7 preface/disclaimer stating what this answer lacks
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A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 30% beef, 70% vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0

This calculation is pretty much worst-case for the bicycle. It doesn't take into account that food production has actually stored CO2 from the atmosphere which is now just released back, while fuel was originally underground and its CO2 is added to the carbon cycle. Neither does it take into account mercury/other emissions, nor the wear-and-tear in cars and bicycles, nor the enormous benefits if the bicyclist doesn't even own a car.

A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 30% beef, 70% vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0

A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 30% beef, 70% vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0

This calculation is pretty much worst-case for the bicycle. It doesn't take into account that food production has actually stored CO2 from the atmosphere which is now just released back, while fuel was originally underground and its CO2 is added to the carbon cycle. Neither does it take into account mercury/other emissions, nor the wear-and-tear in cars and bicycles, nor the enormous benefits if the bicyclist doesn't even own a car.

A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 30% beef, 70% vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0

6 allow 20kg for bike etc. making total weight 100kg; recalculate
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A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 1/330% beef, 2/370% vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0


And here's the calculation. The initial assumption is that the choice between car and bicycle doesn't affect the amount of other exercise. In practice, it might be different, but this is the only way we can calculate.

Car

CO2 emissions for the average new car in 2006 were 167.2 g/km, so let's assume this amount. For 25km the car pollutes 4.18 kg CO2.

Bicycle

The extra food may be significant

Riding a bicycle uses up 1.62 kJ/(km∙kg). Let's assume the rider weighs 80kg, which is below or above average for a male depending on country. Allow 20kg for bike, clothes etc. and we have 100kg. Thus the 25km takes 3240kJ4050kJ total -- that is 774967 kcal.

Now, the food CO2 equivalent per kcal depends a lot on the type of food. For example:

  • soy 0.07g/kcal
  • chicken 1.67g/kcal
  • beef 13.82g/kcal

So, the CO2 equivalent from the extra food needed for cycling would be:

  • 0.06068 kg for soy
  • 1.36 kg for chicken
  • 1013.74 kg for beef

The extra shower doesn't really matter

The bicyclist also takes an extra shower. Let's use the same assumptions as a CBC campaign:

Assumes average shower time in Canada of 7.6 minutes (Source: Ipsos-Reid poll for GoBlue.org, 2008), average shower flow of 15 L per minute, and five showers per week. Also assumes 0.06 kWh electricity to heat one litre of water, and 22 g CO₂eq produced per kWh electricity used (Source: BC Hydro).

For 7.6 minutes the water usage is 114 liters, which requires 6.84kWh to heat. The CO2 equivalent from taking the shower is thus 0.15kg. This is just 3.6% of what the car is using so it's quite negligible.

The total

For most foods other than pork, beef or lamb, the total energy consumption is below what the car uses. For example, eating only chicken, the bicyclist's total would be 1.45kg75kg, which is significantly less than the car.

The limit where the bicycle pollutes more than the car is if the food creates more than 54.2117 g/kcal CO2 equivalents. So the bicyclist can easily afford to eat some beef, if the main energy source is vegetables.

A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 1/3 beef, 2/3 vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0


And here's the calculation. The initial assumption is that the choice between car and bicycle doesn't affect the amount of other exercise. In practice, it might be different, but this is the only way we can calculate.

Car

CO2 emissions for the average new car in 2006 were 167.2 g/km, so let's assume this amount. For 25km the car pollutes 4.18 kg CO2.

Bicycle

The extra food may be significant

Riding a bicycle uses up 1.62 kJ/(km∙kg). Let's assume the rider weighs 80kg, which is below or above average for a male depending on country. Thus the 25km takes 3240kJ total -- that is 774 kcal.

Now, the food CO2 equivalent per kcal depends a lot on the type of food. For example:

  • soy 0.07g/kcal
  • chicken 1.67g/kcal
  • beef 13.82g/kcal

So, the CO2 equivalent from the extra food needed for cycling would be:

  • 0.06 kg for soy
  • 1.3 kg for chicken
  • 10.7 kg for beef

The extra shower doesn't really matter

The bicyclist also takes an extra shower. Let's use the same assumptions as a CBC campaign:

Assumes average shower time in Canada of 7.6 minutes (Source: Ipsos-Reid poll for GoBlue.org, 2008), average shower flow of 15 L per minute, and five showers per week. Also assumes 0.06 kWh electricity to heat one litre of water, and 22 g CO₂eq produced per kWh electricity used (Source: BC Hydro).

For 7.6 minutes the water usage is 114 liters, which requires 6.84kWh to heat. The CO2 equivalent from taking the shower is thus 0.15kg. This is just 3.6% of what the car is using so it's quite negligible.

The total

For most foods other than pork, beef or lamb, the total energy consumption is below what the car uses. For example, eating only chicken, the bicyclist's total would be 1.45kg, which is significantly less than the car.

The limit where the bicycle pollutes more than the car is if the food creates more than 5.21 g/kcal CO2 equivalents. So the bicyclist can easily afford to eat some beef, if the main energy source is vegetables.

A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 30% beef, 70% vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0


And here's the calculation. The initial assumption is that the choice between car and bicycle doesn't affect the amount of other exercise. In practice, it might be different, but this is the only way we can calculate.

Car

CO2 emissions for the average new car in 2006 were 167.2 g/km, so let's assume this amount. For 25km the car pollutes 4.18 kg CO2.

Bicycle

The extra food may be significant

Riding a bicycle uses up 1.62 kJ/(km∙kg). Let's assume the rider weighs 80kg, which is below or above average for a male depending on country. Allow 20kg for bike, clothes etc. and we have 100kg. Thus the 25km takes 4050kJ total -- that is 967 kcal.

Now, the food CO2 equivalent per kcal depends a lot on the type of food. For example:

  • soy 0.07g/kcal
  • chicken 1.67g/kcal
  • beef 13.82g/kcal

So, the CO2 equivalent from the extra food needed for cycling would be:

  • 0.068 kg for soy
  • 1.6 kg for chicken
  • 13.4 kg for beef

The extra shower doesn't really matter

The bicyclist also takes an extra shower. Let's use the same assumptions as a CBC campaign:

Assumes average shower time in Canada of 7.6 minutes (Source: Ipsos-Reid poll for GoBlue.org, 2008), average shower flow of 15 L per minute, and five showers per week. Also assumes 0.06 kWh electricity to heat one litre of water, and 22 g CO₂eq produced per kWh electricity used (Source: BC Hydro).

For 7.6 minutes the water usage is 114 liters, which requires 6.84kWh to heat. The CO2 equivalent from taking the shower is thus 0.15kg. This is just 3.6% of what the car is using so it's quite negligible.

The total

For most foods other than pork, beef or lamb, the total energy consumption is below what the car uses. For example, eating only chicken, the bicyclist's total would be 1.75kg, which is significantly less than the car.

The limit where the bicycle pollutes more than the car is if the food creates more than 4.17 g/kcal CO2 equivalents. So the bicyclist can easily afford to eat some beef, if the main energy source is vegetables.

5 image of a bicyclist with vegetables
source | link

A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 1/3 beef, 2/3 vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0


And here's the calculation. The initial assumption is that the choice between car and bicycle doesn't affect the amount of other exercise. In practice, it might be different, but this is the only way we can calculate.

Car

CO2 emissions for the average new car in 2006 were 167.2 g/km, so let's assume this amount. For 25km the car pollutes 4.18 kg CO2.

Bicycle

The extra food may be significant

Riding a bicycle uses up 1.62 kJ/(km∙kg). Let's assume the rider weighs 80kg, which is below or above average for a male depending on country. Thus the 25km takes 3240kJ total -- that is 774 kcal.

Now, the food CO2 equivalent per kcal depends a lot on the type of food. For example:

  • soy 0.07g/kcal
  • chicken 1.67g/kcal
  • beef 13.82g/kcal

So, the CO2 equivalent from the extra food needed for cycling would be:

  • 0.06 kg for soy
  • 1.3 kg for chicken
  • 10.7 kg for beef

The extra shower doesn't really matter

The bicyclist also takes an extra shower. Let's use the same assumptions as a CBC campaign:

Assumes average shower time in Canada of 7.6 minutes (Source: Ipsos-Reid poll for GoBlue.org, 2008), average shower flow of 15 L per minute, and five showers per week. Also assumes 0.06 kWh electricity to heat one litre of water, and 22 g CO₂eq produced per kWh electricity used (Source: BC Hydro).

For 7.6 minutes the water usage is 114 liters, which requires 6.84kWh to heat. The CO2 equivalent from taking the shower is thus 0.15kg. This is just 3.6% of what the car is using so it's quite negligible.

The total

For most foods other than pork, beef or lamb, the total energy consumption is below what the car uses. For example, eating only chicken, the bicyclist's total would be 1.45kg, which is significantly less than the car.

The limit where the bicycle pollutes more than the car is if the food creates more than 5.21 g/kcal CO2 equivalents. So the bicyclist can easily afford to eat some beef, if the main energy source is vegetables.

A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 1/3 beef, 2/3 vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.


And here's the calculation. The initial assumption is that the choice between car and bicycle doesn't affect the amount of other exercise. In practice, it might be different, but this is the only way we can calculate.

Car

CO2 emissions for the average new car in 2006 were 167.2 g/km, so let's assume this amount. For 25km the car pollutes 4.18 kg CO2.

Bicycle

The extra food may be significant

Riding a bicycle uses up 1.62 kJ/(km∙kg). Let's assume the rider weighs 80kg, which is below or above average for a male depending on country. Thus the 25km takes 3240kJ total -- that is 774 kcal.

Now, the food CO2 equivalent per kcal depends a lot on the type of food. For example:

  • soy 0.07g/kcal
  • chicken 1.67g/kcal
  • beef 13.82g/kcal

So, the CO2 equivalent from the extra food needed for cycling would be:

  • 0.06 kg for soy
  • 1.3 kg for chicken
  • 10.7 kg for beef

The extra shower doesn't really matter

The bicyclist also takes an extra shower. Let's use the same assumptions as a CBC campaign:

Assumes average shower time in Canada of 7.6 minutes (Source: Ipsos-Reid poll for GoBlue.org, 2008), average shower flow of 15 L per minute, and five showers per week. Also assumes 0.06 kWh electricity to heat one litre of water, and 22 g CO₂eq produced per kWh electricity used (Source: BC Hydro).

For 7.6 minutes the water usage is 114 liters, which requires 6.84kWh to heat. The CO2 equivalent from taking the shower is thus 0.15kg. This is just 3.6% of what the car is using so it's quite negligible.

The total

For most foods other than pork, beef or lamb, the total energy consumption is below what the car uses. For example, eating only chicken, the bicyclist's total would be 1.45kg, which is significantly less than the car.

The limit where the bicycle pollutes more than the car is if the food creates more than 5.21 g/kcal CO2 equivalents. So the bicyclist can easily afford to eat some beef, if the main energy source is vegetables.

A vegetarian bicyclist certainly wins,

for a meat-eater it depends.

The question is what the bicyclist eats to get the required energy. Estimated from calculations below and this table:

  • WIN (1): chicken, milk, eggs, herring, tuna, farmed salmon or (just about) any vegetables
  • WIN (2): half vegetables, half some other fish or pork
  • WIN (3): 1/3 beef, 2/3 vegetables
  • LOSE: a lot of lamb or shrimp; (2) or (3) with too little vegetables

Note that the fractions above are of energy, not weight.

The cargo by Pulpolux !!! on Flickr Image by Pulpolux !!! on Flickr. CC-BY-NC 2.0


And here's the calculation. The initial assumption is that the choice between car and bicycle doesn't affect the amount of other exercise. In practice, it might be different, but this is the only way we can calculate.

Car

CO2 emissions for the average new car in 2006 were 167.2 g/km, so let's assume this amount. For 25km the car pollutes 4.18 kg CO2.

Bicycle

The extra food may be significant

Riding a bicycle uses up 1.62 kJ/(km∙kg). Let's assume the rider weighs 80kg, which is below or above average for a male depending on country. Thus the 25km takes 3240kJ total -- that is 774 kcal.

Now, the food CO2 equivalent per kcal depends a lot on the type of food. For example:

  • soy 0.07g/kcal
  • chicken 1.67g/kcal
  • beef 13.82g/kcal

So, the CO2 equivalent from the extra food needed for cycling would be:

  • 0.06 kg for soy
  • 1.3 kg for chicken
  • 10.7 kg for beef

The extra shower doesn't really matter

The bicyclist also takes an extra shower. Let's use the same assumptions as a CBC campaign:

Assumes average shower time in Canada of 7.6 minutes (Source: Ipsos-Reid poll for GoBlue.org, 2008), average shower flow of 15 L per minute, and five showers per week. Also assumes 0.06 kWh electricity to heat one litre of water, and 22 g CO₂eq produced per kWh electricity used (Source: BC Hydro).

For 7.6 minutes the water usage is 114 liters, which requires 6.84kWh to heat. The CO2 equivalent from taking the shower is thus 0.15kg. This is just 3.6% of what the car is using so it's quite negligible.

The total

For most foods other than pork, beef or lamb, the total energy consumption is below what the car uses. For example, eating only chicken, the bicyclist's total would be 1.45kg, which is significantly less than the car.

The limit where the bicycle pollutes more than the car is if the food creates more than 5.21 g/kcal CO2 equivalents. So the bicyclist can easily afford to eat some beef, if the main energy source is vegetables.

4 summary of what you can eat
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3 initial assumption
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2 the limit where car becomes more ecological
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1
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