Monday, August 06, 2007

Why not walk it?





Andrew R said...

So people driving cars don't eat?

Walking emits no C02. Producing food emits C02. If people were in the habit of adding up their calorific output and then eating exactly the amount of food needed to replace it, you might be able argue that being energetic led to higher C02 emissions. But we don't. We go to the shops, buy (say) a hamburger, and then eat that burger. Regardless of whether we drove to the shops, or walked, cycled, ran, cartwheeled etc.

This isn't an interesting new perspective on environmentalism, it's shoddy, thoughtless manipulation of numbers in an attempt to find an excuse for ignoring the obvious.

Matthew Sinclair said...

I agree that most people don't make calory calculations but that, ceteris paribus, more active people eat more seems quite plausible. A rough rule of thumb is enough for this to work.

I reckon quite a few people probably accept a certain weight and then with more activity will eat more. Wanting to eat more is a common physiological response to more exercise.

Besides, this study isn't the work of a sceptic. It is from a book by a "leading environmentalist", "Chris Goodall, campaigning author of How to Live a Low-Carbon Life".

Andrew R said...

According to the USDA, Americans are consuming hundreds more calories per person per day now than they were in the 1950s. Do you really think this is because on average they're more active now?

I just can't believe that there is a significant link between walking to work and increased calorie consumption.


Ruthie said...

That might work in Europe, but here in the U.S. our cities and towns are totally car-oriented. A lot of streets here where I live don't even have sidewalks!

Matthew Sinclair said...


I'm not saying that walking is the only determinant of diet. It doesn't have to be for this result to hold. All it requires is that, ceteris paribus, an increase in exercise is matched by an increase in calory intake.


Kevin Raymond said...

That’s an interesting point however I don’t think it means we should always chose the car instead of walking. Research shows that half of all car journeys in outer London are less than two kilometres – a distance that can be easily walked by most people in 25 minutes. Treehugger has a very interesting article on this issue here:

Not only does walking help reduce pollution but is helps improve health and ease congestion. The Mayor is spending £126 million improving conditions for pedestrians. If you walk about London over the next three years you will see new pedestrian crossings, lowered curbs and improved signage.

Andrew R said...

But, Matt, there's nothing to show that an increase in exercise does lead to an increase in calorie consumption. There are many factors that determine how much we eat (and how energy-intensively it was produced). If you buy processed food, for example, one driving factor in your calorie intake will be the price of different fats on the world commodity market. As they fluctuate, the ingredients of (say) supermarket own label frozen pizza change from batch to batch.
Even in terms of how much you choose to eat, there are a host of different drivers. If you're going to the beach in two weeks, maybe you're walking to work and eating less. Maybe you had a stressful drive and can't be arsed cooking so you order a Chinese takeaway. Hell, one of the biggest factors in how much people eat is how big their plates are. Is buying larger crockery bad for the environment?

As an example, I should have cycled into work today, but instead I drove because I faffed around and ended up running late. I'm going to eat the same lunch I've brought with me, and tonight I'm going to eat the meal my wife is planning on cooking and that we've already bought the food for. Tomorrow I will cycle, and I'll still have a sandwich for lunch and whatever's on the menu for tea. Today, my environmental impact is higher than tomorrow's.

If you can show that people actually do change their diet when they start to walk more, or that they reduce it when they drive more, fine. But given that it's long been observed that a)developing a more sedentary lifestyle leads to weight gain and b) making more journeys on foot rather than by car can help lose weight, I'll be very, very surprised.

In the meantime, there doubtless are issues concerning the cost of food production and transport that it would be interesting to explore. But asserting that driving to the corner shop for a pint of milk is an environmentally friendly choice is a really bad way to draw attention to them.

Meg said...

Yeah, I don't think the ceteris paribus thing works at all-- for one thing, getting more exercise means you're more likely to be knowlegable and thoughtful about your health, which is correlated with eating healthier as well. Healthier eating, even if you were to eat the same portion size (or even a bit bigger), means FEWER calories than less healthy foods, not to mention fewer processed calories, which as the article says are the worst for the environment. Exercise may not show a drastic downward correlation with calories, but it certainly isn't positively correlated.