If vertical growth is hormonally driven, couldn’t horizontal growth be too?

Some of you will be familiar with Gary Taubes’ book The Diet Delusion (entitled Good Calories, Bad Calories in the USA). In this book, I think Taubes does a good job of presenting obesity as not a problem to do with gluttony and lack of exercise, but a problem of fat storage. He argues, quite convincingly I think, that if we want to stem the tide of overweight and obesity, we need to eat less foods that promote fatty deposition in the body. And seeing as the fat storage hormone in the body is insulin, this means eating a diet low in certain carbs. Don’t let this super-condensed version of Taubes’ book put you off reading the whole thing ” it’s well worth a read if your interested not in the rhetoric that ‘healthy’ eating messages are awash with, but what the science shows.

Another of Taubes’ ideas is that obesity is hormonally driven. He uses childhood and adolescent growth spurts as a sort of analogy. Here’s his thinking: kids and adolescents can go through growth spurts during which they eat voraciously. The huge volumes of food these kids can pack away are not necessarily due to gluttony, right? Right ” they’re due to hormonal signals in the body that stimulate appetite. Taubes quite legitimately asks, if vertical growth can make us hungry as a result of hormonal signals, why can’t it be the same for horizontal growth?

In Taubes’ mind, it could well be that as we put on weight, hormonal changes enhance the appetite which can cause ‘overeating’ and therefore more weight, and so the cycle repeats. This seems utterly plausible to me. Though the mere mention of this concept can, I’ve noticed, not sit too comfortably with those who have been brainwashed into believing that all overweight people must be eating too much or exercising too little as a result of their lack of self control/weak will/inadequate personality or whatever.

I came across a study recently which appears to support Taubes’ theory. I’ll say up front it was done in rats. I prefer generally to stick to human research on this site, but do make exceptions when I feel there is something genuinely interesting to learn from work done in animals.

In this study, scientists focused on two sorts of rat: lean ones and rats bred to be fat (especially around the middle) ” known as ‘Zucker’ rats. The scientists found evidence that the fat found in both these types of rats produced a substance called ‘neuropeptide Y’ (NPY). This substance, among other things, stimulates appetite. It was previously thought to originate only in the brain, so finding that it can be made by fat cells too is quite a step forward in our understanding of this substance.

So, in short, fats cells themselves appear to have the ability to produce hormones that stimulate the appetite. What is more, this research found that in the fat (Zucker) rats, NPY levels were significantly higher than those in the lean rats. The authors of this study suggest that abdominal obesity may cause rises in NPY levels which may cause overeating and therefore more abdominal obesity and so on and so forth. I’m sure you won’t need me to point out that this research seems to provide support for Taubes’ notion that that just as vertical growth can be hormonally driven, horizontal growth can be too.

References:

Yang K, et al. Neuropeptide Y is produced in visceral adipose tissue and promotes proliferation of adipocye precursor cells via the Y1 receptor. The FASEB Journal [Epub before print 7 March 2008]

3 Responses to If vertical growth is hormonally driven, couldn’t horizontal growth be too?

  1. Jenny Ruhl 21 May 2008 at 2:23 pm #

    It’s worth noting that the incretin hormones impact on Neuropeptide Y, whcih probably has something to do with the way that, when the new incretin hormone drugs, Byetta and Januvia, work, which is not always, they cause something a lot like anorexia.

  2. Daisy 23 May 2008 at 5:23 pm #

    Why are these hormonal signals so much stronger in Americans (in certain parts of the US) and to a lesser extent, Brits (ditto the UK) than in other peoples in other parts of the world?

  3. Liz 25 May 2008 at 6:18 pm #

    While calorie balance matters and most dieting relies on the Micawberish principle that if you eat fewer calories than you expend you’ll lose weight, this is certainly not the whole story.

    The calorie balance theory of dieting presupposes that the human body is a simple thermodynamic system with no outside influence to change the way calories are used in this mechanistic model.

    The rules of thermodynamics work well in a closed system. But the human body is not a closed system because the thermodynamics are upset by the hormone influences.

    And boy are they complex!

    I recently gave a lecture on satiety mechanisms and I prefaced it by saying to the students, all of this is true and none of it is true. Each of the satiety mechanisms identified seem to work but put them all together into one complex system (i.e. the hungry human) and they don’t always work very well.

    Perhaps this is an example of chaos theory – very small changes in complex systems give unpredictable results.

    Or maybe it’s the interactions between stress hormones and the brain.

    Or another unpredictable factor in humans is their emotional attachment to food ” if you see a donut as a source of comfort and love, isn’t that going to change your hormone levels and upset the delicate neurotransmitter balance in the satiety centres? And how to we replicate that in the rodents? Split them up with their boyfriends? Make them have a row with the boss? Give them teenagers (doing A levels) to look after for a week?

    I think Taubes has the right idea but, phew, disentangling that one is going to be difficult!

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