Health benefits of fruits and vegetables discovered ‘locked’ to plant cell walls

Forgotten phenolics for intestinal wellbeing

Scientists have been trying to solve the mystery of why most fruit extracts don’t show the same health benefits compared to eating the entire fruit.  The same phenomenon occurs with vegetables.  It is very difficult to capture the full benefit of the original food. Dr. Kelly Ross at Agriculture and Agri-Food Canada (AAFC) in Summerland believes that the plant cell walls may be hiding the missing ingredients.

We have all heard about vitamins, minerals and dietary fibre that we get when we bite into that apple or carrot, but the goodness doesn’t stop there.  Much of what we love about fruits and vegetables, such as their colour and taste, is influenced by a group of compounds known as phenolics.  These compounds are found in the plant cells and have been shown to provide antioxidant, anti-inflammatory and anti-carcinogenic benefits.  Past research has found that when we eat foods high in phenolic compounds we can protect ourselves from certain degenerative diseases, such as cardiovascular diseases, diabetes, cancer and arthritis. 

More recent research has discovered that phenolics attached to plant cell walls, once dismissed as indigestible, are actually released and absorbed further along in our gastrointestinal (GI) tract, after they leave our stomach, and provide potent health benefits to our intestines.  

Why does this matter?

This line of research will likely lead to the production of more powerful extracts with increased health benefits for dietary supplements or enhanced nutrition of processed foods.

Traditional laboratory methods used to determine phenolics content in food leave compounds that are bound to the plant cell walls behind, which Dr. Ross tells us is not what happens during human digestion. In fact, in laboratory tests sometimes more phenolics are left attached to cell walls than get extracted and measured.  Dr. Ross has authored a review demonstrating growing evidence of the importance of these forgotten phenolics.  She hopes her review will stimulate research using different methods of extraction to improve our understanding of these compounds on human health, and improve our ability to accurately assess the benefit of specific fruits and vegetables.

“This line of research will likely lead to the production of more powerful extracts with increased health benefits for dietary supplements or enhanced nutrition of processed foods” advises Dr. Ross.  Understanding how phenolics linked to plant cell walls behave in our digestive system may reveal new ingredients important for human health.

What happens during digestion?

Plant cell walls contain the dietary fibre that health experts so often recommend for improved digestion and intestinal regulation.  These same molecules bind to a variety of phenolics while fruits and vegetables are growing, ‘locking’ the phenolic benefits to the cell wall. 

This bonding creates larger molecules, which move through the digestive tract once the fruit or vegetable is eaten.  The fibre we have been told to consume ‘escorts’ these beneficial phenolics through our GI tract to their final destination. 

Simulated digestion shows that eventually many of these phenolics detach from the plant cell wall, becoming available for absorption by our small or large intestines.  Some phenolics make it all the way to the colon where they are digested by bacteria, or microflora, that help us break down food. The advantages associated with phenolics - reduced inflammation and protection against oxidative damage and cancer – are thus delivered to the cells of our intestines and our colon. 

How can we unlock this potential?

Phenolics linked to plant cell walls should be considered when assessing the health benefits of specific fruits and vegetables.  Knowing more about these compounds and how they improve our health will allow us to create more accurate food composition databases and better tailor fruit and vegetable extracts to achieve health benefits. 

“There are phenolics in fruits and vegetables that have health benefits that have not been measured or considered.” Dr. Ross explains. “Greater understanding of which fruits and vegetables have high levels of these compounds will give us the power to better support our intestinal health – unlocking the potential to enhance our overall wellbeing.” 

Where can we learn more?

Ross, K.A. (2014). Concepts important in understanding the health benefits of phenolics in fruits and vegetables: extractable and non-extractable phenolics and the influence of cell wall polysaccharides on bioaccessibility and bioavailability. Research in Health and Nutrition, 1: 29-43.

Meet Dr. Ross:

By: Naomi DeLury

Photo of Naomi DeLury, MSc Naomi writes about research conducted at the Summerland Research and Development Center, AAFC

Photo of Kelly Ross, PhD Dr. Kelly Ross, AAFC Scientist, hopes studies of phenolics attached to plant cell walls will lead to improvements in human health