than just a double-burger with bacon, cheese but no bun -- even though the latter may have equal calories.

So where do the extra calories go to in the second case?

[fgummett]

So where do the extra calories go to in the second case?Magic! :D

Well... as we both already know they would not disappear into thin air as that would contravene the laws of physics BUT please note I did not say they would disappear... I said that one would lead to more fat storage than the other... perhaps the remainder goes through undigested, or is used up by an increased metabolic process or any one of a large number of variables as explained ably in this link : Junkfood Science: The first Law of Thermodynamics in real life (http://junkfoodscience.blogspot.com/2008/10/first-law-of-thermodynamics-in-real.html) ... which I would fully expect anyone with an open mind who is wiling to question that perhaps they don't already know everything would read.

For even more discussion on the misuse of this law check out this presentation : Big Fat Lies with Gary Taubes, 02/06/08 Stevens Institute of Technology (http://video.google.com/videoplay?docid=4362041487661765149)