Scientists have calculated the prebiotic content of thousands of types of foods using existing literature. Those that have been shown to be richest in these components are dandelion leaves, Jerusalem artichokes, garlic, leeks and onions. In addition to favoring the intestinal microbiota, foods rich in prebiotics contain large amounts of fiber, something that most people do not consume in sufficient quantity.
According to Cassandra Boyd, a master's student at San Jose University in the United States who conducted the research with Associate Professor John Gieng, PhD, previous research has shown that eating foods rich in prebiotics is beneficial to health. "Eating in a way that promotes microbiota well-being while consuming more fiber may be more achievable and accessible than you might think," she adds.
Prebiotics, which can be considered microbiota foods, are different from probiotics, which contain live microorganisms. Both can benefit the health of the microbiota, but they act in different ways.
Studies have linked the consumption of prebiotics with better regulation of blood glucose and greater absorption of minerals such as calcium. Although most dietary guidelines do not specify the recommended daily allowance for these components, the International Scientific Association for Probiotics and Prebiotics—a nonprofit organization that established the current definition of prebiotics—recommends 5 grams per day.
For the study, which Boyd will present at NUTRITION 2023 (the annual meeting of the American Nutrition Society), researchers used previously published scientific results to analyze the prebiotic content of 8,690 foods listed in the Food and Nutrient Database for Studies. Dietetics, a resource that many scientists use to study nutrition and health.
About 37% of the foods in the database were found to contain prebiotics. Dandelion greens, Jerusalem artichokes, garlic, leeks and onions contained the highest amounts, between 100 and 240 milligrams of prebiotics per gram of food (mg/g). Other prebiotic-rich foods included creamed onions, cowpeas and asparagus.
"Findings from our preliminary review of the literature suggest that onions and related foods contain multiple forms of prebiotics, leading to a higher total content," Boyd says. "Multiple forms of onions and related foods appear in a variety of dishes both as flavorings or main ingredients. These foods are commonly eaten and would therefore be a feasible target for people to increase their intake of prebiotics."
Based on the team's findings, Boyd notes that a person would need to consume about half of a small onion to get 5 grams of prebiotics. Foods that contain wheat are at the bottom of the list. Foods with little or no prebiotic content are dairy products, eggs, oils, and meats.
The researchers hope the study will serve as a foundation to help other scientists assess the health implications of prebiotics and inform future dietary guidelines. They noted that more research is needed to understand how cooking influences prebiotic content and to better evaluate foods that contain multiple ingredients.
