tell me what you think of this question

[tum]

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An obese man has been on a strict diet with very small amounts of carbohydrates, yet serum chemistries show a low-normal level of glucose in his blood stream. Which of the following is the source of the majority of the newly synthesized glucose?

A. Amino acids from protein degradation
B. EtOH synthesized by bacteria
C. FA from fat breakdown
D. Glycerol from fat breakdown
E. Purine catabolism

From Q-bank. Tell me your reasoning.

 

[Ramoray]

depends on how long the diet was going on. But in general id say its the FA degradation with no other info given. Since glucose is low it will drive gng in the liver instead of being oxidized for energy.

 

[Idiopathic]

Really a tough call. Knowing that the major source of glucose in a diabetic in DKA is muscle breakdown, I would also go with that here. Some will be generated from glycerol (which logic says would be the choice), but most of the energy from FA is from ketones. I pick muscle breakdown, jsut because it gives 4 kcal (all for glucose) whereas the 9 kcal generated by 1 gram of fat is mainly due to ketones. Is A right?

 

[nuclearrabbit77]

theoretically i'd say amino acids but "fatkins diet" people will tell you it's fat catabolism with liver using glycerol->gluconeogenesis.
i think i remember a qbank question asking this..they went with fat.

 

[nuclearrabbit77]

just for reviews sake...ketones and fatty acid will never ever give you gluconeogenesis so you can already toss those out.

 

[optiplex]

well...TG breakdown to FFA and Glycerol...and acetyl Coa never really participate in gluconeogensis (simply, if you trace the TCA cycle, the 2 carbons in acetyl Coa get lost as CO2). But I think glycerol does get go to glycerol-phosphate which goes to Dihydroxyacetone. This way via DHEA, glycerol can go to G3P which can participate in gluconeogenesis.

If you look in Lippincott, you can find the pg where all the pathways are summarized...not sure which page...but the pathway is there....just that no one gives a s#*& about it...cause we are always told that fat does contribute to glucose genesis.

Hope this helps =)

 

[Idiopathic]

'MAJORITY' source...got to be protein, the more I think about it. The majority source of ATP might even be from FA synthesis, but the blood glucose has to be from muscle. Specifically: alanine-->pyruvate and aspartate-->oxaloacetate

 

[nuclearrabbit77]

fatty acid synthesis would cost atp. i think you mean beta oxidation.

i say both glycerol and the gluconeogenic aminoacids. with the fatkins diet, this doesn't fit in a normal starvation model and i don't really see why it can't be both.
screw qbank anyways.

 

[tum]

From Q-bank:

The correct answer is D. The amino acid degradation pathway s that produce oxaloacetate and pyruvate can be used to synthesize glucose and are commonly stressed in biochemistry books. These pathways are important in true starvation. Also stressed in biochemistry books is that AcCiA cannot be used for gluconeogenesis, and thus fatty acids are not gluconeogenic. But this does not mean that "fat" cannot be used to make at least some glucose, since the stored fat is predominantly in the form of triglycerides, and the glycerol backbone is glycogenic. Specifically glycerol can be phosphated by Glycerol-kinase (which uses ATP) to form G3P which can in turn enter the gluconeogenic pathway via oxidation to DHAP. This pathway contributes about 80% of the glucose in dieting obese individuals, and about 20% of the glucose (behind the aa pathways) in truly starving individuals.

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My question -- the distinction between 'starvation' and 'strict dieting' is 1 week of "fasting"? For some reason in my head I have it that the body refuses to break down protein after a week and goes more to fatty acids (thus the ketone switch). So my reasoning was reversed. I also recall reading this in "Body for Life" by Bill Philips, and unfortunately, my biochemistry background is mad ghetto. Please explain to me--where's the error in my thought process?

 

[Idiopathic]

Well, like I said, for me...glycerol was the logical choice. I just didnt figure it would be that simple. In DKA, nearly all of your blood glucose comes from protein, so I just figured this might be a similar case.

 

[coconut lime]

idiopathic, i thought that in DKA you were breaking down all your lipid stores to get energy, thus creating an unusually high level of ketones in the body, and therefore you'd use the glycerol that came off to make glucose?

 

[Gswami]

You are right coconut, in DKA you are getting the glucose from the glycerol backbone of FA. The acetyl Coa from fatty acid breakdown then is "pushed" in the direction to make Ketoacids.

 

[lattimer13]

You are right coconut, in DKA you are getting the glucose from the glycerol backbone of FA. The acetyl Coa from fatty acid breakdown then is "pushed" in the direction to make Ketoacids.

correct, because hormone sensitive lipase cannot be dephosphorylated by phosphodiesterase, which is activated by insulin, which a type one diabetic is not producing. thus, hormone sensitive lipase is going to town degrading triacylglycerols which feed into ketogenesis producing the ketoacids acetoacetate and beta-hydroxybutyrate.

just got done with biochem, and i'm sure i'll forget this in about a week. 😀

 

[Idiopathic]

You are right coconut, in DKA you are getting the glucose from the glycerol backbone of FA. The acetyl Coa from fatty acid breakdown then is "pushed" in the direction to make Ketoacids.

Sorry, if you are asking where the primary source of blood glucose is in DKA, we learned it is muscle. FA give you mostly ketones, with one glycerol that can be fed into gluconeogenesis for each TG. (As you all know)

 

[Idiopathic]

idiopathic, i thought that in DKA you were breaking down all your lipid stores to get energy, thus creating an unusually high level of ketones in the body, and therefore you'd use the glycerol that came off to make glucose?

I reiterate...DKA individuals are not getting blood glucoses of 800+ just from breakdown of FA and that one measly glycerol.

 

[Gswami]

I thought protein degradation stopped within 1-2 days into the fasting state. Most of the glucose then in your body is coming from the breakdown of fat. I don't know how long it takes for a diabetic to become ketotic ( is that even a word?).

 

[tum]

would it be fair to say you get most of your energy from ketones/fa but all of your glucose from amino acids?

 

[Idiopathic]

thats what i am saying

 

[tum]

actually just realized that's not entirely true. during fasting the liver can make sugar from fat using glycerol kinase (enzyme only present in the liver) but i guess because this enzyme is only in the liver, the B-oxidation of FA accounts for way more of the energy. odd chain FAs can make glucose via succinyl CoA too. so for the record, not all of the glucose is from amino acids, just most of it.

look how much we all learned woo.

 

[DeLaughterDO]

let's not all forget that this person with DKA is still eating, and thus has glucose intake on top of the triglyceride/protein catabolism, etc. This could also be a significant source of glucose, especially since thirst increases with dehydration - and what is the drink of choice in the US? Coca-cola!! (or pepsi, if you're a freak! j/k).

Just a thought about the high sugars.. nothing to do with the OP.

jd

 

[bigfrank]

actually just realized that's not entirely true. during fasting the liver can make sugar from fat using glycerol kinase (enzyme only present in the liver) but i guess because this enzyme is only in the liver, the B-oxidation of FA accounts for way more of the energy. odd chain FAs can make glucose via succinyl CoA too. so for the record, not all of the glucose is from amino acids, just most of it.

look how much we all learned woo.

The above post is somewhat correct. I've been following a low-carb diet for some time now and have increased my muscle mass through workouts. Anyone who says that most of the body's glucose comes from its own protein stores' degradation is mistaken. This happens in starvation.

I recall putting D on the QBank question. I think the one about Fatty Acids is a distracter (i.e., Acetyl-CoA cannot be used directly in Gluconeogenesis).

And the diet doesn't hurt your cognition either, as many "experts" on TV claim. 😉

 

[azzarah]

An obese man has been on a strict diet with very small amounts of carbohydrates, yet serum chemistries show a low-normal level of glucose in his blood stream. Which of the following is the source of the majority of the newly synthesized glucose?

A. Amino acids from protein degradation
B. EtOH synthesized by bacteria
C. FA from fat breakdown
D. Glycerol from fat breakdown
E. Purine catabolism

From Q-bank. Tell me your reasoning.

I would put either A or D.
A--if he is eating protein and using the amino acids in gluconeogenesis to make sugar.
D--glycerol from his lipid stores or from dietary lipids to make sugar.

I did not pick:
B--it doesn't say anywhere that he is consuming ethanol.
C. FA from fat breakdown makes ketone bodies I think
E. Purine catabolism--doesn't that make uric acid?

Edited to say--seeing that he is really obese, I would go with D. And sorry, I am too lazy to read other ppl's responses if you have the correct answer already! 😳