Is commuting 10 km on an empty stomach harmful?

Question

I recently moved to a new place and I started taking my bike to work. It is a ride of 10-15km, depending on how fancy I feel about taking detours. I wake up at 7:45, and 15 minutes later I am already on the bike. I eat breakfast at work, after 30-40 minutes of biking. My question is: does it have health ramifications if I do it every day? I did some looking around on the internet, but everything I find relates to high-intensity sports cycling, not a leisurely commute.

Some facts that might be helpful:

• I maintain a steady pace, enough to get sweaty, but this is more from the length of the ride than from the intensity. I stay dry for the first part of the ride.
• I feel strong and capable most days. Rarely I will feel worn out on the last kilometer or two, but this is pretty rare and I guess indicative of bad sleep.
• The ride is 100% flat. The biggest climbs are speed bumps.

Answer 1

As far as I can tell, no. I've been riding 30 minutes or more every workday before breakfast for more than 10 years with no detectable ill effects. When I was riding an hour to work I'd sometimes have a small snack before riding, but only rarely. When I'm cycle touring I'll often ride for an hour before I have breakfast, as that wakes me up and gets me warm, then I can stop and eat somewhere pleasant (I usually stealth camp so I'm not always sleeping in a nice place to hang round during the day). But an hour isn't an unreasonable ride before breakfast. For me!

What matters is being aware of your body. If you're feeling bad, stop and work out why. If you're hungover... what did you expect? But if you normally feel fine and one day your stomach hurts, or you feel weak, or something else changes, worry. Stop, work out what the problem is. Eat, drink, pee, whatever. It's the same as if your bike feels funny or starts making a weird noise.

Normally I carry breakfast to work, so I have it with me if I need to stop and eat. I also have money, which is surprisingly useful for solving problems :) If I need to I can get a taxi to work, buy food, whatever.

FWIW I was vegetarian for most of that time, of late I've gone back to eating meat every couple of weeks (I'm getting older and meat seems to help me maintain muscle mass). I don't know if being vegetarian helps, but it doesn't seem to hinder the ride before breakfast.

(ok, I've been doing this for more than 15 years, possibly more than 20)

Answer 2

The myosin heads of muscle fibres move using the energy produced by converting ATP to ADP. The energy extracted is about 30.5 kJ/mol of ATP.

Muscle tissue has limited ATP storage. Your muscles' primary fuel storage is local Glycogen.

Converting Glucose to ATP

Glycogen is converted to Glucose.

Glycolysis, the Citric Acid Cycle (aka TCA Cycle, Krebs Cycle) and Oxidative Phosphorylation each produce ATP based on the byproducts of the previous process. These three processes produce 39 moles of ATP for each mole of Glycogen.

For more detail, see http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect12.htm

From http://ajcn.nutrition.org/content/48/2/240.abstract:

Glycogen storage capacity in man is approximately 15 g/kg body weight.

Glycogen has a molar mass of 666.58 g/mol

For an 80kg man: Glycogen storage capacity: 15 * 80 = 1200g = 1.8mol ATP producible aerobically = 1.8 * 39 = 70.2mol Energy available: 70.2 * 30.5 = 2141.1 kJ = 511 kCal

Using this calculator: http://www.tribology-abc.com/calculators/cycling.htm

80kg cyclist, 15kg bike
Rolling resistance Cr 0.005
Air resistance Cw 0.9
Frontal area Af 0.6 m2
Power for 20km/h => 86W
for 40 mins => 465 kCal

This calculation assumes you begin at 20km/h and travel at constant speed on a flat surface with no wind.

Replenishing sugar from body fat

Lipolysis releases fatty acid chains into the blood stream. In cell mitochondria, a ligase enzyme breaks these down to acyl-CoA. Beta oxidization breaks acyl-CoA and produces acetyl-CoA, which feeds the Citric Acid Cycle. The oxaloacetate from the Citric Acid Cycle is reduced to Malate, transported out to the Cytosol, where it's oxidised back to oxaloacetate then decarboxylated by phosphoenolpyruvate carboxykinase (PEPCK) to phosphoenolpyruvate (PEP). In the Liver, PEP is converted to pyruvate which can be converted (Glugoneogenesis) to Glucose, which is released into the bloodstream. The decarboxylation in the Cytosol is the rate limiting step in fat metabolism.

Conclusion:

Assuming you had a normal evening meal and you have breakfast when you arrive, this commute will probably not lower your blood glucose levels to dangerous levels.

Answer 3

Here in the UK on BBC TV last night was a program 'Trust me I'm a Doctor' in which they examined the effect of exercise in men and women and whether to eat before exercising or after.

On average most men (having more muscle) burnt more carbohydrates from their body stores so are better eating after exercise. Most women (tending to have more fat in their body)are better eating before they exercise.

Answer 4

I've been reading a couple of questions on weight loss lately, and cycling or jogging before breakfast was one of the tips.

The justification is it kick starts the body's metabolism into "make energy" rather than "make fat"

10 km isn't a huge ride - should be about 20-25 minutes on the bike. You should remember to hydrate sufficiently too.

The full video on cycling for weight loss was

Answer 5

Dinner the night before is more important as that is digested food. Breakfast is not going digest in 30 minutes (or even 2 hours). Breakfast would just bog you down as digestion burns calories. A healthy body has calorie store for 30+ minutes. You are only going to burn like 400 calories. If your body did not have the calories it would tell you. Eat breakfast or a healthy snack when you arrive.

Me I will only eat before if it is 2+ hours ride. And then eat an hour before. I think it is more comfortable to exercise on an empty stomach.

Avoid sugary foods as spike for energy.

Answer 6

No, it is not harmful. Some training schemes include doing a 100 km ride on empty stomach to get the body used to ride .

Despite there is no research to prove, "anecdotal evidence suggest a fasted ride could improve your fat burning metabolism, improve riding economy and aid weight management. Especially if you find you are having difficulties sticking to lower heart rate zones, regular fasted rides can help your body to adapt."

https://www.britishcycling.org.uk/knowledge/nutrition/article/izn20150818-All-Cycling-Fasted-Morning-Rides-0

I have heard friends recommed long fasted rides with moderate effort, on the basis that they will get your body used to work when glycogen reserves are depleted.

Answer 7

Not directly linked to the question but interesting all the same - I saw a health program on telly last night - it had an article in it about exercising before or after breakfast (breakfast being carb based). It concluded - for fat burning - women were better off after breakfast and men better off before.

They didn't go into huge detail but it was thought the reasoning was men having more muscle mass and therefore more glycogen storage capability. Iirc - the men burnt on avg 8% more over those men who exercised after breakfast.

Answer 8

10km is not much. I've "run dry" on calories while biking. You'll slow down to a crawl and need to stuff yourself next opportunity (not that it helps all that much at the time). And you say you'll be at work, so starting with an hour of being stupid and exhausted would be a bad idea. But you'd probably need to skip your evening meal and go at least 50km to get to that stage.

At 10km, you'll probably not even gone far enough digesting stuff to use it. If you eat before you go, all you get is a headstart on blood sugar levels after you start work.

Now that's the food/calory aspect. Have a water bottle with you: being dehydrated is bad for the joints. Biking is a lot nicer on them than running, but the thirst may hit while on the way rather than right after getting up.

Answer 9

I'd say no, I used to do 32km to work before I moved closer (do 18km now) and both routes I ate after my ride. Riding on a full stomach in my experience will leave you feeling sick and lethargic part way through your ride.

Just make sure you have a sugary drink on the bike to avoid dropping sugar levels.

Answer 10

I don't know of clinical data to back me up, but I think it is a fine thing to do – in general. Some of the specifics may be more important. I can still stand to loose some weight. So my thinking is that the feelings of hunger at the outset of my riding more were due to my body expecting to get most of its energy from sugar/carbohydrate sources.

When I first started – as a weight loss strategy – it felt pretty tough some mornings, but after a bit (at max, a couple of weeks) I found that I no longer felt like I was starving and that I didn't feel like I needed to eat a lot after the ride either.

If you're pretty lean then the hunger some days may be a sign that a banana or something else quick to eat would make sense on those days. If you can stand to loose some weight it might be a sign that you've run out the carbohydrate sources and you're feeling the drop in easily available energy sources as your body figures out how to make a smooth transition to using fat as the primary energy source.

In Eat Bacon, Don't Jog Grant Peterson makes a persuasive argument that exercising before eating in the morning is a great way to loose weight. The idea is that in the morning you don't have (as) much carbohydrate available so your body turns to fat for energy. The book is addressed at "normal people" not "serious athletes" so you may find the information there more adapted to your needs/experience.

Answer 11

It's actually an awesome thing to do! It's basically the best way to exercise for fat loss, and to keep it off.

This concept is called Fasted Cardio.

This vid explains it bette:

Summary added by andy256:

• the video implicitly supports fasted cardio.

• claims it's the safest way of losing fat.

• claims 30 minutes of pre-breakfast cardio is worth 90 minutes of post breakfast cardio.

• says you'll only throw up once!

Answer 12

While I do agree with what is written in all the other answers so far given, I still come down to a different conclusion. The reason is that when considering whether or not something is harmful, you must consider how things can go wrong instead of how things will usually work out fine. Consider the case where you are ill. If you just jump out of your bed and hop on your bicycle and start pedaling, you may not even notice that you are not feeling all that well only half way on your ride.

A slower start by eating breakfast might have made you notice this before you decide to go to work. Also, even if you do decide to cycle to work, the energy from the food may still help to prevent you from collapsing during your ride.

While this may be an untypical event, if you consider a long time period, the probabilities become much larger. E.g., a one in a ten thousand probability per day is a 30% probability in a ten year period.

Answer 13

Time pushed here, so haven't read the previous posts. So with that in mind, short answer, NO! Unless you are coming off the back of a carb depleting ride, you will be fine. The question you haven't asked is "what should I consume at the end of a good 10k ride on an empty stomach"?. That, my friend, is a golden question. Recovery shake, banana, carbs, proteins? Hell, yes. Just do your research on this. Kindest regards, Gary.