吃水果与肺癌有关？了解这项新研究的真相

The idea that fruit and vegetables might cause cancer sounds bizarre. For decades, studies have shown that people who eat more plants tend to live longer, healthier lives, with lower rates of heart disease, stroke and several common cancers.

Lung cancer is no exception: in many large studies, higher intakes of fruits and vegetables are linked with lower risks, especially in smokers.

Against that backdrop, a new suggestion that fruit and veg might be driving lung cancer in young adults is surprising.

The story behind this latest wave of anxiety doesn’t come from a definitive, landmark trial. It comes from a brief presentation at a scientific conference, based on 187 people with early‑onset lung cancer.

Most had never smoked. When researchers asked about their diets, a lot of them reported eating plenty of fruits, vegetables and whole grains – the sort of pattern most of us would call “healthy”.

Instead of measuring pesticides in their food or blood, the team estimated probable pesticide exposure using average residue levels from other sources. From there, they speculated that pesticides on otherwise healthy foods might help explain why some young non‑smokers develop lung cancer.

That is a very long way from proving that fruit and vegetables themselves are harmful. Studies like this are meant to raise questions – “could pesticides be part of the story in young lung cancer?” – not to rewrite dietary advice on their own.

Crucially, this particular study looks backwards from people who already have cancer, rather than following healthy people forwards over time, so it cannot tell us whether their diet played any role in causing the disease. Nor does it show that these patients had higher pesticide exposures than comparable people without cancer. It only shows that they ate foods that, on average, can carry residues.

The bigger picture

When you zoom out from this single, tiny study to the broader body of evidence, the picture changes from alarming to reassuringly familiar. Large studies have followed tens or hundreds of thousands of people over many years, asked them what they ate, then waited to see who develops lung cancer. Time and again, those eating more fruit and vegetables either do better or, at very worst, no differently from those eating less.

Meta‑analyses that combine data from multiple studies find reductions in lung cancer risk with higher fruit intake and benefits from vegetables, too. These are the studies that inform official guidelines. They are not perfect – no nutrition study is – but they are far more informative than a single unpublished study of 187 patients.

So why do small studies like this latest one sometimes seem to say something different? One reason is simple statistical noise.

With small numbers, chance plays a huge role. If, for whatever reason, the particular group of young adults who turned up to that clinic happened to be unusually health-conscious, then fruit and vegetable intake will look high among people with lung cancer, even if diet has nothing to do with their disease.

Another issue is what scientists call “confounding”. People who eat more plants often differ in many other ways. They may exercise more, drink less, have different jobs, live in different neighbourhoods, or be more on the ball about seeking medical help.

When you start from patients and look backwards, it is very hard to disentangle these overlapping factors. That is why we place more weight on large, prospective studies that follow people forward in time and can better account for these differences.

Pesticides

Then there is the question of pesticides – the part of the story that understandably unnerves people. It is true that many conventionally grown fruits and vegetables carry measurable pesticide residues, and that people who eat a lot of produce tend to have higher levels of some pesticide breakdown products in their urine.

It is also true that farm workers who handle pesticides regularly and at high doses have higher rates of certain cancers, including some lung cancers. That tells us pesticides are not benign. But what it does not tell us is that eating sprayed apples or lettuce at normal dietary levels causes lung cancer in the general population.

That doesn’t mean we should be complacent: there is an ongoing discussion about cocktails of many different chemicals, about vulnerable groups such as children and pregnant women, and about longer‑term hormone or brain effects that might not show up in crude cancer rates. However, these are arguments for improving how we farm and regulate pesticides, not arguments for abandoning fruit and vegetables.

If you are still uneasy about pesticides, there are practical, proportionate things you can do that don’t involve swapping an orange for a packet of crisps. Washing produce under running water helps remove surface residues and soil, and varying the types of fruit and veg you eat means you are not relying heavily on any one item that tends to carry higher residues.

If your budget allows, choosing organic versions of a few “high‑residue” foods can make sense. But the key point is that these are tweaks at the margins. They don’t change the central message that a diet rich in plant foods is overwhelmingly associated with better health.

Perhaps the most important lesson from this episode is about how to read nutrition headlines. Whenever you see “X food causes cancer” or “Y ingredient is the next miracle cure”, it helps to ask a couple of simple questions. How big was the study? Was it in healthy people followed over time, or patients looked at after the fact? Did the researchers actually measure what they are claiming(like pesticide levels)? And how do the new findings sit alongside decades of existing research?

In the case of the early-onset lung cancer study, the answers are sobering: it was small, it was retrospective, it used indirect exposure estimates, and its suggestion that fruit and vegetables might be harmful sits awkwardly with a much larger body of work pointing the other way.

None of this means we should ignore the possibility that pesticides contribute in some way to cancers in non‑smokers, or that diet is irrelevant to lung health. But we should be wary of turning one provocative conference talk into a reason to fear the very foods that consistently show up as markers of better health.

Justin Stebbing does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.