January 16, 2009

Fine Tuning the Metabolic Calculator

UPDATE: 1/19/09: Kg/Cm option added to calculator for our non-U.S. users.

I got some good feedback here and from some of the low carb dieters on the Low Carb Friends forum. Many of you find that the predicted calorie levels the calculator comes up with are lower than what they can lose weight eating on a ketogenic diet.

So to check this out further, I dug out the detailed records I kept during my year of weight loss on a ketogenic diet back in 2003. This was a year long ketogenic diet, without insulin or diabetes meds. My usual daily carb input was between 40-60 grams. I lost a total of 33 lbs, starting from a high of 170 lbs though I only started logging when I was already at 160 lbs. I then compared the values the calculator gave me against my actual calorie intake and weight loss.

I found that I was burning many more calories than were predicted using the basal metabolic rate calculated by the Mifflin-St Jeor formula and adding activity calories based on the 1.2 factor which is used to estimate calories burned at a sedentary activity level.

I then figured out, based on my actual weight loss for each month, what the actual activity factor would have been for each month that would have yielded my actual calories burnt.

The actual activity factor was always higher than the standard 1.2 rate, though it fluctuated each month between a high of 1.56 and a low of 1.28 during the period when I achieved most of the 23 lb loss tracked by this data. (I had dieted for a few months earlier without tracking, for a total loss of 33 lbs.)

I was sedentary the first three months logged here, then I started going to the gym five or six days a week and doing an hour of treadmill. This did not make any appreciable difference in how many calories I burned. When I added some weights several months later at a time when I was exercising at maximum intensity on the treadmill, the activity factor had dropped closer to the traditional value given for light exercise (1.37) which was lower than it had been during my sedentary weight loss period. Some months when exercising and eating similarly, I gained weight. This is typical of what happens six months into a diet.

I then analyzed how wmy eight loss related to changes in my monthly carb intake, protein and fat intake and the percentage of the diet made up of the different nutrients. I did not see any clear patterns that were sustained over the 10 months I had logged. Early in the diet raising fat and lowering other nutrients appeared to help with weight loss, but later in the diet nothing seemed predictive.

After thinking this through, I came up with a new activity factor that may produce a more realistic idea of calories burned during the early months of a ketogenic diet and I have added it to the metabolic calculator.

This new activity level is called "Sedentary with metabolic advantage." It multiplies calculated Basal Metabolic Rate by a factor of 1.43 rather than the usual sedentary factor of 1.2 to estimate what the maintenance calorie level would be.

I also retained the standard sedentary calculation and added a new one for light activity. You can chose between these factors and use the one that best matches your experience.

If you are stalled using the "metabolic advantage" number, drop back to the sedentary number. Avoid the temptation to overestimate how hard you are exercising.

Finally, I also added to the calculator's display your calculated basal metabolic rate and of the factor being used to add calories for activity.

Here's the link to the calculator again:

Calculate Your Nutrient Balance on a Ketogenic Diet



Anonymous said...

It’s a very helpfull calculator.

Please make it work for your foreign readers too and add a footnote: m = ... inch and kg = ... lbs.

Thanks, Rainer

Anonymous said...

A great tool in conjunction with your recommendation to track diet and macro nutrients on FitDAy.

Can you straighten me out with regard to 'net carbs', please?

The 'Metabolic Calculator' seems to assume no dietary fiber carbs when it calculates total calories. For example my numbers today were 123g fat, 110g carbs, and 154g of protein (can't wait for lower protein requirement in week 4!) -- but my dietary fiber was 35g. So, does this mean I hit my target of <80g of carbs?

Thank you,

Jenny said...


I ignore net carbs because too many of the carbs people ignore when they use this concept DO turn into glucose in our body. especially the sugar alcohols. But some soluble fiber also can digest into glucose, I've been told.

So it is really up to you how you want to treat the fiber you eat, as only you know how much of it is really inert.

olaf675 said...

Another metabolic calculator that might be of use to some people is at -- http://www.phord.com/cc/

It doesn't include some of the features in your calculator.