Although deficiencies in polyphenol intake do not result in specific deficiency diseases, adequate intake of polyphenols could confer health benefits, especially with regard to chronic diseases. Tea, cocoa, fruits, and berries, as well as vegetables, are rich in polyphenols. Flavan-3-ols from cocoa have been found to be associated with a reduced risk of stroke, myocardial infarction, and diabetes, as well as improvements in lipids, endothelial-dependent blood flow and blood pressure, insulin resistance, and systemic inflammation. The flavonoid quercetin and the stilbene resveratrol have also been associated with cardiometabolic health. Although polyphenols have been associated with improved cerebral blood flow, evidence of an impact on cognition is more limited. The ability of dietary polyphenols to produce clinical effects may be due, at least in part, to a bi-directional relationship with the gut microbiota. Polyphenols can impact the composition of the gut microbiota (which are independently associated with health benefits), and gut bacteria metabolize polyphenols into bioactive compounds that produce clinical benefits. Another critical interaction is that of polyphenols with other phytochemicals, which could be relevant to interpreting the health parameter effects of polyphenols assayed as purified extracts, whole foods, or whole food extracts.

/pdf/the-effects-of-polyphenols-and-other-bioactives-on-human-28t0879ogm.pdf

The effects of polyphenols and other bioactives on human health

Flavonoids are plant‐derived dietary components with a substantial impact on human health. Research has expanded massively since it began in the 1930s, and the complex pathways involved in bioavailability of flavonoids in the human body are now well understood. In recent years, it has been appreciated that the gut microbiome plays a major role in flavonoid action, but much progress still needs to be made in this area. Since the first publications on the health effects of flavonoids, their action is understood to protect against various stresses, but the mechanism of action has evolved from the now debunked simple direct antioxidant hypothesis into an understanding of the complex effects on molecular targets and enzymes in specific cell types. This review traces the development of the field over the past 8 decades, and indicates the current state of the art, and how it was reached. Future recommendations based on this historical analysis are (a) to focus on key areas of flavonoid action, (b) to perform human intervention studies focusing on bioavailability and protective effects, and (c) to carry out cellular in vitro experiments using appropriate cells together with the chemical form of the flavonoid found at the site of action; this could be the native form of compounds found in the food for studies on digestion and the intestine, the conjugated metabolites found in the blood after absorption in the small intestine for studies on cells, or the chemical forms found in the blood and tissues after catabolism by the gut microbiota.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12351

The Bioavailability, Transport, and Bioactivity of Dietary Flavonoids: A Review from a Historical Perspective.

Current evidence on the effect of dietary polyphenols intake on chronic diseases

Role of microbiota-derived short-chain fatty acids in nervous system disorders

Plant-based diets are associated with reduced risk of lifestyle-induced chronic diseases. The thousands of phytochemicals they contain are implicated in cellular-based mechanisms to promote antioxidant defense and reduce inflammation. While recommendations encourage the intake of fruits and vegetables, most people fall short of their target daily intake. Despite the need to increase plant-food consumption, there have been some concerns raised about whether they are beneficial because of the various ‘anti-nutrient’ compounds they contain. Some of these anti-nutrients that have been called into question included lectins, oxalates, goitrogens, phytoestrogens, phytates, and tannins. As a result, there may be select individuals with specific health conditions who elect to decrease their plant food intake despite potential benefits. The purpose of this narrative review is to examine the science of these ‘anti-nutrients’ and weigh the evidence of whether these compounds pose an actual health threat.

https://www.mdpi.com/2072-6643/12/10/2929/pdf

Is There Such a Thing as "Anti-Nutrients"? A Narrative Review of Perceived Problematic Plant Compounds.

BACKGROUND: Recent clinical studies have indicated the beneficial impact of dietary flavonoid intake on human cognitive performance. Although the mechanisms that mediate such improvements are currently unclear, animal and human trial data suggest that changes in neurotrophin expression, and related signalling apparatus, may be involved.

OBJECTIVE: To investigate the link between changes in serum brain-derived neurotrophic factor (BDNF) and changes in human cognitive performance following flavonoid intake.

METHODS: The relationship between serum levels of BDNF and age, gender, BMI, waist circumference, blood pressure and cognition at baseline, and following flavonoid intake, was investigated in two distinct randomised, controlled clinical trials. Trial 1 was conducted in men and women (aged 26–70 y; consuming an average of 3 portions of fruit and vegetables per day) and delivered high-flavonoid (>15 mg/100 g) or low-flavonoid (<5 mg/100 g) fruit and vegetables and increased intake by 2 portions every 6 weeks. The control arm was habitual diet over the same time frame. Trial 2 was conducted in an older males and female cohort (aged 62–75 y) intervening with a high-flavanol cocoa drink (494 mg total flavanols) and a low-flavanol cocoa drink (23 mg total flavanols) for 12 weeks.

RESULTS: Serum BDNF levels increased linearly to the age of 65, after which BDNF levels were found to decrease markedly. All other physiological and anthropometric measurements proved to not be significantly associated with serum BDNF levels (p > 0.05), although higher levels in males compared to females almost achieved significance (p = 0.056). At baseline, higher serum BDNF levels were associated with significantly better global cognition scores, relative to individuals with lower serum levels. In addition, following intervention for 18 weeks, high-flavonoid, but not low-flavonoid, fruit and vegetable intake induced significant improvements in cognitive performance and increases in serum BDNF levels (p = <0.001). Flavanol intervention for 12 weeks also resulted in significant increases in serum BDNF (p = <0.001), and such increases were correlated with improvements in global cognitive performance.

CONCLUSION: Increases in global cognition induced by high flavonoid fruit and vegetables, and cocoa flavanols were paralleled by concurrent changes in serum BDNF levels, suggesting a role for BDNF in flavonoid-induced cognitive improvements. Furthermore, we provide further data suggesting that serum BDNF levels may represent a biomarker of cognitive function.

High-flavonoid intake induces cognitive improvements linked to changes in serum brain-derived neurotrophic factor: Two randomised, controlled trials.

Dietary interventions may have the potential to ameliorate cognitive changes, e.g. those preceding a diagnosis of Alzheimer’s Disease (AD). Cognitive changes are part of normal healthy ageing, but in AD the rate of change is more rapid than that considered to be in the normal range. The initial amnesic stage of AD is often followed by impairments in attention; indeed, these attentional difficulties may appear earlier than suggested by current research. Animal research has shown significant improvements in spatial working memory after 8 weeks of supplementation with a flavonoid-rich blueberry (Vaccinium spp.) diet. The present study followed on from an acute intervention trial carried out with young adults (18–30 years). A key finding from this first investigation into the effects of flavonoid-rich blueberries on cognitive function was an improvement in attention in the absence of reaction-time changes. Using a randomised double-blind placebo-controlled cross-over design an acute intervention trial was carried out with older adults (Selected from Ageing Panel – healthy adults; 60–78 years; MMSE score > / = 24) using a single acute supplementation of blueberry (200 g blueberries in 150 ml milk) or a placebo control. The effects on mood, memory, executive function and motor skills were measured before the drink and 1 h and 5 h following consumption, and were assessed as previously described. There was a trend for improvement in sustained attention 5 h after the blueberry drink compared with a decline in attention 5 h following the placebo (see Figure). The difference in the mean number of correctly-detected targets on the ‘go–nogo’ task (a measure of the executive function of attention) compared between the blueberry drink and the placebo, 5 h after the drink, was marginally significant (P = 0.08; n 16). Motor performance improved over time (P = 0.003), irrespective of the type of drink, but no significant improvements in performance were found on measures of spatial and working memory (P>0.05).

The impact of plant-derived flavonoids on mood, memory and motorskills in healthy older UK adults

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High-flavonoid intake induces cognitive improvements linked to changes in serum brain-derived neurotrophic factor: Two randomised, controlled trials.

The impact of plant-derived flavonoids on mood, memory and motorskills in healthy older UK adults