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Our body does not produce two polyunsaturated fatty acids (PUFA): linoleic acid and alfa-linolenic acid.

I am thinking reasons for it.

Saturated fatty acids have more energy than unsaturated. Saturated fatty acids do not need NADPH and some many other enzymes as unsaturated in beta oxidation. This means that less storage places in the body needed to have energy in the form of saturated fatty acids such as for muscles and heart.

There are four main reasons why our body does not use PUFAs as the primary source of the energy but saturated:

  • PUFAs lower metabolism and interfere with thyroid function
  • PUFAs spontaneously oxidize, speed up the process of glycation, since too much glucose
  • PUFAs decrease mitochondrial respiration - more oxygen and CO2, less lactate

where one reason is missing.

One complication of PUFA is

  • PUFAs promote diabetes, cancer, inflammation and biological stress

which cannot be thought as a reason why our body does not use PUFAs as the primary source of the energy.

There are positive sides of the PUFAs when they are used in other way. - PUFAs replace trans fats and saturated fats in certain types of foods. - PUFAs can help your body to eliminate high cholesterol levels - PUFAs decrease the risk of heart disease

There are also some types of essential fats that your body cannot produce on its own - omega-6 and omega-3 fatty acids. PUFAs are used to create these. You can get PUFAs from vegetable oil, fish and nuts for instance. Balanced diet is essential.

Normal lipid metabolism depends directly on food lipids. Both the essential fatty acids and right amounts of PUFAs can be obtained from food. Body converts the essential fatty acids to long PUFAs, which serve as the precursors of prostaglandins and leucotrienes for instance.

There are so many reasons why our body does not produce polyunsaturated fatty acids.

Why our body does not produce polyunsaturated fatty acids?

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    $\begingroup$ I think the framing of this question is wrong. I would guess that our body doesn't produce PUFAs because they were present in adequate amounts in our ancestors' diets, so there was little pressure to gain the ability to synthesize them. The common ancestor of animals probably just didn't possess these enzymes, and we've evolved to make do with what's available in the diet. $\endgroup$
    – Lucas Wiman
    Feb 19, 2013 at 19:56
  • $\begingroup$ I am interested on the biochemical sides, not on epidemiological. However, good point to bring the epidemiological sides too. $\endgroup$
    – Léo Léopold Hertz 준영
    Feb 20, 2013 at 4:22
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    $\begingroup$ Can you pleasse tell me that how PUFA lowers metabolism and how they spontaneously oxidize, speed up the process of glycation, since too much glucose.And howw PUFAs decrease mitochondrial respiration - more oxygen and CO2, less lactate and how PUFAs promote diabetes, cancer, inflammation and biological stress???if you elaborate these points it'll be helpful for me... $\endgroup$
    – Haya Dar
    Aug 2, 2014 at 7:44
  • $\begingroup$ @HayaDar Thank you for your notice! I am thinking this thread again. I fixed one thing in the body. More explanation about those specific sentences can be found in some Biochemistry textbooks. $\endgroup$
    – Léo Léopold Hertz 준영
    Aug 3, 2014 at 8:37
  • $\begingroup$ The question is unclear for me as it is mostly an inconsistent alaborate on PUFAs in human body. An example of inconsistency: you write there are four reasons andthen enumerate only three of them. And there is an especially confusing part "There are so many reasons why our body does not produce polyunsaturated fatty acids. Why our body does not produce polyunsaturated fatty acids?" It suggests the elaborate contains answer to your question, thus it should be an answer. $\endgroup$
    – abukaj
    Feb 22, 2018 at 10:20

2 Answers 2

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Simply, it’s because our bodies add double bonds in MUFAs by delta 9 desaturase which adds double bonds between delta 9 and delta 10 carbons, hence additional double bonds can be formed between existing double bond and the carboxilc group but cannot be formed between the existing double bond and the omega carbon. As a result, our body cannon synthesize parent omega 3 alpha linolenic acid and parent omega 6 linoleic acid, but can form timnadoneic acid which is an omega 3 PUFA

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    $\begingroup$ Welcome. Can you add sources to your claims,preferably links to journal papers? That way people can background read on your material. $\endgroup$
    – AliceD ♦
    Nov 23, 2018 at 12:31
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Animals, including fish, do not possess any DNA for producing PUFA. No cultured fish can produce PUFA internally. However, human is known to produce milk containing DHA. The only explanation is all PUFA synthase enzyme are exogenous. They come from food. This explains some people are prone to be obese and some aren’t, but the reason is not in genes. Dinoflagellates are known to have large DNAs Some have DNA for producing important PUFA such as DHA. No land plant, nor animals have the DNA for such enzyme. Only explanation is the enzyme comes through the food chain exogenously. Fortunately, these dinoflagellates are ubiquitous in ocean, and thus all the sea creatures are benefitted from these enzymes. Modern food production by human however, strips these good enzymes by heat processing and other extraction processes.

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  • $\begingroup$ Welcome to Biology.SE! Without supporting references only an expert in this area could evaluate the correctness of your answer. Consequently, your answer is much more likely to receive a favorable response if you include supporting references (primary literature is best). In addition, I don't think your connection to obesity is correct and it isn't directly relevant to the original question. ——— Please take the tour and then consult the help pages for additional advice on How to Answer effectively and then edit your answer accordingly. Thanks! 😊 $\endgroup$
    – tyersome
    Oct 16, 2019 at 20:25

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