Stilbenes (Resveratrol) in Plant Foods

Stilbenes are a class of polyphenols synthesised by plants in response to stress, particularly fungal attack. Resveratrol is the most studied stilbene, found primarily in red grapes (~12 mg/100g), blueberries (~32 mg/100g), red wine, peanuts (~14 mg/100g), and various berries. Stilbenes are concentrated in the skins of grapes and berries, so whole fruits provide more than juiced versions. Other plant sources include mulberries, pistachios, and cranberries. Stilbenes act as phytoalexins — plant defence compounds with potential antioxidant and anti-inflammatory benefits in human physiology.

Resveratrol is a stilbene — a type of polyphenol — synthesised by plants as a protective compound against pathogenic fungi and UV radiation. It is most abundant in the skins of grapes (especially red and purple varieties) and berries. Resveratrol production increases when plants experience stress, making it an example of a phytoalexin. In human diets, resveratrol has been studied for its potential to activate cellular stress-response pathways (SIRT1), support mitochondrial function, and provide antioxidant and anti-inflammatory benefits. However, bioavailability from whole foods is limited, and effects depend on overall dietary pattern and lifestyle.

Blueberries are the richest source at approximately 32 mg/100g stilbenes. Peanuts provide ~14 mg/100g, red grapes ~12 mg/100g, and mulberries ~11 mg/100g. Other significant sources include grape juice (~8 mg/100g), pistachios (~6 mg/100g), strawberries (~5 mg/100g), and cranberries (~4 mg/100g). Bilberries (~3 mg/100g) and blackberries (~2 mg/100g) also contribute. Note that resveratrol concentration is highest in grape skins; white grapes contain much less than red or purple varieties. Whole grapes and berries are superior to juices because most stilbenes reside in the skin.

Stilbenes, particularly resveratrol, have been studied for multiple potential health benefits. Resveratrol activates SIRT1 (sirtuin) enzymes, which regulate cellular stress responses, mitochondrial health, and metabolic homeostasis. It exhibits antioxidant properties by neutralising reactive oxygen species and reducing lipid peroxidation. Additionally, resveratrol has anti-inflammatory effects, modulating NF-κB signalling and reducing pro-inflammatory cytokine production. Epidemiological studies associate regular consumption of grapes and berries with reduced cardiovascular disease risk, better metabolic markers, and improved cognitive function in ageing. However, whole plant foods provide both resveratrol and complementary polyphenols, creating synergistic effects superior to isolated compounds.

Stilbenes are one of several major polyphenol classes in plant foods. Flavonoids (found in berries, tea, cocoa) are the most abundant polyphenols by weight. Phenolic acids (in whole grains, seeds, legumes) and lignans (in flaxseeds, sesame) are also prevalent. While stilbenes represent a smaller portion of total dietary polyphenols, resveratrol is uniquely well-studied due to its SIRT1-activating properties. The optimal dietary approach combines diverse polyphenol sources: berries and grapes for stilbenes, tea and cocoa for flavonoids, whole grains for phenolic acids, and seeds for lignans. This diversity ensures comprehensive phytochemical benefits through multiple mechanisms.

Stilbene stability depends on temperature, pH, and processing method. Fresh berries and whole grapes retain maximum stilbene content. Light steaming or gentle heating minimally affects stilbenes, but prolonged boiling or high-temperature cooking can reduce content by 20–40%. Freezing preserves stilbenes effectively — frozen berries maintain most of their stilbene content when thawed. Fermentation (in wine production) can increase apparent resveratrol extraction from grape skins, though overall bioavailability remains modest. Juice processing removes skin-based stilbenes, reducing content by 50–80% compared to whole fruit. Drying (raisins from grapes, dried berries) concentrates stilbenes per gram but increases serving size required for equivalent intake. For maximum stilbene preservation, consume whole fresh or frozen berries, whole grapes, or minimally processed foods.

Resveratrol bioavailability is limited by its poor intestinal absorption (less than 20% in humans). However, the colonic microbiota transforms resveratrol into bioavailable metabolites, particularly dihydroresveratrol and smaller phenolic compounds that cross the intestinal barrier more readily. Individuals with diverse gut microbiota produce more metabolites, enhancing net resveratrol bioavailability. Fermented foods (sauerkraut, tempeh, miso) and high-fibre diets increase microbial diversity and resveratrol metabolism. Dysbiosis (microbiota imbalance) reduces resveratrol conversion, limiting benefits. Additionally, polyphenols themselves act as prebiotics, feeding beneficial bacteria that then enhance absorption of subsequent polyphenols — creating a synergistic cycle. This emphasises the importance of whole plant foods (fibre + polyphenols) and diverse dietary sources for maximising stilbene bioavailability.

A 100g serving of blueberries (~1 cup) provides approximately 32 mg stilbenes. A cup of red grapes (~160g) delivers ~19 mg. A small handful of peanuts (~30g) provides ~4 mg. A typical Western diet provides 0.5–5 mg resveratrol daily, while Mediterranean diets with regular wine and grape consumption may reach 10–30 mg. However, bioavailable resveratrol reaching systemic circulation is much lower due to limited intestinal absorption and first-pass metabolism. Rather than targeting specific resveratrol intake, the evidence-based approach emphasises consuming diverse polyphenol-rich whole plant foods (berries, grapes, nuts, seeds, legumes, whole grains) regularly. This ensures multiple polyphenol pathways activate and synergistic effects compound — likely more beneficial than chasing high resveratrol doses alone.