Body Fat

Intervention: Day 8, 190 hours, 320 lbs, BMI 45.9

Measuring body fat is one of those inexact sciences where you are going to get mixed results regardless of how you try to measure it. NerdFitness has a fairly good article on this. Sufficient to say that unless you are willing to go in for a DEXA Scan anything you do is going to be off by some percentage compared to your actual body fat percentage.

For example,

  • Using BMI, my body fat percentage is 52.8%
  • Using an Omron Fat Monitor, my body fat percentage is 42.9%
  • Using the US Navy Formula, my body fat percentage is 44.4%

I’m going to state up front here that there is an easy 4th method to figure out body fat which is to use a skin caliper like in the picture above. However, these types of devices are only meant for people who have body fat less than 32% (35% for women). The charts that convert caliper measurement to body fat do not go above these values. While calipers are another good method for measuring body fat, for people like myself who are outside this range, you need to wait until your body fat levels are below 30% before starting to do a pinch test.

Why is body fat important?

There are a few things body fat tells you other than how fat you are.

1) What is your ideal Target Weight

Based on your body fat you can figure out what your lean muscle mass is. From your lean muscle mass, you can then figure out your ideal target weight based upon your preferred body fat that you are trying to achieve.

For myself, I am using 18% body fat as my initial target goal.

Using BMI – 320 lb at 52.8% body fat gives me a lean muscle mass of 151 lbs which when multiplied by 1.18 (+18%) means a target weight of 179 lbs;

Using a Fat Monitor – 320 lb at 42.9% body fat gives a lean muscle mass of 183 lbs and a target weight of 216 lbs; and

Using USNavy Formula – 320 lb at 44.4% body fat gives a lean muscle mass of 178 lbs and a target weight of 210 lbs.

Your body composition will change as you gain or lose body fat and these numbers will change with them. Especially if you are overweight. So while these numbers are helpful in trying to keep track of a potential target, you will need to re-evaluate your goals periodically based on how your body has changed.

For example, when I started the water fast I was at a BMI of 49.2 or 57.4% body fat and 146lbs of lean muscle mass. That is a 5 lbs difference from today which is obviously not possible based on fasting. Both the body monitor and the US Navy Formula give better results but as the saying goes, your mileage may vary.

2) What is your ideal Calorie Intake

We burn calories all the time even when we are doing nothing. Your lean muscle mass is responsible for the majority of the calories you burn. However, the lean muscle mass number in the calculation above is misleading because the human body is 70% water. So for this piece, we need to remove the water from our lean muscle mass calculations by reducing it by 70%.

Sedentary people will burn on average about 50 cals per lb of lean muscle mass (less water content).

Athletes will burn on average about 100 cals per lb of lean muscle mass per lb.

This is before you add any physical activity. A normally fit person can add about 100 calories per mile of walking. So if you do the recommended 10,000 steps per day, that is 5 miles or 500 calories. Athletes are a special kind of crazy all to themselves and it would take a book to go through all the various formulas that cyclists, runners, and other extreme fit people use to figure out their basic calorie intake. I’m not even going to try to touch on that here.

Because of my lifestyle, I use the bottom end of the scale.

Using BMI – 320 lb at 52.8% body fat gives me a maximum calorie intake (before activity) of 2270 cal;

Using a Fat Monitor – 320 lb at 42.9% body fat gives me 2740 cal; and

Using US Navy Formula – 320 lb at 44.4% body fat gives me  2670 cal.

Why are the numbers different

The numbers are different because body composition is different for each person. BMI typically overstates body fat, especailly for people like me who have the skeletal structure of an NFL linebacker. Using a fat monitoring device can be more accurate, however, electrical signals are subject to how hydrated you are and other factors, such as when you last ate, that can give different readings at different times of the day. And the US Navy formula is mostly meant for people who are within the given range of fitness expected for military service.

Each method has its own inherent standard deviation and each is only intended for a population within a given set of parameters. People like myself who fall outside those parameters will always get wildly different results from what is considered normal.

Knowing body fat is important in order to realistically set target goals at any body fat percentage.

There are two things you can do to compensate for this

1) Take the weighted average of multiple results

Since I’m using three different measurement tools, the weighted average formula I use is (lowest value + highest value + 3 x middle value)/5.

This will give a good starting approximation of what your target state should be.

For me, as of today, that means a target weight of 205 lbs and an estimated daily calorie intake (before activity) of 2600 calories (not accounting for my VCO2 requirements).

2) Watch the scale

Let’s assume you have a 2000 cal/day dietary requirement.

If you are eating 2000 calories and walking 6000 steps per day (approximately 300 calories) and you are losing more than 2.5 lbs per month on average, then your lean muscle mass is higher than what you calculated (i.e. less fat). Similarly, if you are losing less than 2.5 lbs per month then your lean muscle mass is lower than what you calculated (i.e. more fat).

Formulas and numeric targets are just approximations of real life. While they are helpful, ultimately it comes down to a question of body image and where you feel comfortable. Right now I’m not comfortable with a BMI of 46. I’ve come to realize that after seeing recent pictures of myself, notwithstanding the health effects that I’ve been feeling every time my weight goes over 330lbs.

Since I’m technically not hungry yet (which still surprises the heck out of me), onwards we go.


Hydration and Salts
Activity Indoors verses Outdoors

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