How much should I be eating?

I wanted to calculate exactly how many calories I should eat to maintain a steady weight.

Basically, how many miles do I have to run to work off snacks like this…

Mmmmmm homemade pretzels with Trader Joe's jalapeno pub cheese and a Great Lakes Brewery Rye of the Tiger IPA.

But more generally, what should my net calorie goal (calories eaten - calories burned by exercise) be for a steady state? I want to make sure I’m getting enough food calories to balance out running and have a good amount of energy without gaining (or losing) any weight.

Data: calories eaten - calories burned

I’ve just finished participating in a nine week health and fitness challenge competition at work that required a weigh-in and weigh-out measurement. To help make sense of any progress, over those nine weeks I logged everything I ate (as accurately as possible) every day over that time period using MyFitnessPal. This gives me a good estimate for calories eaten.

I also logged every exercise activity I completed using Nike+ (I just used the running app and the training club app). These apps give an estimate for calories burned for each activity.

Over a 64 day period (weigh-in to weigh-out), my daily net calorie average (eaten - burned) was 1010 calories. I also measure a weight loss of 14.4 lbs. I’ll assume 1 pound is 3500 calories and calculate how many calories my body burns just being me (without exercise):

  • 1 lb = 3500 calories
  • days = 64
  • average net calories per day = 1010 cals/day
  • total weight loss = 14.4 lbs
  • average weight loss per day = 14.4 lbs / 64 days = 0.225 lbs/day
  • 0.225 lbs/day * 3500 calories/lb = 787.5 calories/day extra burned

Meaning my daily energy expenditure is about 1010 + 787.5, or about 1800 calories. Neat! Ok, so I guess I can probably eat about 1800 net calories and maintain a steady weight.

Basal Metabolic Rate

How does this match up with what I’ve read about calorie expenditure and basal metabolic rate (BMR)? I googled around a bit to verify if 1800 calories is an appropriate estimate of calorie needs for someone of my person.

The interwebs says that 1332 is my BMR, based on my current height, weight, and age. To calculate daily calorie needs, according to the Harris Benedict Equation, multiply BMR by an appropriate activity factor, as follows:

  • If you are sedentary (little or no exercise) : Calorie-Calculation = BMR x 1.2
  • If you are lightly active (light exercise/sports 1-3 days/week) : Calorie-Calculation = BMR x 1.375
  • If you are moderatetely active (moderate exercise/sports 3-5 days/week) : Calorie-Calculation = BMR x 1.55
  • If you are very active (hard exercise/sports 6-7 days a week) : Calorie-Calculation = BMR x 1.725
  • If you are extra active (very hard exercise/sports & physical job or 2x training) : Calorie-Calculation = BMR x 1.9

If my Calorie-Calculation = 1800 (remember this is net calories, already accounting for exercise), then my estimated activity factor for everyday life is as Calorie-Calcuation/ BMR = 1800/1332 = 1.35. So excluding all the running, that would mean my daily life qualifies as “lightly active.” Ok, I’ll buy into that.

Alternatively, with a BMR of 1332, a sedentary person would need about 1600 calories and a lightly active person would need about 1830 calories.

My estimate of an 1800 net calorie daily goal based on tracking my calories and exercise seems just about right or is at least consistent with other estimates. And I think I’m under for today…hmmm…time for a snack!!