Two apples a day keeps the doctor away: Regular consumption reduces cholesterol while increasing gut-boosting bile acids
17 Dec 2019 --- The daily consumption of two apples can lower serum cholesterol, which is often associated with heart disease, according to a group of international researchers. Their study revealed that increased apple intake changes bile acids, signaling molecules that help the gut microbiota communicate within the human body. This research shows how important eating raw, unprocessed plant foods is for maintaining heart and gut health and the researchers call upon industry to develop minimally processed apple products to maintain the healthy potential of fruit.
“The improvement in cholesterol levels was not surprising. What was surprising was our ability to link this change in cholesterol levels to changes in gut microbiota-produced bile acids,” Dr. Kieran Tuohy, one of the study’s researchers at the Department of Food Quality and Nutrition, Research and Innovation Centre, Fondazione Edmund Mach, Italy, tells NutritionInsight.
The research team chose the Renetta Canada apple, a cultivar known to be particularly rich in fiber and polyphenols. Both are beneficial compounds, which can influence the gut microbiota and may also work in synergy to improve human health. For eight weeks each, 23 female and 17 male study participants with high starting levels of cholesterol consumed two apples per day, which resulted in decreased total serum cholesterol and low-density lipoproteins (LDL) cholesterol. However, the apple consumption had no effect on blood pressure or other cardiovascular disease markers.
“We saw a significant reduction in cholesterol and other markers of heart disease, but also discovered that this improvement in vascular health could be explained by changes in certain bile acids produced by the gut microbiota. This is an important insight into how diet and certain foods – apples in this case – interact with the gut microbiome to help keep us healthy,” Dr. Tuohy explains.
The researchers advise eating apples that grow in cool climates and pristine mountain areas.The healthy choice
The study’s control group consumed a sugar- and energy-matched apple control beverage in parallel to the apple eating group. The research team found that apples in their fruit form were able to reduce cholesterol more than in their juice form.
Dr. Fulvio Mattivi, Dr. Tuohy's colleage and another of the study's researchers, tells NutritionInsight that juice production tends to remove most fiber and polyphenols from the apples themselves. Moreover, they preserve or increase undesired ones, such as fruit sugars. “Juices should not be regarded as a substitute for the fresh fruit. Their consumption should not be encouraged,” they warn.
Dr. Mattivi also advocates for purchasing fruits based on their nutritional value, not their physical appearance. “Nowadays, consumers purchase fruit based on what they look like. But beauty does not always equate to good nutrition. Consumers should look for apples from varieties that are rich in fiber and polyphenols, giving preference to those apples growing in a cool climate and pristine mountain areas. The Renetta apple, used in our study, is not the only example, but is certainly a good one.”
Follow-up research
The research team has not yet concluded its project and has a series of follow-up papers in preparations, further researching the mechanism of action of the apples and their bioactive components, Dr. Mattivi says. One of their main goals is to formulate hypotheses about which among the apple compounds account for the observed effects in order to reach a mechanistic understanding of the process.
“This knowledge can be then exploited in the breeding for nutritionally improved apple cultivars, and in the formulation of improved processed food and providing scientific support for existing healthy eating guidelines,” he concludes.
By Anni Schleicher
