What this is, and what we changed.
The original issue was a short piece about depression, the gut, and whether probiotics belong in the conversation. It was written for readers, not for clinicians, and it had a point of view: that treating depression as one broken chemical had not served people well.
That framing has held up. Some of the specifics have not. The 2020 text carried a percentage for how many people do not respond to antidepressant treatment, a mechanism story about cortisol and brain cells, a claim about probiotics being an approved depression treatment in Canada, and an invitation to call us about building a probiotic approach around your own gut bacteria. None of those could be traced to a source we would stand behind, so they are gone rather than reworded.
What follows is the rest of the piece, with its sources named. If you want current information on depression instead of a 2020 snapshot, the condition guide linked at the bottom of this page is the better place to start.
Depression was never a single-chemical story.
The newsletter's opening argument was that drug advertising in the 1990s taught a generation to think of depression as a chemical shortage with a chemical fix, and that the picture is bigger than that. The National Institute of Mental Health describes depression as a condition that can cause severe symptoms affecting how a person feels, thinks, and handles daily activities such as sleeping, eating, or working, with symptoms present most of the day, nearly every day, for at least two weeks.
On what causes it, NIMH says research suggests that genetic, biological, environmental, and psychological factors play a role. That is a wider and vaguer answer than the 2020 text gave, and the vagueness is the honest part. The original listed fat cells, hormones, B vitamins, autoimmunity, and the microbiome as established contributors to depression physiology. We could not source that list, so we are not repeating it.
The newsletter was right that not everyone responds to the first thing they try. NIMH defines treatment-resistant depression as depression that does not get better after a person has tried at least two antidepressants, and notes that esketamine is FDA-approved for it. That is a real clinical category with a real treatment pathway — which is a different statement from the number the 2020 issue attached to it.
There are about as many bacteria in you as cells of you.
This was the fact the 2020 issue clearly enjoyed most, and it survives the check. Sender, Fuchs, and Milo, writing in PLoS Biology in 2016, estimated roughly 3.8 × 10¹³ bacteria — about 38 trillion — in a 70 kg reference man, against about 3.0 × 10¹³ human cells.
Their paper is also a correction, and worth knowing as one. The often-repeated line that bacteria outnumber our own cells ten to one does not hold; the two numbers are of the same order, closer to a rough tie. The newsletter's version (37 trillion to 30 trillion) was close enough to the real estimate, and the real estimate is remarkable enough without inflating it.
Diet does move the microbiome — quickly.
The piece argued that what you eat shapes which bacteria thrive, and this part has support. A 2017 review in the Journal of Translational Medicine reports that dietary changes can induce large, temporary microbial shifts within 24 hours, with a return toward baseline within 48 hours of stopping. It also describes a Western dietary pattern — high in animal protein and fat, low in fiber — as associated with a marked decrease in total bacteria and in beneficial Bifidobacterium and Eubacterium species.
The same review notes that gut bacteria produce short-chain fatty acids such as butyrate, propionate, and acetate from dietary fiber, and that these serve as a major energy source for intestinal cells. It is equally clear that the exact mechanism by which gut flora modulate immune responses is still not well understood. The 2020 issue described inflammatory bacteria as rogue criminals; that is a good image and a claim the evidence does not yet make.
The newsletter's other image was a field full of weeds: you can plant flowers among the weeds, or you can pull the weeds first and then plant. It used that to argue that adding one thing to a system rarely does much on its own. As an illustration of why single-ingredient thinking disappoints, it still lands. It is an argument, not a finding, and it was never evidence that any particular plan works.
What we can actually say about probiotics.
The 2020 answer to "do probiotics help depression?" was a marginal yes. We cannot support that today. The National Center for Complementary and Integrative Health, the federal agency whose job this is, defines probiotics as live microorganisms intended to have health benefits when consumed or applied to the body, and its consumer guidance does not present probiotics as a treatment for depression or any mental health condition.
NCCIH is blunt about the state of the evidence generally: in most instances, we still don't know which probiotics are helpful and which are not. It also points out something people rarely hear at the store — many probiotics are sold as dietary supplements, which don't require FDA approval before they are marketed, unlike a product marketed as a drug, which has to be proven safe and effective through clinical trials.
There are safety limits too. NCCIH reports cases of severe or fatal infections in premature infants given probiotics, and an FDA warning to providers about that risk; seriously ill people and people with compromised immune systems are named as higher-risk groups. Its advice is the advice we will repeat: if you're considering a probiotic dietary supplement, consult your health care provider first. The 2020 issue invited you to call us instead. That was the wrong order.
- Probiotic supplements are not reviewed by the FDA for safety or effectiveness before they go on sale.
- Evidence is condition-specific and strain-specific; "probiotics help" is not a claim any one product has earned.
- Talk to your health care provider before starting one, especially if you are seriously ill or immunocompromised.
If this issue is what brought you here.
NIMH states that most people with depression benefit from mental health treatment, that antidepressants usually take four to eight weeks to work, that sleep, appetite, and concentration often improve before mood lifts, and that finding the best treatment may take trial and error. It also says to talk to a health care provider before starting or stopping any medication — including if you read something here and it makes you reconsider what you are taking.
Gates Brain Health provides functional neurology care in Reno, and the practice has publicly stated that its approach complements rather than replaces conventional psychiatric care, and that Dr. Randall Gates, D.C., DACNB coordinates with a patient's existing care team, including primary care physicians and psychiatrists, when appropriate. Nothing on this page can tell you whether that is a fit for your situation. A conversation can start to. Call (775) 507-2000, Monday through Friday, 8:00 AM to 5:00 PM, and please keep medical details to the phone rather than the website.
If you are thinking about suicide or in emotional distress, the 988 Suicide & Crisis Lifeline is available 24/7 by call, text, or chat at 988lifeline.org. It is free and confidential. If someone's life is in danger right now, call 911 or head to the nearest emergency department.