Professor Marjukka Kolehmainen, Institute of Public Health and Clinical Nutrition
What is the essence of an apple from the viewpoint of a professor focusing on food and health?
“That is an interesting question because the viewpoints offered by nutrition are also broad, ranging from societal-level perspectives to the tiniest elements of human physiology. When thinking about nutrition, the first thing that comes to mind is the nutrient content of apples and its effects on humans. Apples belong to a food group that contains vegetables, fruit and berries, the daily intake of which should be at least 500 grams per day, according to the latest Finnish nutrition recommendations. We Finns could eat more foods from this category, as findings from the FINDIET study show that very few Finns meet this guideline.”
Why are apples an important source of human nutrition – and an interesting topic of research?
“Apples are nutrient-dense food, i.e., they contain very little energy and plenty of different nutrients and vitamins. They are also a good and tasty source of fibre, when eaten as part of diet. Compared to most berries, however, apples contain considerably less fibre and vitamin C. In addition to the ‘traditional’ nutrients, apples also contain bioactive compounds, the health effects of which are of great interest to researchers. Apples are especially rich in flavanols and flavonols, both of which are polyphenols. Some of these compounds may be absorbed from the small intestine and they make use of the transport mechanisms of glucose, thus possibly also contributing to post-prandial glucose metabolism.
Often, bioactive compounds are transported in the dietary fibre fraction of fruit – apples in our case – and they are attached to the apple fibre, i.e., the plant cell structure. Fibre is not absorbed from the small intestine but carried further to the large intestine where it is subjected to fermentation by microbes. Gut microbes use undigested components of food, that is, mainly fibre and compounds attached to fibre, in their own metabolism. Nowadays, gut microbiome-mediated health effects of food are a topic of huge research interest in nutrition.
Over the past few decades, we’ve come to understand the significance of the gut microbiome in mediating health effects, and it seems that these effects keep on extending to broader health effects and disease prevention. We’ve known for quite some time that vegetables, fruit and berries, thanks to being nutrient-dense and fibre-rich, are associated with a lower risk of cardiovascular disease, type 2 diabetes and some types of cancer, for example. Nowadays, we also know that some of this effect is mediated via gut microbial function both through effects on the microbial composition and through microbial metabolites. The fermentation of fibre in the gut produces short-chained fatty acids that can, for example, enhance glucose and lipid metabolism in people who have problems in them. Microbial quality and metabolites continue to affect the well-being of the gut wall, which is also of great importance in maintaining balanced metabolism and preventing problems in it.”
How is the University of Eastern Finland’s nutrition research related to berries and fruit?
“The University of Eastern Finland has a long history of research into the health effects of berries. In particular, this line of research deals with the positive effect of berries on post-prandial glucose metabolism, and with the effect of longer-term consumption of berries on low-grade inflammation. We have also studied, for example, how side streams of juice production, which are particularly rich in bioactive compounds, affect the composition and function of the gut microbiome. However, nutrition is not just about studying food, food components or physiological effects of nutrients. As I mentioned, we Finns could eat much more vegetables, fruit and berries, and only a small proportion of us eat the recommended amount. These perspectives are also important in research addressing eating behaviours: how could we nudge people towards eating more vegetables, fruit and berries as part of their diet, and how could we make it easier for people to choose these foods in the grocery store or at lunch, for example.”