Friday, May 13, 2016

Uncoupling in a can?

In response the suggestion from E-S, at top of comments to the last post, that caloric output should be measured using a calorimeter:

Direct calorimetry identifies deficiencies in respirometry for the determination of resting metabolic rate in C57Bl/6 and FVB mice

"In a carefully controlled study, Walsberg and Hoffman (10) examined the accuracy of respirometry in multiple species, including the kangaroo rat (Dipodomys merriama Mearns), dove (Columbina inca Lesson), and quail (Coturnix communis Linnaeus), by comparing simultaneous outputs from animals studied with both direct and respirometry methods. Those authors concluded that when disparate species were studied under various conditions that estimations of heat production by RER-based respirometry calculations led to errors averaging 21% for kangaroo rats, 15% for doves, and 17% for quail".

"Here, we demonstrate that the rate of inaccuracy of respirometry [for the CL57Bl/6 mouse] is roughly 10–12% and posit that this magnitude of inaccuracy, given the target range, is unacceptably large. We conclude that the challenges faced by the obesity therapeutics research community in identifying or validating novel therapeutic targets in mice (and likely other species as well) may be compounded by the inappropriate yet almost universal and sole reliance upon respirometry".

RER underestimates calorie output, compared to a calorimeter. But you can't buy a calorimeter off the shelf.

So folks use RER and that table. "Everyone does it". Yeah. Well.



Ash Simmonds said...

But c'mon, it's still just the "calories" hokey-pokey though yeah?


js290 said...

Yeah, but which metabolic process converts kg*m^2/s^2 into kg? Where does the (meter/sec)^2 go?

Zachary said...

Ash: LOL @

Reminds me of the Getting Fat is Good post, which never fails to make me laugh with these images:



Passthecream said...

js290: "Where does the (meter/sec)^2 go?"

Every dietitian in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

Also I think everyone can't work out how to measure either the change in entropy or in the Gibbs free energy and without that things will just never add up. Seems to me that a living organism should be considered as anholonomic ie the path taken through a given parameter space from a certain initial state determines the final state.

The CICO parameter space is singular, just 'calories' whatever that means, and the model is simplistically holonomic. Deterministic. The lchf paradigm is a little more sophisticated, there are eg fat calories, starch and protein 'calories' and many more parameters in that space and it really does matter how you travel through it, as to where you end up.

E-S said...

Nice find ! And thanks for the laughs :)

js290 said...

Gibbs and holonomic... yikes just had flash backs of graduate level dynamics...

It's funny when engineering types start spouting CICO, I remind them CICO are boundary/constraint conditions to the system, and you can see the light bulbs coming on. Then tell the physics types that calories and mass only makes sense in the context of mass-energy equivalence... minds blown.

Dieticians and nutritionists are essentially faith healing quacks if for nothing else they haven't studied enough math.

Passthecream said...


This covers it

Sec 1.2 sets out the basics very clearly eg that the entropy functions differ greatly between open and closed systems etc.

Given a few months I might be able to remember enough to understand some of the nastier bits.

js290 said...

Lagrangian, Hamiltonian, variational principles... suffered through all of that. In fact, I'm pretty certain someone (much more clever than me) can use variational principles to describe Nature's optimization on beta oxidation. That is, the glucose-fatty acid cycle (Randle hypothesis) can be proven mathematically.

One of the most important lessons I learned suffering through all that math is coupled systems cannot be magically decoupled. Again, "nutritional science" trying to decouple obviously coupled systems is effectively alchemy. We definitely see the ill effects of their unscientific nonsense.