You would be forgiven for thinking that the recipe for a healthy life is cut and dried: exercise is good, and too much fat is bad. Overindulging in the latter is firmly tied to obesity and heart disease – conditions that could be prevented, or at least eased, by dusting off your running shoes. But this one-size-fits-all formula to achieve a healthy lifestyle doesn’t work for everyone.

When long covid first emerged in the wake of the coronavirus pandemic, millions of people were facing a debilitating condition with no obvious treatment. Some studies suggest that exercise, often seen as a cure-all, might offer some relief. But as we report here, for some people with long covid it does the exact opposite, potentially triggering severe muscular and cellular damage.

Fat, meanwhile, isn’t a universal villain. The high-fat, very-low-carb keto diet has been dismissed by many as a fad, and there is certainly evidence that it can cause high cholesterol, kidney failure and pregnancy complications. But again, the story is more complicated. Evidence is mounting that for some people, going keto could help treat mental health conditions including depression, anorexia and schizophrenia.

It is time we remember that people are unique – and so, too, are their medical conditions

The only way to reap these benefits, and avoid harm, is to stop framing medical interventions as a cure-all or overhyped trend. For every condition, there will be people for whom a drug or lifestyle change helps, and people who experience side effects with no benefit. The only way to predict where an individual will fall is to separate conditions into subtypes that are treated differently, such as with diabetes.

This would be a gargantuan effort, requiring us to collect huge amounts of data and carry out more in-depth clinical trials. And then, if we have the knowledge to identify subtypes, doctors will need more time and resources to be able to select a tailored treatment for individuals, rather than reaching for the one-size-fits-all solution. But it is worth doing. It is time we remember that people are unique – and so, too, are their medical conditions.

Long covid symptoms appear to differ substantially between younger children and adolescents. A better understanding of how the condition can present could aid diagnoses.

To date, most long covid research has focused on adults. That is partly due to a “misperception that children don’t get long covid”, says at New York University.

Now, Gross and her colleagues have tracked 751 children aged 6 to 11 and 3109 aged 12 to 17, who had previously had an infection with the SARS-CoV-2 virus, according to their caregivers.

The researchers defined long covid as having at least one symptom that lasted for more than one month, started or became worse during the covid-19 pandemic and was present at the time of the study.

Among the younger children, these symptoms mainly included sleep problems, trouble focusing and abdominal issues, such as pain, nausea, vomiting and constipation.

These symptoms were much less common among nearly 150 children of the same age who hadn’t previously been infected, verified by them having no antibodies against the virus in their blood samples.

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In contrast, the teenagers’ long covid symptoms generally included pain, fatigue and a loss of smell or taste, compared with 1300 of their uninfected counterparts.

Why these different symptoms occur between the age groups is unclear, but it could be down to variations in their hormonal and immune systems, says Gross. Alternatively, teenagers may simply be better able to vocalise their symptoms than younger children, says at the Gemelli University Hospital in Rome, Italy. For example, a teenager may complain of fatigue, while caregivers may only notice that a younger child has prolonged symptoms when they vomit.

Off the back of this data, the researchers have developed a score that ranks how closely a young person’s symptoms correspond to possibly having long covid. Currently, diagnoses hinge on doctors ruling out other conditions and being aware of the different forms long covid can take. “Doctors like to have scores or more objective criteria, and these kinds of tools are definitely useful to help clinicians to at least recognise a child can have long covid,” says Buonsenso.

A daily cocktail of prebiotics and probiotics may help treat fatigue, memory loss and gastrointestinal upset in people with long covid – a condition where��people experience lingering symptoms for months or years after contracting covid-19.

While long covid is poorly understood, previous research has shown that people with the condition have lower levels of certain gut microbes than those without. In particular, they lack gut bacteria that produce compounds called short-chain fatty acids, which regulate immune responses.

at the Chinese University of Hong Kong and her colleagues concocted a mixture to boost short-chain fatty acid production. Called SIM01, it contained three probiotics – live strains of bacteria – and three prebiotics, compounds that help beneficial gut microbes grow.

They gave the cocktail to 232 adults; another group of 231 adults took a mixture containing starch and low-dose vitamin C. Both mixtures were taken twice daily for six months. All participants lived in Hong Kong, had previously tested positive for covid-19 and met the US Centers for Disease Control and Prevention’s criteria for long covid.

Researchers used a questionnaire to assess 14 long covid symptoms in participants before the treatment began and after it stopped. At the end of the trial, they found that people given SIM01 were, on average, about 2 to 2.5 times more likely to experience alleviation of five long covid symptoms – fatigue, memory loss, difficulty concentrating, general unwellness and gastrointestinal upset. The team also found no significant side effects of the therapy.

Analysis of faecal samples collected before and after the trial revealed SIM01 enhanced the diversity of gut microbes and fostered the growth of beneficial gut bacteria, says Ng. Therefore, it could potentially help treat other conditions that have been linked to disrupted gut microbiomes, such as chronic fatigue syndrome, she says.

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How these changes in the gut alleviate long covid symptoms is ambiguous, though, says at Emory University in Georgia. “While it does make sense that the microbiome has the capacity to mediate immune responses…�� it is not clear that the [immune system] is what is actually underlying the [long covid] symptoms,” he says.