Exercise: fuelling a marathon swim

(Mimi Munro) #1

Hi everyone,
I’m on my 3rd month of keto - all going pretty… …swimmingly! I’ve just signed up for a 10K open water swim. This will take me roughly 3.5 hours of continuous freestyle.
I have only been taking 20g dextrose right before my sprint training sessions - working repeatedly at max capacity. All other sessions I have been fuelling with bullet proof coffee. My times are down a little, but nothing that causes me concern.
I want to practice fuelling during my longer training swims - 6k or more so I can settle on a protocol that will work on race day.
Thoughts or tips would be hugely welcome! Liquids preferably: chewing and Swimming is not my forte!
Thanks everyone

(Saleem) #2

Hey… have you tried Ucan. It worked for me.

(Mimi Munro) #3

I live in Singapore and it costs an eye watering amount of money… I’ll see if I can find it a bit cheaper somewhere! Thanks!

(Saleem) #4

What about betahydroxyburate supplements like keto os.

They are all expensive…

(Jacob Wagner) #5

Have you tried just taking MCT oil?

–Jacob

(Tim W) #6

I second the MCT oil beforehand OR just do it fasted. I think it might be possible if you have trained distance in the fasted state “enough”. What is enough, you’ll have to explore that and determine if, based on your fasted endurance training if you are ready.

I did a 50K on nothing more than a bottle of water (had nothing to eat since 8PM the night before). The run took 5 hours and 15 min.

I replicated this a few weeks later, paced a 5 hour marathon group with a few sips of water (it was cold and rainy so no hydration needed).

On the more extreme end, I ran 12 miles on day six of a total fast, it was slow, it was painful, it took a hell of a long time, but I made it and felt GREAT!

I was “about” 12-15% body fat (it can be hard to tell true body fat without really fancy tests, I use a single point caliper test and tape measurements), at 165ish (up or down a few based on beer consumption) at 5’11" so I’m not “running” on tons of stored body fat, though there is still plenty to “run on” until you get down to 3-4%.

Lastly, have you read Art and Science of Low Carb Performance? Lots of good intel there.

Good luck in your training and the big swim, sounds like a hell of a good time!

(ianrobo) #7

Why do you need anything ? If doing long endurance sports you should be in your fat burning zone anyway and thus no need to fuel during the event ?

In fact from my experiences as I have documented int he cycling forum I really do believe you need minima if none supplements and especially if not in an explosive event.

(Jacob Wagner) #8

That depends on how much body fat you have. You can only use 31.5 kCal per pound of body fat per day. If you are doing an endurance swim (run/ride/etc.) then your overall energy need may exceed that.

–Jacob

(Tim W) #9

I’ve seen this number before and, like many/most things dealing with fitness/diet/nutrition, I’d argue that it’s probably a “rough estimate” and not a hard and fast “rule” for everyone. In my opinion, if you can train fasted long enough and develop the “ability” there may be no upper limit/higher than most would account for, to your endurance on fat stores.

Case in point, I ran a 50K without consuming anything. My garmin says I burned 2382 calories, sure that number is likely to be off but it’s a good place to start. Since I was “about” 14% BF, we’ll multiply that by the 31.5, which gives us 441. I’m assuming we multiply the 441 by 1000 for a total caloric availability of 4,410, is that tracking? After my run I walked to the mall to meet up with my wife, using another 230 cals so I had used up 2,612 cals, in the covering of 34 total miles. That means I should have had at least another 1,798 cals left. That’s a significant number of cals left over, even for 14% BF and over 6 hours of moving.

Bottom line, I think our fasted endurance ability/capability is greater than most would assume.

(ianrobo) #10

Totally with you on that. If you check the pro cyclists most have body fat < 10% and most will train on no feed during it, the only reason they do on races is for the extra power carbs give you. Remember unless you have less than 5% bf which is skeletal ! Then we all have more than enough to compete in long distance events.

(ianrobo) #11

Should note @Jacob4Jesus that is it not a fact 10% body fat will give you min 20k cal of energy and that is more than enough ?

Take my ride on Saturday - 100 miles, average hr Zone 3 average power high zone 3 so how come I needed no food ??

(Mimi Munro) #12

Thanks for your input! I’ve got Science of Low Carb performance on order from amazon - looking forward to a good read!
I’ve also ordered mct powder from phat fibre so I’m going to stick that in my drinks bottle and give it a go.
Did a pretty good job of a 4K race yesterday. Just on a bulletproof. Feel great today, but that’s probably because I lunched on pate smeared on pork scratchings afterwards. The waitress at the restaurant thought there was something wrong with me when I asked for extra pig fat to go with the pig fat.

(Mimi Munro) #13

I do agree, but I feel like I need a bit of juice to get me through the first 1000m. I’ll swim that at threshold pace to get a good position. Then I’ll need to sprint for overtaking going around the buoys.
If I was just cruising at 120bpm then I wouldn’t need anything. I’m also quite new to
Keto and this is my first time at 10k too. Certainly there’s an element of dumbos feather - I reckon mct is the way forward for me…

(Mimi Munro) #14

I’m too stupid to work this thing - I’ve written you a reply and it’s gone to the wrong bit!

(ianrobo) #15

I do think periodising carbing works for sure for a ride/swim or run but if you are going at tempo then I do think during it I see no reason to top up

(Jacob Wagner) #16

I don’t know it well enough to defend it, I just know what I have heard from @richard on the podcast.

However, both of you seemed to base your calculation on the % of body fat without accounting for what the total weight is, which is important. A person with 10% body fat who weighs 200 lb can muster twice the energy from body fat as someone with 10% body fat at 100 lb.

For example, I weigh about 360 and have an estamated body fat of ~45%. That gives me 162 lb of fat mass. So, by that calculation I should be able to produce 162 * 31.5 kCal per day for a total of 5102. Adding to that maybe 2200 kCal from glycogen and I should be able to burn somewhere near 7300 kCal durig an endurance event. If you exceed that then your body starts to use organ tissue for energy (which is perfectly safe in the short term and will come back in a day or two after the event). Most of you are not going to have as much as I do.

You didn’t say if you “carbed up” before your 50k. If you did then your 2382 kCal probably came mostly from glycogen stores.

That would be my guess as well. But even if the number can vary, there is still a limit.

Does anyone know the science behind the 31.5 number?

–Jacob

(Jacob Wagner) #17

After my last post I went looking and found the study where the 31.5 comes from:

–Jacob

(Richard Morris) #18

It was determined by extrapolating from the data from Ancel Keys’ (yes THAT Ancel Keys) Minnesota Starvation experiment, a maximum rate that body fat can release energy. The math however is pretty straightforward. But I’m not convinced about the underlying data, it is after all from Ancel Keys. Unfortunately we can’t ask Seymore Alpert, he died a few years ago from complications of surgery. And as far as I can tell no-one else has attempted to improve on his work.

#19

For @infromsea, 165 pounds multiplied by 14% bodyfat = 23.1 pounds of fat

31.5kCals per pound of bodyfat per day multiplied by 23.1 pounds = 727.65kCals per day

Likely 2000 kCals of glycogen can be added to that number = 2,728 kCals per day

I hypothesize that the number of 31.5kCals/pound per day is very rough. For instance the body likely doesn’t care so much about a 24-hour period. There likely is a limit on energy that the body can use from a pound of bodyfat, but the relevant time period is likely something more like an hour than a day.

You came very close to your daily maximum, but surely would have had the energy to walk around for the day (or at least breath) and continued to get energy from fat.

Perhaps eating fat can permit more energy to be burned per hour of exercise??? Perhaps eating carbs can give more energy (which is pretty well considered true by top athletes).

In any event, DEPENDING ON EXERTION LEVEL, there is a requirement for fuel other than bodyfat because one can burn only so much bodyfat in a given time period. However, if I were training for swimming (when it is hard to eat), I’d likely just try to increase my fat burning ability so that there was a lot of fat/minute that can be burned for fuel, e.g. 1.6g/minute, and limit my exertion to that fat-burning ability.

I would love to hear a podcast on this issue even if there is not a lot of research as there must be many trainers out there with experience.

(ianrobo) #20

so I am approx 182 pounds and apron 15% fat so that is 27.3lbs of fat. So according this I can only burn 859kcal a day … yet I cycled 100 miles, approx 5000 kcal burnt and felt OK after it and could have done much more if needed.

Maybe I am not getting this but surely the figures on this rough estimate are way wrong ?