By E. Kirsten Peters, College of Agricultural, Human & Natural Resource Sciences
Some of the components of apples survive their trip through the upper part of the human digestive tract. Non-digestible compounds, including fiber and substances called polyphenols, stand up to chewing and the effects of enzymes in spit. They even remain intact after a bath in stomach acid.
These compounds move all the way to the colon, where they undergo a transformation that can be quite beneficial to you.
The non-digestible compounds are fermented in the colon. That’s right, you could say you have a little brewery at work in your body. The fermentation allows for the growth of certain bacteria in the gut.
Which bacteria flourish in your colon really matters. Studies have shown that obese mice have different bacterial families and diversity of bacteria in their gut than do lean mice.
Granny Smith and healthy bacteria
Researchers at Washington State University have concluded that apples – especially Granny Smith apples – may lead to healthy bacteria in the colon and this, in turn, may help prevent a variety of medical disorders.
“Apples are a good source of non-digestible compounds,” Professor Giuliana Noratto told me. “We have now studied the differences in apple varieties to look for the most useful types.”
Results of the study were recently published in the journal Food Chemistry by Noratto and co-researchers Luis Condezo-Hoyos and Indira P. Mohanty.
The research indicates that Granny Smiths contain more non-digestible compounds than many other apples including Braeburn, Fuji, Gala, Golden Delicious, McIntosh and Red Delicious.
Animal trials under way
As a first step toward understanding the gut processes better, Noratto’s team simulated colon fermentation in test tubes. Fecal bacteria were cultured in apple compounds that survived gastrointestinal enzyme digestion.
“The non-digestible substances in the Granny Smith apples actually changed the proportion of fecal bacteria from obese mice to be similar to what you find with lean mice,” Noratto said.
Now she is feeding Granny Smiths directly to rats. This takes the ideas suggested by the test tube experiments and tries them out in the real-world condition of flesh-and-blood guts. Noratto expects results from the animal trials sometime in the New Year.
Gut bacteria and obesity
One thing about the rats interested me as an aside. The obese and lean rats are fed the same number of calories each day. But a high fat diet produces overweight rats, while a lower fat diet leads to lean rats. I’ll try to remember that the next time a bowl of ice cream is calling to me.
Down the road, Noratto’s work with apples could be important in the battle of the bulge that so many of us face. Beyond that, it could be useful in combatting diabetes.
From her perspective, obese people have an unfortunate community of bacteria in their gut. The bad bacteria make for byproducts that can lead to inflammation and influence metabolic disorders associated with being overweight.
It would be interesting if modern science can show that “an apple a day” really is a helpful addition to the human diet. Stay tuned!
Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.