Deep Dives

Polyvagal Theory: A Critical Appraisal

Alyssa Luck · Oct 29, 2022 · 3 Comments

Pressed for time? Jump to Summary and Conclusions.

If you’ve ever seen the terms “ventral vagal” or “dorsal vagal” outside of an advanced anatomy textbook, you’ve probably encountered polyvagal theory. This theory, introduced by psychologist Stephen Porges, makes specific claims about the evolution, anatomy, and physiology of the vagus nerve and autonomic regulation of the heart, and parlays those claims into hypotheses about the interplay between the autonomic nervous system and human psychology and sociality.

Polyvagal theory as an explanatory model, while receiving little to no acceptance in the fields of autonomic physiology or neurobiology, has become – dare I say – gospel in the communities of “trauma-informed” somatic and psychotherapy. (6, 7, 8)

Polyvagal theory also makes frequent appearances in communities that promote “rewiring” the autonomic nervous system as a way to treat illnesses such as chronic fatigue syndrome, POTS, and various autoimmune diseases.

I’ve even seen it in health and wellness spaces that aren’t focused on trauma or illness – for instance, on the Bulletproof YouTube channel, or in the Instagram posts of “pro-metabolic” nutrition influencers. It seems that polyvagal theory has become relevant for just about anyone interested in human health.

The comments below the Dave Asprey video give an idea of the enthusiasm and gratitude with which polyvagal theory is most often received. However, the theory has also been criticized by some scientists, most notably psychosomatic researcher Paul Grossman.

The exchanges between these two researchers have been largely unproductive, and I suspect this is in large part due to the fact that Grossman is critiquing polyvagal theory purely at the level of biology, while Porges conceptualizes the theory primarily within the contexts of experimental psychophysiology or broadly integrative “mind-body” research. Thus, I propose that polyvagal theory and its attendant controversy cannot be understood through analysis at the level of biology alone.

As such, in this article I’ll provide a critique of polyvagal theory as biology, as a model for psychophysiology, and as a biopsychosocial framework. I also include two additional levels of analysis that reflect the sociocultural roles that polyvagal theory has taken on: as direction and justification for clinical therapies, and as an “illness myth.”

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Heart Rate Variability 101: What It Is, How It’s Measured, and Controversies in the Literature

Alyssa Luck · Jul 12, 2022 · Leave a Comment

Updated September 26, 2022; text and figure added in Does HRV index autonomic tone?, and text added in Respiratory sinus arrhythmia.
Updated August 10, 2022; text added in “Measuring RSA” section.

Heart rate variability (HRV) is a fascinating metric. It’s been around for over a century in the clinical and research space, and has exploded in popularity both in research and household settings because it can be measured easily and noninvasively, providing a window into the complexities of physiological and psychological processes without perturbing the underlying systems. Athletes use it to optimize training and recovery, doctors use it to predict patient outcomes, and psychologists use it to measure a whole host of cognitive activities…yet still today, nobody seems to be able to agree on precisely what these measurements actually mean.

As I’ll explain below, HRV is not a single measurement but rather a biological phenomenon that can be quantified in a number of different ways, which one needs a fair bit of technical and mathematical expertise to correctly interpret. A thorough understanding of the physiology underlying HRV has lagged well behind enthusiasm for its potential, which has led to a number of very persistent misunderstandings and a glut of unhelpful or misleading research. Reading through recent reviews and editorials, you often get the sense that the experts in the field are sighing with exasperation at the fact that controversies that ought to have been laid to rest in the late 1990s are still alive and well today.

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Ketogenic Diet for Ulcerative Colitis and Crohn’s Disease

Alyssa Luck · Mar 22, 2022 · Leave a Comment

Summary: Ketogenic diets have exploded in popularity for weight loss and overall health optimization. While we are still sorely lacking in clinical research on ketogenic diets for IBD, there are a few compelling mechanisms – particularly modulating intestinal immunity and overcoming energy starvation in colonocytes – indicating that ketosis could be a helpful therapeutic strategy for some people. However, there are also some risks, with a potential increase in hydrogen sulfide production being a particular concern since hydrogen sulfide is often already elevated in people with IBD. Therapeutic effects of the diet are likely mediated both metabolically (by emulating fasting) and via the microbiome, but both of these mechanisms appear to be highly context-dependent, contributing to significant disparity in results across the existing literature on ketogenic diets in health and disease. In the context of IBD, my current assessment is that a strict ketogenic diet could be helpful as a short-term strategy for certain people, but is unlikely to be an optimal long-term strategy.

This article is part of the IBD Index. Last updated on April 27, 2022.

As the name would suggest, a ketogenic diet is a diet that promotes the metabolic state of ketosis. This is generally accomplished by consuming very few carbohydrates, a moderate amount of protein, and getting most calories from fat.

Note that I discuss the carnivore diet separately, because while a carnivore diet is necessarily ketogenic, its defining feature is the elimination of all plant foods, which is not necessary on a non-carnivore ketogenic diet.

For information about exogenous ketones (including brands), MCT oil, and some comments about breath vs. urine vs. blood testing for ketosis, check out my article on ketone supplementation.

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The Science Behind the Specific Carbohydrate Diet (SCD): Brilliant or Bunk?

Alyssa Luck · Mar 14, 2022 · Leave a Comment

Summary: In her 1987 book Breaking the Vicious Cycle, Elaine Gotschall proposed the hypothesis that digestive diseases – including IBD – are perpetuated by a vicious cycle of carbohydrate malabsorption, bacterial overgrowth, and intestinal injury, and can therefore be resolved by removing specific carbohydrates from the diet to break the cycle. Much of her research was quite prescient, but key claims fail to stand up to scrutiny, and the science does not support adherence to SCD principles. A modern look at Gottschall’s hypotheses reveal that modulating the intestinal bacteria through diet is indeed as important as she suspected, but that strategies other than the SCD are better able to accomplish that goal.

This article is part of the IBD Index. Last updated April 20, 2022.

This article is a deep dive into the science behind the Specific Carbohydrate Diet, and is a companion post to the high-level summary post: The Specific Carbohydrate Diet (SCD) for IBD: Everything You Need to Know.

The Specific Carbohydrate Diet as laid out in the 1987 book Breaking the Vicious Cycle (BTVC) by Elaine Gotschall is respectably science-driven. She lists dozens of references in the back of the book to support her recommendations (which is impressive considering she was conducting this research in the pre-internet era), and the book itself has been cited in the literature over 100 times. The SCD is also increasingly showing up as an intervention in clinical research, first in case studies and more recently in a large randomized controlled trial.

I said this in my main post on the SCD, but in many ways, Gottschall was truly ahead of her time with the theories she lays out in her book, although of course she leaned heavily on the work of Dr. Haas. In researching this post, I was struck by how relevant her work still is, and how many modern lines of inquiry flow naturally from her hypotheses.

That said, the big wheel of science keeps on turning, and there’s much to be critiqued in BTVC, with quite a few issues that are – in my view, at least – highly relevant to patients. When you have a dietary protocol with rules that are as specific as those of the SCD – and when the diet originator claims they must be followed with “fanatical adherence” – you gotta make sure they stand up to scrutiny, right?

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Is the Low-FODMAP Diet Effective for IBD?

Alyssa Luck · Mar 14, 2022 · Leave a Comment

Summary: A low-FODMAP diet, which is a common intervention for IBS, is being increasingly studied in IBD patients. Unfortunately, the diet does not currently show efficacy for reducing inflammation, but has been shown in clinical trials to be effective at managing functional gastrointestinal symptoms in patients whose disease is in remission. Although a common concern with low-FODMAP diets is potential adverse effects on the microbiome from removing fermentable substrates, its actual effects on the microbiome in practice have not yet been clearly characterized, with inconsistent results across studies. For those who wish to support their microbiome on a low-FODMAP diet, resistant starch and Sunfiber are good low-FODMAP prebiotic options.

This article is part of the IBD Index. Last updated on April 20, 2022.

The low-FODMAP diet is somewhat unique among IBD interventions because it promises to intervene in the common but oft-overlooked situation of continuing functional gastrointestinal symptoms even in the absence of inflammation.

I cover the basics and practical aspects of a low-FODMAP diet in The Low-FODMAP Diet for IBD: Everything You Need to Know. In this article, I take a deep dive into all the evidence regarding the effectiveness of a low-FODMAP diet for IBD, both from the perspective of reducing inflammation and managing symptoms. I also address the most common concern about a low-FODMAP diet: its effects on the microbiome.

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Akkermansia Muciniphila: Bane or Boon for IBD?

Alyssa Luck · Mar 21, 2021 · Leave a Comment

Summary: Akkermansia muciniphila is a commensal bacteria found in healthy human colons that is widely regarded as a promising next-generation probiotic. Researchers have mainly focused on therapeutic potential for obesity and diabetes, but there’s also substantial interest in the field of IBD, particularly for its beneficial effects on gut barrier function. However, a minority of researchers have suggested that Akkermansia muciniphila could worsen colitis. Despite that, most of the evidence thus far suggests that A. muciniphila could potentially be leveraged as a beneficial therapy for IBD and gut health in general once more research has been done.

This post is part of the IBD Index.

Lactobacillus and Bifidobacteria species may still be the darlings of the probiotic world, but there’s a new kid on the block: Akkermansia muciniphila.

This bacteria was isolated for the first time in 2004 (1) so it’s still relatively new to the game, but you can see from this fun trend analysis (2) that research has exploded, especially in the last couple years.

Source: Hojat et al., Global scientific output trend for *Akkermansia muciniphila* research: a bibliometric and scientometric analysis, 2020

So what is Akkermansia muciniphila, and why the interest all of a sudden?

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