Let’s say I have a desk job, so mostly sedentary, but I exercise 2 times a week (a good vigorous jog, 30-45 minutes, burns around 500-700 calories for me). According to the rather vague definitions of Activity Factor, that seems to put me in the category of Light Activity, so I use BMR x 1.375 to find my calories to maintain my weight (Maintenance Calories). I want to consume 500 less than that to lose weight at approximately 1 pound per week. So I add up all the calories I eat each day and compare that to the Maintenance Calories number.

The question is, should I count the calories burned during discrete bouts of exercise, or are they already included in determining that I am in the Light Activity range? E.g., is it this?
Calories consumed: 2575
Exercise calories: 500
Net calories consumed: 2075
Maintenance Calories (BMR x 1.375): 2873
Calorie Deficit (consumed minus burned): 2075 – 2873 = -798
(this is what I am currently doing)

Or this?
Calories consumed: 2575
Exercise calories: 500
Net calories consumed: 2075
Maintenance Calories (BMR x 1.2): 2507
Calorie Deficit (consumed minus burned): 2075 – 2507 = -432
(only counting exercise once, subtracting from daily consumption)

Or this?
Calories consumed: 2875
Exercise calories: (included in Activity Factor)
Net calories consumed: 2875
Maintenance Calories (BMR x 1.375): 2873
Calorie Deficit (consumed minus burned): 2875 – 2873 = 2
(only counting exercise once, in determining Activity Factor)

The Activity Factor has a huge impact on the Maintenance Calories number. If I choose 1.375, I get 2873. If I choose 1.2, I get 2507. That’s a large cookie’s worth of difference! So I want to choose Activity Factor correctly, and also I don’t want to count exercise twice if it shouldn’t be. Or maybe I should adjust my Activity Factor to match reality (my actual tracked weight as I lose it)?

In general, your BMR is the calories you consume per day is meant to satisfy your basic body functions for respiration, muscle repair, etc. More calories are required for the thermic effect of food (digestion, peristalsis). Still more are necessary for activity.

If you eat below your estimated BMR, you are not providing enough energy for your basic body needs and activity you do beyond this level diverts calories from your basic function toward activity. This is not appropriate unless you have a legitimate amount of EXCESS body fat to lose.

Activity factors are meant to account for the amount of activity you do plus exercise. I don’t know the research on the accuracy of activity factors. But, ignoring them completely is unlikely to produce a healthy weight loss.

I would recommend using the BMR at 90% of estimated, plus an appropriate activity factor and subtracting 250-500 cal/day of food intake. You will not get a super quick weight loss, but you will be less likely to feel hungry, be prone to binge eating or “cheating”, and use the minimum amount of muscle protein for energy.

Also, it’s most important that you are making relatively accurate assessments about the amount of food you eat since weight loss tends to be tripped up by inaccurate reporting of intake and underestimating the portion sizes and thus the calorie counts of food.

If you are following the above information, have a reasonable weight and normal amount of body fat, you might not lose weight but that might be your biological set point. It would take you longer and more effort to lose weight than someone who has actual excessive body fat to lose. This isn’t because you are doing something wrong, take it as a compliment from nature. Shift your focus to building muscle (which you should not restrict calories to do) and you might achieve the more toned look you want.

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