The Homeoviscous Adaptation to Dietary Lipids (HADL) Model

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circular
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The Homeoviscous Adaptation to Dietary Lipids (HADL) Model

Post by circular »

Chris Kresser did a recent podcast with Marit Zinocker: "Reevaluating Cholesterol and Its Effect on Our Health." [#49] It will be interesting to see how her model plays out in future studies.

Marit's model was recently published in American Journal of Clinical Nutrition:

The homeoviscous adaptation to dietary lipids (HADL) model explains controversies over saturated fat, cholesterol, and cardiovascular disease risk
Abstract

SFAs play the leading role in 1 of the greatest controversies in nutrition science. Relative to PUFAs, SFAs generally increase circulating concentrations of LDL cholesterol, a risk factor for atherosclerotic cardiovascular disease (ASCVD). However, the purpose of regulatory mechanisms that control the diet-induced lipoprotein cholesterol dynamics is rarely discussed in the context of human adaptive biology. We argue that better mechanistic explanations can help resolve lingering controversies, with the potential to redefine aspects of research, clinical practice, dietary advice, public health management, and food policy. In this paper we propose a novel model, the homeoviscous adaptation to dietary lipids (HADL) model, which explains changes in lipoprotein cholesterol as adaptive homeostatic adjustments that serve to maintain cell membrane fluidity and hence optimal cell function. Due to the highly variable intake of fatty acids in humans and other omnivore species, we propose that circulating lipoproteins serve as a buffer to enable the rapid redistribution of cholesterol molecules between specific cells and tissues that is necessary with changes in dietary fatty acid supply. Hence, circulating levels of LDL cholesterol may change for nonpathological reasons. Accordingly, an SFA-induced raise in LDL cholesterol in healthy individuals could represent a normal rather than a pathologic response. These regulatory mechanisms may become disrupted secondarily to pathogenic processes in association with insulin resistance and the presence of other ASCVD risk factors, as supported by evidence showing diverging lipoprotein responses in healthy individuals as opposed to those with metabolic disorders such as insulin resistance and obesity. Corresponding with the model, we suggest alternative contributing factors to the association between elevated LDL cholesterol concentrations and ASCVD, involving dietary factors beyond SFAs, such as an increased endotoxin load from diet-gut microbiome interactions and subsequent chronic low-grade inflammation that interferes with fine-tuned signaling pathways.
Here's a rebuttal out this month that seems worth considering as well:

The homeoviscous adaptation to dietary lipids (HADL) hypothesis is probably incorrect

(I find it amusing that the rebutters accuse Marit and her co-authors of bias as if they themselves have no bias.)

Marit addresses some of their rebuttals at the end of the podcast with Chris.

What I'm wondering is whether it's possible that both perspectives are true. Heck, maybe neither are and the joke's on Science :lol:
ApoE 3/4 > Thanks in advance for any responses made to my posts.
Fiver
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Re: The Homeoviscous Adaptation to Dietary Lipids (HADL) Model

Post by Fiver »

Hi Circular. I liked your suggestion that both sides might be right. Nice attempt at conflict resolution!

The authors propose an interesting model. It's fun to think about. But that rebuttal was brutal, mostly because there is a ton of evidence on their side. (Although the familial hypercholesterolemia example seems to to support the opposite of what they suggest it might - that confused me.) The original authors are going to need some really compelling evidence to change minds.

In any case, it's like many others here say often: it's probably the combination of LDL particle size and number combined with sugars and inflammation that together makes it "good" or "bad". And that seems like it would hold true no matter which side is right here. So practically, for all of us, we sort of know what we need to aim for, at least in this regard.
circular
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Re: The Homeoviscous Adaptation to Dietary Lipids (HADL) Model

Post by circular »

Fiver wrote:Hi Circular. I liked your suggestion that both sides might be right. Nice attempt at conflict resolution!
You mean there's no Zen of Science? :cry: In that case I'll stick with the joke being on science altogether ;)
ApoE 3/4 > Thanks in advance for any responses made to my posts.
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