Today’s Dietitian Interviews Dr. Bob Rastall on:
Prebiotics and Mood:
Exploring the Gut-Brain Axis
Dr. Bob Rastall is Senior Tutor within the Department of Food and Nutritional Sciences at the University of Reading in the UK where he also holds the post of Professor of Food Biotechnology, teaching food chemistry and biochemistry. Dr. Rastall has a BSc in Applied Biology and a PhD in Microbial Biochemistry from the University of Greenwich, London. Professor Rastall’s research interests are around developing novel enzymatic manufacturing technologies for functional carbohydrates targeted at gut health.
Q: The gut-brain axis is complex. Can you summarize how it functions and why prebiotics are important in supporting this connection?
Dr. Rastall: The gut-brain axis refers to the two-way communication between the gut and the brain, involving neural, hormonal, and immune pathways. The gut is home to trillions of microbes that play a vital role in producing neurotransmitters, like serotonin, which regulate mood and anxiety.
Prebiotics, such as chicory-derived inulin and oligofructose, nourish beneficial gut bacteria (like bifidobacteria), which in turn produce metabolites, such as short-chain fatty acids, that positively affect brain function. Studies show that prebiotics such as oligofructose, can alleviate symptoms of anxiety and depression. This is why prebiotics could be a crucial alternative treatment for mental well-being, as they directly support the gut, which in turn impacts the brain.
Q: There was a recent study with Chicory root fibers and HMOs on mental wellbeing, can you elaborate on the main findings and how do you see the recommendation of taking prebiotics to positively affect mood?
Dr. Rastall: The recent study included 92 healthy adults with mild-to-moderate anxiety and depression. Participants received daily doses of either oligofructose (a prebiotic from chicory root), 2’-fucosyllactose (a human milk oligosaccharide, or HMO), a combination of the two, or a placebo. The findings were remarkable—beneficial bacteria in the gut increased significantly, and participants showed meaningful improvements in their mood scores, particularly in anxiety and depression measures.
What makes this study so compelling is that the improvements were observed within just 28 days of supplementation. The reduction in both state traits for anxiety and depression would indicate that prebiotics not only help manage current feelings of anxiety and depression but may also lower an individual’s general anxiety and depression levels over time. The study supports the use of prebiotics from chicory root as interventions to enhance mood in addition to bringing about desirable changes in the gut microbiome. This suggests that prebiotics can be a powerful tool in managing not only gut health but also mental health.
We can certainly recommend prebiotics to improve mood, we have convincing data that most people responded to the oligofructose from chicory root. In terms of dose, a dose-response study would be needed but for general well-being, I’d recommend starting with about 3 grams of chicory root fibers per day to improve digestive health. However, for mental health benefits, this study shows that 8 grams per day of oligofructose from chicory is effective in positively impacting mood. Consistency is key—regular intake helps maintain a healthy gut microbiome, which is crucial for both digestive and mental well-being.
Q: Inulin is sometimes added to foods, is this as good as eating foods naturally rich in inulin? At what dosages do we see health benefits?
Dr. Rastall: That’s a great question, and one that comes up often. Inulin, whether naturally present in foods like onions, garlic, asparagus, and chicory, or added to foods like yogurt or cereals, is chemically identical and metabolized by the body in the same way. The difference lies in the quantity—foods naturally rich in inulin generally don’t contain large amounts of it, so adding inulin to everyday products can help people meet effective doses more easily.
In the study we discussed, 8 grams per day of oligofructose showed significant mood-enhancing effects, but digestive health benefits can be observed at lower intakes, starting at around 3 grams per day. When choosing products, I recommend looking for proven prebiotics on the label, such as inulin, oligofructose (FOS), chicory root fiber, or galacto-oligosaccharides (GOS)—these are recognized as effective by authoritative bodies like the International Scientific Association for Probiotics and Prebiotics (ISAPP).
Q: You mentioned in your talk, the definition of a prebiotic. There are so many products claiming ‘prebiotic’, how can the public identify proven prebiotics from all the rest?
Dr. Rastall: The term "prebiotic" is indeed often used loosely. According to ISAPP, for a compound to qualify as a prebiotic, it must be selectively utilized by beneficial gut bacteria and have a proven health benefit for the host. This means there should be human studies that demonstrate specific benefits, such as improved gut health or enhanced immune function.
Proven prebiotics include inulin, fructo-oligosaccharides (FOS), oligofructose, and galacto-oligosaccharides (GOS). These have substantial research backing their effects. On the other hand, while other fibers may be beneficial as dietary fibers, they often lack the same targeted action and research validation and can be mislabeled as prebiotics. To identify proven prebiotics, look for these specific names on product labels, or check for certifications from reputable scientific organizations like ISAPP.
Q: What are the implications of the recent findings on prebiotics and mental health for dietitians and healthcare professionals?
Dr. Rastall: These findings present a new opportunity for healthcare professionals to support their patients’ mental health through nutrition. Dietitians can recommend prebiotics as part of a holistic approach to managing mild-to-moderate anxiety and depression. Prebiotics are safe, natural ingredients that are generally well-tolerated, though they may initially cause some digestive discomfort as the body adjusts. Chicory root fiber, in particular, is a readily accessible prebiotic backed by a strong body of evidence. As more studies emerge, we’re hopeful that prebiotics will become a more regular part of treatment strategies for mental health, particularly in combination with other lifestyle changes. It’s important to note that while prebiotics are not a substitute for medications, they can play a valuable role in supporting mental well-being as part of an overall healthy diet and lifestyle.
For more information visit
www.dietaryfiber.org
