Fueling for Long Distance Athletics
- Alex Klintworth
- Oct 13
- 8 min read
Long distance athletes are infamous for being particular about their nutrition routines. Ultimately if you feel great with whatever your fueling habits are, I'm happy! That doesn't mean you shouldn't experiment to find improvements. Every body is different and what's optimal for me may not quite suit you. What I aim to do in this article, as I do as a professional nutrition coach, is to explain the physiological mechanisms of the body and how to best support these mechanisms with food and lifestyle. This article isn't meant to take the place of personalized one-on-one coaching which considers your personal health context including lifestyle, genetics, preferences, and goals, but I hope it sheds light on a perspective that you may not have considered. I ask that you entertain the thought that perhaps you can feel and perform even better than you do right now. You’ll never know unless you dare to try something new!
Note: My primary endurance exercise is cycling so I'm going to be myopic here and refer to biking. You can substitute swimming, running, rowing, hiking or whatever other endurance exercise you prefer. We won't explore the nuances between sports here, but the overarching concepts can be applied across disciplines.
We're going to mostly focus here specifically on energy itself - providing our muscles with the fuel to support long athletic efforts of ~30 minutes or more. There are lots of other considerations including micronutrients needed support energy production (Vitamins B1, B2, B3, B5, C, phosphorus, sodium, magnesium, potassium, copper, iron, and more), sleep and recovery, proper hydration, and so on, but we'll leave all that for another day.
What are the primary energy sources for our body?
When functioning well, our bodies are impressively efficient at converting certain carbs and fats into cellular energy, ATP (Adenosine Triphosphate). Your liver can convert protein into sugar for energy, but that's not efficient. 'Making carbs' in this manner is mostly on standby as a backup. That means there's little use for protein right before or during a long ride - I'm looking at you, protein bar. Protein is vital but best saved for a meal after endurance exercise.
Certain organs also thrive on ketones and lactic acid as fuel, but those are produced by our bodies, not consumed. That leaves certain types of carbs and fats as the primary candidates as food for our long bouts of exercise.
I need lots of carbs to make sure I don't bonk during my 50-mile ride, right?
Probably yes, but ideally no. We should be able to seamlessly switch between both carbs and fats to fuel our muscles, but only ~7% of the American population is metabolically healthy enough to do so. There are a handful of biomarkers that indicate metabolic health; Ultimately metabolic health means your cells excel at extracting and using the energy and nutrients from your food. I was one of the 93% metabolically unhealthy despite being a nationals-level triathlete in college. Riding 200 miles a week cannot overcome poor eating habits. The good news is, even if you're in the cohort of the 93%, it only takes a few months of effort to flip the scales in the other direction. A key sign of metabolic health is metabolic flexibility where you're able to use both carbohydrates and fats to fuel your body.
What should I use to fuel my rides?
It depends on what your goals are and what type of riding you're doing! Are you an elite competitor sustaining above-VO2max* efforts regularly during training and competitions? Or do you fancy yourself a social athlete who loves cycling, challenges yourself on hard rides, and is eager to maintain great health and longevity? Most of us fall into the second category.
*VO2max is the fastest you can use oxygen to produce energy for your cells. Endurance athletes can usually sustain ~75% intensity of their VO2max for long efforts before lactate** buildup becomes the limiting factor. Essentially, trained athletes can maintain long efforts at their lactate threshold, ~75% of VO2max.
**Lactate is not just a waste product; it's a fuel for the brain during exercise! However, as exercise intensity ramps up, your muscles produce lactate faster than the brain can use it for energy. Lactate buildup in the blood stream is one of the limiting factors in sustaining aerobic output. Carbohydrate metabolism produces lots of lactate while fat metabolism doesn't produce any. The more fat is contributing to powering your muscles, the higher percentage of your VO2max you can sustain over long efforts.
Scientific Advances
The popular and deeply ingrained concept of fueling athletic endeavors with carbs stems from the idea that once physical effort is above ~60% of your VO2max your body must primarily use carbs instead of fat for fuel.
If you wanted to train or compete at your lactate threshold and your body could only sustain that intensity with carbohydrates, then it makes perfect sense to carb load for dinner and gulp down goos, chews, and bars during your ride! While that strategy can work, it turns out, new research with advances in how we measure metabolism reveals that athletes with a fully functioning metabolism can power their efforts upwards of 90% of their VO2max primarily with fats - well above the 75% threshold effort of a carb-only athlete! It all depends on how well your body can tap into its own energy stores, your body fat. And that is substantially determined by your overall diet both on and off the bike.
How Does Alex Fuel?
I want to be metabolically flexible, to be able to use both carbs and fats for energy. Carbs indeed will power my all-out sprint efforts, but I want my body fat to help supplement my energy needs during rides lasting longer than an hour. Why?
When I'm healthy enough to be able to use fat for energy, my body is also better at using carbs for energy than if I could only use carbs for energy.
My muscles and liver can store a maximum of ~1500 calories of sugar and I'll burn over 800 calories per hour on a hard ride. We're only capable of digesting ~200 calories of sugar per hour (without specific training that is likely detrimental to general wellbeing). Relying on sugar means carefully managing refuels during rides and 'bonking' once I've depleted my sugar stores.
Tapping into body fat, I can supplement as much energy as I need. My limit is no longer fuel related; My limit is endurance, strength, oxygen exchange, heat, etc related.
Training in a fat-adapted state increases mitochondrial biogenesis. Mitochondria are the organelles in our cells that produce cellular energy. Fueling with fat will tell my muscles to make more of these little power plants, increasing the maximum rate I can make more cellular energy!
The ability to use fat for energy is a signal of full metabolic health, drastically reducing my risk for nearly every chronic disease - cardiovascular disease, cancer, dementia, kidney and liver disease, and so much more. Most disease states happen in part because our organs can't energize themselves properly, meaning they can't function properly and slowly degrade over time.
In my quest for metabolic flexibility, I sometimes ride fueled with carbs and sometimes ride fueled with fats. There's absolutely no need to do so, but oftentimes I even exercise completely fasted like during hiking the tallest peak in Colorado and biking the Skull Valley Loop. Again, it's not required to train fasted, but it's very possible and can be beneficial.
Carbs on the Bike
When I'm fueling with carbs, I'll bring lots of food for the ride. I can only store so much sugar in my muscles and liver, so I'll need to supplement. What do I bring? First, I want simple sugars. All carbohydrates - sugar, bread, fruit, grains, starches, etc. - get broken down into sugar during digestion. During a ride, I don't want to stress my digestive system, so the simpler the sugar the better. I also want micronutrients that my body needs to assist the energy conversion process. Lots of processed sports nutrition products have synthetic vitamins, but they rarely work as well as the real versions found in whole foods. I also like a combination of glucose and fructose because they're processed through different pathways, so having both provides a quicker energy delivery. My go-to carb-based fuel is fruit! My favorites are dates, figs and bananas. Honey and sushi rice are other fantastic options for carbs. A goo, gel, or bar is great in a pinch, but they also usually have lots of additives that aren't great for overall health if you eat them day after day, ride after ride. Easily the best energy bar I've found are Bare Bars, full of nutrient and energy dense carbs and fats.
Fats on the Bike
When I'm fueling with fats, unless I'm completely fasted of course, I want to bring sources of fats that my muscles actually want to use for fuel. The graph below shows how much of the energy in your food your cells can actually turn into energy for your cells. Whole food sources of polyunsaturated fats - think seeds and nuts - can be healthy, but our cells don't like to use them for energy. These fats are way too fragile to speed-feed into your mitochondria, our cell's energy producers, so relying on these fat sources means the energy your muscles receive look like the orange and red lines on the graph below.
I know the classic outdoor adventure snack is nut-filled trail mix. That may fill you up and is extremely energy dense. But the calories in nuts do not equate to energy for your muscles. I don't avoid nuts as a garnish on my meals, but I do stay away when my intent is to fuel for athletic performance.
Instead, your mitochondria love monounsaturated and saturated fats* - the green lines on the graph! Some of my favorite sources of these fats are beef, coconut, avocado, dark chocolate, cheese, and eggs. Of course, carrying some of these foods on the bike can be messy on a hot mid-summer ride, but I guess years of growing up at swim meets with warm string cheese conditioned me. I've found the easiest foods to bring on a summer bike are pre-peeled and salted hard boiled eggs, pre-cut avocado, coconut flakes, and summer sausage. In cool weather, cheese and chocolate are much easier.
*A side note: the surprisingly tiny association between saturated fat, LDL cholesterol, and cardiovascular disease completely disappears in the population that's metabolically healthy. And without the vital nutrient of cholesterol, you cannot produce sex hormones, grow healthy cells, maintain a healthy brain and a healthy immune system, produce vitamin D, and much more.
Tradition vs. Growth
Carbohydrates to fuel performance is deeply ingrained into athletic lore. And the science used to back it up. But we now have more precise tools to measure metabolism and more curious scientists pulling research threads nobody had previously ever even considered. We're discovering time-honored traditions are not as scientifically robust as we thought.
I had prided myself on fantastic nutrition throughout my nationals-level swimming and triathlon careers from 6 years old till college graduation. I ate lots of lean protein, whole food carbs, and almonds. I was fit and fast, but now after adjusting my nutrition as I've dug deep into research I wonder how much better I could have been. Post-graduation I took a near decade hiatus from any swim-bike-run training. Now in my 30s, one short summer back on the bike, I'm stronger on a completely fasted Saturday SVL ride than at my peak carb-loaded fitness in college. I also feel better, and my overall health is much improved.
About Alex
My wife Karli and I are independent health researchers, nutrition coaches, and founders of Hi Energy. We specialize in metabolic health for both athletics and general wellbeing. Most of our clients are either middle-aged to retired, many of them are athletes, and all are seeking to maintain and improve their health span, without pharmaceuticals. You can read our bios here and learn more about our coaching services here. We've obviously only scratched the surface of nutrition for performance and longevity. If you'd like to chat with us about your health goals and how we can help you reach them, contact us and sign up for a complimentary consultation call here.
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