In our gut lives a complex and rich population of bacteria. Known as the gut microbiome, this microscopic community helps us digest food, produces certain vitamins and neurotransmitters and helps our immune system.

Research shows that the composition and function of the gut microbiome is affected by what we eat, and that this in turn may have an impact on health. In simple terms, eating a high-fibre diet rich in fresh fruit and vegetables tends to increase the variety of microbes in the gut microbiome, especially beneficial ones, leading to a lower risk of metabolic diseases such as type 2 diabetes.

On the other hand, a less balanced diet that is high in sugar and fat leads to a gut microbiome that has not only less diversity, but also a greater capacity to extract energy from food, which then gets stored as fat and leads to a higher risk of metabolic diseases.

However, in reality the relationship between the gut microbiome and diet is more complex than this, and more research is required. Now, a study led by Professor Bernhard Breier from Massey University and funded by the Health Research Council is investigating the relationship between taste, diet, eating behaviour, sleep, physical activity, the gut microbiome and health outcomes.

The role of diversity

Specifically, the research aims to test whether people with a reduced gut-microbiome diversity are more at risk of metabolic diseases such as type 2 diabetes and, on the other hand, whether increased gut-microbiome complexity is protective against those diseases.

Professor Breier is Chair in Human Nutrition at the Institute of Food, Nutrition and Human Health at Massey. His research brings together nutrition, metabolism and endocrinology, combining basic and applied nutrition and engagement with industry. His research themes include appetite regulation and metabolic flexibility, exercise and its metabolic consequences, public health nutrition and nutrition for health in ageing.

His work has been recognised with the Hamilton Prize of the Royal Society of New Zealand, an Alexander von Humboldt Fellowship, and a Principal Research Fellowship from the Health Research Council of New Zealand.

Professor Breier and his team will conduct a study of 136 women of Pacific descent and 136 Pākehā women; half the participants in each ethnic group are ranked normal on the BMI scale and the other half are ranked obese. This will be the first study to characterise the gut microbiome in two populations with markedly different metabolic-disease risk (Pacific and Pākehā women) and different body-fat profiles.

“We will test whether taste perception, diet, sleep and physical activity are key pathways that modify the gut microbiome,” Professor Breier says. “Our strength is that we can do a very detailed dietary assessment. We have a huge toolbox to allow us to very accurately assess what people eat.

“In essence, we want to test whether taste perception, dietary intake, eating behaviour, sleep and physical activity influence and modify the gut microbiome and how it impacts health, such as metabolic diseases like type 2 diabetes. Our hypothesis is that when the diet is varied, there is diversity in the gut microbiome, and that is protective against metabolic disease. But when the diet is highly processed, energy dense and nutrient poor, then that leads to a gut microbiome that is not very diverse, and this is not protective, which leads to disease. So we are looking at the interaction between diet, the gut microbiome and health outcomes.”