Wednesday, 25 April 2012

Epic Obesity Rant

Following on from our "basal energy expenditure failing to predict obesity" post, it seems the same author has written what I can only describe as an epic rant towards the medical industry. It makes for a fantastic read and is well worth 1-2 hours of your time, however towards the end it becomes slightly disappointing as the author converges to the solution of obesity being a "low-fat" diet since his argument is that the body strives to maintain substrate balance and not energy balance per se.

This is because of the observations made in carbohydrate overfeeding studies whereby they generally do not produce significant increases in de novo lipogenesis, and it is therefore wrongly concluded that only dietary fat can contribute to adiposity. Ofcourse, this presents a paradox, as the thing we measure, de novo lipogenesis, does not translate into the phenotype we observe, adiposity, because many people following a ~5% fat vegen diet still manage to produce significant increases in adiposity. This is the fallacy of the above overfeeding study, I can only wonder what the above study would have shown if they had measured changes in adiposity.

Problems in applying the energy balance concept

The author makes the argument that the energy balance theory...
Energy Balance = Energy Intake – Energy Expenditure

fails to consistently predict not only changes in adiposity for every individual, but fails to explain the level of adiposity at which they become weight stable. Most obese people are actually weight stable, but it is at a higher level of adiposity. It should be obvious that, like most things in biology, adiposity is trapped in and regulated by a negative feedback loop ( 1 , 2 ). The only way to successfully change adiposity levels is to change the equilibrium or "middle" point that the feedback loop operates around.

A good analogy is seen with water and drinking. Drinking more water may increase our short-term water balance, but in the long-run we just end up pissing it all out again. And it works in the same way in the negative direction too. For how long can you dehydrate(calorie restrict) yourself for?, before thirst(hunger) becomes overwhelming? - thanks for this notion sidereal :P

The misleading emphasis on the importance of low resting metabolic rates

As we saw previously, BMR does not predict adiposity, the author also makes the point that stature ( height ) which is positively correlated with energy expenditure also does not predict adiposity. This is quite blatently true, I know many tall people who struggle with bodyfat as much as anyone, and I know just as many small people who remain skinny while eating junk food diets.

The author also mentions that things like futile cycles and uncoupling proteins do not make significant contributions to energy wastage that can change levels of adiposity. I personally have seen first hand hundreds of rodent studies showing all sorts of manipulations with UCP's, and various other enzymes/proteins that produce dramatic changes in adiposity, however none of it seems actionable or practical for humans.

1 comment:

  1. LOL, Kindke, I just noticed last night that you raised the issue of selective hepatic IR from Lustig's paper on Carbsane's blog. I noticed how she conveniently ignored it. :p