Dietitians are the best equipped health professionals to answer the question: What should I eat for better health? But when you’re sitting in a clinic asking this question, your dietitian faces a dilemma—what should they tell you when they know that not everyone responds the same way to exactly the same diet? According to Dr. Genelle Healey from the Department of Pediatrics at University of British Columbia (Canada), dietitians will be better equipped in future to give detailed personal dietary advice—and it might be enabled by what we’re learning about the gut microbiota.

A growing number of scientific studies show diet can affect health through the gut microbiota—but Healey noticed that when she and her fellow scientists tested the effect of a certain diet or food item on people’s gut microbiota, they didn’t always find a distinct pattern. For example, one recent study from Denmark found a diet high in whole grains (as compared to refined grains) had beneficial effects on people’s body weight and their levels of inflammation, but it did not affect the gut microbiota in a predictable way in all the subjects.

According to Dr. Genelle Healey, dietitians will be better equipped in future to give detailed personal dietary advice

“In most studies now, you’ll just group participants together and analyze [their] data,” Healey explains in an interview with Gut Microbiota for Health editors. “But what’s becoming increasingly clear is that certain foods and dietary patterns actually have differing effects on the gut microbiota between individuals.” That is to say, the same food item could change the gut microbiota in different ways in different people. So when the scientists take an average over many people, there’s no clear pattern.

Determined to find a way forward, Healey and co-authors argued in a recent scientific review paper that concrete personalized dietary recommendations could be developed more easily if scientists took into account two things about their study participants: (1) their dietary habits, and (2) their gut microbiota composition and/or function at the beginning of the study. Based on these measures, she thinks, it may be possible to group people into categories that are going to respond in a predictable way to an item in the diet. This could lead to a new era in dietetics practice where individuals are ‘stratified’ into groups that will respond in a certain way to a certain nutritional intervention.

The same food item, in different people, may cause different changes in the gut microbiota

As an example, Healey describes two imaginary people who might be trying to move their gut microbiomes toward a “more favourable profile”: Person A typically eats very little fiber and therefore may have a gut microbiota that’s less rich, depleted of key bacterial species. Person B eats a high-fiber diet and has a gut microbiota rich in many different species; when both of them consume a prebiotic, Person B might experience more dramatic changes in her gut microbiota because her set of bacteria already have the enzymes capable of using the prebiotic to make beneficial short-chain fatty acids—possibly resulting in a greater overall health benefit. The rich, as it were, get richer. (In the end, a different approach would likely be needed for person A.)

This is indeed what Healey and colleagues found in a just-published experiment in which they tested people’s gut microbiota responses to a daily prebiotic supplement. People who normally had high dietary fibre intakes showed greater modulation of gut microbiota composition when they consumed the prebiotic (which was an inulin-type fructan) than those with low dietary fibre intakes.

Says Healey, “It shows that aspects such as baseline gut microbiota composition, but also habitual diets, may be having a profound influence on responsiveness of the gut bacteria and host health as well.” She feels with more research along these lines, dietitians could more confidently personalize their dietary advice.

“At the moment, dietitians are [personalizing] the dietary advice they provide patients [based on] a person’s food preference or some biochemical markers like blood glucose… However, I believe in the future, incorporating… gut microbiota and habitual diet data, may lead to better personalized diets that are tailored to a specific individual.”


Healey G, Murphy R, Brough L, Butts CA, Coad J. Interindividual variability in gut microbiota and host response to dietary interventions. Nutr Rev. 2017; 75(12):1059-80. doi: 10.1093/nutrit/nux062.

Healey G, Murphy R, Butts C, Brough L, Whelan K, Coad J. Habitual dietary fibre intake influences gut microbiota response to an inulin-type fructan prebiotic: a randomised, double-blind, placebo-controlled, cross-over, human intervention study. British Journal of Nutrition. 2018; 119(2):176-189. doi: 10.1017/S0007114517003440