Dear Doctor: I just read about a study where people who were depressed actually had a different gut microbiome than people who weren’t depressed. Is that true? Does your gut determine how you feel?

Dear Reader: The recognition of the link between emotions and the gut is so ancient, it’s been hardwired into our language. There’s the gut feeling, going with your gut, butterflies in your stomach, a sinking feeling, bad news that’s a punch to the gut, having a gut response, or finding something to be nauseating, sickening or gut-wrenching.

Now, new research suggests that not only does the brain affect the gut, but that the connection actually goes both ways. Specifically, that the composition of the gut microbiome may play a role in how someone feels. This is a new and sometimes controversial field of research, and it is the subject of (occasionally fractious) debate.

The study you refer to may be one published in February in the scientific journal Nature Microbiology, which focused on 1,054 people from Belgium. Of those, 173 were either diagnosed with depression or did poorly on a questionnaire that asks participants to rate their quality of life.

When the composition of participants’ microbiomes were analyzed and compared, researchers found an interesting difference. Specifically, people with depression lacked two types of microbes, known as Coprococcus and Dialister, which were present in the guts of those who were free from depression.

Data in the Nature study were compared with a study of 1,064 Dutch people in which researchers found that the same two microbes were missing from the guts of those who either reported or were diagnosed with depression. In addition, the two different groups with depression had greater numbers of a certain microbe believed to be involved in Crohn’s disease.

This adds weight to the theory that inflammation has a role in mental health. The specific reason that these two missing microbes affect depression is unclear. One promising line of thought, according to the researchers, is that that Coprococcus has been linked to dopamine, a brain chemical that influences feelings of pleasure and satisfaction. The microbe also makes a substance that acts as an anti-inflammatory.

Such studies can suggest cause-and-effect relationships, but they shouldn’t be considered “proof” of a connection. They don’t prove them.

It’s fascinating that the depressed people in the studies lacked certain microbes in their guts, but more research is needed to show direct causality. The good news is that each new study adds to our understanding and sets the stage for new research to come. The hope is that, over time, this line of inquiry will lead to new therapies such as microbiome profiling or precision bacterial supplements, which will offer new avenues of relief to people living with depression.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: A friend who was working on his old Victorian home in New Orleans started getting bad headaches. He tested high for heavy metals, and now he’s supposed to do something called “chelation therapy.” What is that?

Dear Reader: Chelation therapy is a treatment that rids the body of heavy metals such as lead, copper, mercury, zinc, arsenic, cadmium and iron.

Although these metals are naturally present in the environment, concentrated amounts become toxic. Since your friend was working on an older home, he may have been exposed to high levels of lead in the original paint. According to the Environmental Protection Agency, there’s a high likelihood of finding lead-based paint in homes built prior to 1978, when a federal ban on lead paint went into effect. When someone is renovating a house that contains lead paint, the sanding and scraping that typically take place create toxic dust, which is easily inhaled or may be accidentally ingested.

Signs of lead poisoning in adults include headaches and abdominal pain. Other symptoms can include tingling and numbness in the hands and feet, confusion or trouble concentrating, exhaustion, high blood pressure, nausea and diarrhea.

If one of a group of blood tests reveals that someone has heavy metal poisoning, a chemical process known as chelation therapy is the preferred method of treatment. It works by introducing certain chemicals into the blood, which have the ability to bind to the toxic metal ions. One such chelating agent is ethylene diamine tetra-acetic acid, a synthetic amino acid commonly referred to as EDTA.

With chelation therapy, a medication binds with the lead so that it is then excreted in urine. A possible side effect of the therapy is a burning sensation at the site of the injection. Less common are headache, nausea, high blood pressure, rash or vomiting. Years ago, when chelation therapy was delivered in high doses, it was linked to more dangerous side effects, like irregular heartbeat or kidney damage.

It’s important to note that chelation therapy is approved by the FDA only for heavy metal poisoning. We mention this because of its use as an alternative therapy for other conditions, including heart disease, autism and Alzheimer’s disease. Studies on using chelation therapy to treat heart disease show minimal benefit, and only in certain cases. It has not been shown to be successful in treating Alzheimer’s. And the American Academy of Pediatrics warns against chelation therapy, saying there's no evidence it’s is effective for autism, and that it can be dangerous.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I’ve always heard that it’s the saturated fat in red meat that leads to a heart attack. But now I’m reading that it has something to do with the gut? Does that mean probiotics will make it OK to eat steak, which my wife and I just love?

Dear Reader: You’re referring to a study published earlier this year that found a connection between a diet heavy in red meat and a marked increase in a certain compound produced by gut bacteria, which has been linked to an increased risk of heart attack and stroke. That byproduct is trimethylamine N-oxide, also referred to as TMAO. In earlier studies, researchers uncovered a link between elevated levels of TMAO in the blood and the development of arterial plaque, which can block blood vessels and lead to heart disease.

The study you’ve been reading about, which was published in the European Heart Journal last February, analyzed how each of 113 volunteers responded to three different diets. The diets, which the volunteers followed for four weeks, used either red meat, white meat from poultry, or non-meat products such as legumes, nuts and grains as a source of protein. Every aspect of the meals, from portion size to ingredients to preparation methods, was uniform and highly controlled. The volunteers followed the three different diets in random order.

Only the red meat diet resulted in increased levels of TMAO, both in the blood and in the urine. The majority of volunteers following the red meat diet had levels of TMAO that measured two to three times higher than volunteers who were getting their protein from white meat poultry or vegetal sources. In some cases, the levels of TMAO in blood and urine were as much as 10 times higher in the red meat group than in the white meat and vegetal groups.

Researchers also discovered that the red meat diet interfered with the kidneys’ ability to excrete TMAO. That kept the circulating levels of the potentially damaging bacterial byproduct high. The good news is that a month after they stopped eating a diet rich in red meat, both blood and urine levels of TMAO had fallen significantly. The researchers speculated that the metabolic pathways suggested by this study might account for why the Mediterranean diet, which is low in red meat, is associated with lower risk of heart attack and heart disease.

Since the study shows that red meat causes the gut bacteria to produce potentially harmful compounds, your idea about taking probiotics as protection won’t actually work. However, if it’s only as an occasional splurge, it’s probably fine for you to have that juicy steak.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)