Phytonutrients, Bioavailability and Health

In my last blog, I discussed the role of phytonutrients in the promotion of health and the prevention of metabolic disorders and disease. Many studies have revealed that a higher intake of plant products which are rich sources of carotenoids, phytosterols, polyphenols, indoles, organosulphur compounds, glucosinolates, and saponins positively contributes to lowering the risk of chronic diseases. Accordingly, The World Health Organisation (WHO) recommends increasing the intake of varied plant-source food materials to derive maximum benefit from these plant metabolites.

In general, the bioavailability of phytonutrients that are present in a complex food matrix is reasonably low and suggestions have been made to increase the bioavailability of these nutrients by modifying the chemical structure using food processing techniques, understanding the competition and inhibition of intestinal cell transporters, encapsulation of bioactive molecules, designing synergies between the molecules, nanoencapsulation, and food pairings to enhance absorption.

An understanding of food pairing for the effective absorption of bioactive molecules is a very useful technique, however, our knowledge in this area is rather limited. Some of the known food pairings to promote absorption include:

·         Enhanced absorption of non-heme iron from plant sources such as spinach, legumes, and grains, in the presence of foods rich in ascorbic acid (Vitamin C).

·         Enhanced absorption of fat-soluble vitamins such as vitamins A, D, E, and K in the presence of dietary.

·         Enhanced absorption of Calcium in the presence of Vitamin D.

·         Enhanced absorption of curcumin from turmeric in the presence of black pepper or dietary fats.

·         Enhanced absorption of lycopene from tomatoes when ingested with dietary fats.

·         Enhanced absorption of quercetin from apples when ingested along with dark chocolate.

·         Enhanced absorption of phenolic compounds from cumin and coriander if taken together.

·         Enhanced absorption of resveratrol from red wine if taken along with almonds, a rich source of vitamin E.

In addition, we should also take notice of certain nutrients that affect the absorption of bioactive materials, e.g.,

·         A diet deficient in proteins inhibits absorption of vitamin A.

·         Carotene absorption is inhibited in the presence of polyunsaturated fats.

·         Phosphates and zinc supplements inhibit the absorption of iron.

·         Tea and coffee inhibit the absorption of iron.

·         Non-heme iron inhibits the absorption of magnesium and zinc.

·         Supplements of magnesium inhibit the uptake of zinc.

·         Calcium interferes with the absorption of zinc.

Further bioavailability is also affected in the presence of some drugs such as:

·         Corticosteroids inhibit the absorption of calcium and vitamin D.

·         Oral contraceptive pills decrease the levels of vitamins C, Vitamin B12, and B9 (folic acid).

·         Antibiotics inhibit the absorption of iron, calcium, zinc, and magnesium.

·         Salicylates reduce the absorption of vitamin C and amino acid tryptophan.

·         Antacids inhibit the absorption of vitamin A, B1 (thiamine) and iron.

·         Alcohol inhibits the absorption of fats, and fat-soluble vitamins A, D, E, and K.

Further gut microbiota in the colon is associated with the metabolism of unabsorbed phytonutrients to produce small molecules that are absorbed hence increasing the bioavailability of phytonutrients. They also modulate the composition of the gut microbiota to render improved health benefits. I will discuss the role of gut microbiota on health in a separate blog.

Scientific studies therefore recommend ingesting reasonable quantities of fresh and seasonal plant-based foods daily as the bioactive components have been shown to exhibit antioxidant, anticarcinogenic, anti-inflammatory, and antimicrobial properties.

For more details refer to chapters 5 and 6 in my book Science of Food Nutrition and Health.

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