Not really much about swimming underwater

*****MAJOR ERROR********

Down in the comments section Mateusz has very kindly found the error in my arithmetic for me. It makes the whole of this post completely incorrect and requires a great deal of working through posts based on this conclusion to correct my mistake and the implications this has for blood supply and oxygen consumption.

Fats require around about 5% more O2 per ATP cf glucose.

With apologies to everyone.

I know I said (first paragraph) that I would take this post down in embarrassment if I'd made an arithmetical error but, on balance, I think it should stay as a warning, to me as much as anyone else.

So I’m going to leave this post up unchanged, with this edit, as a warming to the immense power of confirmation bias. There’s a lot to do.

*****MAJOR ERROR********







Just before I hit post: I think the arithmetic and the logic here are sound on a ball-park basis but if anyone can point out any major flaws I stand to be corrected and will take the post down in embarrassment. But this is so simple in concept that I don't see why it's not standard fare... Here we go.

In the comments after a previous post it became pretty obvious that several LC eating folks noted a significant improvement in their ability to breath-hold while running their metabolism on fat rather than on glucose. Although this is rather counter intuitive based on the RQ (more oxygen is required per unit CO2 generated when you oxidise fat compared to glucose) what matters is the generation of ATP per unit oxygen or ATP per unit CO2 produced. I started with oxygen. Arithmetic goes like this:

Glucose oxidation is simple. Six carbons give 2ATP from glycolysis and a mix of NADH and FADH2 from the TCA:

6(CH2O) + 6O2 = 6CO2 + 6H2O      
RQ: CO2/O2 = 6/6 = 1.0
2 ATP + 10NADH + 2FADH2


A theoretical six carbon section of a chain of a fully saturated fatty acid gives this:

6(CH2) + 9O2 = 6CO2 + 3H2O        
RQ: CO2/O2 = 6/9 = 0.67
15NADH + 6FADH2


Three of the FADH2s are from acetyl CoA turning the TCA, the other three are from beta oxidation. For PUFA a theoretical alternating sequence of single and double bonds yields this:

6(CH1.5) + 8.25 O2 = 6CO2 + 4.5 H2O
RQ: CO2/O2 = 6/8.25 = 0.73
15NADH + 3FADH2


The first step of beta oxidation for PUFA yields no FADH2, so we just have the three from the TCA. Assuming the ETC works efficiently we pump these protons from our hydrogen supply:

NADH = 12H+
FADH2 = 8H+

And, very crudely, let’s assume at complex V, ATP synthase, we have 4H+ = 1 ATP (not true IRL!)

So we can calculate protons pumped, what this is worth in ATP and combine this with the O2 needed (from the chemical equations above) giving:


Glucose protons
10NADH = 120    2FADH2 = 16, total = 136 H+
ATP 34 + 2 = 36

ATP-gluc/O2 = 6.00

Saturated fat protons
15NADH = 180     6FADH2 = 48, total = 228 H+
ATP = 57

ATP-sat/O2 = 6.33

PUFA protons
15NADH = 180 3FADH2 = 24, total = 204 H+
ATP = 51

ATP-pufa/O2 = 6.12


Clearly fatty acids are better at generating ATP per unit O2 consumed. If a 70kg person, at rest, is consuming 200ml of oxygen per minute to produce a given amount of ATP while burning glucose they should be able to maintain that same amount of ATP on less oxygen.


But the difference seems pretty small. How small?

Through sins of education I tend to think of O2 consumption for an anaesthetised, mechanically ventilated patient. That person needs about 200ml/min of oxygen.

200ml O2 gives 6.00 x10^bw ATP if running on glucose (where 10^bw is a crude scalar to whole body ATP needs). On saturated fat:

200ml O2 gives 6.33 x 10^bw ATP

Or, more realistically:

190ml of O2 gives 6.00 x 10^bw ATP on fat, equivalent to 200ml O2 used on glucose. An oxygen sparing effect of 10ml/min is underwhelming on first consideration. It’s a 5% improvement. But this should be maintained at VO2 max. When oxygen delivery is the limiting factor in performance, running on fat gives you a 5% advantage.

This is simple arithmetic applied to the most basic of biochemistry processes.

Is butter a performance enhancing drug?

Yes, provided it displaces carbohydrate.

Should folks with ischaemic problems eat butter?

Yes, provided it displaces carbohydrate.

Does it taste good?

Yes, unqualified.

Of course, once you add in ketones, magic starts to happen to the energy yield of ATP hydrolysis. Ketones are not as arithmetically simple as fatty acids but we all know, from Veech and D'Agostino's work, that magical indeed they are.

Peter

Oh, I calculated CO2 per unit ATP produced too. On carbs ATP/CO2 = 6.00 as you would expect but on saturated fat the amount ATP produced per unit CO2 evolved is 9.5. CO2 build up makes you breathe, you make less per minute on fats. Breath holding is, arithmetically thinking, expected to be easier running on saturated fat. This is what we find.

*****EDIT*****

Hans pointed out in comments that the TCA provides a molecule of GTP which can convert to ATP from each acetyl-CoA. This gives two extra ATP's per glucose and three more ATP's per six carbons from saturated fat. I can't be *rsed to re do the math, but you get the picture.

*****END EDIT*****