A few things to note:

1. Day-to-day variation in my weight is somewhat typical. The churn is probably from water. Hence, the seven day moving average as a more accurate measure.

2. Each pound of fat contains 3500 (kilo) calories. Therefore, the half pound gain over the week represents about 250 extra calories a day. (Hey, it was the holidays.)

So, how many calories did I average on a given day? About 2126. Subtract the 250 or so extra a day, and we’ll say that 1875 calories a day would be about right for me to just maintain weight. To lose a pound-a-week, I need to eat no more than about 1400 calories a day. A half-pound-a-week? 1625 calories a day.

1875 calories a day is an interesting number. Per the USDA charts, a typical person of my height, age, gender, activity level and weight would need 2858 just to maintain weight. I do it with a third fewer calories. Here is some empiric evidence that I’m an energy sparing person–with the combination of genes, epigenetics and microflora that is more efficient than most at extracting and saving energy from food.

If I ate as many calories as a typical person like me ate, their weight would stay the same; I’d gain about a hundred pounds a year, two pounds a week.

I’ve known this qualitatively for a while, coming from a family of big people and always being prone to gaining weight. Still, seeing the numbers is pretty startling. If I wish to lose weight, I have to eat less, much less, than the average person.

Now I know the number to target. I’m starting at a goal of a half-pound a week, or about 1625 calories.

On my slight five-foot-ten frame, that represents about a fifth more of me since 2001. How did that happen? Very slowly, and with both fat and muscle gains contributing.

Arriving at 135 pounds to Seattle, I was close to being underweight, my BMI above 18.5. Now at 165, I’m not officially overweight, my BMI is still below 25.

BMI isn’t the greatest measure of health. According to the Met Life tables, my ideal body weight is about 155 pounds. Putting aside the numbers for a moment, it’s where I’ve gained fat that matters more from a health perspective. Belly fat, like many men gain as they exit their twenties, is the most worrisome, with negative effects upon blood sugar, lipid profiles and general health.

At some point in the near future, I’m sure to find myself telling a patient to lose weight–ten, twenty, thirty, fifty pounds. How hard is it? By many of the measures I’d use with patients, I could stand to lose ten. Using the best available scientific data, can I do it?

Well, let’s try.

The first step: for the next week, each day I’ll carefully record what I eat and my weight. The goal is to stay about as close as possible to a “typical” week of eating for me, in an attempt to figure out my particular equilibrium between the calories I consume and use in a given day.