Training for endurance -- Fat is where it's at

I've read a ton of resources about endurance training and the until recently most I've been able to find about fat metabolism has been that studies have drawn conflicting conclusions. In his definitive work on endurance running, "The Lore of Running" Tim Noakes discussed Ironman distance racing as a 'Metabolic impossibility', noting that Mark Allen's 2:40 record IM-marathon time required him to burn fat at a 50% higher rate than observed in 'national champion' athletes. What has been discovered more recently is that the changes necessary to stimulate/train the body to increase fat-utilization require a month or more to actuate (explaining why studies that varied diet and training protocols for a week or less found no effect).

What is certain but rarely discussed is that the body stores intra-muscular triglycerides (i.e. fat stores) in much the same manner as we store glycogen. Research suggests that these IMTG stores can exceed glycogen stores and can be drawn on at moderately high exercise intensity (70% of VO2-max), so an athlete of moderated size who may have glycogen stores of 1500Kcal could also develop IMTG stores of 2500 Kcal or more.

Details and some references

The protocol that is said to help both increasing storage of IMTG and improving ability to metabolize adipose fats in training involves adopting a higher-fat diet, as well as focusing on longer distance/duration training. Triendurance.com reports finding that 2 hours/day training sessions on alternating days work substantially better at teaching the body to metabolize fat than daily hour-long sessions. Mark Twight, a highly accomplished high-altitude mountaineer and training guru discusses the same effect but also makes the important point that burning carbs is always acidifying the system, which fat-metabolism doesn't do. -- Raising body pH is a significant source of training stress, In order to buffer acidity developed in exercise, the body draws on reserves of iron and calcuim. Dietary and training acidification is discussed extensively in Joe Friel's The Paleo Diet for Athletes. With thanks to teammate Adam Brown, here's Mark Allen's words on base-phase training (which he's also called the 'patience phase').

How To Do It: longer training sessions and increased intake of (healthy) fat

1: One big piece of this is going to happen naturally for anyone training for iron or half-iron distances, that is training sessions of 2 hours or longer or multiple sessions per day require the body to burn fat and we naturally learn how to spare muscle glycogen reserves and to parcel them out over the course of the day. As you might expect, teaching the body to utilize more fat at higher output rates requires that we train at those rates. We're targetting 70% of max HR output, meaning that we need to exercise discipline and avoid pushing up into higher output for our long rides / training sessions.

2: The research suggests we don't get the full benefit until we also change up the fueling plan to increase the percentage of fat intake. This season, I'm doing just that, I've moved from a diet that was very low in fat and big on complex carbs coupled with simple carbs for training and recovery to increasing my intake of fats to about 30-35% of overall intake. Particularly, I'm using hemp-seed and flax-seed oils as well as increasing my fish intake some to keep the Omega-3:Omega-6 ratios in proper balance. (These, by the way are all highly anti-inflamatory which will help with post-training recovery). A 40:30:30 carb/protein/fat diet ratio is a good target

To be sure, training itself still requires carb intake -- "Fat burns in a flame of carbohydrates". So we're going to be taking in 200-250 calories per hour on long training days. (Note: even at moderate 15-16mph pace, we're using 600 or more calories per hour so at steady state we're getting 60% or more of our output from burning fat).

Longer Distances, Durations

While half and full iron distance races are surely long, when you look at alpine mountaineering or Ultra-running, the distances and durations are far longer with 100 mile foot races taking 24 hours or more to complete and mountaineering routes running to a week or more. Ultra distance runners, including a seemingly high proportion of the winners are eating the likes of nut-butter sandwiches, pizza and ice cream during races of 100 miles/24hours or more. Ultra-runners recommend incorporating 10% or so of their race-day calories from protein, Scott Jurek writes that while the science dictates against substantial fat intake during exercise, he finds he needs it for relief from the monotony of pure carbs.

On long training days I believe you do best to approach training with as much an eye to the next day's recovery as to today's performance. I try to get a jump-start on recovery by backing off the pace near the end of the day and starting to take in more protein and carbs.

In climbing / alpine mountaineering we find it best to start the day with someting very like a recommended pre-race breakfast, e.g. some carbs with a healthy dose of proteins and fat, after which I will typically fuel with gels for a few hours but this won't sustain for the whole day and I will switch to energy bars or a sandwich, trying to time these for easier sections of the climbing to allow for digestion. Because there's another day to follow, my nutrition plan incorporates anticipating as much recovery-nutrition into the day as possible because there's another long day to follow the one in progress.