## Wednesday, September 29, 2010

### Some Calorie Math

Yesterday, I played racquetball with a friend of mine. I immediately noticed that he was significantly thinner than he was when I had seen him last. Once we got to talking, he told me that he had lost 25 pounds over the last 10 weeks. When I asked him what he has done differently, he told me that it mostly has to do with eating better. And, because he cut the junk out of his diet, he is dropping the pounds rapidly on his way to a healthier weight.

Of course, exercise burns calories. Unburned calories equal extra pounds, so exercise is the key to losing weight, right? Not quite. Although it is important, exercise isn't a quick fix to a weight problem. A better diet is usually the key to success.

As I could stand to lose some weight myself, I did some simple math to figure out the best way to get to a healthier weight. There are plenty of great resources online for this.

Disclaimer: I am no nutritionist and I'm overweight, so do not take my post to be "expert advice." Think of it as me reporting what I have learned over the past week.

Losing Weight By Expending Calories

Consider two facts:

1. A person must burn 3500 calories more than he/she consumes to lose a single pound of weight.
2. A 230-lb man (that's me) can burn 184 calories running a mile (Go to the website. Type 230 in for the weight, 8 minutes for the time, and look for "Running 7.5 mph").

That means that I would have to run 19.02 miles at 8 minutes per mile to burn enough calories to lose a single pound. For someone who is out of shape (and looking to get into shape), that seems like a lot of work to go from 230 pounds to 229 pounds.

Note: It is more about distance than effort. By that same website, I could walk a mile at 4 miles per hour and burn 124 calories. That means I would have to walk 28.22 miles to lose one pound. The extra 60 calories per mile must come from elevating your heart rate and moving your arms more. An economist like me would rather run, anyway, because there is an opportunity cost to time spent exercising. If you expend more calories in a shorter amount of time without making it unbearable, that's an economical exercise routine.

Losing Weight By Dieting

A Costco apple crumb muffin

and a cup of coffee have been my breakfast every weekday this summer. Only yesterday did I discover that this delicious muffin has 690 calories. What if I cut the muffin in half? That's shaving 345*5 = 1725 calories off of my diet every week. That's almost half a pound per week.

If the only goal is to lose weight, calories not consumed are just as good as calories expended through exercise (FYI: I'd also like to get in shape). With that in mind, compare running to the "half-muffin diet." I could run 10 miles in a week (2 miles per weekday) and burn 1840 calories per week (same website: 8 minute miles).

Which is easier for me? I think I'll cut the muffin in half, and a little exercise wouldn't hurt either. By that same calorie expenditure website, my racquetball match yesterday (40 minutes to an hour) burned 515 calories. It was fun too. Is anyone up for a game?

1. I'm no expert on this either, but aren't we pretty bad at converting food into energy the body can use? The muffin may have 690 calories, but it wouldn't surprise me to learn that half of that just passed right through the system. It takes a lot of wildebeest to support a few lions, and a whole lot more grass to support the wildebeest. Apparently the energy conversion is tremendously inefficient...so maybe dieting has less of an edge than it seems on paper.

Furthermore, our weights, together with the eating and exercise habits that support them, are a sort of equilibrium...and even if we can pin down the forces at play there, it doesn't mean they're going to hold themselves constant when we start to move away. Maybe our bodies have a good deal of say in how they're going to react to different attempts to deviate from this equilibrium? (For example, there is that anecdote that if you diet hard, lose a lot of weight, and then eat normally again, your body thinks it needs to prepare for future famines and stocks up quickly on fat).

If the body is currently converting a 690 calorie muffin into 400 calories, but you stop eating that muffin, it doesn't necessarily mean your body will retain 400 fewer calories. penny saved != penny earned...

2. I think that you're right that there is an equilibrium weight and eating, but I am not advocating "famine" and then returning to eating normally. Even with the simplistic way I have come to think about weight, diet, and exercise, that wouldn't keep the lost pounds off.

My impression is that the equilibrium is (in part) driven by the fact that heavier people burn more calories in a resting state than lighter people. Hence, after losing weight, a person can't just return to eating normally and expect to keep the weight off. That is, one need not rely on the intuition that the body is saving up after a famine. In the steady state, calorie intake will *have* to be less to maintain the lower weight because lighter people burn fewer calories, even while doing the same activities as heavier people.

Then again, human biology is more complicated than the way I think about it. As an evolutionary motive, it makes sense that our bodies would respond to a calorie deficit by storing whatever extra calories for later "tough times."