Monday, January 7, 2013

Barbie says "Math is hard!"

Weight Loss Math - the bane of my existence.


Don't get me wrong.  I married a math major. I can add large sums in my head.  I am a multiplication wiz.  I know my change before the neanderthal clerk can get the computer to spell it out for them.  I was raised before calculators were allowed within a 2 mile radius of schools.
It's not math itself that is the problem, it's the information that this particular branch of math conveys.  Weight loss math's main downfall is this conclusion that it forces one to arrive at:  It is possible for an obese adult to maintain their weight on VERY little food.  And it takes A LOT of exercise to lose weight without changing what/how you eat. And we are not given this information by any reliable source.  I didn't learn it in high school health class.  They didn't teach it in physiology class at Muhlenberg.  I didn't get it in med school, residency or fellowship.  I figured it out on my own, after spending many years picking over diets, studies and textbooks.

Here are a few numbers to keep in mind when trying to figure out where your weight loss efforts are going amiss:

One pound of fat = 3500 calories

Basal metabolic rate of the average middle aged female =  1272 calories per day
(based on the Katch-McArdle equation)

Maintenance calorie needs for average middle-aged female = 2100 calories per day
(from the American Cancer Society: Calorie Counter Calculator )

(the difference between these 2 is that BMR is if you are lying in bed all day, maintenance calories are if you get out of bed and go about life)

Number of calories you need to eliminate per day if you wish to lose 1 lb per week = 500 calories

Number of calories you need to eliminate per day to lose 2.5 lb per week = 1250 calories

Number of calories burned by running = 105 calories per mile

Number of calories burned by walking =  74 calories per mile

(these are both from the 2004 Syracuse university study showing that we are  overestimating the amount of calories used in exercise:  Energy expenditure of walking and running )

Number of hours needed walking on the treadmill to lose one pound = 12 hours
(based on a 4 mph pace)

So if you eat only 850 calories a day or walk at a fast pace for 24 hours per week you can reasonably expect that in an entire month of that behavior, you will have lost 10 lbs.  That's just flat out depressing.  However, the good news is that if all you want to do is maintain your current weight, you can eat 2100 calories a day and do absolutely no exercise and you should be ok.

Before you start arguing with me that you aren't sedentary or that you walk at a 4.2 mph pace, not 4.0 mph, remember that these numbers are all estimations.  If your goal is to lose weight then you have nothing to gain by manipulating these numbers to suit your circumstances.  None of my patients have ever come to me and said, "I'm burning more calories than your data assumes and now I'm losing too much weight so I think we should adjust my calorie intake up."  Any fudging you do on the front end of these calculations only worsens the impact of the cheating/fudging you do on the back end.  And lets face it, we all slip at times. 

And just FYI, that whole "starvation mode" metabolism thing is utter bull.  I'll address that in a future post, but suffice to say that no overweight or obese person will go into "starvation mode" on a low calorie diet.  There are no studies to support it and I've seen first hand that it just doesn't happen.  I put all my bariatric surgery patients on a 600 calorie per day diet for 2-4 weeks before surgery and while they are purely miserable, if they adhere they lose around 5-8 pounds per week. 

Ultimately, you may ask, "What am I supposed to do with all this math?"  The answer is simple;  whatever you want.  You may use it to decide that you need to ramp up the intensity, duration or frequency of your exercise.  You may use it to decide that you need to start carving calories out of your life.  You may use it to decide that it's hopeless and give up the ghost entirely (I hope not, cuz it isn't hopeless, I promise)  But at least you've got the information in it's distilled form.  My hope is that it will motivate you to do both of the first two and find that it actually does make a difference knowing the math.

New week, new information.  Keep up your food journaling and keep track of the numbers - you may be surprised!

Coming Wednesday:  HOW to eat...really.

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