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Asteroid 2024 YR4 Could Hit the Moon, Measles Cases Rise, and States Sue HHS

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Monday, April 7, 2025

American Lifespans, Monkeys That Yodel, Measles, and MoreStates sue HHS for public health cuts, measles cases continue to rise, and a study finds Americans live shorter lives compared with their European counterparts.By Rachel Feltman, Fonda Mwangi & Alex Sugiura Anaissa Ruiz Tejada/Scientific AmericanRachel Feltman: Happy Monday, listeners! And happy April. For Scientific American’s Science Quickly, I’m Rachel Feltman. Let’s kick off the week with a quick roundup of science news you might have missed.To start we have some public health updates. Last Friday the Texas health department reported that there have been 481 known measles cases since late January, up from 400 on March 28. Texas Public Radio recently reported that several children with measles have also needed treatment for toxic levels of vitamin A. As I explained in the March 10 news roundup episode, U.S. Health and Human Services Secretary Robert F. Kennedy Jr. has publicly touted vitamin A supplementation for measles patients while seemingly downplaying the importance of vaccines. According to a recent report by ProPublica, U.S. Centers for Disease Control and Prevention leaders blocked the release of an assessment on the ongoing outbreak written by the agency’s own experts. The planned messaging around the assessment reportedly would have emphasized the need for vaccinations to prevent measles. In a statement to ProPublica, a CDC spokesperson claimed that this report was not published “because it does not say anything that the public doesn’t already know” and that the CDC still presents vaccines as “the best way to protect against measles.” But the spokesperson went on to add that “the decision to vaccinate is a personal one,” saying folks “should be informed about the potential risks and benefits associated with vaccines.”Now the good news is that we know a lot about the risks associated with the measles vaccine, and they’re extremely low. For instance, one study used the mass vaccination of 14.3 million kids in China from September 2007 to March 2008 to track the rate of serious adverse events. The researchers saw a rate of just over two such events for every million vaccine doses given. In contrast, one in every 1,000 cases of measles is associated with encephalitis, or swelling of the brain, which can be deadly. And several major studies have found no link between the measles-mumps-rubella vaccine and autism diagnoses.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.The CDC’s stifling of this new measles report isn’t the only indication that the current administration is downplaying the importance of vaccines. Late last month top U.S. Food and Drug Administration vaccine official Peter Marks resigned from his position. According to the Wall Street Journal and New York Times, Marks was given the choice between quitting and being fired.Meanwhile, lawmakers from 23 states and Washington, D.C., are suing HHS for slashing more than $11 billion in funding for public health initiatives. We actually mentioned those cuts in last week’s news roundup. They mainly target funds that were allocated to local and state health departments during the peak of the COVID pandemic. According to the lawsuit, which was filed last Tuesday, that money was never earmarked as being solely for pandemic-response initiatives like COVID testing. Some of the funding has been directed toward strengthening public health infrastructure to make states and communities more resilient to pandemics and other major crises, including measles outbreaks, the spread of bird flu and the ongoing opioid epidemic, according to the lawmakers. Last week, NBC News reported that the Dallas County Health and Human Services Department had to cancel dozens of planned free measles vaccination clinics due to these same funding cuts.Speaking of health in the U.S., a new study suggests that folks in America live shorter lives than their economic counterparts in Europe. In a study published last Wednesday in the New England Journal of Medicine, researchers compared data from more than 73,000 adults aged 50 to 85. The scientists found, unsurprisingly, that in any given country, people with more money tended to live longer. But the researchers also found that the wealthiest U.S. subjects had shorter lifespans, on average, than the richest participants from Europe. And in parts of western Europe such as Germany, France and the Netherlands some of the poorest residents had lifespans in line with the wealthiest Americans. The study authors say this is a reminder that systemic issues in the U.S. such as stress, diet and environmental contaminants aren’t something you can spend your way out of.Okay, let’s pivot to lighter news. Remember that killer asteroid we were all worried about for a minute? Wouldn’t you rather talk about killer asteroids? I know I would.The good news is that observations made with the James Webb Space Telescope have confirmed that 2024 YR4 functionally has zero chance of hitting Earth in 2032. Yay! The bad news is that there’s still a nonzero possibility that our moon will take the hit instead—about a 2 percent chance, to be exact.And it turns out that a moon collision might not be bad news at all. Several astronomers told New Scientist that such an event would represent a huge opportunity for research. One even said he had his fingers crossed. We know the moon is pelted with smaller asteroids all the time, and its iconically pocked surface tells us it’s taken on bigger bruisers in the past. Knowing in advance that something was going to collide with the moon—and having the time to be certain of its dimensions and trajectory—would enable unprecedented study of the formation of lunar craters. That could help us understand the moon’s past.We’ll wrap up with a fun animal story. Because you’ve earned it!When you think of yodeling you probably imagine people in the Alps wearing wooden shoes or maybe Julie Andrews in The Sound of Music. But a study published last Thursday throws a dark horse into the competition for world’s best yodeler: monkeys.Researchers were interested in structures called vocal membranes, which apes and monkeys have in their throats but humans no longer do. Using CT scans of several species of monkey, along with computer simulations and fieldwork, researchers found that these structures help monkeys accomplish so-called voice breaks, where they quickly switch between using their vocal membranes and vocal folds to produce sound. The result is that quick change in frequency we hear when humans yodel or make that quintessential Tarzan yelp.Here’s an example from the tufted capuchin.[CLIP: A tufted capuchin vocalizes.]Feltman: That might not sound very yodel-y, but things get clearer when you slow the call down.[CLIP: The tufted capuchin’s vocalization is slowed down.]Feltman: Previous research has suggested that humans gave up these membranes to make our speech more stable. But I guess that might have come at the cost of some sick yodelling skills.That’s all for this week’s science news roundup. We’ll be back on Wednesday.Science Quickly is produced by me, Rachel Feltman, along with Fonda Mwangi, Kelso Harper, Naeem Amarsy and Jeff DelViscio. This episode was edited by Alex Sugiura. Shayna Posses and Aaron Shattuck fact-check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news.For Scientific American, this is Rachel Feltman. Have a great week!

States sue HHS for public health cuts, measles cases continue to rise, and a study finds Americans live shorter lives compared with their European counterparts.

American Lifespans, Monkeys That Yodel, Measles, and More

States sue HHS for public health cuts, measles cases continue to rise, and a study finds Americans live shorter lives compared with their European counterparts.

By Rachel Feltman, Fonda Mwangi & Alex Sugiura

A small blue sphere orbits a larger blue sphere on a purple and blue background, with "Science Quickly" written below.

Anaissa Ruiz Tejada/Scientific American

Rachel Feltman: Happy Monday, listeners! And happy April. For Scientific American’s Science Quickly, I’m Rachel Feltman. Let’s kick off the week with a quick roundup of science news you might have missed.

To start we have some public health updates. Last Friday the Texas health department reported that there have been 481 known measles cases since late January, up from 400 on March 28. Texas Public Radio recently reported that several children with measles have also needed treatment for toxic levels of vitamin A. As I explained in the March 10 news roundup episode, U.S. Health and Human Services Secretary Robert F. Kennedy Jr. has publicly touted vitamin A supplementation for measles patients while seemingly downplaying the importance of vaccines. According to a recent report by ProPublica, U.S. Centers for Disease Control and Prevention leaders blocked the release of an assessment on the ongoing outbreak written by the agency’s own experts. The planned messaging around the assessment reportedly would have emphasized the need for vaccinations to prevent measles. In a statement to ProPublica, a CDC spokesperson claimed that this report was not published “because it does not say anything that the public doesn’t already know” and that the CDC still presents vaccines as “the best way to protect against measles.” But the spokesperson went on to add that “the decision to vaccinate is a personal one,” saying folks “should be informed about the potential risks and benefits associated with vaccines.”

Now the good news is that we know a lot about the risks associated with the measles vaccine, and they’re extremely low. For instance, one study used the mass vaccination of 14.3 million kids in China from September 2007 to March 2008 to track the rate of serious adverse events. The researchers saw a rate of just over two such events for every million vaccine doses given. In contrast, one in every 1,000 cases of measles is associated with encephalitis, or swelling of the brain, which can be deadly. And several major studies have found no link between the measles-mumps-rubella vaccine and autism diagnoses.


On supporting science journalism

If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.


The CDC’s stifling of this new measles report isn’t the only indication that the current administration is downplaying the importance of vaccines. Late last month top U.S. Food and Drug Administration vaccine official Peter Marks resigned from his position. According to the Wall Street Journal and New York Times, Marks was given the choice between quitting and being fired.

Meanwhile, lawmakers from 23 states and Washington, D.C., are suing HHS for slashing more than $11 billion in funding for public health initiatives. We actually mentioned those cuts in last week’s news roundup. They mainly target funds that were allocated to local and state health departments during the peak of the COVID pandemic. According to the lawsuit, which was filed last Tuesday, that money was never earmarked as being solely for pandemic-response initiatives like COVID testing. Some of the funding has been directed toward strengthening public health infrastructure to make states and communities more resilient to pandemics and other major crises, including measles outbreaks, the spread of bird flu and the ongoing opioid epidemic, according to the lawmakers. Last week, NBC News reported that the Dallas County Health and Human Services Department had to cancel dozens of planned free measles vaccination clinics due to these same funding cuts.

Speaking of health in the U.S., a new study suggests that folks in America live shorter lives than their economic counterparts in Europe. In a study published last Wednesday in the New England Journal of Medicine, researchers compared data from more than 73,000 adults aged 50 to 85. The scientists found, unsurprisingly, that in any given country, people with more money tended to live longer. But the researchers also found that the wealthiest U.S. subjects had shorter lifespans, on average, than the richest participants from Europe. And in parts of western Europe such as Germany, France and the Netherlands some of the poorest residents had lifespans in line with the wealthiest Americans. The study authors say this is a reminder that systemic issues in the U.S. such as stress, diet and environmental contaminants aren’t something you can spend your way out of.

Okay, let’s pivot to lighter news. Remember that killer asteroid we were all worried about for a minute? Wouldn’t you rather talk about killer asteroids? I know I would.

The good news is that observations made with the James Webb Space Telescope have confirmed that 2024 YR4 functionally has zero chance of hitting Earth in 2032. Yay! The bad news is that there’s still a nonzero possibility that our moon will take the hit instead—about a 2 percent chance, to be exact.

And it turns out that a moon collision might not be bad news at all. Several astronomers told New Scientist that such an event would represent a huge opportunity for research. One even said he had his fingers crossed. We know the moon is pelted with smaller asteroids all the time, and its iconically pocked surface tells us it’s taken on bigger bruisers in the past. Knowing in advance that something was going to collide with the moon—and having the time to be certain of its dimensions and trajectory—would enable unprecedented study of the formation of lunar craters. That could help us understand the moon’s past.

We’ll wrap up with a fun animal story. Because you’ve earned it!

When you think of yodeling you probably imagine people in the Alps wearing wooden shoes or maybe Julie Andrews in The Sound of Music. But a study published last Thursday throws a dark horse into the competition for world’s best yodeler: monkeys.

Researchers were interested in structures called vocal membranes, which apes and monkeys have in their throats but humans no longer do. Using CT scans of several species of monkey, along with computer simulations and fieldwork, researchers found that these structures help monkeys accomplish so-called voice breaks, where they quickly switch between using their vocal membranes and vocal folds to produce sound. The result is that quick change in frequency we hear when humans yodel or make that quintessential Tarzan yelp.

Here’s an example from the tufted capuchin.

[CLIP: A tufted capuchin vocalizes.]

Feltman: That might not sound very yodel-y, but things get clearer when you slow the call down.

[CLIP: The tufted capuchin’s vocalization is slowed down.]

Feltman: Previous research has suggested that humans gave up these membranes to make our speech more stable. But I guess that might have come at the cost of some sick yodelling skills.

That’s all for this week’s science news roundup. We’ll be back on Wednesday.

Science Quickly is produced by me, Rachel Feltman, along with Fonda Mwangi, Kelso Harper, Naeem Amarsy and Jeff DelViscio. This episode was edited by Alex Sugiura. Shayna Posses and Aaron Shattuck fact-check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news.

For Scientific American, this is Rachel Feltman. Have a great week!

Read the full story here.
Photos courtesy of

New method improves the reliability of statistical estimations

The technique can help scientists in economics, public health, and other fields understand whether to trust the results of their experiments.

Let’s say an environmental scientist is studying whether exposure to air pollution is associated with lower birth weights in a particular county.They might train a machine-learning model to estimate the magnitude of this association, since machine-learning methods are especially good at learning complex relationships.Standard machine-learning methods excel at making predictions and sometimes provide uncertainties, like confidence intervals, for these predictions. However, they generally don’t provide estimates or confidence intervals when determining whether two variables are related. Other methods have been developed specifically to address this association problem and provide confidence intervals. But, in spatial settings, MIT researchers found these confidence intervals can be completely off the mark.When variables like air pollution levels or precipitation change across different locations, common methods for generating confidence intervals may claim a high level of confidence when, in fact, the estimation completely failed to capture the actual value. These faulty confidence intervals can mislead the user into trusting a model that failed.After identifying this shortfall, the researchers developed a new method designed to generate valid confidence intervals for problems involving data that vary across space. In simulations and experiments with real data, their method was the only technique that consistently generated accurate confidence intervals.This work could help researchers in fields like environmental science, economics, and epidemiology better understand when to trust the results of certain experiments.“There are so many problems where people are interested in understanding phenomena over space, like weather or forest management. We’ve shown that, for this broad class of problems, there are more appropriate methods that can get us better performance, a better understanding of what is going on, and results that are more trustworthy,” says Tamara Broderick, an associate professor in MIT’s Department of Electrical Engineering and Computer Science (EECS), a member of the Laboratory for Information and Decision Systems (LIDS) and the Institute for Data, Systems, and Society, an affiliate of the Computer Science and Artificial Intelligence Laboratory (CSAIL), and senior author of this study.Broderick is joined on the paper by co-lead authors David R. Burt, a postdoc, and Renato Berlinghieri, an EECS graduate student; and Stephen Bates an assistant professor in EECS and member of LIDS. The research was recently presented at the Conference on Neural Information Processing Systems.Invalid assumptionsSpatial association involves studying how a variable and a certain outcome are related over a geographic area. For instance, one might want to study how tree cover in the United States relates to elevation.To solve this type of problem, a scientist could gather observational data from many locations and use it to estimate the association at a different location where they do not have data.The MIT researchers realized that, in this case, existing methods often generate confidence intervals that are completely wrong. A model might say it is 95 percent confident its estimation captures the true relationship between tree cover and elevation, when it didn’t capture that relationship at all.After exploring this problem, the researchers determined that the assumptions these confidence interval methods rely on don’t hold up when data vary spatially.Assumptions are like rules that must be followed to ensure results of a statistical analysis are valid. Common methods for generating confidence intervals operate under various assumptions.First, they assume that the source data, which is the observational data one gathered to train the model, is independent and identically distributed. This assumption implies that the chance of including one location in the data has no bearing on whether another is included. But, for example, U.S. Environmental Protection Agency (EPA) air sensors are placed with other air sensor locations in mind.Second, existing methods often assume that the model is perfectly correct, but this assumption is never true in practice. Finally, they assume the source data are similar to the target data where one wants to estimate.But in spatial settings, the source data can be fundamentally different from the target data because the target data are in a different location than where the source data were gathered.For instance, a scientist might use data from EPA pollution monitors to train a machine-learning model that can predict health outcomes in a rural area where there are no monitors. But the EPA pollution monitors are likely placed in urban areas, where there is more traffic and heavy industry, so the air quality data will be much different than the air quality data in the rural area.In this case, estimates of association using the urban data suffer from bias because the target data are systematically different from the source data.A smooth solutionThe new method for generating confidence intervals explicitly accounts for this potential bias.Instead of assuming the source and target data are similar, the researchers assume the data vary smoothly over space.For instance, with fine particulate air pollution, one wouldn’t expect the pollution level on one city block to be starkly different than the pollution level on the next city block. Instead, pollution levels would smoothly taper off as one moves away from a pollution source.“For these types of problems, this spatial smoothness assumption is more appropriate. It is a better match for what is actually going on in the data,” Broderick says.When they compared their method to other common techniques, they found it was the only one that could consistently produce reliable confidence intervals for spatial analyses. In addition, their method remains reliable even when the observational data are distorted by random errors.In the future, the researchers want to apply this analysis to different types of variables and explore other applications where it could provide more reliable results.This research was funded, in part, by an MIT Social and Ethical Responsibilities of Computing (SERC) seed grant, the Office of Naval Research, Generali, Microsoft, and the National Science Foundation (NSF).

Gas Stoves Are Poisoning Americans by Releasing Toxic Fumes Associated With Asthma and Lung Cancer

In the United States, gas stoves are the main source of indoor nitrogen dioxide—a toxic gas tied to many health problems—according to a new study

Gas Stoves Are Poisoning Americans by Releasing Toxic Fumes Associated With Asthma and Lung Cancer In the United States, gas stoves are the main source of indoor nitrogen dioxide—a toxic gas tied to many health problems—according to a new study Sarah Kuta - Daily Correspondent December 11, 2025 9:13 a.m. Gas stoves are responsible for more than half of some Americans’ total exposure to toxic nitrogen dioxide, a new study suggests. Pexels A hidden danger may be lurking in your kitchen. Many Americans are breathing in nitrogen dioxide—a harmful pollutant that’s been linked with asthma and lung cancer—from fumes emitted by their gas stoves. A new study, published this month in the journal PNAS Nexus, suggests that gas stoves are the main source of indoor nitrogen dioxide pollution in the United States, responsible for more than half of some Americans’ total exposure to the gas. “We’ve spent billions of dollars cleaning up our air outdoors and nothing to clean up our air indoors,” study co-author Robert Jackson, an environmental scientist at Stanford University, tells SFGATE’s Anna FitzGerald Guth. “As our air outdoors gets cleaner and cleaner, a higher proportion of the pollution we breathe comes from indoor sources.” Scientists and public health experts have long known that nitrogen dioxide is bad for human health. The reddish-brown gas can irritate airways and worsen or even contribute to the development of respiratory diseases like asthma. Children and older individuals are particularly susceptible to its effects. Nitrogen dioxide is a byproduct of burning fuel, so most emissions come from vehicles, power plants and off-road equipment. However, indoors, the primary culprit is the gas stove, the household appliance that burns natural gas or propane to produce controlled flames under individual burners. It’s relatively easy to keep tabs on outdoor nitrogen dioxide concentrations and estimate their corresponding exposure risks, thanks to satellites and ground-level stations located across the country. By contrast, however, indoor sources are “neither systematically monitored nor estimated,” the researchers write in the paper. Did you know? Bans on gas Berkeley, California, became the first city to prohibit gas hookups in most new buildings in 2019, although the ordinance was halted in 2024 after the California Restaurant Association sued. Still, 130 local governments have now implemented zero-emission building ordinances, according to the Building Decarbonization Coalition. For the study, Jackson and his colleagues performed a ZIP-code-level estimate of how much total nitrogen dioxide communities are exposed to. Information came from two databases tracking outdoor nitrogen dioxide concentrations and a building energy use database, which helped the team construct characteristics of 133 million residential dwellings across the country, along with their home appliances. Among individuals who use gas stoves, the appliances are responsible for roughly a quarter of their overall nitrogen dioxide exposure on average, the team found. For those who cook more frequently or for longer durations, gas stoves can be responsible for as much as 57 percent of their total exposure. “Our research shows that if you use a gas stove, you’re often breathing as much nitrogen dioxide pollution indoors from your stove as you are from all outdoor sources combined,” says Jackson in a Stanford statement. Individuals who use gas stoves are exposed to roughly 25 percent more total residential nitrogen dioxide over the long term than those who use electric stoves, which do not emit the gas. Total exposure tends to be highest in big cities, where people often have small living spaces and outdoor levels are also high. Switching from a gas to an electric stove would help roughly 22 million Americans dip below the maximum nitrogen dioxide exposure levels recommended by the World Health Organization, the analyses suggest. The authors recommend replacing gas stoves with electric models whenever possible. “You would never willingly stand over the tailpipe of your car, breathing in pollution,” Jackson tells Women’s Health’s Korin Miller. “Why breathe the same toxins every day in your kitchen?” Dylan Plummer, acting deputy director for building electrification for the Sierra Club, a nonprofit environmental organization, agrees. Plummer, who was not involved with the research, tells Inside Climate News’ Phil McKenna that “years from now, we will look back at the common practice of burning fossil fuels in our homes with horror.” If swapping stoves is not possible, experts have some other tips for reducing nitrogen dioxide exposure. “One thing people could do is to minimize the time the stoves are on,” Jamie Alan, a toxicologist at Michigan State University who was not involved with the research, tells Women’s Health. “Another suggestion would be to increase ventilation,” such as by turning on the range hood and opening a window. Other suggestions by the New York Times’ Rachel Wharton include using a portable induction countertop unit or electric kitchen gadgets like tea kettles, toaster ovens and slow cookers. Get the latest stories in your inbox every weekday.

Parents Might Pass Depression Down To Kids Through One Specific Symptom, Experts Say

By Dennis Thompson HealthDay ReporterTHURSDAY, Dec. 11, 2025 (HealthDay News) — Children of depressed parents are more likely to develop depression...

By Dennis Thompson HealthDay ReporterTHURSDAY, Dec. 11, 2025 (HealthDay News) — Children of depressed parents are more likely to develop depression themselves, and a new study suggests this risk might be tied to one specific symptom of depression.It’s already known that depression in parents can affect how children’s brains respond to positive and negative feedback, researchers said.“If parents are experiencing forms of depression where they’re not enjoying things and aren’t interested in things, that seems to be impacting how their kids are responding to what’s going on around them,” senior researcher Brandon Gibb, director of the Mood Disorders Institute at Binghamton University, said in a news release.“They’re less reactive to positive things and negative things,” he continued. “It seems that parents’ experiences of anhedonia is the key feature of depression impacting how children’s brains are responding, at least in our study, rather than other common symptoms of depression.”For the new study, researchers performed a lab experiment involving more than 200 parents and children ages 7 to 11.The experiment was designed to see how parents’ anhedonic symptoms affect children’s brain responses to positive and negative feedback.“The idea is that if you have this risk factor of being less interested or less engaged or finding things less enjoyable, maybe that’s reflected in how your brain responds to environmental feedback,” said lead researcher Alana Israel, a doctoral student at Binghamton University, a branch of the State University of New York. “Children of parents who have higher levels of anhedonic depressive symptoms should show a reduced response while other depressive symptoms theoretically should not be as related to this specific brain response,” Israel explained in a news release.In the experiment, children were presented with two doors and asked to guess the one with a prize behind it. If they chose the right door, they won money; if they chose wrong, they lost money.Results showed that kids’ response to either winning or losing money was blunted if their parents had higher levels of anhedonic symptoms. “What that tells us is that there is something specific about parents’ anhedonia that may impact children’s neural responses,” Israel said. “It further specifies a group of children who might be at heightened risk for loss of interest or pleasure and lack of engagement, which is a core feature of depression.”Future research should investigate how family dynamics might change if parents with anhedonic symptoms receive treatment or start to feel better, the team said.Researchers said it’s also important to examine whether children’s responses to other sorts of feedback, like social feedback from peers, are also affected by parents’ depression.“There are researchers looking at interventions that are designed to increase positive mood, positive engagement and positive parent-child relationships,” Israel said. “It will be important to see if these findings can identify families who might be most likely to benefit from those types of interventions.”SOURCE: Binghamton University, news release, Dec. 4, 2025Copyright © 2025 HealthDay. All rights reserved.

We may finally know what a healthy gut microbiome looks like

Our gut microbiome has a huge influence on our overall health, but we haven't been clear on the specific bacteria with good versus bad effects. Now, a study of more than 34,000 people is shedding light on what a healthy gut microbiome actually consists of

The trillions of microscopic bacteria that reside in our gut have an outsized role in our healthTHOM LEACH/SCIENCE PHOTO LIBRARY We often hear talk of things being good for our microbiome, and in turn, good for our health. But it wasn’t entirely clear what a healthy gut microbiome consisted of. Now, a study of more than 34,000 people has edged us closer towards understanding the mixes of microbes that reliably signal we have low inflammation, good immunity and healthy cholesterol levels. Your gut microbiome can influence your immune system, rate of ageing and your risk of poor mental health. Despite a profusion of home tests promising to reveal the make-up of your gut community, their usefulness has been debated, because it is hard to pin down what defines a “good” microbial mix. Previous measures mainly looked at species diversity, with a greater array of bacteria being better. But it is difficult to identify particular communities of interacting organisms that are implicated in a specific aspect of our health, because microbiomes vary so much from person to person. “There is a very intricate relationship between the food we eat, the composition of our gut microbiome, and the effects the gut microbiome has on our health. The only way to try to map these connections is having large enough sample sizes,” says Nicola Segata at the University of Trento in Italy. To create such a map, Segata and his colleagues have assessed a dataset from more than 34,500 people who took part in the PREDICT programme in the UK and US, run by microbiome testing firm Zoe, and validated the results against data from 25 other cohorts from Western countries. Of the thousands of species that reside in the human gut, the researchers focused on 661 bacterial species that were found in more than 20 per cent of the Zoe participants. They used this to determine the 50 bacteria most associated with markers of good health – assessed via markers such as body mass index and blood glucose levels – and the 50 most linked to bad health. The 50 “good bug” species – 22 of which are new to science – seem to influence four key areas: heart and blood cholesterol levels; inflammation and immune health; body fat distribution; and blood sugar control. The participants who were deemed healthy, because they had no known medical conditions, had about 3.6 more of these species than people with a condition, while people at a healthy weight hosted about 5.2 more of them than those with obesity. The researchers suggest that good or bad health outcomes may come about due to the vital role the gut microbiome plays in releasing chemicals involved in cholesterol transport, inflammation reduction, fat metabolism and insulin sensitivity. As to the specific species that were present, most microbes in both the “good” and “bad” rankings belong to the Clostridia class. Within this class, species in the Lachnospiraceae family featured 40 times, with 13 seemingly having favourable effects and 27 unfavourable. “The study highlights bacterial groups that could be further investigated regarding their potential positive or negative impact [on] health conditions, such as high blood glucose levels or obesity,” says Ines Moura at the University of Leeds, UK. The link between these microbes and diet was assessed via food questionnaires and data logged on the Zoe app, where users are advised to aim for at least 30 different plants a week and at least three portions a day of fermented foods, with an emphasis on fibre and not too many ultra processed options. The researchers found that most of the microbes either aligned with a generally healthy diet and better health, or with a worse diet and poorer health. But 65 of the 661 microbes didn’t fit in. “These 65 bacteria are a testament to the fact that the picture is still more complex than what we saw,” says Segata, who also works as a consultant for Zoe. “The effects may depend on the other microbes that are there, or the specific strain of the bacterium or the specific diet.” This sorting of “good” versus “bad” bacteria has enabled the researchers to create a 0 to 1000 ranking scale for the overall health of someone’s gut microbiota, which is already used as part of Zoe’s gut health tests. “Think of a healthy gut microbiome as a community of chemical factories. We want large numbers of species, we want the good ones outnumbering the bad ones, and when you get that, then you’re producing really healthy chemicals, which have impacts across the body,” says team member Tim Spector at King’s College London and co-founder of Zoe. This doesn’t mean the ideal healthy gut microbiome has been pinned down, though. “Defining a healthy microbiome is a difficult task, as the gut microbiome composition is impacted by diet, but it can also change with environmental factors, age and health conditions that require long-term medication,” says Moura. “We really need to think about our body and our microbiome as two complex systems that together make one even more complex system,” says Segata. “When you change one thing, everything is modified a bit as a consequence. Understanding what is cause and effect in many cases can be very intricate.” Bigger studies are needed to tease out these links and cover more of the global population, says Segata. However, once we have established the baseline of your health and microbiome, it should become possible to recommend specific foods to tweak your gut bacteria, he says.

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