Low carb endurance training

Continuing the discussion from NuSI metabolic ward study on low-carb & the insulin hypothesis:

Thanks! I’d certainly like to experiment with this. It’s good to know the lipid metabolism doesn’t go away with the addition of a few carbs (the keto discussions talk a lot about falling out of nutritional ketosis with a carb meal). Granted I’m not really seeking nutritional ketosis, but rather merely to lower my RQ at moderately high heart rates (75%-85% max HR). I’m fine not carbo loading the night before a marathon (my GI tract is much more predictable after 24-36hrs of Soylent)… But it is nice to know I could start in with the gatorade and/or gels early in the race or at the very start without critically damaging my potential lipid metabolism. It’s a tough balance though, if I take sugar my RQ will certainly shoot up right?

One other thing I noticed on the two latest marathons was that my HR went up in the 2nd half (about the same time I started the sugar)… I had been trying to maintain a 145-150 HR but by mile 18 or 19 I was willing to push 155-160 to see how that would last. I’m not sure how much of the late kick from 24-26 was due to the sugar vs just psychological (being near the finish line). But I’ve had many other marathons where “hitting the wall” around mile 20 leads to nothing but progressively slower and slower miles…

For general training though, it would be interesting to know for example:
What is the RQ for a 30 minute workout at 150 pbm HR after
A: a week of eating 40% fat 40% carb 20% protein
B: a week of eating 50% fat 30% carb 20% protein
C: a week of eating 60% fat 20% carb 20% protein
D: a week of eating 70% fat 10% carb 20% protein

It’s too bad that it’s so hard to measure the RQ although I suppose if I found a local lab that could hook me up on a treadmill for a reasonable price I might try it…

edit: btw Respiratory Quotient (RQ) is a measure of the carbon dioxide exhaled relative to the oxygen inhaled. 0.7 indicates nearly complete fat oxidation whereas 1.0 is nearly complete carbohydrate oxidation.

Also, here are my last two marathons both were preceded by a mostly 1.5+oil and 2.0 diet (45-47%fat) with the last few days prior to the marathon being straight 1.5 (40% fat). At Eugene I actually had some diluted 1.5 stashed at mile 9 as well…
Jack&Jill Marathon
Eugene Marathon


Or find your local Ray Cronise or other freak who pays $30k for their own equipment to measure RQ.

Interesting stuff to experiment with… I can’t comment more on running, not being a runner and not really reading up on it, but I wish you lots of luck and lots of fun!

Exactly right. A single high-carb meal can knock you out of ketosis, but that just means the body isn’t making ketones for the brain to run on in the absence of adequate glucose. It doesn’t mean that fat metabolism is acutely affected.

Lyle McDonald talked about that in some detail in his UD2.0 (Ultimate Diet 2.0); it was, in some ways, a highly-optimised Cyclical Ketogenic Diet… but he stressed that ketosis, if it happened, was strictly incidental. He designed the diet & protocol to ramp up the fat burning as much as possible as quickly as possible, and it really didn’t matter whether or not the body was getting into ketosis each week. I seem to recall him saying that he observed some individuals still losing body fat the day after their carb load day, even while eating normal carbs and full maintenance calories, just because their fat metabolism was so ramped up.


What does fat adaptation look like? Is it simply a bloodstream full of ketone bodies?

No… ketones aren’t actually part of it.

The primary thing is that the metabolism within each bodily cell (muscles, organs) is primed and capable of getting a large fraction of energy from fats as fuel. The maximum energy output it can produce while running on fat alone is higher than it is in someone who doesn’t have much fat.

In addition, the adipose tissue (fat cells) in a fat-adapted person may be better at “giving up” fat into the blood on demand. There are limits to how quickly fat cells can pump triglycerides into the bloodstream when it’s needed. Some people think this is a fixed property of fat cells, but others think the fat-adapted person can more easily turn on the fatty acid pumps.

Lastly, there is the question of BAT… Brown Adipose Tissue, which we now know that we actually do have as adults, but only if we expose ourselves to cool conditions now and again. BAT is fat tissue which burns fats to create body heat. (Babies have lots of it.) If you’re fat-adapted, you may be able to produce more heat from fats because your BAT is more capable of burning the stuff. Possibly. This part is well in the land of conjecture, at this point.

Brain tissue does not become fat-adapted; it insists on glucose. But your body does a great job of keeping the glucose for your brain if you don’t have very much.

To become fat-adapted, all you have to do is be running on mostly fat for a while. It doesn’t matter whether your carbs are so low that your body panics and creates ketones for your brains to run on… and I don’t think the muscle and other cells that are running on fats use the ketones, anyway. (I’m unsure about that.)


What he said… ^

Probably not much on the outside… But my interest is in burning less glycogen and more fat at higher heart rates. In general low heart rate activity (like walking) is predominantly fat burning whereas high heart rate (like sprinting) requires mostly glycogen. In the middle (say running a marathon) it’s a mix of the two. Since the body can store dramatically more energy in the form of fat than in glycogen, my goal would be to train my body to slide more towards the lipid side of the scale to make better use of the energy stores already on my body. The body simply can’t store enough glycogen to use it as a dominant energy source for 26 miles which is why many runners either “hit the wall” or get by with large quantities of sugar (Gatorade, gu etc)… If your gut can stand it.

The only way to really see where you are on that fat v. carb metabolism scale (your RQ) is by measuring exhaled carbon dioxide relative to inhaled oxygen.