Eight weeks ago, as I was just starting to get my running volume back up post Achilles tendon injury, I began planning out what my build towards a 100 mile ultramarathon would look like. I had already committed to keeping cycling more of a structured input through the full build, but I also decided to make one other change. I decided to change my nutrition approach for a full training cycle by moving from a low carbohydrate diet to a moderate to high carbohydrate diet approach. I am not committing to anything permanent. Maybe curiosity has gotten the best of me, but never attempting a 100 mile ultra on a moderate to high carbohydrate approach, and perhaps watching endurance sports challenge the limits with respect to in race fueling targets, has motivated me to give it a try. I will use this experience, along with my prior 14 years of low carbohydrate to decide how to use this, or some combination of both in the future. Ultimately, when I initially switched to a low carb approach in 2011, my mindset was, if it doesn’t work I can always go back. So, here we go again. Worst case scenario is it doesn’t work for me and I go back to what I have proven can produce my fastest 100 miler to date, 11 hrs 19 min 13 sec.
I have been doing my best to take note of what I have noticed in both training, recovery, and general day to day life with this switch, so I can share my experience. I expect the transition to have tradeoffs. Things I would find preferable, and others that are less desirable. I tend to view most changes to have this balance. The more interesting conclusion for me is whether all the changes, positive and negative, yield a net positive or negative. This will at least partly be individual. What I prioritize may differ from someone else, which can add more or less weight to how much a specific change impacts the final assessment. For me, the biggest three variables I am considering include; performance at ultra distance events with a main focus on runnable 100 milers, ease of adherence and general health, and how it impacts everything I do outside of training and racing in my work and social life. These three things stand out to me as the highest value points.
Performance has a lot of variables within it when building up for a 100 mile ultramarathon. There is some combination of easy/recovery running, base running, long intervals, short intervals, long runs, and ultra specific long runs. It hasn’t escaped me that improved performance within one of these training inputs does not necessarily translate to better performance on race day, especially when the target event is as long as a 100 miler. The best example of this may be short intervals near VO2max compared to the relatively low intensity effort required for a quality 100 mile performance. It is very possible I exceed my low carb performance data points for short intervals, but fail to perform as well or better at the 100 mile distance. I generally assume faster paces at the higher end of the aerobic intensity spectrum gives a runner advantages on race day, even at the 100 mile distance, but it can come with a cost if I am unable to fuel the metabolic demands required on race day. At the end of the day, this approach necessitates I at least double my in race fueling totals of the past. If I end up unable to do it, I could end up worse off on race day, despite having faster paces at the top end of the aerobic intensity spectrum in training.
Adherence, health, and quality of life are things that I also value. I don’t want to take on a dietary approach that I cannot sustain to a meaningful enough degree that it can be thoroughly utilized. This just means I have to enjoy eating this way enough to feel like it isn’t a massive chore. I find this to be the most interesting thing about dietary inputs as a whole, regardless of goals. I don’t really care how two dietary approaches stack up against each other with respect to population level health outcomes, other than giving reasonable starting points to consider, if the individual is unable to adhere to it.. I am more interested in how easily a person can adhere without feeling like they are constantly restricting or avoiding what they would rather be eating. This isn’t to say one should completely ignore health outcomes, as short term enjoyment or adherence that causes long term problems just sets the future self up for failure. This is why health markers will also play a role. I plan to get blood testing done and take a closer look inside to see if there are any reasons to doubt this approach long term, and potentially guide how I make adjustments within this approach.
I see myself as a runner, and running is a huge part of who I am, but it isn’t everything. I also have a great life outside of my own training and racing. I love to coach others on their running journey, whether just getting started or life long runners looking to optimize. I love creating content, whether it be long forum podcasts/posting, or short form social media. I also enjoy feeling stable in how I engage socially to fully maximize my own experience, along with the experience others have when socializing with me. I believe dietary protocols can impact these things, so to the degree I can, I want to pay attention to this as well.
Now I want to jump into some things I have noticed with this approach over the first eight weeks. It has taken some time to adjust, which I expected, but I believe I am getting closer to a set up I can thoroughly test.
The first few weeks were really interesting. When low carb, I usually found it preferable to eat fewer meals/snacks but have higher caloric intakes per meal/snack. Almost immediately, I found this to be a bad path when carbohydrates make up the primary macronutrient input. Larger meals/snacks feel like a rollercoaster ride I do not want to be on. Far too much variance in highs and lows than I prefer to tolerate. It also was really hard to feel comfortable when fiber rich carbohydrates made up a meaningful amount of my carb sources. I would fill up really quickly without getting to my energy intake goals. I made two main adjustments to help combat this, which have felt pretty good so far. First, I increased the frequency of meals/snacks so I could take in smaller amounts each time. Second, I greatly reduced the amount of fiber rich carb sources. This is likely a unique need for my lifestyle. If I was more sedentary, focusing on fiber rich carbohydrate sources may feel fine. When I start hitting 20+ hours per week between running, biking, strength, and accessory work my energy demands double or triple. This makes fiber rich carbohydrates, like fruits and vegetables, land at such high overall fiber intake, digestion feels terrible and I end up using the bathroom way more than I prefer to tolerate. On top of that, I just generally don’t feel great in that framework. I ended up focusing on more water based fruit sources like melons and grapes, and lower fiber starches like sourdough bread, rice, honey, and sports products when training.
Performance has been a fun metric to track so far. Here are a few things I have noticed. Warming up feels much quicker. The best way to describe this is it is a shorter ramp to the paces I would expect at a given intensity. Simply put, I am faster at the onset of a run. A greater urge to push harder during lower intensity training sessions has also been noticeable. When out for an easy/recovery run, or a base run, I find I have an increased amount of moments where I intuitively want to go faster. Faster paces at the higher end of the aerobic intensity spectrum has been noticeable. I did much of my early interval work for this block on the bike, but since fully returning to running, the sessions I have done have produced faster paces than I have been seeing the prior few years, and on par with the fastest I experienced during my time low carbohydrate. My long runs are just getting built out, and I have not done any ultra specific long runs, spare one weekend of back to back long runs, so that is to be determined for the most part.
I generally find these changes to be net positive so far. It does require a different mindset. If I am out for an easy run, I don’t necessarily want to get carried away, or motivated to go faster than necessary in the early stages of a warm up or longer training session. I see this as mostly an adjustment I need to make with my own perceived effort under current circumstances. My intuition is that finding the right balance is a bit more sensitive. When low carb, I found perceived effort to be more durable at a given intensity. I could basically put it on autopilot. With moderate/high carb, I do sense more variance with how a given pace feels. So far, this has all netted improved performance metrics, but it is definitely a different experience that I have to navigate differently. Here are a couple examples. If I am on a 90 minute run, I may feel the perceived effort shift more abruptly at a given pace. When intensity is relatively low, I can typically throw in a short surge if things begin to feel sluggish and things normalize. In a longer session of 2 hours or more, I usually take this as a sign to take some carbohydrate and it has normalized pretty soon after. Logistically, this feels more burdensome, but hasn’t risen to the degree of intolerable. I will be curious how this plays out with the ultra long runs, and ultimately races. For more direct performance, I had one session that really stood out. I use a hill here in Austin for short interval hill repeats. It is approximately a quarter mile long and just a shade under 10% incline. I have done 184 reps on this hill since moving to Austin in 2022. I recently did an interval session of 8 reps with an easy jog down. I typically don’t look at splits for this session. I just dial in the effort I am looking for from the session and assess the data afterwards. My recent session produced my eight fastest splits on this hill to date, with the fastest being four seconds quicker than my previous best. I anticipated this to improve, but to the degree it did was a surprise.
Adherence, quality of life, and health is going to be a longer term assessment for the most part. I am simply too early into the approach to come to any bold conclusions. So far, adherence hasn’t been an issue after making the above adjustments to sources. I haven’t found that I feel like I am missing out, or working too hard to realistically make this strategy something I can tolerate. Quality of life is going to be unique to me here, but I would describe it as similar to performance so far. It is a harder balance to strike with respect to feeling how I like to feel, but when I strike it right, I feel as motivated and excited about what I am doing as I ever have felt at the pinnacle of my experience with low carbohydrate. Health is something I don’t really have any clear data on yet. I will get closer to this metric with some blood work and will share it when available. Ideally, I’d like to get the first draw at about 12 weeks into the approach. What I can say is I feel a bit more fresh first thing in the morning, my caffeine intake has gone down (currently 100-150mg/day, and my total sleep duration has gone down by 30-60 minutes per day without any noticeable negatives with respect to loss of sleep.
Other life focuses have been fairly similar to the phases I felt my best on low carb, or slightly better than average. I think this is more of a time will tell metric, as these sort of things are not entirely dietarily related, and it is very possible the relatively short duration of this experience has lined up with other positive influences. In life, I generally find that I am most happy when I have a clear organized purpose in my training, variety in the types of problem solving with my coaching clients, and a lengthier list of interesting podcast topics I want to explore. Those are all trending well at the moment, so it is worth noting those variables are likely powerful.
To conclude, I just want to share that I will continue to assess the above and report on any new findings and changes, but also give you a glimpse at what a typical week day structure has looked like for me.
Sample Day:
4:30-5am:
wake up
coffee/tea with ½ pack of LMNT chocolate, honey, 2 capsules of CurraNZ
AM Training: ~90 minute run (easy, base, or intervals), either solo or with Rogue Running
8-9am:
smoothie: 1 scoop of ProBio, berries, honey, milk
sourdough bread, salmon, olive oil, salt, water
delatG Ketone shot (interval days)
9am-11am:
emails, calls, coaching programs
11am:
rice, ground beef, salsa
11:15-3pm:
podcast recording/editing, social posting, emails, calls, coaching programming
sipping on ⅔ - 1 liter of water
3pm-5pm:
grapes, melon, kefir, LMNT Sparkle, water
mobility, stretching, massage, strength, and/or accessory work
1 hour bike, or 45 minute run
5-6pm:
random snack (fruit, smoothie, energy bar)
finish any lingering work or calls
6-8:30pm:
potatoes, scrambled eggs with cheese, sourdough bread, salt, water
relax and hang out with Nicole
8:30-9:00pm:
bedtime
Very interesting. In your sample day, am I reading right that you aren’t fueling at all during workouts? Gels, drinks, etc.? I generally think of high carb as 90g+ carbs per hour during workouts. Looks like you are maybe getting 10-50g carbs from honey/fruit before workouts but nothing during?
Zach, super interesting that after 14 years of low-carb you’re experimenting with high-carb again — especially in the context of ultramarathon prep. What hit me most was your point about adherence + quality of life. I had the same struggle early on (low point: two straight weeks living on “keto cookies”… never again).
What’s fascinating is that research shows a pretty sharp split: for folks with overweight and insulin resistance, low-carb tends to lower triglycerides and keep LDL stable. But in lean, highly active bodies, the opposite often happens — LDL skyrockets, even though triglycerides drop . It’s called the Lipid Energy Model, and it basically explains why BMI <25 correlates with those big LDL jumps .
Your observation about feeling “faster out of the gate” on carbs almost sounds like the flip side: your muscle metabolism is shifting from a fat-flywheel into carb-boost mode.
I just wrote about this exact divergence (“Why Low-Carb ‘Fails’ Lean People but Fixes Overweight Metabolism”) — digging into the science and some of my own fails. Might be useful for your readers who’ve seen wildly different outcomes on the same diet:
👉 https://leareset.substack.com/p/why-low-carb-fails-lean-people-but