The Fat Adapted Ironman Lean Startup Experiment Is Progressing Nicely


Hi folks! Thanks for stopping by!

Chez Ollie “What does it mean to be fat-adapted?” From Mark’s Daily Apple. Click on image for full article.

I love to learn, read a great book, which is currently The Lean Startup by Eric Ries, and experiment around my Ironman training to make it more effective. It turns out that success in a startup company (mine is called Old Dogs in Training, and last year I made $80, which is apparently a good start) also depends upon experimentation. My current Ironman experiment is with the use fats as an energy source, in place of carbohydrates, or as Chez Ollie.

In the past, when undertaking long distance endurance training or Ironman races, I had to eat all the time. About 300 calories per hour on the bike and 200 during the run. This was a real hassle, and if I missed a gel or PowerBar I’d start to feel sick (hypoglycemia = low blood sugar), because I was running on carbohydrates, an inefficient energy source.

Ironman tee-shirt by Duncan, available at RedBubble - click on figure for link.

Ironman tee-shirt by Duncan, FitOldDog’s n #2 son, available at RedBubble – click on figure for link.

These carbohydrates include those stored in my liver (enough for the 2.4-mile swim and a few hours of the 112 miles on the bike), those I consume as I train or race, and those my body manufactures from proteins, using energy derived from fats, in a process called gluconeogenesis (making new sugar), undertaken by my liver, kidneys, and to a lesser extent other organs. My body was largely fueled by sugar!

As a result of encouragement from my eldest son, Nick (#1 son) of ‘Shirts That Go‘ fame (great tee shirts for young kids interested in diggers, trains, boats, planes and any machine that moves and is cool), I decided to essentially remove carbohydrates from my diet, but increase the amount of fat I consumed. This strategy pushes my metabolism into a quasi-fasting (like fasting) state, decreasing insulin release and increasing the effects of another hormone, glucagon – basically it will train my body to burn fats in the form of free fatty acids and ketones (yes, ketones, those sweet-smelling chemicals that can indicate diabetes, are a normal energy source, and an important one at that). The first thing I noticed was a general lack of hunger and a steadily decreasing body weight.

Two of FitOldDog's supporters, Xan and River.

Two of FitOldDog’s supporters, Xan and River, watch him head off for another 32 miles on the bike, after filling a water bottle and dropping excess clothing – and great supporters they are. Photo by Meghan Truesdell.

Sorry for all the biochemistry, but how can you understand your food and what it does without it, I would like to know? Chez Ollie. So, in a couple of months my body has learned to use fat as it’s major energy source, only making enough sugar for the red cells in my blood (they totally rely on glucose for energy, as they have no mitochondria) and my brain (it gets 20% of it’s energy from blood glucose, and the rest is essentially from ketones).

As I have plenty of fat, and one pound of fat generates about 3,500 calories (I use only about 10,000 calories in a 140.6 mile Ironman race), whilst glucose stores are very limited, burning fat should remove my need to eat during long-distance training and racing as long as the load is low and sustained (that’s the Ironman for older athletes). So I am experimenting. Today I completed a 75-mile bike ride followed by a 5-mile run, during which time I didn’t consume any power bars, gels or whatever, just lots of water (and half an avocado, because it was right under my nose at the end of the bike ride, but I didn’t need it). I didn’t bonk, feel hungry, or have low energy levels. My engine was running largely on storage fat.

I suspect that fat-adapted older endurance athletes might do well, but I guess that remains to be seen, as does the success of my startup company.

Isn’t life interesting?

-k @FitOldDog



  1. Congrats Kevin… Sounds like the experiment is going great!

  2. In what form do you eat your fat? Presumably not fried food.

  3. Avocado, nuts, eggs, pork, dark meat chicken, plus I eat plenty of fresh vegetables and some fruit, often blueberries and pineapple. -k

  4. Oh! Yes! And plenty of butter, full cream milk, and cheese. -k

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Disclaimer: As a veterinarian, I do not provide medical advice for human animals. If you undertake or modify an exercise program, consult your medical advisors before doing so. Undertaking activities pursued by the author does not mean that he endorses your undertaking such activities, which is clearly your decision and responsibility. Be careful and sensible, please.