Keto-Friendly Brain Boosting Nutrients: Polyphenols

Vegetables - Polyphenols

Next up in our series on Keto-friendly brain boosting nutrients is…Polyphenols!

Polyphenols are naturally occurring compounds found in many plants. These compounds are vital to our body’s defense responses, such as anti-aging, anti-inflammatory, and antioxidant actions. The brain is particularly susceptible to oxidative damage because it utilizes a large amount of oxygen for energy and has relatively low antioxidant defense enzymes, especially during aging.

Foods high in polyphenols can help protect both the brain and body against oxidative stress, which is an imbalance between free radicals and antioxidants in your body. This process is believed to be pivotal to the development of age-related diseases. Over 8000 polyphenol-derived compounds of plant origin have been identified, many of which are widely studied and recognized for their brain-protective properties1.


This subgroup of polyphenols possesses a powerful antioxidant activity and comprises the most common group of polyphenols. Flavonoids are found in a wide variety of fruits and vegetables and have been identified as a group of promising compounds capable of influencing different aspects of brain and cognitive health. They boost mood and brain function by increasing cerebral blood flow, potentially helping to reduce the risk of stroke2.

Major classes of natural flavonoids and some of their ‘keto-friendly’ dietary sources: 3

  1. Flavonols (i.e. kaempferol, quercetin, rutin, fisetin): onions, kale, chives, tomatoes, tea, olive oil, olives, broccoli, wine, cocoa
  2. Flavones (i.e. apigenin, luteolin): parsley, celery, thyme
  3. Isoflavones (i.e. daidzein, genistein): soy and soy products
  4. Flavanones (i.e. hesperetin, naringerin, naringin): citrus fruit (lemons, limes), tomatoes, and aromatic plants such as mint, ginger, oregano, and licorice
  5. Flavanols (i.e. catechin, epicatechin, epigallocatechin, epigallocatechin-3-gallate, or EGCG): cocoa, olive oil, olives, green tea, red wine
  6. Anthocyanins (i.e. cyanidin, delphinidin, pelargonidin, peonidin): red cabbage, eggplant, red onions, radishes, red wine, berries

1. Flavonols

Flavonols, such as quercitin and rutin, have been associated with a variety of beneficial effects including:

  • Increased activity of an important antioxidant enzyme found in red blood cells
  • Decreased DNA damage to white blood cells
  • A decrease in markers of oxidative damage
  • An increase in the ability to scavenge free radicals in the plasma.

2. Flavones

Flavones are non-essential nutrients that provide additive nutritional value to our diet. Flavones have received increasing attention due to their anti-inflammatory, anti-microbial and anti-cancer activities. However, the mechanisms responsible for these activities are just starting to be understood.

3. Isoflavones

Isoflavones have potential health benefits that may include protection against age-related diseases including cardiovascular disease, osteoporosis, hormone-dependent cancer, and loss of cognitive function. Data supports the potential cognitive effects of soy isoflavones in older adults, as observed in a study of subjects on a soy isoflavone supplement who performed better on several cognitive tests 4 5. There is also accumulating evidence that supports the protective effect of genistein, the primary plant estrogen in soy, on nerve cells against oxidative damage6.

4. Flavanones

Flavanones, such as hesperetin and naringenin, have been shown to cross the blood-brain barrier in live research models. Naringin has also been reported to exhibit several protective effects including antioxidant activities. These compounds appear to have direct protective and regulatory actions on the brain’s nerve cells.

5. Flavanols

Flavanols, which include catechin, have been found to increase the levels of the natural antioxidant enzymes in the cells. The daily consumption of a flavanol-rich cocoa beverage has been shown to positively affect cognitive health, leading to improvements in mental performance both in older adults with early memory decline and in those with intact cognitive function7. This appears to be related to cocoa’s ability to increase cerebral blood flow following consumption, accounting for a sharp improvement in mental function8. These findings seem to support epidemiological evidence indicating that regular cocoa flavanol intake possesses the potential to boost cognitive function, particularly in older populations 9 10.

The flavanol EGCG is the principal bioactive component found in green tea that has been utilized in China as medicine for at least 4000 years11. It is most renowned for both its high antioxidant activity and its anti-inflammatory properties, providing EGCG with potentially brain-protective properties. As with cocoa flavanols, several studies have discovered beneficial effects from the consumption of tea and green tea on neurological impairment, highlighting their potential in both the prevention and treatment of degenerative brain diseases12 13.

6. Anthocyanins

Over the last decade, a vast and growing body of research has been focusing on the potential of dietary polyphenols for aiding preservation of cognitive function during aging while reducing risk for degenerative disorders of the nervous system, such as Parkinson’s Disease14This research supports the findings that anthocyanins in berries and citrus may be a valuable asset in preventing against aging by reducing or delaying the development of age-related neurodegenerative diseases15. Their consumption throughout life may actually have the potential to limit or even reverse age-related deteriorations in memory and mental performance. This mechanism is thought to be associated with the ability of anthocyanins and other flavonoids to inhibit nerve inflammation and improve blood flow to the brain. It also appears that some dietary anthocyanins can cross the blood-brain barrier, allowing the compounds to have a direct beneficial effect16.

Non-flavonoid polyphenols

Non-flavonoid polyphenols include curcumin from turmeric, resveratrol from red wine and nuts, and coumarin from licorice, strawberries, and cinnamon. All of these compounds are antioxidants. Curcumin may help prevent the accumulation of plaque formations linked with Alzheimer’s disease. Studies have also shown the ability of curcumin to protect against cognitive decline, lessen impairment in traumatic brain injury, and even stimulate new brain cell production17Evidence also shows that curcumin can alleviate symptoms of depression by enhancing nerve cell formation in the hippocampus and frontal cortex of the brain18. Resveratrol is the main non-flavonoid polyphenol found in grapes and red wine and has been shown to help protect the memory center of the brain from both oxygen and glucose deprivation19.

Phenolic acids

Phenolic acids include ellagic acid in walnuts, tannic acid in tea and berries, cinnamic acid in cinnamon, gallic acid in tea, soy, and strawberries, hydroxycinnamic acid in tea, cocoa, and wine, chlorogenic acid in coffee beans, eggplant, and tomatoes, as well as caffeic acid, found in coffee and blueberries. Hydroxycinnamic acids are the most widely distributed phenolic acids in plants and present a wide range of potential therapeutic effects useful in the treatments of several diseases including cancer, diabetes, and cardiovascular diseases. These compounds have also been shown to protect against nerve cell damage, and exhibit both antimicrobial and anti-inflammatory activities20. It is through one or more of these mechanisms that phenolic acids have the potential to help prevent neurodegenerative disorders, such Parkinson’s disease21.

Next up on our list of brain-boosting nutrients: Caffeine, Choline & Dietary Nitrates!


  1. Dietary Polyphenols as Modulators of Brain Functions: Biological Actions and Molecular Mechanisms Underpinning Their Beneficial Effects: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3372091/
  2. Flavonoids and brain health: multiple effects underpinned by common mechanisms: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2775888/
  3. Flavones: From Biosynthesis to Health Benefits: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4931407/
  4. Polyphenols and brain health: https://www.ocl-journal.org/articles/ocl/full_html/2017/02/ocl170010/ocl170010.html
  5. Cognitive effects of soy isoflavones in patients with Alzheimer’s disease: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4657545/
  6. A preliminary study of the safety, feasibility and cognitive efficacy of soy isoflavone supplements in older men and women: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2720778/
  7. Protective Mechanisms of Flavonoids in Parkinson’s Disease:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4630416/
  8. Enhancing Human Cognition with Cocoa Flavonoids: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5432604/
  9. Intake of flavonoid-rich wine, tea, and chocolate by elderly men and women is associated with better cognitive test performance: https://www.ncbi.nlm.nih.gov/pubmed/19056649?dopt=Abstract
  10. The neuroprotective effects of cocoa flavanol and its influence on cognitive performance: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3575938
  11. Natural mood foods: The actions of polyphenols against psychiatric and cognitive disorders: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3355196/
  12. Potential neuroprotective properties of epigallocatechin-3-gallate (EGCG): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4897892/
  13. Beneficial Effects of Green Tea Catechins on Neurodegenerative Diseases: www.mdpi.com/1420-3049/23/6/1297/pdf
  14. Protective Mechanisms of Flavonoids in Parkinson’s Disease:  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4630416/
  15. Neuroprotective effects of berry fruits on neurodegenerative diseases: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4192974/
  16. The neuroprotective potential of flavonoids: a multiplicity of effects: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2593006/
  17. Curcumin Stimulates Proliferation of Embryonic Neural Progenitor Cells and Neurogenesis in the Adult Hippocampus: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2386914/
  18. Botanical phenolics and brain health: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2682367/
  19. Polyphenolic Antioxidants and Neuronal Regeneration: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4892323/
  20. Hydroxycinnamic acids as natural antioxidants: https://www.soc.chim.it/sites/default/files/chimind/pdf/2001_7_201_ca.pdf
  21. Polyphenols and Neurodegenerative Diseases: https://pdfs.semanticscholar.org/dbc4/3743f1d111036423d8db3d59a6f8f005c4ac.pdf
Mary Paley

Fearless Dietitian; 30+ years as a professional dietitian; Master’s Degree in Nutrition and Dietetics at the MGH Institute of Health Professions; Lead research dietitian for several major pharmaceutical companies; Currently focused on health and wellness and the benefits of ketogenic diets for both obesity and diabetes management. MS, RDN, CDE, LD/N

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