How and When a Keto-Enhancing Diet can Help Triathletes

This post was prompted by Julia Belluz' excellent article on Vox entitled: "The keto diet, explained: Is eating a lot of fat really the best way to lose weight?"

First, I want to be clear that while I am on a keto-enhancing nutrition regimen, I prefer to avoid avoid fads and the word "diet", so instead I say I'm on "carb restriction".  (The title above is so Google will like me more.)

Though I have no need for weight loss, I eat this way for a different reason; to avoid "bonking".

When I started in triathlon a decade ago at age 52, I kept hitting a wall 60-90 minutes into my longer workouts. In triathlon, this wall is called the bonk.

I sought advice from coaches, doctors, fellow athletes, and online. I decided to try pretty much everything anyone suggested that didn't sound harmful.  At worst, I figured I'd just bonk again.

What I first learned is that bonking is most likely due to the exhaustion of stored glycogen, leading to a sharp drop in blood ("serum") glucose levels.  The standard advice was to consume simple carbs during long activities, especially things like gels.

Didn't work for me. I still bonked, even when I ramped up active carb intake to nauseating levels.  I also attacked the issue of "gastric distress", and while some products did better in my stomach than others, none did much for my bonking.

Then it was mentioned that moderate carb-loading 24-48 hours before endurance activities, though "old school", could help. Which for me meant eating more carbs all the time, due to my workout schedule. Tried it several times, and I still bonked.

Others suggested I was simply pushing too hard, or I had inefficient form.  I tried modifying both.  Going slower did help, but I had to go much slower, barely above a jogging pace.  No way I would ever call that "race pace".  Technique changes also helped, though while they make me slightly faster, they didn't affect my bonking; I was just a bit further down the road when I bonked.

I finally started doing my own investigation, starting with the fuel sources of endurance athletes (this article provides a brief overview). It turns out most endurance athletes get about 65% of their endurance muscle energy from carb metabolism (glycogen -> glucose) and the remaining 35% from fat metabolism (triglycerides-> fatty acids). This ratio can shift during activity, with fat dependency increasing with time to 50% or more.

But fatty acids can't be used by the brain or nervous system, so another fat metabolic path in the liver activates to generate "Ketone Bodies" when glucose becomes scarce.  Ketones can replace glucose nearly everywhere.

My working theory for my bonking wasn't just the exhaustion of stored glycogen, but also a simultaneous failure of both of my fat energy systems. While fatty acid metabolism and carb metabolism can work fine together, it is well documented that ketone production shuts down in the presence of glucose or carbs, even when the carbs were just eaten and not yet digested (the stomach sends "carbs coming!" signals).

Perhaps the main problem wasn't my glucose dropping during workouts (a normal effect), but rather my ketones failing to rise to meet demand.

To me, this meant I needed my glucose levels to taper more gradually, to give ketones more time to ramp up.  I also needed my base ketone production level to be a bit higher.  And, ideally, I'd like my peak ketone production rate to also increase.

I studied "ketone boosting", which required I gradually reduced my carb intake while increasing protein and fat to meet my calorie needs (no net calorie change in my diet).  It is important to note that I didn't even try to get to "zero" carbs: That's both impractical and potentially harmful (insert Atkins Diet horror stories here).

I simply banned all simple carbs: Potatoes, rice, and all milled grain (bread, pasta, etc.).  I could have all the dark green veggies I wanted.  I increased my egg intake for protein, and kept my meat consumption relatively low, averaging under an ounce per day.  My fat needs were met by vegetable fats and occasionally a little pork with breakfast (bacon or sausage).

It took several months for my digestion to get the message, but eventually my gut bacteria adapted to the lack of carbs in my meals. Which precisely matched the duration of my carb cravings. As the carb cravings faded, so did my bonking.

A small level of carb metabolism is needed to make fat metabolism more effective (faster and more efficient).  This meant I would still need a trickle of carbs during a race or long/hard workout, but no carbs before.  So I created my own electrolyte + simple carbs + caffeine race "gel" to meet those minimal needs with only abundant water needed otherwise.

With these changes in place, I was finally ready to train at higher levels.  I found I could comfortably handle an 8-minute mile pace, an 8:30 5K pace, a 9:00 10K pace, and a 9:30 half-marathon pace.  These were my "comfortable" limits, with relatively little emphasis on speed work. Still, they were fast enough to ensure PRs in my future races.

A year ago, at age 60, I did my first 70.3 mile "half-Ironman" triathlon. While I had lots and lots of problems during the 7+ hours of that race, bonking wasn't one of them.

I have found no studies or research covering my specific experience, but the logic seems unassailable.  So I can contribute only one anecdotal datum, to be filed under: "It works for me!"

Since my half-IM I've been experimenting with how much of what I can eat how soon before endurance exercise.  I've found I don't need to be quite as strict as I was before.  First, absolutely no carbs in the 4 hours prior to any workout of 60 minutes or more (instead of a near-total ban).  No meals in the 3 hours prior to a hard workout (mainly to keep my GI tract happy).

Given my exercise schedule, these restrictions still interfered with my eating habits.  So I next tried daily "light" fasting, where my biggest meal of the day was immediately after my last workout (and well before bed).  During the day I could have tiny snacks of nuts as desired, and some fruit (bananas, dried fruit),  I could have a glass of OJ on mornings without a workout.

On days with one or no workouts, I could eat pretty much anything I wanted, so long as I kept my total carbs restricted and met the pre-workout eating exclusions.  I also found that simple carbs were the main issues, allowing me to occasionally have super-dense carbs such as tortillas and bagels.

To make things practical, and to limit temptation, I've banished all simple carbs from my house, so my carb restriction gets attention only during shopping.  This lets me eat anything in the house, whenever desired.  For the few meals I eat away from home each week, I can have whatever everyone else is having.

A rather long multi-year path to what turned out to be a relatively straightforward solution.  My continuing investigation indicates my diet may also be a good aging diet, potentially reducing (or at least not aggravating) the risk and/or severity of  several age-related conditions and illnesses.