Re: Regulation of Fatty Acid Metabolism

From: Dunne E. Dawe (never_at_never.again)
Date: 11/08/04 

Date: Mon, 08 Nov 2004 11:03:53 +0800

On 6 Nov 2004 12:07:28 -0800, tunderbar@hotmail.com (tcomeau) posted:

>Biochemistry
>Donald Voet, University of Pennsylvania
>Judith G. Voet, Swarthmore College
>John Wiley and Sons, 1990
>
>Chapter 23, Lipid Metabolism
>Page 641
>
>5. Regulation of Fatty Acid Metabolism
>
>Discussions of metabolic control are usually concerned with the
>regulation of metabolite flow through a pathway in response to the
>differing energy needs and dietary states of an organism. For example,
>the difference in the energy requirement of muscle between rest and
>vigorous exertion may be as much as 100-fold. Such varying demands may
>be placed on the body when it is either a fed or fasted state. For
>instance, Eric Newsholme, an authority on the biochemistry of
>exercise, enjoys a two-hour run before breakfast. Others might wish
>for no greater exertion than the motion of hand to mouth. In both
>individuals, glycogen and triacylglycerols seve as primary fuels for
>energy requiring processes,and are synthesized in times of quiet
>plenty for future use.
>
>*Synthesis and breakdown of glycogen and triacylglycerols, as detailed
>in Chapter 17 and above, are processes that concern the whole
>organism, with its organs and tissues forming an interdependent
>network connected by the bloodstream.* The blood carries the
>metabolites responsible for energy production: triacylglycerols in the
>form of chylomicrons and VLDL (Section 11-4A), fatty acids as their
>albumin complexes (Section 23-1), ketone bodies, amino acids, lactate
>and glucose. The pancreatic a and b cells sense the organism’s
>dietary and energetic state mainly through the glucose concentration
>in the blood. The a cells respond to the low blood glucose
>concentrations of the fasting and energy-demanding states by secreting
>glucagon. The b cells respond to the high blood glucose concentration
>of the fed and resting states by secreting insulin. We have previously
>discussed (Sections 17-3E and F) how these hormones are involved in
>glycogen metabolism. *They also regulate the rates of the opposing
>pathways of lipid metabolism and therefore control whether fatty acids
>will be oxidized or synthesized.* Their targets are the regulatory
>(flux-generating) enzymes of fatty acid synthesis and breakdown in
>specific tissues (Fig. 23-33).
>
>************
>
>* indicates italization as in the textbook

There you go, I knew you would eventually find it. Don't bother
thanking me :-)

>Recap:
>
>too many refined carbs in the diet = high blood glucose concentrations

Only in diebetics. Normal folk keep their blood glucose level within
very narrow limits. Refined carbs should be eaten in very small
quantities or not at all. Sam for all higly refined foods.

>= higher insulin secretions = fatty acid synthesis = obesity

>From where? Are you reverting back to this imaginary "appearance out
of nowhere", the energy requirements for this synthesis?
There is no net synthesis over a week for a normal healthy individual
eating the correct amount of energy containing molecules.

>low carb diet = lower blood glucose concentrations = higher glucagon
>secretions = fatty acid oxidation = no obesity

And if you are eating too many calories? You seem to be neglecting
several parameters and reconfusing yourself.

>They mention energy needs but they give no indication of where,
>exactly, it fits in vis-a-vis fatty acid synthesis.

Fatty acid synthesis over a week depends entirely on how many calories
are absorbed and how many are expended. If the two of these are equal,
NO fatty acid synthesis occurs.

>"The a cells respond to the low blood glucose concentrations of the
>fasting and energy-demanding states by secreting glucagon. The b cells
>respond to the high blood glucose concentration of the fed and resting
>states by secreting insulin. We have previously discussed (Sections
>17-3E and F) how these hormones are involved in glycogen metabolism.
>*They also regulate the rates of the opposing pathways of lipid
>metabolism and therefore control whether fatty acids will be oxidized
>or synthesized.* "
>
>It is the freakin' hormones, not the damned calories.

No, I told you it was the concentrations of different molecules. If
there are no excess calorie-containing-molecules, it doesn't matter
what the hormone status is, there will be no net fat synthesis, or
storage from dietary fat.

>It ain't the fat, it's the carbs.

Its the molecules, and each mole of fat has two-and-a-half times as
much energy as a mole of glucose

You have reverted to your old confusion, unfortunately.
Please try to start thinking of molecular concentrations that the body
reacts to.

Relevant Pages

  • Regulation of Fatty Acid Metabolism
    ... Regulation of Fatty Acid Metabolism ... too many refined carbs in the diet = high blood glucose concentrations ...
    (sci.med.nutrition)
  • Re: Regulation of Fatty Acid Metabolism
    ... Regulation of Fatty Acid Metabolism ... The b cells respond to the high blood glucose concentration ... Not according to the above referenced textbook. ...
    (sci.med.nutrition)
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  • Re: News: Evolution is slowing snails down.
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  • Re: News: Evolution is slowing snails down.
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    (talk.origins)