Keto-adapted military fitness

Today’s post will be all about military ‘style’ physical training whilst consuming a ‘primal’ or ‘paleo’ diet (i.e. a diet generally low in carbohydrate and sugar, higher in saturated fats).  Whilst there is a strong affinity for the paleo diet amongst the crossfit community,  I have yet to read anyone’s experience of conducting longer duration military training on this type of diet.  It’s all very well training in a gymnasium and easing off a little/finishing your session early due to an issue with your energy levels, but when half-way through a long route march over Dartmoor it’s quite another matter!

So, last week, after a year eating a ‘primal’ type of diet (well, 80% of the time!) I went on my first 8 mile weighted march (55lbs plus rifle).  This is an annual test in the British Army.  The distance is covered as a squad, in 1 hour 50 minutes.  If you fall more than 10 meters behind the squad, you fail!  Whilst it isn’t particularly difficult (in terms of pace think a mix of ‘airborne shuffle’ and speed walking) I was curious to see how my energy systems would react: in the past I have always felt my blood sugar wax and wane, and kept a stash of sweets in my map pocket just in case.

I was pleasantly surprised.  We started at 8 o’clock in the morning, after my usual breakfast of two cups of black coffee.  Every couple of miles we’d stop for a minute or so to allow those without camel baks to take in some water.  What struck me was how many people, whilst coping perfectly well with the activity, were also sucking down sports drinks and chewing handfuls of sweets.  My energy levels were just right, and  I only needed some water.  Two hours later, rifle handed back in and stretching off, I still felt great.  It was mid-morning and I was able to quite happily wait a couple of hours and then have a lunch of wild salmon and eggs.

But should I have been so surprised?  I read this fascinating article on the exploits of Frederick Schwatka (1849-92) recently, and it only seems to confirm that this phenomenon is anything but special.   Schwatka graduated from West Point in 1871 and went on to pass not only the Nebraska bar but to also graduate from Bellevue medical school whilst serving as an Army Officer.  He became fascinated by the fate of the Franklin expedition and volunteered to lead a search to determine the facts.  He was accepted, and in 1879, after a long winter camped at Daly Bay with the rest of the expedition and their guide ‘Eskimo Joe’ Ebierbing, they set off with a number of Inuit. They walked, with dogs dragging sledges for 5232km, a journey that lasted over 11 months.  In this time Schwatka located the grave of the Third Officer of HMS Terror, and several artefacts.

Photo courtesy of Gilder, W. H. 1881 Schwatka'a Search: Sledging in the Arctic in Quest of the Franklin records. New York: Charles Scribner's Sons.

Although they had a month’s reserve of walrus blubber, the party of 18 men and 44 dogs survived on what they were able to hunt and kill on their epic journey.  They returned to Hudson’s Bay in good health.  So, what’s happening here?  How is it we can survive quite happily on diets with absolutely minimal carbohydrate (not quite zero, there being glycogen etc.. in liver and muscle consumed) yet the perceived wisdom is that ‘carbo-loading is required for exercise?

When first thrown wholly upon a diet of reindeer meat, it seems inadequate to properly nourish the system, and there is an apparent weakness and inability to perform severe exertive fatiguing journeys. But this soon passes away in the course of two or three weeks.

Frederick Schwatka

If one reads the various Paleo diet community blogs, this idea of a period of almost ‘withdrawal’ or ‘carb flu’ is a recurring one.  So after two to three weeks, where does this ‘fresh’ energy come from?  A later anthropologist and Arctic explorer, Vilhjalmur Stefansson, noted that the Inuit ate mainly of the fat and organ meats, giving excess muscle meat to their dogs.   So there we have it.  Eat lots of fat and have boundless energy!


In War Medicine in 1946, a study reported that a high fat animal based ration for troops seemed unwise:  troops were switched to pemmican (a mix of fat and dried meat) from their usual (carbohydrate containing) rations abruptly, and within 3 days the study had to be abandoned as the soldiers were unable to drag their sledges the requisite 25 miles through deep snow. Sounds like a fun study to participate in!

So what happened?

Fed the ‘average diet’, (for generalisation let’s say a roughly equal mix in terms of % of calories from protein, fat and carbohydrate) the body is adapted to use the readily available glucose (derived from carbohydrate in digestion) to produce energy, first by glycolysis in the cytosol of our cells, and then the majority of the energy is extracted inside the furnaces of our cells, the mitochondria in a cyclical series of reactions known as the TCA cycle (also known as the citric acid cycle or Kreb’s cycle).  This latter stage is considered aerobic, as the cycle is coupled to oxidative phosphorylation, a process that truly is aerobic.   Initial excess glucose will be used to replace expended liver and skeletal muscle glycogen.  If still in abundance, there is a regulatory mechanism intrinsic to the TCA cycle that syphons off citrate for conversion to fatty acids and thus storage as triglycerides (3 fatty acids bound to a glycerol).  And what a source of fuel it is – Beta oxidation of a gram of triglyceride, sitting quietly in my adipose fat, has the potential to generate over 6 times the ATP (the energy currency of our cells) as does the hydration of a gram of the glycogen in my liver or skeletal muscle.

Figure 1: How the body meets its basal demand over a 24 hour fasting period. Image courtesy of Cahill, G.F. Starvation In Man. New England Journal of Medicine Vol 282 No. 12 1970 668-675.

Figure 1 shows in broad terms the key issues with the fasted (or for that matter, the carbohydrate restricted) state – that 75g of protein has been broken down into amino acids to enter gluconeogenic pathways and thus produce (in the case of the hepatocytes of the liver) free glucose, which can travel until it attaches to GLUT receptors on the surface of cells where it is required.  At this rate, after a few weeks the musculature will be rapidly vanishing.  The body really requires a means of limiting the requirement to use amino acids to generate glucose.

Luckily it has one.  As a first aside, this information is the basis of the supplement industry’s fixation with consuming vast amounts of whey protein.  Sadly they figure it best to keep quiet about the next stage…

Figure 2 shows us the response, as ‘discovered’ by Schwatka after a few weeks on his diet of reindeer meat.  If substrate levels in the TCA cycle are low (in particular oxaloacetate) then Acetyl CoA is diverted to the production of ketone bodies (acetoacetate and D-3 hydroxybutyrate) from fatty acids.  The CNS (which usually has a very sweet tooth) once ‘adapted’ uses these ketone bodies as a source of energy in preference to glucose, thus sparing the amino acid pool in our musculature from the ravages of gluconeogenic activity.  This single adaptation enables us to go for long periods in this ‘ketogenic’ (producing ketone bodies) state and not watch our muscles evaporate before our eyes!  Figure 2 shows us that a mere 20g of protein a day is required to maintain the basal metabolic rate.

As a second aside, we can see now why we store energy as triglycerides; they really are the ‘meat and two veg’ of energy provision to mammalian cells:  the glycerol is converted to dihydroxyacetone phosphate (DHAP), which allows hepatocytes to generate free glucose (once again saving our amino acid pool) for the few cells types which are really picky and require glucose, such as red blood cells, and the fatty acids are released go around and around in circles with Coenzyme A, producing Actyl CoA and subsequently ketone bodies.

Figure 2 ... After 5 to 6 weeks of adaptation. Image courtesy of Cahill, G.F. Starvation In Man. New England Journal of Medicine Vol 282 No. 12 1970 668-675

There is a catch though.  If you insist on performing the sort of activity that we in the west regard as ‘fitness activities’ such as ‘cardio training’, you are going to rapidly deplete your glycogen stores and run into trouble.  Whilst this can be delayed significantly and athletic performance improved by opting to be ketogenic, once energy demand outstrips the supply of oxygen, the beta oxidation of fatty acids runs into problems.  Glycogen (and thus glucose, can fuel our anaerobic activity by producing lactate from pyruvate, but the conversion of pyruvate to Acetyl CoA for entry into the TCA cycle is for all intents and purposes, one-way.  So all those fatty acids rushing to the rescue cannot produce energy anaerobically.

So if you want to perform aerobic activity, such as running a marathon, in a really decent time, then ketogenic training and a good supply of glycogen are both required. If you want to march 30 miles across the Falklands, or 5232km around the Canadian Arctic, then ketogenic adaptation and the optimal utilisation of our triglyceride stores are key.

Having thought a lot recently about energy systems in the human body, my thoughts on the whole low-fat/high-fat diet issue are that looking dispassionately at how our bodies choose to store energy yields the answer. As a result, the concept of deriving the bulk of my calories from fat (in the form of well-sourced animal meat, bones and organs) holds little fear for me.  The key factor though is the nose-to-tail consumption of the Inuit:  (they even had a term for the malaise suffered by people who only had access to lean rabbit meat as a food source in the spring) eat more skin, tendon, marrow and organs.

So what’s next?  Well, my plan is another n=1 experiment in May: this time, to re-run the British Commando course’s final test  – a 30 mile ‘yomp’ carrying a weighted pack and rifle across Dartmoor.  Ration choice?  I need to find a recipe for pemmican… photos and results to follow!


5 Responses to Keto-adapted military fitness

  1. Pingback: Nose-To-Tail Eating « finalprimate

  2. This was absolutely amazingly explained. I have a slightly vain question though, with being ketogenic, do you find that it makes your breath smell? I have heard that it can have that affect and am just wondering. Thanks!

    • finalprimate says:

      Thanks for the compliment – it’s quite hard to get this complex subject across simply, so glad you found it interesting. By smell, I take it you mean an acetone type smell? Well, it’s not something I’ve experienced! I think it’s more common with ketoacidosis, where ketone body concentrations would be much higher…

  3. Yes thats exactly what I was talking about. My brother is diabetic, so when he has high blood sugars that is what his breath smells like and I was seeing it on some information sights. Good to know that it’s not a given and only happens in extremes. 🙂

  4. Pingback: How to live, Part 1: Keeping Fit | finalprimate

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