Hi, all. I'm trying to understand how our bodies handle "dual fuel" (carbs vs fat) intake during endurance activities (in my case, mountaineering and search-and-rescue).

One thing I love about low-carb is that I'm already past what marathoners call "the Wall." My glycogen's ALREADY depleted; I may not be quite as fast at first as someone fueled on carbs, but I have nearly boundless reserves of fuel (body fat) and never "bonk."

But when climbing or helping with a multi-day search, it's hard to avoid carbohydrates. That's what the sheriff's department gives us! Of course, we're working hard enough to burn them almost immediately. But what happens, physiologically, when we eat a couple hundred grams of carb during a 12-hour endurance activity? Or when we eat a couple hundred grams of carb at the end of one long day and right before we launch into another one?

My HOPE is that once our bodies know how to make energy from fat, they can return to that mode quickly, as soon as any carbs are gone. But my FEAR is that once my body has cranked out insulin to digest carbs, I'll be right back where I started (metabolically), and will have to undergo 2-3 days of weakness and "Atkins flu" before I get back to that powerful state of lipolysis.

So my Q for discussion is: does anyone know of any research on how well long-time low-carbers switch metabolic modes during high activity? Can we temporarily add substantial carbs without sacrificing our wonderful efficiency at buring fats for fuel a few hours later?

Thanks!

I can only tell you how my body reacts to that scenario.

When I first started my keto diet over a year ago it took me weeks to really feel the benefits of a low carb diet. I had an Atkins flu that lasted for 3 days, it was horrible... I honestly did not have enough energy to walk, it was brutal. I spent that time in bed sleeping as best I could.

About 3 months in to my diet I took a 1 week break for a local Greek Food Festival, so many carbs. After this it took me about 4-5 days to feel at my peak strength again and my "atkins flu" was only one afternoon that I had to leave work early because I was tired (still significant mind you, but much, much less).

Since those times I have taken some breaks from the diet and then hop back on. I took a month off thanksgiving/christmas, then went back on for a few months (I don't recall any Atkins flu). Then I ended up eating carbs for a few months in a row.

I went back on my keto diet about 2 weeks ago. I had no problems transitioning to work (I'm a stone mason so I am asking as much from my body as you are from yours). There wasn't a day, or even a few hours where I felt as though my body was deprived of energy. Thursday (a little over a week in) I shoveled 32 tons of gravel, something I would only have the energy for if I was in full-blown ketosis (which is supposed to take 4-6 weeks).

I imagine that everyone's body's would likely have a different reaction... But mine seems to (after transitioning from carbs to keto several times now) have absolutely no problems at all.

Now, your question seemed to be a little more directed towards say doing something physically intensive that would require say, 2k calories; eating 2k carb calories and going back to fat. I have never tried this as I have much more energy available (not just sustained, but also that) in ketosis.

***edit
What about taking Pemmican for your search and rescue stuff?

Great info, euphoricme; thanks! My experience is similar to yours: I went somewhat off the diet on a vacation to Mexico, and was able to come back much more quickly than I went on. Ditto during a family event last month. What I don't have a good sense of, though, is HOW quickly the recovery now takes: since my usual life is pretty sedentary, I don't know if my return to efficient fat-burning during extended exercise would be an hour or two or a day or two, which obviously makes a big difference in the backcountry.

Of course, the best way to find out will be through experimentation. (Still hoping someone can find a study on this issue -- Google isn't working for me, for once!)

As for pemmican: agreed. I already carry macademia nuts and well-cooked bacon in bags (which if combined might be labeled "Atkins trail mix"), and a vial of olive oil to plain drink. I should look into actual pemmican recipes.

Thanks again!

If you do find any information on that send me a PM or post it or something. I to (out of general curiosity) have wondered "if you are going to burn 200 calories in ketosis - eating 200 carb calories to do that - will you be back in ketosis immediately afterwards?"

Just a thought, but I would think if you're simply eating a small amount of carbs before and immed after the workout, you should be fine. So long as you're basically filling the immediate need for the energy as opposed to refuelling glycogen stores, I would think your body would still be able to be in ketosis quite quickly.

I still haven't found my balance yet in trying to get back into running while fighting an injury and doing regular interval training.

Requin: I agree, with regard to a small amount of carbs. I'm more concerned about meals with 40-50% carbs like most MREs (military rations), cafeteria food, etc. If I hike/climb all day, bivy in the field with a MRE for dinner and another for breakfast, then resume another high-energy day, will I be off lipolysis and in danger of hitting the wall, or will I take it in stride and go back to fat burning once those carbocalories are gone?

Granted, I did Canadian boot camp, and the cafeteria had plenty of low carb options. MRE's a pain in the arse, but if you're not overseas, but I was able to survive by keeping nuts, jerky, and other lowcarb-room temp stable foods handy in the field, and eating less of the high carb stuff.

Far as I understand it, ketosis occurs after the carbs are used- including the glycogen stores. I would think that while one starting a low carb diet tends to take a few days to get into ketosis, one could speed up their arrival in ketosis by simply doing some super intense carb burning exercising while still eating low car.

It would be a matter of finding your own personal balance. Trial and error for a while unfortunately.

I don't have research for you, but I can share with you what works for my body. When I'm doing intense exercise for several hours without stopping (hiking to mountain peak, etc.) I run completely out of energy a few hours into it if I don't eat some carbs. My theory is that my body can't convert fat to fuel fast enough to keep up. But at that point I eat carbs, have energy again, and keep going. After the hike, I go back to doing my low carb with no problem whatsoever, as in no induction flu, etc.

That doesn't exactly answer your question, since you mentioned you have gotten past the "wall", which I never have been able to do without taking a rest. But in my opinion, if you're burning the carbs for fuel immediately, that makes all the difference.

But as they say, your mileage may vary.