Gut issues can manifest very quickly if you go past what your stomach can handle, particularly if exacerbated by heat, dehydration, race day stress, etc. For that reason I’d take a different angle on nutrition to some of what’s been suggested above. I would work out how many calories you think you need, including a suitable buffer, and use that as your target. You might be able to handle 100 or even 120g/hour, but if you don’t need that much why put that extra load on the body and take the risk of giving yourself problems?
The way I approach it is:
- Estimate total calorie consumption for the event. Swim is a bit of a guesstimate but if you have a PM for the bike and a running watch that is properly calibrated with your weight and HR zones you should be able to get a reasonably accurate number. Let’s say it’s 1000 calories/hour for a 5 hour finish time = 5000 calories
- Estimate how many of those calories come from carbs. E.g. if half your calories come from fat burning then you’re burning 2500 carbs
- Assuming you’ve carb loaded reasonably well you should have glycogen stores of ~2500 calories in your body at the start line
- If all those estimates are spot on, and you wanted to cross the line just as you emptied the tank, you could do the race on water alone! Clearly that’s a terrible idea, you don’t want to be totally emptying the tank for both performance and recovery reasons, and your calculations are likely to be off somewhere. So let’s add on 1000-1500 calories to give you a decent buffer, that’s 2-300 per hour or 50-75g carbs/hours. That should be plenty enough to allow for any wrong assumptions (e.g. if fat only contributes 40% of your calories) and allow you to finish with some reserves.
Calculation will be different for everybody depending on weight, power, estimated finish time, etc. But a 70.3 isn’t actually that long an event, and I suspect very few people actually need to be taking on 100g carbs/hour or more. Nate might be at an extreme end of the spectrum as a heavy guy with a high FTP who will therefore burn through a lot more calories. He’s also somebody who has a lot of experience taking on very high amounts of carbs while racing and knows he can handle it (though I do think there is often a big difference between what you can handle on the bike and what you can handle on the run), so for him it may be pretty low risk taking on that much.
If the race is something like IM, Leadville or Dirty Kanza and you’re going to be out there for 8, 9, 10+ hours, then it’s a very different proposition. Those races are long enough that your glycogen stores need to be eked out much more carefully, which means you need to be much closer to replacing all the carbs you’re burning during the race.