Fats in Food

[Carl Fredrik Ahl]

Hi,

I know that there are a lot of different days in different food and that unsaturated fats doesn't have any hydrogen atoms but only carbon atoms and that saturated fats have both of them. What I wonder is that when you consume fat, say unsaturated fat for example, it will behave just like carbohydrates and get converted to glucose and used up by cells if the body needs energy and otherwise store it as fat? Or does it get stored as fat directly and then burned?

[Sensei]

22 minutes ago, Carl Fredrik Ahl said:

and that unsaturated fats doesn't have any hydrogen atoms but only carbon atoms and that saturated fats have both of them.

That's certainly not true..

Unsaturated fat differs from saturated fat that it has one or more C=C bond. Unsaturated fat HAS Hydrogen atoms. (at least) two less Hydrogen atoms than saturated form.

 

[Carl Fredrik Ahl]

2 hours ago, Sensei said:

That's certainly not true..

Unsaturated fat differs from saturated fat that it has one or more C=C bond. Unsaturated fat HAS Hydrogen atoms. (at least) two less Hydrogen atoms than saturated form.

 

Oh ok, thx for the info. So what happens when you eat those fats?

[iNow]

5 hours ago, Carl Fredrik Ahl said:

I know that there are a lot of different days in different food

I don't know what this means. Different days?

5 hours ago, Carl Fredrik Ahl said:

and that unsaturated fats doesn't have any hydrogen atoms but only carbon atoms

This isn't true. They're not "saturated" with hydrogen atoms, but that doesn't mean they have none. 

5 hours ago, Carl Fredrik Ahl said:

What I wonder is that when you consume fat, say unsaturated fat for example, it will behave just like carbohydrates and get converted to glucose and used up by cells if the body needs energy and otherwise store it as fat? Or does it get stored as fat directly and then burned?

Fat doesn't get converted to glucose. It gets converted to triglycerides and stored.

It appears you may have some fundamental misunderstandings of how these processes work. If you wish to learn more, suggest exploring terms like ketosis and lipolysis in more detail.

[BabcockHall]

To reemphasize one point above, fatty acids (the main component of triacylglycerols) can be used for energy (by aerobic catabolism), but they cannot be converted into glucose.  The question of how monounsaturated or polyunsaturated fatty acids are different from saturated ones from the point of view of our diet is a large and complex one.  Ideally the question should be narrowed down before it could be addressed in a forum.

[Carl Fredrik Ahl]

Thx for the info, yeah I forgot how it was.

Edited August 22, 2018 by Carl Fredrik Ahl

[BabcockHall]

To paint with a very broad brush, the health of one's arteries may depend on the nature and the amounts of the fats that one consumes.  Some have claimed that there is a correlation between the amount of trans-fat in the diet with the relative amounts of so-called good versus bad cholesterol.  I realize that this is a slightly different question from the one that you asked, but I offer it for the purposes of illustration.

[CharonY]

On 8/21/2018 at 1:55 PM, BabcockHall said:

but they cannot be converted into glucose

It is mostly a question for even-chained fatty acids IIRC (animal phys is a bit hazy). However odd-chain fatty acids goes via suc-CoA and pyruvate into gluconeogenesis, unless I am missing something here.

[BabcockHall]

Yes, the odd chain fatty acids give rise to propionyl CoA, which can be converted into succinyl CoA in several steps, one of which is dependent on vitamin B12.  I don't know what percentage of fatty acids have an odd number of carbons.  For completeness we should probably also mention that the glycerol backbone of a typical triacylglycerol can be converted into glucose.

[BabcockHall]

Just to finish out my thought, succinyl CoA can be converted into oxaloacetate in several steps, and oxaloacetate can be converted into glucose via gluconeogenesis.

[CharonY]

The issue is actually quite interesting. Theoretically everything entering the TCA has the potential to be used for gluconeogenesis purely from a pathway perspective. However, in the absence of a glyoxylate shunt oxaloacetate would be imbalanced (as it would need to react with Ac-coA and have a loss of two carbons which would not allow a net gain of carbon, obviously). Since in animals you typically even-chain fatty acids the textbook answer is "no", but it leaves out a lot of nuance here (though without doubt, if asked in an exam is safe to state it that way). Odd-chain fatty acid are assumed to be of dietary nature.

However, the systems biological view is quite interesting as we can draw up theoretical pathways by coupling a pathway from Ac-coA to acetone and subsequent degradadation to lactate and pyruvate. There are additional possibilities if we assume the incorporation of microbiota-dervied short-chain fatty acids into the system. However, I am not sure whether there have been precise experimental flux data to support these models. But there have been some interest into those mechanisms as natives in the arctic region as they do not have ready access to sugars or odd-chain fatty acids. There is at least some speculation that those pathways may contribute to conserve protein degradation. But again, I think it is still somewhat speculative and quite a bit away from entering text books (or eventually dismissed pending experimental data).

Edited August 24, 2018 by CharonY

[MAYusuf]

CMIIW

First, I agreed with @Sensei that unsaturated fats have less H on its fatty acid chain, have two less H or less,  like linoleic (C18, with 2 C=C) or linolenic (C18, with 3 C=C). And what happen when consuming unsaturated fats? It will metabolized to energy or kept as energy source reserve as body fat (triacylglyceride, TAG) but some unsaturated fats has another structural function to specific cells like DHA, EPA, ALA, etc.

Is it behave like carbohydrate and converted into glucose? Nope, it converted to Ac-CoA and then converted to energy. Glucose can be made from non-sugar (non carbohydrate) substance via gluconeogenesis but only used glyserol (TAG backbone, not the fatty acid), lactic acid (from anaerob metabolism), and alanin (from muscle). However, gluconeogenesis strictly occur when body's energy reserve was nearly/depleted (in prolonged fasting condition) to maintaining the blood glucose level.

Does it stored directly as body fat? Its depend how much carbohydrate that you consume. The body has priority in metabolizing energy source (carbohydrate, fats, and protein). Priority depends on the ease of metabolism and body needs. Carbohydrates have highly priority to be metabolized. This is very reasonable because carbohydrate metabolism is very simple and energy efficient (compared to fat and protein). And in fact, our brain cells rely heavily on glucose as an energy source because fatty acids and proteins cannot reach brain cells due to brain barrier. And then, next priority was fat then protein. 

When is fat stored as body fat? Its stored when glucose level maintained. When is fat metabolized to energy? Fat metabolized when stored carbo (glycogen) reserve almost depleted (in fasting and heavy activity condition).