Thursday, 19 May 2011

Hot-Blood

So the paleo diet wars are raging.  What to do?  For me, nothing.  I have no change to make.  My approach was pretty much to divide my plate in half and fill half with meat (including any fat that comes with the cut), and half with green veg and some seasonal fare.  I used to restrict potatoes, but they have been back on the menu for a while.

Other meals included soups made from the juices of roasted chicken and lamb.  The soups comprised of squash, turnips and other starchy tubers.  So I am not sure I could ever have been 'low carb' although I have never worked out the macro nutrient composition and I don't count calories.  Ever.
It is good that these debates stir up from time to time.  We should follow the science but it is hard to keep up with the complexities.  Most of us should have our diet dialled in sufficiently to not have to change things up too much when various paleo luminaries say they are eating less fat, more carbohydrate and so forth.

Bottom line for me is that you should never be in fear of REAL food!

But this is not the first big bust up I have come across in paleoland.  A year or two ago there seemed to be a flurry of activity with regard to running - and in particular endurance/distance running.  My position on it was more towards the pro-sprinting side of things, although I have no problem with the idea of exhausting and prolonged 'black swan' events.  However I drew the line at running anything over 5-10k (ish).  Certainly I was against marathon distances.

However, recently I have been reading Nick Lane's truly superb 'Life Ascending' and he actually makes quite a good case for hot blooded creatures evolving for stamina.  Now this still does not make the case to pull on your Nikes and knock of 24 miles, but it is food for thought...

Hot blood is all about metabolic rate and being hot-blooded is a truly expensive adaption.  We are not hotter than cold blooded creatures, they simply use the sun's energy to warm themselves rather than BAT, and what is more when they do cool down (at night), it is at a time when they are usually inactive. 

Lane notes that the metabolic cost of living in the cold for a mammal is a hundred times that of a lizard, and, as a general rule, being a mammal or a bird 'starts at around ten times the cost of being a lizard'.  This means that we have to eat proportionately more food to fuel this furnace.

The benefit of being hot-blooded is 'niche expansion'.   We can hunt at night and through the cold winters of temperate climates.  It also seems to relate to a larger brain.  As lane observes, if a lizard and a mammal dedicate 3% of their energy to their brain, given the figures above, the brain of the mammal can be ten times the size of that of a lizard. 

The price of the super-charged metabolism is, as a general rule, fewer offspring and shorter lifespans.  This would seem to be something that natural selection should penalise us for, but Lane suggests that hot-blooded animals have an ace up their sleeve in stamina.

Lizards can easily match mammals for speed (and exceed them), over short distances but they rely on anaerobic respiration, and so quite soon they are crippled with the cramp of lactic acid!  This whole idea of stamina being the driver in hot-bloodedness is based up the 'aerobic capacity hypothesis'.

Quoting Bennet and Reuben (1979), Lane states that 'selection is not for temperature, but for increased activity'.  A broad selection of 'hardware' (mitochondria, heart, capillaries, blood pressure, lungs etc...) is required to handle a high level of metabolic activity which in turn appears to draw upwards resting metabolic rate.

I'm not sure I will be putting the miles in any time soon, but it will certainly keep me to my lunchtime practice of training or walking.

4 comments:

Chris said...

Walking is always good. And of course sprints make you a more efficient walker. Which is why we should sprint ;-)

Methuselah said...

You've just described my diet. However, I do have periods of very low carb where I restrict tubers and stick to low carb veg. These are to offset the high carb binges which occasionally happen - or more to the point to accelerate the process of losing the fat accumulation they led to. As you know, I throw in 5-10 very long fell races per year. But of course the line between fell racing and hiking is a thin one. On a tough course, you'll spend up to 50% of the time power hiking anyway. I reckon that a long, vigorous hike is not a million miles from the kind of endurance activities we're built for.

Asclepius said...

@Chris - agreed. The consequences of long runs is evident in the bodycount at the first aid posts of major races! Walking, some running and sprints still look like the optimal approach to me.

@Methuselah - I hope to detail my diet in a post. When I explain it to people I call it a 'Paleo Ketogenic Diet' (or 'Power Law Ketogenic Diet'), and like yourself, there might be high carb days and often there are low carb days.

Thinking about it, I generally have three nutritional states which I would describe as (i)'fasted', (ii)'Mostly animal with green veg/seasonal salad', (iii)'mostly starchy tubers with meat stock'.

This is supplemented with some dairy, nuts and fruit as required.

There is no plan although I have tinkered around with glycogen depletion on a CKD. But as always, too much planning with food gets in the way of life.

Methuselah said...

You forget the 4th dietary state - chocolate and cakes at times like Christmas!