Anti-Aging: Preventing Bonking with Daily Nutrition – Road Bike Rider

By Coach John Hughes

Last week I responded to a question by RBR reader Brian W., “I have been riding on and off for about 35 years. I am 54. I frequently “bonk” after about an hour. It doesn’t matter if I am doing a moderate or higher intensity ride. What can I do to increase my endurance and be able to ride 75 plus miles without bonking?”

Experiment of One

I’ll share with you what I know from the scientific literature, 40 years of coaching and 50 years of turning the cranks. However, we’re each an experiment of one. What follows may or may not work for you.


You are always metabolizing a combination of fat and glucose even when you are sleeping. The more active you are the higher the proportion of glucose providing the energy. Glucose is stored in the body as glycogen. The average person stores about 1,800 calories of glycogen. (1,400 in the muscles, 320 in the liver and 80 in your blood) How much you store depends on your body size and your fitness.  

Your body has about 100,000 calories of energy stored as fat, an unlimited supply of fat.  Even the skinniest pro has enough body fat to fuel a long race.

Above your anaerobic threshold (AT), also called lactate threshold (LT), your major fuel is glucose although you are still burning fat. The harder you ride above AT the more glucose per minute you are burning. If you’re like me and don’t use a heart rate monitor or power meter you’re AT is when you’re breathing too hard to talk although you can get out a few words.

Only about 5 percent of your energy comes from protein.

Endurance training helps to defer bonking and hitting the wall in two ways.  By riding at a conversational pace over many rides your body will shift to metabolizing more fat and less glucose thereby sparing glucose. (This doesn’t mean you’ll lose weight. To do that you need to consume fewer total calories than you are burning.) Endurance training also increases your muscles’ capacity to store glycogen by 20 to 50 percent. If you’ve been doing endurance exercise for years both of these adaptations have taken place but if you’re a relatively new roadie many hours of endurance riding will result in these adaptations. For more information see my column How Should a Beginning Rider Train?

During a one-hour ride it’s impossible to burn more calories than a rider’s glycogen stores, provided the rider’s glycogen is not already depleted. 

The American College of Sports Medicine (ACSM) recommends consuming 25 to 60 grams of carbs(1 to 2 ounces or 100 to 240 calories) per hour after the first hour of exercise. This is sufficient for several hours of exercise. If you are riding for three hours or more start eating carbs in the first hour. If you are relatively small or exercising lightly 25 grams / hour is enough. If you are larger or riding at a moderate to fast pace eat up to 60 grams / hour.

Daily Nutrition and Chronic Glycogen Depletion

What if a rider’s glycogen stores are significantly less than 1,800 calories? Even if a rider follows the ACSM’s recommendation but his gas tank is low when he starts to ride then he probably will bonk.

Whether a roadie is eating enough is a function of three factors:

  1. Basal metabolic rate (BMR) is the calories needed to support your basic bodily function. It doesn’t take into account any activity. To estimate your BMR multiply your weight in pounds by 10 (weight in kilograms by 22). 
  2. Daily activity level: 
    • Add 30 – 40 percent of BMR if lightly active (mostly sitting, desk work, etc.)
    • 50 percent of BMR if moderately active (some walking or standing, household chores, moving frequently, etc.)
    • 60 – 70 percent of BMR if very active (moving a lot, physical labor, etc.)
  3. Exercise: Here are estimates of calories burned at different speeds from The Cyclist’s Food Guide by Nancy Clark MS, RD and Jenny Hegmann MS, RD Speeds are non-drafting on flat terrain with no wind.
    • 1 mph (18 km/h) light effort 2.5 cal / lb / hr (6 cal / kg / hr)
    • 13 mph (21 km/h) moderate effort 3.5 cal / lb / hr (8 cal / kg / hr)
    • 15 mph (24 km/h) vigorous effort 4.5 cal / lb / hr (10 cal / kg / hr)
    • 17+ mph (27+ km/h) racing 5.5 cal / lb / hr (12 cal / kg / hr)

Here’s an example: a 165 lb. office worker who does a two-hour ride at 13 mph. His BMR is 1,650 calories, light daily activity adds 575 calories and his ride adds another 1,150 calories for a total of 3,375 calories burned this day.

Jack’s Case

On Thursday I rode with Jack. Jack is 6’4” tall (great to draft) and his weight has crept up to 200 lbs. so he’s counting calories. His (so-called) smart watch says he should only eat 2,200 calories per day to lose weight. 

The algorithm in Jack’s smart watch probably calculates his BMR (2,000 calories), adds 35 percent for light activity during the day (700 calories) and subtracts 500 calories / day to lose a pound a week. 

Jack gardens, works on carpentry projects in his garage, volunteers at a bike shop and for cycling events, etc., i.e., he’s very active so his daily caloric need is more like 3,200 calories: his BMR (2,000 calories) plus 60 percent of his BMR (1,200 calories). Consuming only 2,200 calories his actual daily deficit is about 1,000 calories. Cutting calories by 1,000 cal / day isn’t sustainable.

Jack’s smart watch also estimates calories burned during a workout and increases his daily allotment when he rides. On Monday, Jack rode about 60 flat miles at 14 mph. The algorithm in Jack’s watch estimated riding at 14 mph he was burning approximately 4 calories / pound of body weight, i.e., about 4 times 200 lbs = 800 calories / hour, probably about half from glycogen and half from body fat. 

Jack followed the recommendation of the American College of Sports Medicine (ACSM) to consume 25 to 60 grams of carbs (1 to 2 ounces or 100 to 240 calories) per hour after the first hour of exercise, i.e., 240 calories of carbs an hour.  By the end of the ride Jack had a significant caloric deficit on top of his large daily calorie shortfall.

On Tuesday Jack barely had enough energy to move around the house — he was glycogen depleted.

All of the above are estimates and different sources may provide different estimates. Recent research suggests the calories burned exercising are lower, which is Why You Can’t Just Pedal Off the Pounds.

The basic point is Jack doesn’t eat enough each day to avoid chronic glycogen depletion.

I wrote detailed columns on:

Related columns

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  • The key role of carbohydrates in providing the energy you need and many of the vitamins and minerals.
  • How much protein you really need, and nourishing protein choices.
  • The important role of fat in your diet, and healthy choices to get needed fat.
  • The principal vitamins and minerals you need.

I review what to consume while exercising, including the key roles of carbohydrates, fluid and electrolytes. I discuss how to eat preventively in order to reduce your risks of the most common health conditions as you age: heart disease including stroke; diabetes; being overweight, which increases your risk of heart disease and diabetes; how to reach and maintain a healthy weight; and osteoporosis. The 28-page Healthy Nutrition Past 50 is $4.99.

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Eating and Drinking Like the Pros: How to Make Your Own Sports Nutrition   

I researched what the former Team Sky, Garmin-Cervélo and RadioShack riders consume before, during and after a stage and discussed the results with cycling nutrition experts. We all require energy and replenishment of lost minerals and nutrients when we ride. Eating and drinking like the pros offers us the same nutritional benefits, which we can customize to our own needs – typically at a fraction of the cost of commercial sports food and drink, if we choose to make our own. I worked with a professor of nutrition and an expert on hydration and electrolytes (both experts are cyclists) in creating recipes for both sports drinks and food. They’re easy to make, with known, unprocessed ingredients, and can be tailored to your specific taste and needs. The 15-page Eating and Drinking Like the Prosis $4.99.

Nutrition for 100K and Beyond: What to eat before, during and after a bike ride. 

I combine the best of current research with 50 years of riding experience to teach you proper nutrition for cycling. Initially written for longer rides the lessons apply to all endurance riders.

If you don’t fuel properly, you won’t get very far either in training or in rides. We all know the basic point: when cycling we are using energy and we need to replace the energy. However, energy needs vary by individual and type of riding and not all fuels are equally effective. This article will teach you:

  • Personal Energy Need: how to estimate how many calories you are burning per hour at different speeds.
  • Types of Fuel: how carbohydrates, fat and protein contribute to your energy needs.
  • Training Implications: what are the training implications of your personal energy needs, your cycling goals and the types of fuel.
  • What to Eat: what you should eat including quantity per hour, types of fuel, complex vs. simple carbohydrates, sports products vs. grocery store food and sample foods.
  • Hydration: how much to drink both to avoid dehydration and to avoid hyponatremia, diluting your blood sodium.
  • Electrolytes: what you need and a comparison of sources.
  • Experiment of One: we are each an experiment of one, how to test and refine your nutrition.
  • Before and After Events: what to eat pre-event for strong performance and post-event for optimum recovery.
  • 24-Hour and Beyond: how to maintain energy over a 24-hour or longer event.
  • Myths: common popular myths about sports nutrition.

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Coach John Hughes earned coaching certifications from USA Cycling and the National Strength and Conditioning Association. John’s cycling career includes course records in the Boston-Montreal-Boston 1200-km randonnée and the Furnace Creek 508, a Race Across AMerica (RAAM) qualifier. He has ridden solo RAAM twice and is a 5-time finisher of the 1200-km Paris-Brest-Paris. He has written over 40 eBooks and eArticles on cycling training and nutrition, available in RBR’s eBookstore at Coach John Hughes. Click to read John’s full bio.

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