Using energy stored in the body vs eating beforehand

Question

I often go for a long ride on Saturday mornings, typically riding about 55km before breakfast.

I do the ride before eating anything in the morning. Another friend does the same ride but needs to eat breakfast before we go. He's much fitter and leaner than I am.

Is it because I've got more body fat stored that I can ride without eating? Or some other conditioning thing?

Answer 1

One way of looking at aerobic function is as the bodies ability to burn fat for fuel at a given pace or speed. Anaerobic function then is the bodies ability to burn sugar for fuel when we move beyond the pace at which we can burn primarily fat. Heart rate is often a good indicator of which mode we're in.

Intervals and speed training, then, burn mostly sugar for fuel. Weight loss when engaged in this type of activity comes from the elevation of the metabolic process extending long after the workout, and is the net result of how elevated the metabolic rate is and for how long, and the caloric intake necessary to provide sugar to fuel this type of workout.

Training at a slightly lower intensity, where we burn primarily fat for fuel, can do two things:

1. Train our body to burn fat more efficiently. Fat is actually a much richer energy source than sugar, so the body will happily burn fat unless we provide it with extraordinary amounts of sugar or train frequently at a rate where it's impossible to burn fat.
2. Increase the pace at which we can train while still in the aerobic metabolic range. For example: I use a heart rate monitor to avoid entering the anaerobic while training. At first, I had to run maddeningly slow to do so, somewhere around 14 minutes per mile. Six months later I was happily running 9-minute-miles at the same heart rate, for the same length of time. This is referred to in pro cycling as the "base-building" training phase, where they ride hours and hours of long, "easy" miles in the winter early spring to prepare for the summer racing season.

This means that the difference between you and your friend is that you burn more fat than he does at a given pace, which while it would seem strange given your statement that he is more "lean and fit" than you, is at least a hypothesis that shouldn't be rejected outright. If you ride lots of slightly slower miles, your aerobic function can indeed be better than your friend, resulting in your ability to burn fat on your Saturday morning rides, while your friend relies primarily on sugar/carbs for fuel and therefore has to replenish them after the ride.

Note: much of what I've said is based on Phil Maffetone's studies of aerobic function and fitness (example here). Phil takes a somewhat eccentric approach to life, training, and medicine, but the aerobic fitness training works for me, so why throw the baby out with the bath water?

Answer 2

Even a very lean person has enough body fat to fuel them for running several marathons, but to metabolise this fat, your muscles also need to use some sugar or protein. That's just how the chemical process works. Your muscles have some sugar stored in them, and they use this up over the course of your ride. This reserve is small enough that you can use it all on one ride. When you "hit the wall" or "bonk" (suddenly feel very weak because of low blood sugar), it's because you've used up the sugar. Even though you still have fat to burn, you can't do it! That's why riders take sugary drinks, bars, and fruits with them instead of fatty foods like bacon or doughnuts.

I can think of a few possibilities why your friend eats before going.

1. If he's fitter than you, is it because he does more long rides during the week? It may be that his sugar reserve is always running on empty, whereas yours has a chance to replenish itself between rides.

2. Is your friend careful what he eats at other times? As I mentioned above, the body can use sugar or protein to metabolise fat. If your friend is trying to eat plenty of protein to build muscle (or aid recovery), perhaps he's being careful to avoid burning protein for fuel when it could be put to better use in the body. It would be like buying expensive wood panelling for your walls and then taking it down to burn on the fire!

3. It could be something unrelated to how fit and lean he is. Maybe you have a very late dinner the night before, or a midnight snack, so you don't feel hungry until later in the morning; whereas your friend doesn't eat much in the evenings, so he's hungry as soon as he wakes up. The body adapts to its eating patterns, and people can have very different habits.

4. Or similarly, it might be that he is just being more careful. Maybe he's "hit the wall" before on a pre-breakfast ride. If that happens it really makes the ride a lot less enjoyable, so perhaps having done it once, he always eats breakfast to make sure it won't happen again. Perhaps he doesn't need to eat breakfast on this ride in particular, but doesn't want to risk misjudging.

More personally, I think you are the odd one and your friend is normal. I can manage about 40 km before breakfast and my fitter cycling friends all think I'm crazy for going that far.