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Science & technology | Well informed
Do** probiotics** work?
For a healthy microbiome, eating your greens is a surer bet
Jul 18th 2025|3 min read
A DAZZLING menagerie of microbes live inside the human gut—by some counts a few thousand different species. Most residents of this gut microbiome are not the disease-causing kind. In fact, many do useful jobs, such as breaking down certain carbohydrates, fibres and proteins that the human body would otherwise struggle to digest. Some even produce essential compounds the body cannot make on its own, like B vitamins and short-chain fatty acids, which help regulate inflammation, influence the immune system and affect metabolism.
As awareness of the microbiome has grown, the shelves of health-food shops have become stocked with products designed to boost good bacteria. These usually fall into two categories: probiotics, capsules containing live (but freeze-dried) bacteria that, in theory, spring back to life once inside your gut; and prebiotics, pills made of fibres that beneficial bacteria feed on.
There may be good scientific reasons to tend one’s microbiome. Having a diverse array of gut bugs, with plenty of the good kind, seems to confer broad health benefits. A varied microbial population can fend off pathogens by competing with them for nutrients and space. Reduced diversity, by contrast, has been linked to obesity, type-2 **diabetes *and* irritable bowel syndrome (IBS)**. Evidence for causal links is growing: randomised-controlled trials have shown that tweaking the microbiome can accelerate weight loss, reverse insulin resistance and improve IBS symptoms.
The microbiome’s influence may stretch well beyond the gut. Microbes seem to be important for mood: people with depression have less microbial variety in their guts than those without do, for example. One study from 2016, published in the Journal of Psychiatric Research, even found that transplanting the microbiome of a depressed person into a rat caused the animal to display behaviour characteristic of depression. An off-kilter microbiome has also been linked to respiratory infections: mice with fewer gut microbes are more likely to catch pneumonia or influenza.
For a diverse microbiome, diet matters. Microbes thrive on foods rich in fibre and digestion-resistant starch, so munching on fresh fruit, vegetables, legumes and nuts is a good place to start. Fermented foods and drinks, such as yogurt, sauerkraut and kombucha, also contain friendly micro-organisms like Lactobacillus. Avoiding unnecessary antibiotics is important, as they wipe out good bacteria along with the bad.
Supplements seem equally appealing, but because they are not regulated as medicines, many have not been rigorously tested. “It is absolute cowboy territory in terms of marketing”, says Ted Dinan, a psychiatrist at University College Cork who studies the influence of the microbiome on mental health. Fortunately for consumers based in America, Britain and Canada, academics in those countries have developed apps (each called The Probiotic Guide) that can be used to search for probiotic products and check what scientific evidence, if any, backs them up. Nothing so comprehensive exists for prebiotics, as yet.
Taking the wrong product may not do much good, but it probably won’t do much harm either. “You really cannot overdose on probiotics,” says Glenn Gibson, a microbiologist at the University of Reading. Taking too many prebiotics, however, could temporarily disrupt the microbiome. The likely side-effect? “Gas,” he says. “But that’s more just antisocial than anything else.”■
科學與科技｜資訊豐富
益生菌真的有效嗎？
若想擁有健康的腸道菌叢，多吃蔬菜才是更穩妥的方法
2025年7月18日｜閱讀時間約3分鐘
人類腸道內住著絢麗多樣的微生物群——據說有數千種不同的物種。大多數腸道微生物並不會引發疾病。事實上，許多微生物對人體有益，例如分解某些碳水化合物、纖維與蛋白質，這些是人體本身較難消化的食物。有些微生物甚至能合成人體無法自行製造的必要化合物，如B群維生素與短鏈脂肪酸，這些物質有助於調節發炎反應、影響免疫系統以及新陳代謝。
隨著大眾對腸道菌叢的認識日益增加，健康食品商店的貨架上也擺滿了旨在促進好菌生長的產品。這些產品主要分為兩類：益生菌——含有活性（但經冷凍乾燥處理）細菌的膠囊，理論上可在進入腸道後復活；以及益生元——由纖維製成的膠囊，提供益菌生長所需的營養來源。
從科學角度來看，照護腸道菌叢確實有其益處。擁有種類多樣的腸道菌群，尤其是大量的有益菌，似乎能帶來整體健康的好處。多樣化的微生物群可透過與病原菌競爭營養與空間來抑制其生長。相反地，腸道菌叢缺乏多樣性則與肥胖、第二型糖尿病以及腸躁症（IBS）相關。這些關聯的因果證據也日益充足：隨機對照試驗顯示，調整腸道菌群可加快體重減輕、逆轉胰島素阻抗，並改善腸躁症症狀。
腸道菌群的影響可能遠超出腸道本身。研究指出微生物對情緒也具有關鍵作用：例如，患有憂鬱症的人，其腸道內的微生物多樣性通常低於未罹病者。一項2016年刊登於《精神病學研究期刊》的研究甚至發現，將一位憂鬱症患者的腸道菌叢移植至老鼠體內，會導致該老鼠出現類似憂鬱的行為反應。失衡的腸道菌叢也與呼吸道感染相關：腸道微生物較少的老鼠更容易感染肺炎或流感。
若想擁有多樣的腸道菌群，飲食至關重要。微生物偏好富含纖維與抗性澱粉的食物，因此多攝取新鮮水果、蔬菜、豆類與堅果是一個良好的起點。發酵食品與飲品，如優格、德國酸菜與康普茶，也含有益菌如乳酸桿菌。此外，避免不必要的抗生素使用也很重要，因為抗生素不分好壞菌，一併清除。
營養補給品看似同樣吸引人，但由於不像藥品那樣受到嚴格監管，因此許多產品尚未經過嚴謹的科學測試。研究腸道菌叢對心理健康影響的愛爾蘭科克大學精神科醫師泰德·迪南（Ted Dinan）表示：「目前的市場行銷簡直就是狂野西部的無政府狀態。」
所幸，對於美國、英國與加拿大的消費者來說，這些國家的學者已開發出名為《益生菌指南》（The Probiotic Guide）的應用程式，幫助用戶搜尋益生菌產品，並查詢是否有科學證據支持其功效。不過，目前尚無同樣完善的益生元產品指南。
選錯產品可能不會帶來太大好處，但通常也不至於造成嚴重傷害。「你基本上不可能攝取過量的益生菌，」雷丁大學微生物學家格倫·吉布森（Glenn Gibson）說。但若攝取過多益生元，則可能暫時擾亂腸道菌叢。最常見的副作用是什麼？「脹氣排氣，」他說，「但這頂多只是讓他人不太舒服罷了。
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