Lactose Intolerance and the Microbiome
Lactose Intolerance and the Microbiome
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Hi! My name is Courtney Smith and I am a Stanford student working in the Relman Lab at Stanford University.
In the lab we're studying a lot of different aspects of the human microbiota, which is a collective term for all the microscopic life forms that are usually found on or in the human body. This is a pretty hot topic right now. For well over a century, people have known about 'germs', the microbes that cause disease, and we've made spectacular progress in reducing the toll of infectious diseases. People have also known for a long time that lots of microbes live on and in our bodies even when we're not sick. But that fact never got much attention, until recently. The reason it's such a hot topic now is that we've discovered that the human microbiota isn't just along for the ride, it's working hard to keep us healthy.
Right now we're enrolling participants for a 3 month-long study of the microbes that live in the large intestine, aka the gut microbes, which account for the vast majority of the human microbiota. It's important to study this stuff, because we know the gut microbiota affects our health, but we don't entirely understand how, and we don't understand all the factors that affect the gut microbiota. This website is part of our effort to recruit participants, so you can find out more about our study and check to see if you're likely to be eligible to participate. But we also want to inspire and motivate you to participate, and the best way to do that is tell you about many of the cool discoveries scientists are making about our microbiota and how it affects our health.
If you want to learn about the microbiome feel free to read more in the about the microbiome section.
Or jump right to checking your eligibility!
Thanks for your interest in our work!
About Our Study
Why are you conducting this study?
This study will examine changes to the composition of the microbiome that occur in response to eating or avoiding dairy products, and the time course of such changes. We hypothesize that certain bacterial species in the gut microbiome are associated with acquired lactose tolerance: they allow hosts to eat dairy products without suffering the negative outcomes characteristic of lactose intolerance. We further hypothesize that regularly eating dairy products is necessary for the persistence of a lactose tolerance in most individuals, with dairy acting as a prebiotic to support the populations of lactose-utilizing, tolerance-associated bacteria. If these hypotheses are correct, our study may support informed consumption of dairy products in lactose intolerant individuals; it would allow them to develop and maintain lactose tolerance and to reap the potential health benefits of dairy, e.g. those related to the uptake of calcium.
What will the study entail?
The study will last three months and involve three main phases: a normal diet consumption phase, no dairy consumption phase, and a gradual reintroduction to dairy phase. During the study, participants will complete four hydrogen breath tests (which entail 4-6 hours of blowing into a tube every 20 minutes at home and doing whatever you like in between) and take their own stool samples regularly (preferably daily).
The study is looking for participants who at some point (past or present) have experienced symptoms such as cramping, bloating, and diarrhea when eating dairy. The study is also looking for participants who will not be travelling during the course of the study.
Why should I participate?
The main reason for people to participate is because they want to help this science to move forward, whether that's so medical science can do a better job of keeping people healthy, or just because it's fascinating!
Another reason would be to learn about your own gut microbiota. Once your samples have been analyzed (which can take a while), you can choose to meet with one of the study staff to find out what we've learned about your own microbes. We'll also discuss how your results compare to those from other people, and how they relate to other published scientific studies. You should know, though, that scientists don't yet know enough to provide specific health or medical advice to generally healthy people based on knowledge of their microbiota. The best advice we can give for you and your microbiota is to eat a balanced, healthy diet - and that advice doesn't depend on knowing what microbes are in your gut already!
The compensation will be $400 per participant but please don't sign up if that's your only motivation.
To find out more and check your eligibility click this link.
About the Microbiome
What is this ‘human microbiota’, anyway? How is it different from the 'human microbiome'?
The microbiota consists of all the microscopic things living in a particular place, so the ‘human microbiota’ is all the microbes found in and on people. As with a lot of biology, the phrase isn’t absolutely precise. For example, living cells of soil-dwelling microbes will surely be found on and in people who have a lot of contact with the soil, even if those microbes are ‘transplants’ that can’t actually grow and divide in the body sites where they’re found – so are they part of the human microbiota or not? Fortunately, phrases like ‘human microbiota’ (and ‘skin microbiota’, ‘gut microbiota’, etc.) are generally useful, despite such ambiguity around the edges.
The term ‘microbiome’ has recently been used in two different ways. One definition is the same as ‘microbiota’, explained above. The other usage of ‘microbiome’ (the recent Human Microbiome Project used this definition) means not the living organisms, but rather all the genetic information of all the microbes that live in a particular place. Since a ‘genome’ refers to all the genetic information of an organism, and ‘metagenome’ means all the genomes of the different types of organisms in an ecological community, this second meaning of ‘microbiome’ could be expressed as ‘microbial metagenome’. (See Elio Schaecter's poll on his Small Things Considered blog on the definition of ‘microbiome’.)
Why should we pay attention to the human microbiota? Since it evolved with us to keep us healthy, won’t it just keep doing so?
It is true that humans and our microbiota have coevolved to have mostly mutualistic interactions, a process that happened without us needing to pay any attention to it at all. However, most humans today live in conditions that simply didn’t exist over most of our evolutionary history, and those differences have the potential to change our microbial interactions.
A child growing up in an American city today, for example, is probably exposed to far fewer microbes from soil and animals, but far more microbes from unrelated humans, compared to her farming grandparents, or to her nomadic, hunter-gatherer ancestors. She may encounter a different mixture of human-derived microbes than they did, with a higher proportion of respiratory and skin microbes but a lower proportion of gut microbes, due to the combined effects of crowded spaces and flush toilets.
Her diet includes more processed and refined foods, with higher sugar and salt content, than that of her forebearers. On the other hand, it may also include a more diverse array of fresh fruits and vegetables throughout the year. She quite likely consumes more meat and more animal fat, but less plant fiber than her ancestors; almost certainly she is less physically active.
She may have been born via cesarean section, fed mainly with infant formula, and exposed, perhaps repeatedly, to potent antibiotics. And while those practices certainly don't guarantee an unhealthy outcome (and sometimes, in fact, they are life-saving), they are also situations that are completely new in our evolutionary history...for us and our microbiota.
We know enough to realize that all these elements of a modern lifestyle have the potential to change our microbiota, and to change our interactions with our microbiota. However, we often don't know enough to predict what the consequences of those changes may be. The correlations that have been found thus far, between various aspects of the microbiota and particular diseases, suggest that at least some of the evolutionarily-recent changes to the human microbiota have important health effects. However, the microbiota can vary a lot between apparently healthy people, so it’s quite possible that some recent changes to the microbiota won't affect our health at all. It would be good to be able to tell the difference.
I still want to know more!
Check out a list here of more links, podcasts, articles, etc.
More About the Microbiome
EPISODE 54: HACKING THE GUT MICROBIOME an interview with Les by Dr. Dan Stickler of ePhysiologix.
What's in My Gut? an interview with Les by Ernesto Ramirez (from Quantified Self) regarding the human microbiota and data access.
Sweet Peach Probiotics, a company that aims to tailor probiotics for the specific needs of a specific woman's vaginal microbiota.
Sawbones: Enemas and Cleanses Dr. Sydnee and Justin McElroy explore the history of enemas and cleanses.
Animal Pharm Podcast, a podcast by Dr. Grace regarding resistant starch.
Science AMA Series: I'm Dr. Les Dethlefsen, staff scientist in the Relman Lab at Stanford University. I study the microbiota of the human gut, focusing on how it varies over time, and on what happens when it's disturbed when we take antibiotics or change our diet. AMA!, an AMA (Ask Me Anything) session by Les.
'The Skinny on Probiotics', a podcast by Stuff You Should Know about probiotics and its affects on the gut flora.
Fecal Transplants: You Gonna Drink that Poop?, a podcast by Stuff You Should Know that explores the topic of fecal transplants.
'How the Human Microbiome Project Works', another podcast by Stuff You Should Know that lays out the fascinating landscape of microbiota research.
'Germs are us', an excellent general introduction by Michael Specter that appeared in the New Yorker.
'Me, myself, us', another outstanding general introduction that appeared in The Economist.
Michael Pollan's story in the NYTimes Magazine about getting his microbiome analyzed.
Moises Velasquez-Manoff is a journalist who's been focused on the connections between the gut microbiota and inflammation, here's an article of his focused on allergies from the NYTimes, and another focused on obesity from Mother Jones magazine. He also has a book on this topic, An Epidemic of Absence.
There is no 'Healthy' Microbiome, an article by Ed Yong (author of Not Exactly Rocket Science blog at NatGeo) in the Sunday NYTimes covering why we can't say one particular composition of the gut microbiota is best.
'The E. coli made me do it' by James Rosenbaum, from the New Yorker, focusing on mood and behavior effects of the microbiota.
Carl Zimmer's piece (author of The Loom blog at NatGeo) in the NYTimes following publication of the first batch of results from the NIH Human Microbiome Project.
A blog post by Ed Yong (Not Exactly Rocket Science at National Geographic) about a study demonstrating the interaction of the gut microbiota with diet in kwashiorkor, a serious malnourishment disease. Here's commentary by my boss, David Relman, about the same study.
A connection between obesity and liver cancer is mediated by the gut microbiota, from The Economist. While this is interesting in itself, it may be even more important as an example of how microbes can be involved in mammalian physiology in unexpected ways (both good and bad).
Similarly, there is a connection between eating red meat and heart disease that is is mediated by the gut microbiota, explained here by Gina Kolata of the NYTimes. It's unclear how much of the oft-reported link between red meat consumption and heart disease might be due to the microbial transformation of carnitine into a damaging chemical called TMAO, compared to the more traditional culprits like saturated fat and cholesterol.
There's a whole series on NPR about the human microbiota (mostly by Rob Stein); some of my favorite bits are:
a cartoon introduction to the human microbiota
native microbes are good for your health
summary of findings from the NIH Human Microbiome Project
relationship between gut microbes and obesity
microbial transmission to babies influences their risk of allergies
gut microbes interact with diet to affect heart disease risk
microbial effects on mood and behavior
fecal microbiota transplants
controlling the gut microbiota through diet
issues surrounding microbiome analysis
Bugs 'R Us, a 50 minute public lecture by Professor Brett Finlay of the University of British Columbia. The first half is mostly pathogen-focused, including a nice historical perspective of the science of microbiology. He then describes several important effects of the native human microbiota on health, although I think in some places he oversimplifies to the point of being a bit misleading.
Finally, here are two online digests of microbiota-related articles that are more comprehensive and more frequently updated than this page:
The Microbiome Digest is a blog by Dr. Elies Bik (a former Relman lab member) that covers the human microbiota and other microbiome/microbiology related topics. While it is oriented more towards articles in scientific journals, it includes many articles written for the general public as well.
Gut Microbiota Worldwatch is a website run by the European Society of Neurogastroenterology and Motility. The News page gives short summaries of notable recent scientific findings about the gut microbiota, and the In the Media page has links to articles in the popular press.