Does an apple a day really keep the doctor away? A nutritionist explains the science behind ‘functional’ foods

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(THE CONVERSATION) We’ve all heard that an apple a day keeps the doctor away, but how true is that?

Apples are not high in vitamin A, nor are they beneficial for vision like carrots. They are not a great source of vitamin C and therefore don’t fight off colds as oranges do.

However, apples contain various bioactive substances – natural chemicals that occur in small amounts in foods and that have biological effects in the body. These chemicals are not classified as nutrients like vitamins. Because apples contain many health-promoting bioactive substances, the fruit is considered a “functional” food.

For years, I have taught university classes on nutrients such as vitamins, minerals, carbs, proteins and fats. But recently I developed a course specifically on functional foods. The class explores the various bioactive substances in food and how some may even function like a medicine.

Functional foods are not the same as superfoods. “Superfood” is a buzzword marketers use to promote foods like kale, spinach and blueberries. Labeling them as “super” appeals to the public and increases sales. But superfood is generally meant to imply a food that has superior nutritional value and that is high in nutrients that are beneficial for health. For example, salmon and tuna are considered superfoods because the omega-3 fats they contain have been linked to heart health.

Superfood advertisements claim that eating the food will improve some aspect of health. The problem is that most of those claims are not based on scientific research, like the criteria for functional foods are.

In addition to the nutrients that our bodies need for growth and development, functional foods contain a variety of bioactive substances, each with a unique function in the body. The bioactive substances can be found naturally in foods or added during processing.

The list of bioactive components in foods grows daily as research expands. Though the components themselves are not new, the evidence-based research…