Talk:Fatty acid

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Fatty acid is included in the 2006 Wikipedia CD Selection, or is a candidate for inclusion in the next version. Please maintain high quality standards and, if possible, stick to GFDL-compatible images.

In the unsaturated section, there is the following item:

Omega-3 or Ω-3 : The first double bond is the third carbon-carbon bond counting from the end of the chain most distant from the carboxyl group. The next

It appears that most of a sentance is missing. I checked history and it has been this way since the distinction between delta and omega terminology was introduced, with no indication of what should go there. Can anyone correct this, or is "The next" unintentional?

Kutulu 19:17, 26 Apr 2005 (UTC)

Contents 1 Muscles perfer fatty acids over glucose? 2 Shape of fatty acids 3 Acetic and butyric acids? 4 cis/trans 5 Typo? 6 Chain? 7 Classification by Length?

[edit] Muscles perfer fatty acids over glucose?

"Free fatty acids are an important source of fuel for many tissues since they can yield relatively large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. However, heart and skeletal muscle prefer fatty acids. On the other hand, the brain cannot use fatty acids as a source of fuel, relying instead on glucose, or on ketone bodies produced by the liver from fatty acid metabolism during starvation, or periods of low carbohydrate intake."

I doubt it. This should be fact-checked. Lantoka 11:43, 6 April 2006 (UTC)

From Tom Brody's "Nutritional Biochemistry" 2nd ed., p. 195:\

Fatty acids are the major fuel of muscle at all times. Creatine phosphate is important only during the early stages of exercise (i.e., during sudden bursts of work). Glycogen tends to become depleted during exercise of moderate duration. With this depletion, the importance of gluconeogenesis as a source of glucose increases. During prolonged exercise, FFAs supply most of the energy requirements of muscle. Ketone bodies, which are made by the liver, are also used as fuel by exercising muscle, but their contribution is quite small compared with fatty acids.

(My emphasis) --Slashme 13:41, 7 April 2006 (UTC)

Really? Wow, everything else I've read on Wikipedia suggests to the contrary. The marathon article talks about runners "hitting a wall" when glycogen levels are depleted because the body has to switch to metabolizing fat (fatty acids). The common practice of football players and other athletes eating lots of pastas and other foods high in carbohydrates also supports this. And also, the article on the Krebs Cycle talks about how fatty acids are metabolized by the liver and other body parts into glucose before being used by cells to generate ATP:

"In fat catabolism, triglycerides are hydrolyzed to break them into fatty acids and glycerol. In the liver the glycerol can be converted into glucose via dihydroxyacetone phosphate and glyceraldehyde-3-phosphate by way of gluconeogenesis. In many tissues, especially heart tissue, fatty acids are broken down through a process known as beta oxidation which results in acetyl-CoA which can be used in the citric acid cycle. Sometimes beta oxidation can yield propionyl CoA which can result in further glucose production by gluconeogenesis in liver."

And here, from Exercise Physiology, 5th ed., p84:

Dietary carbohydrate intake takes on additional importance for individuals involved in a significant amount of physical activity on the job or in exercise training and sports competition. Stored muscle glycogen becomes the prime energy contributor under circumstances of inadequate oxygen supply to active muscles. In addition to this anaerobic role of carbohydrates, stored glycogen (and blood glucose) provides substantial energy during intense aerobic exercise.

The last claim in that quote is citation 21 in that book, coming from Coggan AR, Coyle EF. Carbohydrate ingestion during prolonged exercise: effects on metabolism and performance. Exerc Sport Sci Rev 1991:19:1.

Perhaps I'm misunderstanding something... please elaborate on your claim so that we can figure this out. =) Lantoka 08:12, 9 April 2006 (UTC)

We seem to agree to a large extent here. Athletes can continue on glycogen for quite a while, until the stores run out. Because glycogen produces glucose, that's a faster source of energy than FFA oxidation. This readily available energy can be extended by "carbo-loading" but there's a limit to how much glycogen the liver will store. After a while (typically about 30 minutes), you start liberating your fat deposits, and during prolonged exercise, the Krebs cycle in your muscle mitochondria runs almost exclusively on Acetyl-CoA from beta-oxidation of fat.

As for the bit about glucose being formed from fat oxidation: That is a relatively minor pathway; it's just the last 3 carbons from odd-numbered fatty acids and the glycerol backbone of the triglyceride that go that way. The rest goes straight to acetyl-CoA that feeds the krebs cycle. The body can't make glucose from the main chains of fatty acids.

Then there's the question of what your muscles run on during normal, non-strenuous activity (sitting upright and walking around the office, for example). I'm not really sure. Can anyone clarify this? How much does the balance between carbs and fat in your diet affect this? --Slashme 11:19, 11 April 2006 (UTC)

In answer to your last question, I believe that muscles simply use aerobic respiration for normal activity, keeping enough ATP on hand in the cell to sustain normal activity. Other pathways come into play during different types of strenuous exercise. Sudden bursts of energy (to throw a punch or to swing a golf club, for example) simply come from manufactured ATP on hand in the muscle, which is regenerated through aerobic respiration after muscle contraction. Sustained power (such as sprinting and playing on the line in football) first uses existing ATP, then uses the phosphate group from phosphocreatine to recharge ADP. This is why some weight lifters take creatine supplements. Strenuous exertion over a period of more than 4-8 seconds brings lactic acid fermentation into play, which will exhaust the muscle once too much lactate has built up. Less strenuous exertion over a long period of time (more than 2-4 minutes) will call on normal aerobic respiration (Krebs Cycle and oxidative phosphorylation) to sustain the activity, and people who do extensive aerobic exercise have made this pathway very efficient.

But anyway, back to the original discussion. From research I've done, it looks like muscles keep a reserve of glycogen, fatty acids, and amino acids on hand. Once those reserves are exhausted, the muscle cell can then draw on glucose and amino acids released from hepatocytes in the liver and fatty acids released from adipocytes to power aerobic reactions. For anaerobic reactions, glycolysis must take place, and only carbohydrates (glucose, glycogen) can be used.

So, during short and strenuous exercise, carbohydrates are going to be the "perferred" source of energy. But what about during light and moderate exercise? Research I've done indicates that about 10% of that energy comes from proteins, 30% comes from carbohydrates, and 60% comes from fats. Which makes your original statement, that skeletal muscle perfers fatty acids, true.

Thanks for your responses! This discussion piqued my curiosity and, as a result, has increased my knowledge of nutrition and human physiology, so that I may better contribute to other articles on the subject. Lantoka 02:29, 12 April 2006 (UTC)

Excellent! I have also learned something here. It's this kind of thing that makes me happy to be a Wikipedian. --Slashme 07:37, 12 April 2006 (UTC)

[edit] Shape of fatty acids

The statements that "a chain has many cis bonds, it becomes quite curved" and that "Alpha-linolenic acid, with three double bonds, forms a hooked shape." seem misleading. As long as fatty acids have at least one C-C single bonds along their chain, they can assume an infinite number of conformations, only a subset of which are consistent with these statements. For example the structure of Alpha-linolenic acid drawn in its article is not hooked but straight. It all depends on the free rotation around the C-C single bonds.

It seems more correct to mention that cis bonds, by introducing kinks in the chain, decrease the conformational freedom of fatty acids. The effect of this is that in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer, or triglicerides in lipid droplets, cis bonds limit the ability of fatty acids to be closely packed and therefore could affect the melting temperature of the membrane or of the fat. --InfoCan 16:12, 26 May 2006 (UTC)

You are correct that the double bonds don't entirely prevent straight conformations, but they certainly cause bent, curved, or hooked conformations to be favored. I've made made a few changes to the text to clarify this (hopefully) and I added some of the text that you wrote. (In the future, you can be bold and make the changes yourself, if you like.) --Ed (Edgar181) 18:31, 26 May 2006 (UTC)

[edit] Acetic and butyric acids?

Should acetic and butyric acids be listed as saturated fatty acids when the intro says that fatty acids are generally understood to have 8 carbons or more? --InfoCan 16:18, 26 May 2006 (UTC)

Normally they would not be considered fatty acids. I've removed them from the saturated examples. ChemGardener 16:39, 26 May 2006 (UTC)

[edit] cis/trans

Wouldn't it make more sense to write: "A cis configuration means that the two hydrogens are on the same side of the double bond" and "A trans configuration, by contrast, means that the next two hydrogen atoms are bound to opposite sides of the double bond"?

[edit] Typo?

"Changes in the levels and balance of these fatty acids due to a typical Western diet rich in omega-6 and poor in omega-9 fatty acids is alleged to be associated with depression and behavioral change, including violence."

Shouldn't this be:

"Changes in the levels and balance of these fatty acids due to a typical Western diet rich in omega-6 and poor in omega-3 fatty acids is alleged to be associated with depression and behavioral change, including violence."

[edit] Chain?

Hi - excuse my ignorance about fatty acids, but I'm trying to resolve/understand all the links to Chain and I see there's a reference in the first sentence of this article but I'm not sure what it means. If if refers to chain as a sequence of molecules, it should be a link to Chain (sequence) --Mortice 23:11, 31 October 2006 (UTC)

[edit] Classification by Length?

I have been investigating coconut oil and in the process found that while most articles and discussions mention saturation they do not discuss length and I do not have sufficient knowledge to judge the validity or siginificance of this ommission. There seems to be some rising debate about the relative value of long- versus medium-chain fatty acids. Here is the article that put length on my radar: http://www.westonaprice.org/knowyourfats/skinny.html#fatty

If the length of fatty acids is a significant factor then this article should include some mention of it and even if it is not significant it might be helpful to know why not. Donberg68 23:13, 23 February 2007 (UTC)