On an endurance ride a roadie is cruising along at a conversational pace, burning fat for fuel. Climbing a fairly steep hill, the roadie also starts burning glucose for fuel.
The harder the roadie is going, the greater proportion of the rider’s energy comes from glucose. You can store 1,500 to 2,000 calories of glycogen in your body, which your body metabolizes as glucose to fuel your muscles.
On a longer ride with real climbing, on a shorter club ride hammering with your buddies, and during an interval workout, you’re burning lots of glucose. When you run out of glucose your legs are leaden and your brain is fuzzy (it can only burn glucose) — you’ve bonked!
Because of these metabolic pathways, most coaches recommend a daily diet that is high in carbohydrates. Your body converts carbs to glycogen. We coaches recommend primarily carbs because training hard depletes glycogen stores, and if your glycogen stores are depleted, you won’t train as well the next day.
Carbohydrates include vegetables and fruit, as well as starches like bread, pasta, rice and potatoes.
Ride nutrition also emphasizes carbs. For exercise lasting more than an hour, the American College of Sports Medicine recommends starting to eat in the second hour. The ACSM recommends 30 grams (120 calories) of carbs per hour.
Another reason to emphasize carbs is that chronic glycogen depletion is one of the causes of overreaching and potentially overtraining.
Should You Eat a High-Carb Diet?
Nancy Clark’s Sports Nutrition Handbook (2008) and Clark and Jenny Hegmann’s The Cyclist’s Food Guide (2012) both discuss at length day-to-day nutrition to support cycling. They recommend:
Daily Diet with Carbs as the Primary Macronutrient
| Macronutrient | % of Total Calories | Calories / gram | Healthy examples |
| Carbohydrate | 60 – 65% | 4 | Vegetables, fruits, grains, pasta, bread, rice and potatoes; and limit sweets |
| Protein | 10 – 15% | 4 | Low-fat dairy, eggs, fish, poultry and lean meat |
| Fat | 25% | 9 | Olive oil, canola oil, nuts, avocado and fish |
Too complicated? At each meal your plate should be primarily covered with a variety carbohydrates, with a serving of lean protein about the size of a deck of cards, and limited fat. (See the photo.)
Should You Eat a High-Fat Diet?
In Fast After Fifty (2015) Joe Friel describes a different daily diet in which at least 50% of your calories come from fat, i.e., increase the calories from fat and decrease the calories from carbs proportionally in the above table.
When fat is the primary macronutrient, then ketones, not glucose, are the primary energy source. Ketones are produced by the liver from fat. Your skeletal muscles, your heart, brain and other vital organs all function normally on ketones once the body adapts, which may take a few weeks. The advantage of the high-fat diet is that everyone has enough body fat for multi-hour hard rides, so refueling isn’t a concern.
If you eat a high-carb diet your metabolism adjusts to using glucose for energy. If you eat a high-fat diet your metabolism adjusts to using ketones.
Because your body specializes, you can’t switch back and forth in your daily diet and still ride well! For good recovery you also shouldn’t change your recovery nutrition from your daily nutrition. If you’re on a high-carb diet, then eat carbs after a ride. If you’re on a high-fat diet, then eat fat for recovery.
Eating a high fat diet will not help you lose weight! Assume your regular daily metabolism burns 2,000 calories. You’re on a high fat diet, you go for a slow-paced endurance ride and burn 1,000 calories of fat, for a total of 3,000 calories for the day. Over the 24-hour period you consume 3,000 calories so you’re in equilibrium: 3,000 calories out and 3,000 calories in. Your weight remains the same.
Now, assume you’re on a high-carb diet and instead of going for an endurance ride you do an intensity workout and burn 1,000 calories of glucose from carbs. Again, you consume 3,000 calories over 24 hours. You’re in equilibrium and your weight remains the same. Weight management is simply a function of calories in vs. calories burned.
As a retired pro told me, “In the spring ride more and eat less.” That is how to lose weight.
We’re each an experiment of one. A higher carb or a higher fat diet may be better for you. If you decide to try a higher fat diet, give it several weeks to see if it changes your performance.
Learn More About Cycling Training and Nutrition
I’m putting the finishing touches on a new bundle of five eArticles, including one brand new one – The Best of Coach Hughes: Making You a Better Cyclist. It will include:
1. How to Become a Better Cyclist: The Six Success Factors – A new article to be available only to riders who buy the bundle. Over 25 pages.
2. Your Best Season Ever, Part 1: A 32-page eArticle on how to plan and get the most out of your training published in 2015.
3. Intensity Training 2016: A 41-page eArticle with the latest information on how to use perceived exertion, a heart rate Monitor and a power meter to maximize training effectiveness
4. Optimal Recovery for Improved Performance: A 16-page eArticle with 10 different recovery techniques illustrated with 14 photos. Published in 2011.
5. Eat & Drink Like the Pros: A 15-page eArticle of nutritional insights from pro cycling teams. It contains a dozen recipes for you to make your own food and sports drinks. Published in 2011.
Buy The Best of Coach Hughes: Making You a Better Cyclist, totaling 130 pages.
As a keto athlete (2+ years) I appreciate this article. While it is a brief overview, your statement about weight loss is incorrect. The part you missed, is I can ride for 2+ hours without any nutrition (gels, bars, drinks) except water. In my previous life as a “sugar burner” if I didn’t eat every 45-60 minutes I was a mess (bonk, nausea, etc..). My legs generally give out before my stamina/endurance; just because my engine can go on for almost an eternity doesn’t mean my transmission can keep up. ;o) I encourage you to look up guys like Phinney and Volek for performance info. Aside from athletics, Keto (HFLC) has so many other benefits. I could go on and on……
I am a tourer, whose weekly riding includes endurance, strength training, some sprints, some grinds, some speed; all lead to the fitness that is needed for long days in the saddle pulling gear, and conditions that include hills and wind. I have found on long days that fat really helps. Some fat, combined with lots of carbs. The carbs alone burn too quickly.
I spent about four months recently experimenting with LCHF and intermittent fasting primarily to lose weight and eliminate bonking on long rides. The hardest part about adaptation is the first 2-3 weeks. If you are/were addicted to carbs then you tend to derail frequently. I managed to keep my junk carbs (candy, cookies, bread, pasta, white rice, juices and sport drinks) below 40-50 grams for 6 weeks. I rode on water only, The first 2 weeks were brutal on the bike and I stayed on the back most of the time in 20 mph groups. At 3-4 weeks things improved dramatically as I was dropping about .15 pounds per day as I kept reducing fat mass. Acceleration from a stop is most noticeable first. I achieved the goal of a 100 mile ride fasted on water only at about the 6 or 7 week time frame. Currently I partake of carbs as beer, chocolate, pasta but seem to have maintained my adaptation. I always go out on a morning ride on an empty stomach and ride on water. The liver seems to sense the drawdown in glucose as when I get to the 60-70 mile range I will get a 10 second mild pain in my head and I switch to ketones or something and can continue full power. I no longer bonk when I stick to water only and ride with a 20+ mph group. Mileage seems to bring muscle fatigue but not much else.
If you consume the junk carbs (you should eat the good carbs such as non-starchy leafy greens and berry type fruits) you will slowly aquire the insulin belly over the years and may become pre-diabetic. Excess and continuous high glucose in the bloodstream will destroy the vascular system leading to secondary aging effects. I see plenty of strong cyclists get bigger and bigger with visceral fat who have not taken the effort to limit junk carbs. It is a test of willpower but is also a great pleasure to drop the pounds and ride long distances almost effortlessly on water and some electrolytes. I speak strictly as a recreational cyclist.
One last note. As you continue to ride without carbs you will notice an unusual thing on intermittent anaerobic efforts and/or long rides when your glucose should be gone. If you take glucose readings about 1/2 hour after these lonng or high effort rides, the glucose may be elevated. Mine typically are 100-120 mg/dL, and that is after a 60-75 mile “hard” group ride with nothing but water. The body is generating glucose as needed to give the brain the 40% minimum it needs plus whatever is needed for non-aerobic efforts. Cheers.
I went keto about 2 years ago and I still find it remarkable how you don’t bonk and can ride long distances without refueling. On long rides, I used to constantly down gels and bars or I’d hit the wall. Also, you will lose weight – there’s a lot more to weight loss than calories in, calories out. Fat is more satiating so you tend to naturally eat less without feeling hungry.
Eat whole foods, low carbs, and especially cut out sugar. You will really notice the improved health and endurance.
Unfortunately, the author has made several huge errors in this article. First, they state that your brain can only burn glucose, which is false. Then, they continue on to distill the complicated process of metabolism down to “calories in, calories out”, which is a complete fallacy. The key to fat storage and metabolism is a hormone called insulin, which is regulated by one’s consumption of carbohydrate. I hate to be so harsh, but the author should really do some research on nutrition and basic human metabolism before writing an article like this.
Must reading for anyone doing rides longer than a couple hours (it sounds like all those who replied have read it):
“The Art and Science of Low Carbohydrate Performance” by Jeff Volek and Stephen Phinney.
Also, check out the “Optimized Fat Metabolism” website.