Your Gut Microbes May Be Thwarting Your Diet

 

As if changing dietary habits weren’t hard enough, it turns out there are other elements at play which slow things down: The microbes that live inside us. A new study in the journal Cell Host & Microbe offers some clues as to why it sometimes the body doesn’t seem to respond to changes in eating habits in the way it “should.” It finds that the effects of switching from a typical unhealthy American diet to a calorie-restricted plant-based diet are slowed because of the stubborn microbes that have proliferated during our prior (unhealthy) ways. More and more research has suggested that we’re not alone when it comes to our health. And the new study adds weight to that idea that the food choices we make are complicated by the trillions of microbes living inside us.

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The team from Washington University in St. Louis took fecal samples from people who ate a typical American diet—processed foods, high amounts of animal protein and fewer fruits and vegetables—and from those who ate a calorie-restricted, plant-based diet. The people in the latter group had much more diverse arrays of bacteria, some of which are known to be linked to better health. The team inoculated microbe-free mice with one or the other type of sample, so that their guts would be colonized by the respective assortments of microbes. Then they fed the mice one or the other type of diet—that is, diets that either matched or opposed the type of bacterial culture they’d been given.
It turned out that mice whose guts were colonized with an American diet didn’t respond as well to eating a plant-based diet. Their gut bacteria did shift in that direction, but it was slower to do so, which suggests that healthy eating can’t immediately overhaul a less healthy bacterial makeup.
There was another bizarre finding: When the researchers paired up mice with each other (housing a mouse with American-diet intestines with one with plant-based-diet-intestines), this actually helped things a bit. There was enough exchange of bacteria through contact that the guts of American-diet-mice shifted more quickly—which may suggest that we (if we’re like mice in this way) may also be affected by the microbes of those around us. “Humans continuously shed microorganisms; a vivid and experimentally validated image is that each individual is literally surrounded by a cloud of his/her microbes,” they write. Still, how the current study’s results apply to humans is a question that will need to be addressed more directly in future work.
Other research has certainly shown that shifts in diet can have profound effects on gut bacteria, and on our health. Last year, a study had people swap diets for just two weeks (from American to vegetable-based and vice versa), and recorded remarkable changes in their microbiomes, and even in their colon cancer risk.

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And the current team’s previous research, headed by Jeffrey Gordon, has shown that the makeup of gut microbes can affect weight: Mice given gut bacteria from obese humans gained weight, even while eating low-fat mouse chow. Other studies over the past several years have linked gut microbes to everything from heart disease risk to depression.
"We have an increasing appreciation for how nutritional value and the effects of diets are impacted by a consumer's microbiota," said Gordon in a statement. "We hope that microbes identified using approaches such as those described in this study may one day be used as next-generation probiotics."
This is all to say that, because of the microbes that live in us, what we consume is not so straightforward. The gut is a bewilderingly complicated system and it’s clear from the research that we are much more than what we eat. While researchers are hashing it out, eating a plant-based diet provides well-illustrated benefits to both you and your microbes. Don’t worry too much if eating more healthily doesn’t have an immediate effect on your weight. You may have changed your diet for the better, but it may take some time for the microbes inside you to catch up.

A growing body of research suggests that prenatal stress has a long-lasting impact on an infant's development. A new study adds to the evidence, showing that prenatal stress can negatively affect the child well into adulthood, through a connection via the maternal gut bacteria.

Stress-induced changes in the maternal gut bacteria may affect the child for life, according to new research.

According to an analysis conducted by the Centers for Disease Control and Prevention (CDC), prenatal stress is associated with preterm birth, low birth weight, as well as prenatal and postpartum depression and anxiety in the mother.
An overview of existing research further supports the "fetal origins hypothesis," according to which prenatal environmental factors can have lifelong effects on the brain development and behavior of offspring.
Pregnant women's exposure to a variety of stressors, ranging from common to traumatic, have been linked to significant modifications in the children's neurodevelopment. Stressors such as the loss of a loved one, daily hassles, or financial worries have been connected to autism, affective disorders, and reduced cognitive ability in children.
New research in mice suggests that prenatal exposure to a mother's stress may change the microbiome in a way that negatively affects the baby.

Gut bacteria and mental health

Tamar Gur, assistant professor of psychiatry, behavioral health, neuroscience, and obstetrics and gynecology at Ohio State University, believes the bacteria to be a particularly good medium for researching the connection between a mother and her fetus.
This is why she led a team of researchers to examine exactly how maternal stress affects the offspring. "We already understand that prenatal stress can be bad for offspring, but the mystery is how," says Gur, who is also a member of Ohio State Wexner Medical Center's Institute for Behavioral Medicine Research.
Gur explains that the microbes from a mother's gastrointestinal and reproductive tracts are the first ones to spread to the developing fetus and the newborn. As a result, gut bacteria might provide an explanation for why and how maternal stress can affect a person's mental health for their entire life.
"More and more, doctors and researchers understand that naturally occurring bacteria are not just a silent presence in our body, but that they contribute to our health," says Gur.

How prenatal stress affects offspring in mice

For the study, researchers compared two groups of pregnant mice. One group was subjected to 2 hours of stress-inducing restraint per day for 7 days. The other group was left undisturbed during pregnancy. The gut bacteria of both groups assessed by taking fecal samples.
Researchers found increased markers of inflammation in the placenta, the fetal brain, and the adult brain of the mice's offspring. The scientists also found a decrease in a supportive protein called the "brain-derived neurotrophic factor."
When stressed, pregnant mice displayed a change in their bacterial makeup. These changes could be observed both in the mothers' guts and in the placentas, as well as in the intestines of their female offspring. Bacterial changes lasted all the way into adulthood.
Affected adult mice "were more anxious, they spent more time in dark, closed spaces and they had a harder time learning cognitive tasks even though they were never stressed after birth," Gur explains.
Researchers found a lower ability to learn and behavior indicative of higher levels of anxiety among the female offspring of the mice. According to Gur, the team found alterations in the behavior of male offspring as well, but the details of that part of the study are still a work in progress.
Gur recently presented the study at Neuroscience 2016 - the annual meeting of the Society for Neuroscience, held in San Diego, CA.

Future research to uncover link between brain and bacteria

The author emphasizes that by no means do the findings suggests mothers should be blamed for their children's adult mental health. Rather, the results of the study highlight the importance of having a discussion about mental health for both the pregnant mother and the baby.

"As a psychiatrist who treats pregnant women, if you're stressed, anxious or depressed, I think pregnancy is a prime time for intervention. And what's good for mom is good for the baby."

Tamar Gur

In the future, Gur and team hope to further study the link between the brain and the gut bacteria by examining pregnant women and their babies.
Ultimately, Gur hopes to investigate the role of probiotics in alleviating the negative effects of stress.
Read about the connection between gut bacteria and the brain.

Written by Ana Sandoiu