The FastDay Forum

OK, I burn some 80% of my exercise calories doing cycling. I'm getting into running -- but for now, about 10% exercise calories come from that. In little more than 3 weeks, I'll be doing a 100 mile ride (160 km?) in a 5 hour time span. I'm doubting that fasting two days before the big ride will adversely affect me. Any thoughts?
Incidentally, my first fast day included about 1000 calories of food in and 1000 calories burned during my cycling sessions... and I did notice some modest performance loss on my speed.
TDEE is between 3000 and 3500 depending on which among three sources I believe to be correct.
I'm trying for 5-10 lbs lighter at the end of August -- which makes it easier to pack an extra 5-10 lbs of water on my bike and backpack.

Do you regularly do 100 miles of cycling or is this relatively unusual? If it's the former, then how do you usually feel? How much do you feel you have to take on board during the ride? In your current training rides, do you feel like you might hit a wall sooner on the day after a fast?

2 days before? So you are fasting Thursday and riding Saturday or Sunday? I'd make sure that you've got 2 eating days before the 5 hour cycle. If it means skipping a fast day that week then skip it.

100 miles in 5 hours is certainly do-able but a 20mph average for that long is a challenge so I'd make sure, especially if this is your first one, that you don't jeopardise enjoying it for the sake of a fast.

Out of my league, mate, so I can't really help. You must be fit to average 20mph and regularly ride 80 miles a week so must be adapted to fat-burning, in which case fasting just before will not make much difference (although I would not bother myself). I have done 30 mile rides on a fast day at 17mph with just a coffee inside me and nothing on the bike but would need to feed on a much longer ride or go a fair bit slower. Are you aware of Peter Attia on the net? He can cycle 6 hilly hours on minimum fuel on the basis of being in ketosis and burning fat almost exclusively - maybe lots of cyclists/triathletes are in this state nowadays - the only downside seems to be in ultimate performance is compromised without some carbohydrate assistance.
Anyway, good luck in your endeavours, let us know how you get on!

Applespider: I've done it 6 or 7 times before. My longest ride this year is about 65 miles -- and I'm going to do at least that much tomorrow. Since I fasted (at around 1000 calories) yesterday, I'll get an early look at what, if any, impact the fast will have. My usual fix for low energy after 50 miles is to eat 2-3 100 calorie 'gels', which are just a syrupy mix of sugars squeezed from a tube. Also, I'm going to carry Gatorade sugary drinks (48 oz.) in addition to 70 oz. of regular water.
CreakyPete: I have only heard Attia's scholarly speech ( http://www.ted.com/talks/peter_attia_wh ... betes.html ) and I know nothing of his athletics. 'll have to check out more Peter Attia... I'm sure I've reached the ketosis point on several rides, but I sense that my cycling speed drops about 20-30% when exclusive fat burning takes place.

Hey Faster, how did your test ride go?

Interested because my username is the speed in KPH I'd like to get up to this time next year!

There seems to be a lot of variation in what people need to keep themselves going. I was on a low carb diet when I joined our local club, so gels just weren't an option. When I realised how punishing the club runs were I had a bowl of porridge 2-3 hours before I went out. Not a scrap of difference!

I don't seem to get so tired I need to eat on long runs, or to feel as if my energy has dropped - but then I haven't ridden as far as you guys - furthest this year is 70k - 45 miles with only two short 5 min stops. What I have noticed is slowing down on hills - I can go from a steady 32kph on the flat to 6kph on a hill - any slower and I would fall off - and I have done! So my average speed is under 20kph and that's after spending €1000 on a road bike. So I figure if I can lose about a stone that's got to help on the hills!

I will chase up this Peter Attia chap. Maybe I am a fat burner because of the low carb.

How did your spin go Faster?

Twentyfive. If you are going any farther than 30 (~ 50km) miles on a ride, you absolutely need to refuel with a sugary drink or a gel (even if on a low-carb diet). The blood-sugar developed by your porridge will last you about an hour, and drop off quite quickly after that. Yes, you will be burning fat (and some muscle) to make up the difference -- but you will really need about 100 calories per half hour to continue your efforts.
I recommend that you discontinue the carb consumption some 45 minutes before the end of your ride.