In my week of carefully recording my weight and diet, using the excellent CRON-o-Meter program, I gained a half pound–from 163.5 to 164.0 pounds in the seven day moving average. Just to emphasize, I wasn’t trying to lose weight, rather just to record what a typical week of eating was like for me.

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.