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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.
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I'd be interested in an answer on this as well as I've been doing similar distance commute on an empty stomach for 12+ months. – ynnekkram Jan 7 at 9:02
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One thing to be aware of: You might run into low blood sugar ( Hypoglycemia ) if you do this. For a healthy individual this is not dangerous, but you will feel very weak and dizzy suddenly. Just listen to your body, and take it seriously. If you happen to be a diabetic, speak to your doctor first! – sleske Jan 7 at 12:09
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It might be wise to carry an energy bar or some such with you, in case you have a sudden blood sugar drop. But a healthy person, with no metabolic abnormalities, should be able to do an hour's ride at moderate intensity before breakfast with no trouble. I've had a blood sugar "crash" a handful of times, but it was always in situations where I'd been going for hours, or when I was commuting home without ever having had lunch, or some such. – Daniel R Hicks Jan 7 at 13:01
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I was taught that you should never bicycle on an empty stomach; you should bicycle on a cycle path. – Eric Lippert Jan 7 at 14:31
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Yes cycling on an empty stomach is extremely harmful. In fact you should always use a bicycle, not an empty stomach. – user24037 Jan 7 at 16:19

12 Answers 12

up vote 48 down vote accepted

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)

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+1 "being aware of your body". That's really what it comes down to. Everybody's different. Dogmatic attitudes about things like this, the kind that might override what your body's trying to tell you, are what's most likely to be harmful. – junkyardsparkle Jan 7 at 9:47
    
Anecdotally this seems to fit with my experience. I've recently taken do waking up early and doing 50 minutes on the trainer (Zwift calculates distance at 25 km) in the morning a few days a week. I don't feel low on energy even though I do my morning rides before breakfast. – Kibbee Jan 7 at 13:48
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Studies have shown that training (moderate pace - 175 watts) in a fasted state can actually improve how quickly your body can move to fat metabolism for energy production. I typically ride 1-2 hours in a fasted state (without breakfast). Any longer I find I risk bonking. – Rider_X Jan 7 at 20:37
    
I think it's more/also important to look at your caloric intake window after the exercise ends. My anecdotal experiences (with some suggestions from The Cyclists Training Bible) says that your window for good use of high glycemic index foods lasts from the end of your workout to about as long as the workout took. So if your morning ride took 30 minutes, you have about that long to maximally use sugary jelly or donuts or any other "garbage" breakfast food to replenish glycogen stores. If your breakfast doesn't include anything of the sort, it may not matter as much. – Suspended User Jan 8 at 5:17

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.

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Note: I'm a programmer with a BSc Computer Science, the information above is mostly from Wikipedia and Google search results; Corrections are welcomed. – Emyr Jan 7 at 13:35
    
Your calculation assumes that only glycogen is used and that all glycogen in the body can be used. Glycogen is limited to the muscle where it’s deposited (though most of that will be in the legs ;) ). Fat can and will be used too. – Michael Jan 8 at 15:46
    
Your body will also prefer different metabolic pathways (e.g., glycogen and fat) depending on the length of time since you last ingested food, the intensity of the current exercise, and your training history. It's a complex set of trade-offs your body continually makes. Repeatedly, exercising a fasted state encourages your body to prefer fat metabolism pathway over glycogen metabolism if the effort is low enough. – Rider_X Jan 9 at 0:02
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I'm relieved the problems with my contribution are all of the "spherical cows in a vacuum" type :-) – Emyr Jan 11 at 14:17

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.

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Those are some very simplistic and sweeping generalizations. – Rider_X Jan 9 at 0:06

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

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

Edit, it seems I posted this accidentally before finishing my post.

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.

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Not all training schemes are scientifically sound, though. – Emil Vikström Jan 7 at 12:21
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My 100+ km rides have a pie stop in the middle. – Criggie Jan 7 at 20:24
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It needs to be noted that riding 100km without food risks provoking ketosis, a condition that can be unpleasant and sometimes dangerous. – Daniel R Hicks Jan 8 at 1:47
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reworded without the charged language "..notice that riding 100km without food may start a process called ketosis, by which you are fueled by ketone bodies, not glycogen." But anyway it is not about riding 100 km fasted everyday, (doubt it would be feasible) but do some of them, in certain periods of your train season, with a moderate effort. it looks like this is to get a mild taste of the bonk, so that your body is not as shocked by it as it could be the first times, gets used to burn fat for energy, etc. – gaurwraith Jan 8 at 2:22
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Your post became so much better with the update! Have an upvote :-) – Emil Vikström Jan 8 at 8:30

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.

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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.

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I guess this is the program that GLWday's answer gives a bit more detail about. – David Richerby Jan 7 at 20:11

id 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

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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.

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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.

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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 better. I don't know how to embed it like the user above.

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But is that harmful or not in some way? – Kaz Jan 8 at 4:32

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 peddling, 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.

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That's really only a tiny corner of the bigger (and separate) question of how to plan for the unplanned. What if you have a non-repairable breakdown? What if you fall and hurt yourself? What if you come down with a sudden case of the squirts (due perhaps to the contaminated fruit you had for breakfast)? – Daniel R Hicks Jan 7 at 20:30
    
If you're ill enough that cycling for half an hour is going to be a problem, you'll probably be aware that something is wrong the second you wake up. – David Richerby Jan 10 at 18:25
    
@DavidRicherby If you are rushing things and you are very fit to begin with, you're less likely to notice problems while not exerting yourself. It may feel like not having slept all that well which should just go away while biking but then on the bike you feel like you have less and less energy instead of getting more energy. You may not collapse, but some people are prone to getting a stress response when they suddenly feel weak, which then leads to collapse. – Count Iblis Jan 10 at 18:42

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