Posted by: SLS | September 11, 2011

What is it with these carbs?

Apart from the heaps of uncritical yes-sayers that froth and foam over comment status in semi-intelligent text (read: someone who sometimes uses citations), what really gets under my skin is a systematic hash of bad ideas combined with circumstantial and cherry picked evidence to the tune of sardonic haughtiness.

I can’t help saying a few points just to kind of solidify my stance on this debate between the carbohydrate/insulin hypothesis and the food reward/calories in calories out hypothesis for which Gary Taubes and Stephan Guyenet have ascended their respective soap boxes.

1. The overarching hypothesis Gary Taubes presents is not actually the “carbohydrates increase insulin which causes fat gain.” That’s his proposed mechanism for which he calls for empirical testing. The hypothesis is that obesity is a disorder of excess fat accumulation, and thus his paradigm shift he talks about is that fat accumulation is a physiological problem and not a psychological one. Too many of his critics I think make their mistake of criticizing his proposed mechanism, and so what, it’s a proposal and begs testing. Criticizing that particular mechanism does nothing to dismantle the hypothesis. It just might mean we need more testing.

2. Stephan asserts that insulin’s role in the body is “to coordinate the metabolic shift between burning primarily fat, to burning primarily carbohydrate.” I contend that this is almost a secondary role of insulin. Insulin’s role is to regulate blood glucose and facilitate nutrient storage. It is in fact the hormone nature designed to allow animals to get fat (despite what Stephan says). Insulin is anabolic, period. Without insulin, you cannot gain mass or deposit nutrients. It is one of the most ancient hormones in biological systems, and it is thus so important and so well conserved because of this vital role of allocating nutrients. As for this “metabolic shift” Stephan refers to, that’s definitely a fairytale over simplification of metabolism. The energy substrates overlap, and there is really no one time you would burn pure carbohydrate or pure fat. One or the other can be upregulated while the antagonist is repressed, but they don’t “shift” between each other.

3. Stephan never differentiates between acute and chronic responses of insulin release, both in the body and in the brain. This to me is either extremely ignorant (which he is not) or it is lap-dog excitability getting in the way of remembering facts he should, as a doctored neurobiologist, already know.

4. He includes no discussion of glucagon, the direct antagonist to insulin but one that works in tangent with insulin response to protein and not with carbohydrate and mitigates the hypoglyaecemic effect of insulin. Otherwise, as with the insulin response to carbohydrate, there is an immediate satiety signal, but that is overpowered by the hypoglycaemia that eventually results with insulin secretion.

5. Obese people have higher total energy expenditures (TEE’s) because their resting metabolic rate (RMR) is dependent on mass, and the TEE is dependent on the RMR. I can add these equations in here to show, but at this moment I don’t have the time. So yes of course they have higher TEE than a lean person, but as that is a factor of body mass, it cannot be used as an argument that obese people somehow defy the carbohydrate-hypothesis argument that insulin reduces thermogenesis.

6.Free fatty acids are constantly released from the body fat of obese people because they are also insulin resistant, plus, the body has reached a new set point of fat mass needed for leptin signaling. This does not mean that insulin did not cause them to be fat in the first place because somehow their lypolysis is not inhibited in the face of high insulin. It means there is whole-body insulin resistance. The fat accumulated in the first place because the fat cells remained insulin sensitive while muscle tissue became resistant early on. They are, instead, at a stable weight, just obese.

7. Doubly labeled water cannot tell us where the energy expenditure took place. It only tells us that it did (or did not) take place. The references cited say nothing for the assertion from Stephan that obese people are burning more fat (supposedly proved by doubly labeled water). This looks like just ignorance of DLW method to me (which is in fact a valuable resource for anthropological studies and so I am quite familiar with its methodologies and limitations).

8. His graphs showing macronutrient consumption and percentage of calories from 1900’s through 2005 is just… wrong. It doesn’t account for sugar consumption or HFCS. Ta daaa, history really didn’t confound us, yes there really was a low-fat craze in the 70’s through the 90’s (and maybe is still ongoing).

Ok that’s all for now.

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