BMI Adeu (weightwatcher)!

[Capiert]

m [kg] = 20 * (h^2.5) 

The ideal body mass (ibm)

 in kilograms

 is (ruffly) the height h in meter(s)

 to the exponent 2.5,

 multiplied by the (nice) BMI (body mass index) ~20 [kg/(m^2)].

 

E.g.

m=k*(h^exp),

Both constants(' values, & (their) units):

 k=BMI (with per rooted meter), e.g. 20 [kg/(m^2.5)];

 & exponent exp (2.5)

 can be varried

 for differences in age, sex, fitness muscle training.

 

I don't see why we should perpetuate such an awkward system as the BMI (tables etc)

 when people simply want to know what they should weigh (in mass) for good health.

 

Good luck

Best wishes.

 

P.S.

Simply type your height (in meters) in a calculator,

 root it,

 multiply by your height,

 multiplied by your height,

 multiplied by 20.

 

(root h) * h * h * 20 = m.

 

Formally:

m [kg] = 20 [kg/(m^2.5)] * ((h [m])^2.5).

Edited May 21, 2018 by Capiert

[Sensei]

1 hour ago, Capiert said:

P.S.

Simply type your height (in meters) in a calculator,

 root it,

 multiply by your height,

 multiplied by your height,

 multiplied by 20.

 

(root h) * h * h * 20 = m.

 

Formally:

m [kg] = 20 [kg/(m^2.5)] * ((h [m])^2.5).

Example:

If we will take height 1.9m, and follow your equation, we will get:

sqrt(1.9)*1.9*1.9*20 = 99.5 kg

If we will take original BMI equation, we will get:

1.9 * 1.9 * 20 = 72.2 kg

But according to BMI tables >= 25 is overweight.. let's check what is mass for height 1.9 m for 25:

1.9 * 1.9 * 25 = 90.25 kg

Divide your result by BMI one:

99.5 kg / 90.25 = 1.1 = +10% more

 

1 hour ago, Capiert said:

m [kg] = 20 * (h^2.5) 

The ideal body mass (ibm)

 in kilograms

So, according to your "speculation" what is already overweight by 10% of mass, is "ideal body mass".. ?! How come?

Somebody (typically sportsman) can have BMI overweight, caused by large mass of muscles, but such person is already aware how to take care of his/her body..

 

[Capiert]

1 hour ago, Sensei said:

Example:

If we will take height 1.9m, and follow your equation, we will get:

sqrt(1.9)*1.9*1.9*20 = 99.5 kg

If we will take original BMI equation, we will get:

1.9 * 1.9 * 20 = 72.2 kg

But according to BMI tables >= 25 is overweight.. let's check what is mass for height 1.9 m for 25:

1.9 * 1.9 * 25 = 90.25 kg

Divide your result by BMI one:

99.5 kg / 90.25 = 1.1 = +10% more

So, according to your "speculation" what is already overweight by 10% of mass, is "ideal body mass".. ?! How come?

Not necessarilly. You can bend the details as you need.

Quote

Somebody (typically sportsman) can have BMI overweight, caused by large mass of muscles, but such person is already aware how to take care of his/her body..

Yes, which BMI to use for the ideal is a matter of choice.

I've selected 20 (rounded up),

 because it's an easy number to remember

 for calculators

 (instead of accurate).

But you can use the (exact) smaller BMI value,

 if you want;

 nobody is stopping you.

I've showed how I set up the (simple) formula,

 so it can be fine tuned.

BMI is a guideline,

 but I find it extremely awkward

 especially for people who don't know it.

My (major) point is the height exponent works better with 2.5;

 NOT 2 !

Why NOT setup the formula (as a ruff rule of thumb) on that basis?

I know the exponent "2" is simpler mathematically,

 but it failed for the purpose

 of a simple (universal) formula

 that gives a mass anywhere near what is needed

 without changing BMI's (=the coefficient radically).

 

Naturally,

The devil is in the details, fat %, age, sex, health.

 

Sometime we're going to have to modernize.

Edited May 21, 2018 by Capiert

[hypervalent_iodine]

I don’t really see the benefit over normal BMI calculations. You still appear to suffer from the same major problems, namely that a “good” BMI is not one size fits all when you account for muscle weight etc. 

[Ten oz]

The association between BMI and health risks isn't anymore telling then age, genetics, and lifestyle are. BMI is just a superficial way to guess at what is going on with ones diet and lifestyle. Provided one has a good diet, active lifestyle (relative to age), and feels healthy their BMI probably isn't important. That said it has been my experience that people simply are not honest with themselves about their diets and activity levels or are totally ignorant of them. In such cases a generic standard (BMI) is useful in creating a standard for those otherwise have known.  

Where I work we actually get weighed in a couple times a year at a minimum. As a collateral responsibility I work with people who miss their weight. In my experience the overwhelming majority of people who are over their BMI are so because they are fat. In 12yrs of working with those who weighed in over I  have never seen where someone simply had too much muscle. I think people use the too much muscle excuse to deny the simply truth that they are fat. When  Arnold Schwarzenegger won his first Mr. O he measured 186 cm (6'1) tall at 107kg (236lbs) in weight. Admittedly he was also using steroids. Yet I have known many men over the years heavy as or heavier than 107kg who are no taller than 186cm who insist it is all muscle which would mean they are more muscular than a competition ready  Arnold Schwarzenegger cycling steroids. While it is true some athletes pack on weight for their sport it is also true that most are fat. Athletic skill positions seldom ever require artificial weight. It is generally the the known skill position where one benefits from size and in those non-skill positions the sizes typically includes lots and lots of fat. 

[Capiert]

1 hour ago, hypervalent_iodine said:

I don’t really see the benefit over normal BMI calculations. You still appear to suffer from the same major problems, namely that a “good” BMI is not one size fits all when you account for muscle weight etc. 

Scalability[edit]

BMI is proportional to the mass and inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high, compared to their actual body fat levels. In comparison, the Ponderal index is based on the natural scaling of mass with the third power of the height.

However, many taller people are not just "scaled up" short people but tend to have narrower frames in proportion to their height. Carl Lavie has written that, "The B.M.I. tables are excellent for identifying obesity and body fat in large populations, but they are far less reliable for determining fatness in individuals."^[10]

https://en.wikipedia.org/wiki/Body_mass_index

 

BMI scales poorly. It's poorly proportioned for the human body.

I'll assume most people are neither round like a ball,

 nor flat like a pancake.

Sensei, the same wiki page (chart) also include BMI=25 as normal (limit),

 as well as overweight.

 https://en.wikipedia.org/wiki/Body_mass_index

So there is chaos in (either wiki? &/or) BMI.

International variations[edit]

These recommended distinctions along the linear scale may vary from time to time and country to country, making global, longitudinal surveys problematic.

Hong Kong[edit]

The Hospital Authority of Hong Kong recommends the use of the following BMI ranges:^[16]

Category	BMI (kg/m2)
	from	to
Underweight		18.5
Normal Range	18.5	23
Overweight—At Risk	23	25
Overweight—Moderately Obese	25	30
Overweight—Severely Obese	30

 

The waist to height ratio indicates fatness better.

 

That only needs some factor(ing coefficient) to set the ratio to 1=100%.

4 hours ago, Sensei said:

Example:

If we will take height 1.9m, and follow your equation,

but use k=18.1 (instead of 20)

we will get:

sqrt(1.9)*1.9*1.9*18.1 = 90 kg.

Edited May 21, 2018 by Capiert

[Capiert]

I.e. For the ideal body mass.

We can round k~18 for simplicity.

Edited May 21, 2018 by Capiert

[YaDinghus]

I love twiddling and fiddling with calculations of this sort, and I've come up with all kinds of ways to make myself feel good about my body with math. One of the steps I took was the same as the one proposed by OP, but it wasn't quite satisfactory, because it still went out of scale. What I did next was examine some of the assumptions of the people who developed the BMI, and to me it seemed they were averaging men at 1.7m and women at 1.6m of height - the sizes at which the BMI tables for westerners apply best. So instead of just whopping up another .5 exponent on the size, I made it a factor of (1.7/h)

 

For demonstration: Person weighing 107 kg at 193 cm

 

Standard BMI: 28.73

Adjustment by OP: 20.68

My 'formula': 25.30

 

The deviation is not as extreme as with OP's formula, and let's face it: people with the size I used as an example have a healthy glow in their cheeks, and are definitely too heavyset for military service without being significantly overweight i.e. expecting health issues. Because 20.68 would mean they are in perfect shape to be shipped out to wherever the USA sends them these days.

Though, as I've mentioned above, I did this to feel better about myself when I wasn't working out much and eating too much junk food, just to avoid breaking with my habits, and not to make a 'better' BMI formula. I neither have the resources nor the training to seriously make a better BMI formula...