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  • Now why have we insisted in making all those distinctions in the structure of fatty acids?

  • saturated and unsaturated; mono and polyunsaturated, cis and trans, omega-6 and omega-3? Well,

  • because these structural differences result in very different behaviors of lipids in our

  • body. So the quality of lipids in our diet very much depends on the balance between these

  • different groups of fats. Let’s start examining them from a nutritional point of view.

  • Saturated fatty acids are mainly although not exclusively found in food of animal origin.

  • They are nutritionally non-essential. Remember, this doesn’t mean that they are not important,

  • just that if necessary we can build them ourselves. Our body can build saturated fats from glucose

  • and from some amino acids. Stearic acid, the saturated fatty acid 18 carbons long, is preferentially

  • incorporated into triglycerides for storage in our adipose tissue. Based on what you know,

  • you should be able to figure out why it wouldn’t be possible to use unsaturated fats for storage:

  • at body temperature, they would melt. However an excess of saturated fatty acids

  • in our diet is detrimental because many of them are atherogenic, they promote endogenous

  • synthesis of cholesterol, they raise LDL cholesterol - soon we will learn why this is bad - and

  • they promote the process of atherosclerosis putting us at risk for cardiovascular disease.

  • For these reasons, we don’t want to eat too many of them.

  • However also keep in mind that not all saturated fatty acids are equally atherogenic. It’s

  • not true that all saturated fats are bad. In fact, some of them are pretty much neutral.

  • The above mentioned stearic acid, for example, is quite innocent, it’s used for storage

  • and it can also be easily converted to the monounsaturated oleic acid, so it doesn’t

  • harm anybody. Palmitic acid, C16, is more or less neutral. But then there are other

  • that are really BAD, such as the medium chain lauric, C12, and miristic C14, which are highly

  • atherogenic.

  • This slide shows you some dietary sources of saturated fats. As you can see, most of

  • them are animal. Moving from left to right, the quality of their fat gets worse, due to

  • the highest presence of thosebadfatty acids such as lauric and miristic.

  • Eggs have a lot of stearic so they are pretty much innocuous, then we have chicken meat,

  • milk and dairy, red meat, and then on the very right, you find some vegetable sources

  • of a lot of saturated fats, coconut and palm. We normally don’t use them in the kitchen,

  • but the food industry likes their oils very much because they are cheap and have interesting

  • technological properties, so coconut kernel oil, palm oil and palm kernel oil are commonly

  • used as ingredients in many products. Palm oil is what we make from the pulp of the fruit,

  • the yellow part, and then palm kernel from the white kernel. Not only they are very rich

  • in saturated fats, but they have the worst type of saturated fats, lauric and miristic.

  • We refer to palm kernel and coconut kernel oils astropical fats”, they are bad

  • and we don’t want too much of them in our diet, so make sure to look for them on the

  • ingredient lists and avoid food that contain them whenever possible. Palm oil is a little

  • bit better because it has more palmitic acid. Cocoa butter, from cocoa, also contains saturated

  • fats but it’s mostly stearic, so it’s much better.

  • Let’s move on to the monounsaturated fats. They are also not nutritionally essential

  • because they can be built from the corresponding saturated fatty acids of the same length,

  • so for example stearic C18 can be converted into oleic because our body can introduce

  • the unsaturation in position nine. Even if they are not essential, we still should

  • try to get them from food and especially oleic acid which is probably the best possible fatty

  • acid in our diet because it is very beneficial to our health. It lowers blood cholesterol,

  • improves the HDL to LDL ratio in our bloodstream - again we will understand this better soon

  • - and in general it exerts a protective action against cardiovascular disease.

  • But don’t think that all monounsaturated fats are equally as good. For example, erucic

  • acid, C22, is toxic for us. It was once abundant in rapeseed oil, which is why it couldn’t

  • be marketed for human consumption for a long time, but today we have developed a genetically

  • modified version of rapeseed that builds oleic instead of erucic, we call it canola and it

  • is now ok for human consumption.

  • We find oleic acid in olives and olive oil, which should really be our main dietary sources

  • of this good fat. Olive oil is an excellent oil, it has a rich flavor, it doesn’t easily

  • get oxidized so it’s quite stable during storage, and cooking, although to maximize

  • its health promoting activity it is best eaten raw, so that its good polyphenols are not

  • destroyed. We also have a lot of oleic acid in macadamia

  • nuts, avocados, canola oil, peanuts, and of course peanut butter. About half the fat in

  • peanuts is polyunsaturated, the other half is oleic. Be careful however, peanut butter

  • is one of those products in which the food industry likes to add palm oil for color,

  • flavor, texture and stability, but this also adds saturated fats. Go for the old-fashioned

  • version whenever possible. Finally, we also find some oleic acid in sesame seeds and then

  • nuts and seeds in general, although polyunsaturated fats are prevalent.

  • Now let’s move now to the polyunsaturated fats. Some of these molecules are extremely

  • important. They have key structural functions as part of cell membranes phospholipids, especially

  • in those tissues with complex systems of signal transmission, such as our brain and nerves,

  • the retina in our eyes, and the outer structure of our skin.

  • As if that wasn’t enough, they also have key regulatory functions ad precursors of

  • the eicosanoids, a class of hormone-like substances that we will explore later, and that are master

  • regulators of countless areas of our metabolism, including immunity, inflammation, blood pressure,

  • blood fluidity and stomach acidity.

  • We already know that the most relevant polyunsaturated fats belong to two different families, the

  • omega 6 and the omega 3 family. In the omega-6 family, we know that linoleic

  • acid, C18:2, is essential. There’s no way our body can make it starting from something

  • else, because we do not have any enzyme to introduce unsaturations in position 6. However

  • we can modify the chain length, so all the other omega-6 are not essential because they

  • can be derived from linoleic acid, once we have that.

  • Luckily it is not very difficult to get linoleic from food because it’s quite common,. Its

  • richest sources are nuts and seeds, and of course the oils we make from them, such as

  • corn oil or sunflower oil.

  • In the omega-3 family, alpha-linolenic is the other essential fatty acid in our diet.

  • Again, all the other omega-3 can be derived from it, however this time there’s a couple

  • more problems. The first one is that alpha-linolenic is not as widespread in food as linoleic,

  • so we may very well not be getting enough in the first place. And then on top of that,

  • the conversion of alpha-linolenic into the other omega-3 fatty acids is very slow. And

  • this is the reason why it is recommended to have a direct intake of these two other omega-3

  • fatty acids, EPA eicosapentanoic and DHA docosaesanoic, although they are not strictly essential,

  • but they are very important for their structural and regulatory functions. They are precursors

  • of some important eicosanoids, and they affect lipid metabolism to lower blood triglycerides

  • and improve blood HDL to LDL cholesterol ratio.

  • The richest source of alpha-linolenic acid are flaxseeds and chiaseeds, and of course

  • flaxseed oil but this gets very easily oxidised so it must be stored very carefully and rancidity

  • is a problem. Another good source of alpha-linolenic acid are walnuts, and then there’s some

  • in soy, soybean oil, rapeseed, and rapeseed oil, as well as some type of grass that can

  • be fed to hens to make omega-3 enriched eggs or cows to have omega-3 enriched milk.

  • EPA and DHA are mainly found in fish, especially fatty fish such as salmon, anchovies and sardines.

  • We said it’s advisable to have a direct intake of these fatty acids, and two to three

  • servings of fish a week will provide us with all the EPA end DHA we need. For those who

  • don’t eat fish, some seaweeds are rich in DHA, and then of course there are supplements,

  • or we can make do with the precursor alpha-linolenic from flaxseeds and walnuts.

Now why have we insisted in making all those distinctions in the structure of fatty acids?

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B2 UK saturated acid omega fatty oil palm

Nutrition Steps 5.6 - Fat Quality Is What Really Matters

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    陳秋汝 posted on 2016/05/24
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