Most of a Yaks' sweat glands are non-functioning, hence why they suffer in heat; they can't sweat.

As far as IM nutrition & training, I'd resist using these products every time you go out; unless you intend on running a marathon afterwards I guess. There's nothing stopping you from carrying some solid food of your own choice in a bento box, it doesn't have to be the on-course PB stuff. You'll also find something solid will helps your GI system too, rather than quaffing huge amounts of gel. The affect of salt loss is not as problematic as you might think. Read this: https://sportsscientists.com/...at-and-electrolytes/

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29 years and counting

Train with what you race with and race with what you train with.

As a general rule, the faster one goes, the more likely they will be using all liquids. The slower one goes the more solids your gut can handle.

I have found through testing during training, I can handle 350 cal's per hour on the bike at IM intensity. I'll take 3 salt capsules and one 24oz of liquid per hour while on the bike. If it's hotter, I'll cut back a bit on both the cals and the power. For 70.3, I'll cut back a bit on the cals because I'll be pushing a higher wattage on the bike. My run plan is to take in as much as I can while keeping my stomach happy, and just keep running. As for the salt on the run, my last 2 IM runs, I probably crunched 20 salt capsules in my teeth coming into the aid stations while spitting out the shells. Not a hint of a cramp while running.

All of this has taken multiple attempts to get right.

How did things work out in the 70.3s you've done? That should give you a pretty good indicator. You can get away with fewer calories on a 70.3 as obviously you're not out there so long, but equally the higher intensity on a 70.3 tends to mean there is less room for error.

My advice (I'm 6'1", 180lbs, heavy sweater, don't like the heat) is:
- You need to be replacing all the fluids you're sweating. Use your long rides and runs to try and figure out your sweat rate. I've done quite a few long rides and runs where I've had no solids, kept track of how much liquid I've taken on and have weighed myself before and after to work out my sweat rate (peeing messes up the data...). That gives you a rough guide, on the day itself simply making sure you're drinking enough to need to pee a few times during the day is a simple way of checking (and if your pee is dark yellow, you know you need more!)
- You need to start fuelling as soon as you can (i.e. in or straight out of T1) and keep up a steady intake of calories throughout the day. Little and often is best, dumping a load of calories on your stomach in one go is likely to lead to GI problems, particularly on a hot day
- How many calories you can absorb per hour is dependent on the individual, the conditions, and on how hard/fast you are going, but at IM intensity 250-350 seems to be a reasonable range that most people fall into. Experiment with this in training, preferably in similar conditions and intensity to what you'll be doing on race day.
- Solids vs liquids is largely a personal choice and also a factor of how long you're going to be out there. If you're going to be done in under 10 hours, then that's a reasonable time to go without solid food, and equally the speed/intensity you're going at is going to make solids hard to absorb. But if you're going to be out on course for 15-16 hours that's a very long time to go out without solids and the lower intensity means you shouldn't have an issue taking on bars, sandwiches, chips or whatever else you want.
- Personally I'm in the 11-12 hour range, have a fairly tolerant stomach, and get sick of the taste of energy drinks and gels after too long. I tend to have solids and mostly water on first three quarters of the bike (mix of bananas and bars). If it's a hot day I'll have electrolytes in the water. Towards the end of the bike I'll stop taking on solids as I'm prone to stitches on the run, and will switch to energy drink. I'll aim to do the first half of the run on energy drink. At some point if/when I'm flagging and need a psychological boost and a change I'll switch to gels.
- As always, listen to your body. If you've got a bit of sloshing in your stomach it means you're struggling to absorb what's in there, backing off a little and giving your stomach a chance to catch up is much better than pushing through until you're forced to stop.

I decided 9 mos. out to go with an all-liquid approach. It worked great, for ME (6' & 193# on race day....12:56:xx). I used the same approach on every long training ride and run.

325 cals/hr, all liquid, on the bike. I drank GE on the long runs, gels every 45 min. to mile 15....then coke - because that's what they have on IM courses. Avg. HR of 140 for the race.

I'm 53 and had no GI (or other) issues on race day.

Good luck.