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Alyssa Luck

Alyssa Luck

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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.

Table of Contents
Akkermansia Muciniphila: Fast Facts
Akkermansia Muciniphila Degrades Colonic Mucus – But That’s a Good Thing
Akkermansia Muciniphila Strengthens the Gut Barrier
Akkermansia Muciniphila May Promote Intestinal Wound Healing
Akkermansia Muciniphila May Modulate Immune Response to Commensal Bacteria
From Mechanisms to Colitis Models in Mice
Schrödinger’s Bacteria: Akkermansia Muciniphila Both Promotes and Ameliorates Colitis
So What Does This Mean for Humans with IBD?
Akkermansia Muciniphila and IBD? It’s Complicated.
Should I Take Akkermansia Muciniphila?

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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Hi! I’m Alyssa. I like thunderstorms and cats, hate wearing shoes, and enjoy devising extensive research projects for myself in my free time. This is me in Bali with a monkey on my shoulder. And this is my blog, where I muse about health-related topics and document my relentless self-guinea pigging. If you want to know more about me, click here!

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Photo dump from the last year. Thanks to everyone Photo dump from the last year. Thanks to everyone who made 28 the best yet - excited for 29🥰

(PS. In case anyone wants to know what it’s like in my head, I was going to write something like “year 28” or “my 28th year” but then I realized that the year between your 28th and 29th birthdays is not your 28th year of life, it’s your 29th year. I am turning 29 because I have been alive for 29 years. So then I had a whole thing about how to word it without being inaccurate and ended up going with what you see above which is vague and weird but the point is it was a good year and I love all the people in my life dearly)
Biology of Belief (2005) was written by Bruce Lipt Biology of Belief (2005) was written by Bruce Lipton, who earned a PhD in developmental biology in 1971 and was an anatomy professor and academic researcher in the 70s and 80s. Despite the book's presentation and Lipton's background, this is not a science book. It is an exposition of an ideology, supported by haphazard and poorly contextualized nuggets of evidence, rhetorical leaps, and a mind-boggling overuse of analogies. 

The book largely failed to deliver on its promised content. What it does is argue for the primacy of the environment over DNA in controlling life; propose that the cell membrane rather than the nucleus is the "brain" of the cell; invoke quantum physics to explain why modern medicine fails; explain that our behavior is largely controlled by our subconscious mind; inform parents that they therefore have a great deal of control over the destiny of their children; and conclude that humans must become nonviolent protectors of the environment and of humanity because Everything Is Connected.

It’s not that these points aren’t relevant to the topic at hand - they are. But they were not connected in a coherent way that would explain how “belief” actually works (like…biologically), and the treatment of scientific concepts throughout was careless, or perhaps disingenuous.

I think he's correct about many things, some of them being common knowledge. For instance, the "new" science of epigenetics is now old news, as is the critical role of parenting and early environment in shaping a child’s future. But however important these and attendant concepts may be, the book did not do a good job explaining, supporting, or connecting them. 

As far as practical guidance, he refers the reader to a list of resources on his website, which is fine, but I expected some scientific insight into how/why those modalities work. None was given. 

On the plus side, the book was quite thought-provoking, and I came away with loads of references and topics to follow up on. My favorite line? "There cannot be exceptions to a theory; exceptions simply mean that a theory is not fully correct."
Friedrich Nietzsche, The Gay Science (section 382) Friedrich Nietzsche, The Gay Science (section 382), as quoted in the introduction to Thus Spoke Zarathustra because I like the translation better.
This paper totally changed the way I think about e This paper totally changed the way I think about early nervous system development and the relationship between physiology and sociality. 

The authors propose that newborn babies are not inherently social, and have just one goal in life: physiological homeostasis. I.e. staying alive. This means nutrients, warmth, and regulation of breath and heart rate, i.e. autonomic arousal (it’s well-accepted that newborns sync their breathing and heart rate with caregivers through skin to skin contact). 

All these things are traditionally provided by a loving caregiver. So what the baby experiences during the first weeks of life, over and over, is a shift from physiological perturbation to homeostasis (a highly rewarding event inherently) REPEATEDLY PAIRED with things like the sound of a caregiver’s voice and seeing their face. Thus, over time, the face/voice stimuli become rewarding as well. 

The authors argue that THIS is the beginning of humans’ wiring for sociality, and may explain why loving social interactions can have such a profound regulating effect on physiology throughout life: because the brain was trained for it at an early age. 

This framework holds all kinds of fascinating implications for what happens if that initial “training” isn’t so ideal. What if the return to nutritional homeostasis via feeding is paired with negative expressions and vocalizations rather than loving ones, perhaps as could occur with PPD? What happens if the caregiver has poor autonomic regulation, such that social stimuli become paired with cardiorespiratory overexcitement in the baby? Could that have potential for influencing later introversion vs extroversion? (Because if social interaction is paired with autonomic overexcitement, that could lead to social interaction literally being more energetically draining, which is what introverts experience. Thoughts?)

For my energy metabolism enthusiasts: Table 1 in the paper draws a link between metabolic rate and sociality across species. Swipe for a screenshot. 

Anyway, check out the paper! It’s free, just google “growing a social brain pdf.”
I’ll be under general anesthesia in a couple day I’ll be under general anesthesia in a couple days to have two tooth implants placed, and I think I’ll take the opportunity to have a little heart-to-heart with my subconscious mind. A bit of medically-assisted self-hypnosis, if you will. 

I randomly stumbled upon these papers a couple months ago - an RCT showing reduced post-op pain in patients who listened to recorded positive messages while under general anesthesia, plus a post-hoc analysis of the same data that found reduced post-op nausea and vomiting in a subset of high-risk patients. 

The full review paper from the first slide is unfortunately in German, but it has long been recognized that even when unconscious, the patient is listening (for better or for worse). 

It boggles my mind that it isn’t standard of care to have patients listen to recordings like this while under sedation, considering that almost nothing could be easier, safer, or cheaper, and we have at least some evidence of significant efficacy. I mean c’mon, what more could you want from an intervention? 

(Yeah, I know. Profit. If anyone still thinks that our medical system operates with patient well-being as the foremost goal, you’re deluding yourself.)

“There should be a fundamental change in the way patients are treated in the operating room and intensive care unit, and background noise and careless conversations should be eliminated.”

“Perhaps it is now time to finally heed this call and to use communication with unconscious patients that goes beyond the most necessary announcement of interventions and is therapeutically effective through positive suggestions. When in doubt, assume that the patient is listening.”
If you've seen "vagus nerve exercises" that have y If you've seen "vagus nerve exercises" that have you moving your eyes or tilting your head, you've probably encountered the work of Stanley Rosenberg. The exercises he created and introduced in his 2017 book now appear in instructional videos all over the internet. 
 
The book itself has much to recommend it: it's accessible, it's practical, it's inspiring. But it has one major flaw: the solid practical and informational content regarding the cranial nerves is framed in terms of the scientifically dubious polyvagal theory. 
 
I particularly enjoyed the book as an introduction to the therapeutic arena of bodywork, of which Rosenberg is a skilled practitioner. His book is full of case reports that demonstrate how immensely powerful extremely subtle movements and physical manipulations can be. These do need to be kept in perspective: it's a small sample size of the most remarkable cases, and the results were achieved within the supportive clinical environment of a skilled practitioner. You can tell from his descriptions how refined his technique is. But nevertheless, it was a paradigm-shifting read for me, and the exercises give you something concrete to play around with. 
 
The book also brought the cranial nerves and the concept of “social engagement” to the fore as arbiters of health. Rosenberg has a solid background in cranial nerve anatomy and shares many interesting tidbits and considerations that you don’t typically hear; for instance, the potential impact of dental and orthodontic work on cranial nerve function.
 
So, is it worth reading? If any of the above piques your interest, go for it! Just read my post on polyvagal theory first – you can use the book to practice separating the wheat (solid informational content) from the chaff (pseudoscientific framing). If nothing else, the book is a nice reminder that genuine healers who get lasting results for their patients do exist.

But if you just want to try the exercises, you can easily find them all on YouTube. 

“You learn techniques to understand principles. When you understand the principles, you will create your own techniques.” -Stanley Rosenberg
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  • Autonomic Nervous System 101: Anatomy and Physiology
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