BMI

[Jacomus]

I've struggled through some serious weight problems (a desperate lack of it) and come out of it ok, though I am very conscious of my weight. A couple of Kgs over or under 75Kgs for my weekly average and I take remedial action.

I have just decided to drop that limit by 5kgs, and go down to 70Kgs because I feel that it will be beneficial to my cycling, and it shouldn't do me any harm to shed a bit of fat.

My BMI at current weight of 75kgs is 22.5 and at my target of 70Kgs it is 20.5

As an experiment last year I got down to 63Kgs and I looked very unhealthy, got cold easily and bonked easily on long rides if I didn't take a generous supply of carbo gels and drink. But my BMI was still in the healthy zone at 18.5 (though right on the limit).

I know musculature skews BMI readings, but I'm wondering by how much and whether BMI is worth taking note of?

[andygates]

BMI is a tool for the masses, and works on averages.  Far more reliable is an idea of how much body fat you're carrying, and how fit you feel.  There's clever technical ways to determine this but the mirror jiggle test is the easiest: If it's not wobbling, then it's muscle

[Jacomus]

I've got bugger all jiggle, only the moobs and they stop it if I tense my pecks.

There is the spare innertube round my belly (have been told I can't call it a tyre) but once again, tensing stops it from jiggling.

I guess I'll just do it and see how I feel!

[hellymedic]

BMI is a meaningless kludge that just happens to work if you are of average adult height.
A BMI of below 20 is seldom a good idea for a chap unless he's naturally built like a whippet.
Relating mass to the square, rather than the cube of the subject's height never made sense to me. (100kg is not really excessive for a chap who's 2 metres tall but gives a BMI of 25.)
It isn't always a good idea to be a weight weenie. 70kg strikes me as about the right weight for you.

[Jacomus]

BMI is a meaningless kludge that just happens to work if you are of average adult height.
A BMI of below 20 is seldom a good idea for a chap unless he's naturally built like a whippet.
Relating mass to the square, rather than the cube of the subject's height never made sense to me. (100kg is not really excessive for a chap who's 2 metres tall but gives a BMI of 25.)
It isn't always a good idea to be a weight weenie. 70kg strikes me as about the right weight for you.

Good!

me --> 183cm, 22yrs, 31"waist, currently 75kgs

[MSeries]

BMI is a meaningless kludge that just happens to work if you are of average adult height.
A BMI of below 20 is seldom a good idea for a chap unless he's naturally built like a whippet.
Relating mass to the square, rather than the cube of the subject's height never made sense to me. (100kg is not really excessive for a chap who's 2 metres tall but gives a BMI of 25.)
It isn't always a good idea to be a weight weenie. 70kg strikes me as about the right weight for you.

Good!

me --> 183cm, 22yrs, 31"waist, currently 75kgs

I am glad you put your dimensions down, when we met I thought you looked quite slim.  I am lightweight, today I was 73kg, I am 1.85m and 43 years old. I don't really want to lose weight but do want to lower my body fat % age. By making the weight fat into useful muscle I am hoping my cycling will improve, maybe that is what you should think about instead of weight loss. DO NOT get hung up on your weight you are a healthy weight now.

[mattc]

Slight OT diversion ...

As an experiment last year I got down to 63Kgs ... and bonked easily on long rides if I didn't take a generous supply of carbo gels and drink.

I'm curious as to why this would happen. My understanding is that even a pound or two of fat contains so many calories that you can ride all day on it (well, nearly). So having, say 20% body fat would not protect you from the bonk compared to being 15%

Are there other mechanisms at work here? Does the body go into some sort of starvation mode to limit your fat metabolism?

[andygates]

By making the weight fat into useful muscle I am hoping my cycling will improve

Well, by building muscle and cutting fat.  One does not transform into the other.

[MSeries]

By making the weight fat into useful muscle I am hoping my cycling will improve

Well, by building muscle and cutting fat.  One does not transform into the other.

That's what I meant, yes.

[Maladict]

I are 182cm and 71kg.  Works for me. 

[Jacomus]

Slight OT diversion ...

As an experiment last year I got down to 63Kgs ... and bonked easily on long rides if I didn't take a generous supply of carbo gels and drink.

I'm curious as to why this would happen. My understanding is that even a pound or two of fat contains so many calories that you can ride all day on it (well, nearly). So having, say 20% body fat would not protect you from the bonk compared to being 15%

Are there other mechanisms at work here? Does the body go into some sort of starvation mode to limit your fat metabolism?

Maybe it is something to do with how the body access its reserves?

So, the amount of fat was enough, but it wasn't a spread out (or something) and my body found it harder to get energy from it. Maybe if I had persevered at that weight my body would have adjusted, but I did give it a month.

[andygates]

I believe there's a regulatory mechanism involved which varies from person to person but bascially, no, you don't just suck fat into energy when you'd like - if that was true then bonk training would make me a ripped adonis.  Fat metabolism's relatively slow so you can outpace it.  And it's more of a background, "restock glycogen while sleeping" kind of thing.

[Maladict]

Can you make glycogen from fatty acids?

I thought (based on recollection of a picture Greenbank posted ages ago) that it couldn't be done, which I expect is one reason why fats are considered bad in sports nutrition.

Someone who knows what they are talking about will be along momentarily.

[Gus]

No  the body cant produce glycogen, but something similar under Ketosis

G

[David Martin]

I'm fairly sure that obesity and high BMI are a symptom of an unhealthy lifestyle rather than being unhealthy in their own right.

I'm not hung up about my weight (and rather high BMI) except to the extent that I know I will enjoy cycling more if I am lighter (and fitter). So I have given up weighing myself, have taken up being careful to measure things when I serve them (three spoons of museli rather than tip the packet up..) and concentrate on getting fit.

..d

[border-rider]

Can you make glycogen from fatty acids?

No, but you can metabolise fat breakdown products to power muscles.  It's just less efficient than burning carbs and needs more oxygen.  So it only really works at lowish heart rates ( usually less than 75% of max, but it varies - there's another thread on this)

[border-rider]

I believe there's a regulatory mechanism involved which varies from person to person but bascially, no, you don't just suck fat into energy when you'd like - if that was true then bonk training would make me a ripped adonis.  Fat metabolism's relatively slow so you can outpace it.  And it's more of a background, "restock glycogen while sleeping" kind of thing.

It's the main source of energy on long rides.  If you try to do something like LEL, you'll need to be burning fat because you can't easily eat and digest enough to fuel yourself from carbs.  On long rides, the digesting part of that can be the real issue - most people find that their digestion slows right down as the resources get diverted to the muscles.

You can suck fat into energy, but ti takes  a lot of slow miles to use up any appreciable amount - maybe a pound or so of fat per 12 hours in the saddle  - with no other food. 

[Chris S]

Best way to burn fat:

Grow muscle.
Do intervals (Intensity is the key)
Do Long steady distance rides.
Maintain a daily calorie deficit

Best way to bugger up the chemistry for this:

Drink alcohol regularly

Seriously. All fat burning and glycogen storing chemistry needs your liver. If your liver is busy clearing up after you then the process is compromised.

[Ian H]

You can suck fat into energy...

That sounds utterly disgusting. 

[hellymedic]

Best way to burn fat:

Grow muscle.
Do intervals (Intensity is the key)
Do Long steady distance rides.
Maintain a daily calorie deficit

Best way to bugger up the chemistry for this:

Drink alcohol regularly

Seriously. All fat burning and glycogen storing chemistry needs your liver. If your liver is busy clearing up after you then the process is compromised.

And the calories from alcohol can only be stored as fat...(not glycogen)

[andygates]

So how come "hangover legs" can be so fast while feeling so bad?  I always figured that was a glycogen load.

[border-rider]

I reckon its cos your fat metabolism is so screwed you are only comfortable well into the glycogen-burning zone - ie going faster.

[border-rider]

Some interesting stuff here

Alcohol Metabolism-Alcohol Alert No.35-1997

that suggests that boozing doesn't make you fat.  Possibly the opposite, though I guess it is quite capable of messing up fat metabolism just as Chris said so it may have an effect on attempted weight loss