Wednesday, 31 July 2013

Completing the trine: vive la différence!

First, the obligatory picture of Hannah Spearritt :-)
Women have a harder time losing weight than men. Women retain water more than men for hormonal reasons, but a factor that's overlooked is that, on average, healthy women have higher body-fat percentages than healthy men. This is because women have babies and men don't. Who knew? On the plus side, women produce more DHA than men.

Why should having higher body-fat percentages make a difference to weight loss? See What is the required energy deficit per unit weight loss? The energy deficit required to lose 1lb of body-weight increases with increasing body-fat percentage. It's rarely 3,500kcals per lb.

If you really love mathematics, see The Dynamics of Human Body Weight Change by Carson C. Chow and Kevin D. Hall.

From the above paper:- ΔU = ΔQ - ΔW

where ΔU is the change in stored energy in the body, ΔQ is a change in energy input or intake, and ΔW is a change in energy output or expenditure. This is the Energy Balance Equation. As I said back in Back to black, CIAB, pharmaceutical drug deficiencies & nerds.

Where body weight is concerned, calories count (but don't bother trying to count them).
Where body composition is concerned, partitioning counts.
Where health is concerned, macronutrient ratios, EFAs, minerals, vitamins & lifestyles count.

N.B. Poor health can adversely affect body weight and/or body composition, by increasing appetite and/or by adversely affecting partitioning.


marie said...

Hi Nigel. Interesting posts lately. That paper is a nice find, thanks for sharing! They properly don't choose between their two cases, but I do wonder about the notion of 'set point' in one of the two cases of the model they discuss, does it seem to be defined by the state just before a transient intervention/ transient change or did I miss a variable? That state may well be already perturbed for most people.
Meanwhile, you have a typo in the equation above ;)

Nigel Kinbrum said...

I've been a bit busy today, what with having my new kitchen finished. RE your query: I'll take a look, but may not be able to answer it, as my maths isn't that good.

Well-spotted. Like the proverbial "Elephant in the room", I didn't see the typo, despite multiple checks before posting. Thanks!