1. Introduction

Fruits are a cornerstone of human nutrition, providing essential nutrients and bioactive compounds that play a critical role in preventing malnutrition, metabolic disorders, and chronic diseases [1]. Despite their well-established benefits, global fruit consumption remains inadequate, contributing to the rising prevalence of diet-related health issues such as cardiovascular disease (CVD), type 2 diabetes (T2D), and obesity [2]. Malnutrition, whether due to undernutrition or overnutrition, is a significant public health challenge, and fruits offer a nutrient-dense solution by delivering vitamins (e.g., vitamin C, folate), minerals (e.g., potassium), and dietary fibers that support metabolic and immune functions [3,4]. At the molecular level, fruits are rich in bioactive compounds like flavonoids (e.g., anthocyanins, quercetin) and carotenoids (e.g., β-carotene, lycopene), which exhibit potent antioxidant and anti-inflammatory properties [5,6]. These compounds neutralize reactive oxygen species (ROS) and modulate key inflammatory pathways, such as NF-κB and NLRP3 inflammasome, thereby mitigating oxidative stress and chronic inflammation—two major drivers of aging and disease [7,8]. Additionally, dietary fibers from fruits, such as pectin, reshape gut microbiota composition, promoting the growth of beneficial bacteria (e.g. Faecalibacterium prausnitzii) and enhancing short-chain fatty acid (SCFA) production, which improves metabolic health [9,10]. Despite these benefits, modern dietary patterns often prioritize processed foods over whole fruits, leading to gaps in micronutrient intake and increased chronic disease risks [11]. The specific mechanisms by which different fruit categories (e.g., citrus, berries, tropical fruits) exert their health effects remain underexplored, highlighting the need for a systematic analysis of their physiological and molecular impacts.

Extensive research has investigated the health effects of fruits, with studies spanning molecular mechanisms, clinical interventions, and epidemiological observations. For instance, citrus fruits like oranges and lemons are notable for their high vitamin C content (53 mg/100g) and bioavailability (up to 90%), which surpasses synthetic supplements in enhancing immune function [4,12]. Berries, such as blueberries and strawberries, are rich in anthocyanins and ellagic acid, demonstrating superior antioxidant capacity (e.g., ORAC value of 9,621 μmol TE/100g for blueberries) and anti-inflammatory effects through NF-κB pathway inhibition [5,13]. Tropical fruits like mangoes and pineapples provide β-carotene (2,900 µg/100g) and bromelain, respectively, which support vision and digestive health [12,14].

Clinical trials have shown that short-term fruit interventions yield rapid benefits. For example, consuming two kiwis per day for three consecutive days can significantly increase neutrophil activity and plasma vitamin C levels; a 5-day papaya intervention can accelerate gastric emptying by 25% and reduce bloating; consuming mixed berries for two weeks can reduce fecal calprotectin levels by 15%, indicating a reduction in enteritis [13-15]. Epidemiological studies further support these findings, revealing that daily consumption of 200g of fruit correlates with a 12% lower CVD risk and a 7% reduced T2D incidence, with berries and citrus fruits showing the strongest protective effects [16,17].

The foundational level of nutrition explores the essential nutrients required for physiological functioning, disease prevention and overall health, emphasizing the role of fruits in addressing malnutrition, metabolic disorders, and chronic diseases, while elucidating their potential physiological mechanisms. The study emphasizes the critical role of fruits in preventing malnutrition, metabolic diseases, and immune dysfunction. The physiological mechanisms involve antioxidant activity, enzyme modulation, gut microbiota interactions, and immune enhancement, providing a scientific basis for dietary recommendations. Future research should focus on personalized nutrition and bioactive compound optimization for targeted health benefits. The primary objective of this paper is to bridge the gap between generalized dietary recommendations and personalized, condition-specific nutritional strategies for preventing diseases. While fruits are universally recognized as beneficial, their specific bioactive compounds, metabolic effects, and therapeutic potential vary widely meaning that different fruits can be strategically used to target distinct health risks.

2. Key knowledge in fruit nutrition studies

Fruits contain a wide range of nutrients, but there are differences in the distribution of nutrients among the various fruits. Generally, fruits are categorized as citrus, berries and tropical fruits [1-3]. Short-term intake of fruits benefits the digestive system and enhances immune function. For example, consumption of two kiwifruit per day for three consecutive days significantly enhanced neutrophil activity and increased plasma vitamin C levels, resulting in improved resistance to infection [4]. Further studies at the level of physiological mechanisms, including the molecular mechanisms of antioxidant and anti-inflammatory effects, the relationship between dietary fiber and the regulation of the gut microbiota in the metabolic syndrome, and epidemiological evidence of a negative correlation between fruit intake and cardiovascular disease and type II diabetes could help to characterize the systemic effects of dietary fruit intake on human health from a more microscopic perspective.

2.1. Basic nutritional level in fruits

The core nutrients in fruits can be basically categorized into macronutrients, micronutrients and bioactive compounds. Macronutrients contain carbohydrates and dietary fibers, dietary fibers can be further divided into soluble fibers such as pectin and β-glucan and insoluble fibers, insoluble fibers include cellulose and lignin. Protein is also a kind of macronutrients. Micronutrients are mainly Vitamin C, Potassium and Folate, also known as Vitamin B9. Other common micronutrients are calcium, iron, zinc and magnesium. Bioactive compounds are polyphenols, involving flavonoids such as anthocyanins, phenolic acids, ellagic acid and carotenoids, which include beta-carotene, lutein and lycopene. Anthocyanins such as cyanidin and delphinidin are also a kind of bioactive compounds [5]. There are differences in the nutrient distribution of different fruits, which are usually categorized as citrus fruits, berries and tropical fruits by fruit type [1-3]. In citrus fruits, oranges (53 mg/100g) and lemons (53 mg/100g) contain significantly higher vitamin C content compared to most other fruits. The bioavailability of vitamin C from citrus fruits reaches up to 90%, notably higher than that from synthetic supplements [6]. In berries, the anthocyanins in blueberries and blackberries demonstrate significantly higher ORAC (Oxygen Radical Absorbance Capacity) values compared to other fruits (e.g., blueberries: 9,621 μmol TE/100g), indicating superior antioxidant capacity. Strawberries also contain abundant ellagic acid, and both ellagic acid and anthocyanins kinds of polyphenols which means that berries are richer in the nutrients of polyphenols than other kinds of fruits[7]. In tropical fruits, ripe mango pulp is particularly rich in β-carotene (approximately 2,900 µg/100g), which serves as a precursor to vitamin A. Pineapple contains significant vitamin C (47.8 mg/100g) [8]. Bananas, with their high potassium content (358 mg/100g), can effectively counteract the blood pressure-elevating effects of high-sodium diets and reduce stroke risk (RR=0.87). Other tropical fruits with notable potassium levels include papaya (257 mg/100g) and durian (436 mg/100g) [9]. Bromelain from pineapple demonstrates significant protein-digesting capability and papain from papaya remains stable across a wide pH range (3-9) [9]. As a result, tropical fruits have high content of vitamin precursors and antioxidants, notably β-carotene in mangoes (provitamin A) and ascorbic acid in pineapples (vitamin C), high potassium levels and bioactive proteases - bromelain from pineapple and papain from papaya. Short-term intake benefits for immune function enhancement and the digestive system. Evidence indicates diverse phytochemicals exert immunomodulatory effects via multiple pathways: direct immune cell activation by polysaccharides, cytokine/chemokine balance regulation by hydrophobic compounds, and specific receptor targeting, positioning them as promising natural therapeutics for immune-related conditions [11]. A 3–7 day intervention with pectin-rich fruits (e.g., apples, pears) significantly increased intestinal Bifidobacterium abundance (↑30-40%) and butyrate production, demonstrating rapid improvement in gut barrier function [12]. Five-day papaya consumption, through its papain content, accelerated gastric emptying rate by 25% (p<0.01) and alleviated postprandial bloating in clinical subjects[13]. A two-week mixed berry intervention (blueberries/strawberries) reduced fecal calprotectin levels by 15%, indicating measurable attenuation of intestinal inflammation markers in healthy adults [14]. Thus, a short-term intake of fruits will promote digestion as well as boost the immune system in the human body.

2.2. Effects on human physiological mechanisms

Fruits containing polyphenols, especially involving flavonoids and carotenoids, have antioxidant and anti-inflammatory effects. In molecular mechanisms, flavonoids (e.g., quercetin, kaempferol) directly scavenge reactive oxygen species (ROS) via phenolic hydroxyl groups, forming stable radical intermediates. Simultaneously, they inhibit the Fenton reaction by chelating metal ions (Fe²⁺/Cu²⁺) and enhance endogenous antioxidant enzymes (SOD, CAT) activity through Nrf2/ARE pathway activation [12]. Blueberry anthocyanins (C3G) suppress the NF-κB pathway by inhibiting IκBα phosphorylation, reducing pro-inflammatory cytokine (TNF-α, IL-6) secretion. Citrus hesperidin interferes with NLRP3 inflammasome assembly, thereby inhibiting IL-1β maturation [13]. Showing the flavonoid Antioxidant Mechanisms and polyphenol Anti-inflammatory Pathways. Lycopene physically quenches singlet oxygen (¹O₂) through energy transfer, while β-carotene chemically reacts to form epoxide derivatives, demonstrating complementary oxidative stress mitigation [14]. Carotenoid Dual-action Mechanisms give an effective way to neutralize oxidative stress byproducts. Overall, fruit-derived bioactive compounds, such as flavonoids and carotenoids, operate at genetic, enzymatic, and microbial levels to neutralize oxidative stress by scavenging ROS and enhancing endogenous antioxidants, suppress chronic inflammation through NF-κB and NLRP3 inflammasome inhibition, and enhance cellular resilience via Nrf2 and SIRT1 activation—highlighting the importance of diverse fruit intake for synergistic protection against aging and chronic diseases. Fibers derived from fruits, particularly apple pectin and citrus fibers, remodeled gut microbial ecology by selectively promoting butyrate production (Faecalibacterium prausnitzii abundance ↑2.3-fold, p<0.01). This microbial shift was associated with metabolic improvements that reduced endotoxemia (40% decrease in serum LPS) and enhanced insulin sensitivity (35% decrease in HOMA-IR) while reducing systemic inflammation. Butyrate emerged as the central mediator, activating PPAR-γ signaling in adipocytes to suppress NF-κB-driven inflammatory cascades, thereby breaking the gut-adipose-liver axis dysfunction characteristic of metabolic syndrome [15]. Generally, Dietary fiber is fermented by gut microbiota to produce short-chain fatty acids (SCFAs-acetate, propionate, butyrate), which improve insulin resistance (↓30%) and adipose tissue inflammation through activation of G protein-coupled receptors (GPR41/43) and inhibition of histone deacetylases (HDACs) [16]. Dietary fiber exerts profound protective effects against metabolic syndrome through targeted modulation of gut microbiota and their metabolic outputs. In addition, the intake of fruits has impacts on epidemic diseases. Academics cite the inverse correlation between fruit intake and cardiovascular disease and type II diabetes as epidemiologic evidence. A systematic review and dose-response meta-analysis demonstrated that daily consumption of 200g fruit (~2.5 servings) was significantly associated with reduced CVD risk (RR=0.88, 95%CI: 0.83-0.93), with berries (blueberries, strawberries) showing the strongest inverse association (RR=0.78), likely attributable to anthocyanin-mediated anti-inflammatory effects. Supporting evidence from the NHS & HPFS cohorts (n=187,382) revealed a 19% reduction in stroke risk with citrus fruit intake [17]. Li et al. utilized a meta-analysis to establish a negative correlation between whole fruit intake and the risk of type 2 diabetes mellitus (7% reduction per 100 g/day, 95% confidence interval: 4-10%), with apples, pears, and blueberries demonstrating the greatest protective effect (RR ≈ 0.85), whereas fruit juice intake instead increased the risk (RR = 1.12). Mechanistically, fruit fiber delays glucose absorption, and polyphenols (e.g., quercetin) enhance β-cell function [18].

3. Research rationale and analytical approach

Based on the above analysis, it is recommended to consume at least 200 grams of mixed fruits per day in the daily dietary schedule, prioritizing berries such as blueberries, citrus fruits such as strawberries and oranges that are high in anthocyanins and lemons that are bio-available for vitamin C, as well as tropical fruits such as mangos and papayas to obtain beta-carotene and digestive enzymes. Berries and citrus fruits are effective in reducing inflammation and lowering the risk of stroke, while bananas and papayas help regulate blood pressure, and both types of fruits help protect the cardiovascular system. For metabolic health recommendations such as insulin sensitivity or type 2 diabetes prevention it is important to choose whole fruits over juices, especially high-fiber fruits such as apples, pears, and berries, which enhance the gut microbiome. Consume pectin-rich fruits such as apples and pears for 3-7 days to promote beneficial gut bacteria that contribute to digestive health, or consume papaya for 5 days to improve gastric emptying and reduce bloating. Antioxidant and anti-inflammatory effects by consuming flavonoid-rich fruits (e.g. berries and citrus) and carotenoid-rich fruits (e.g. mango and pineapple) to neutralize oxidative stress and inhibit inflammatory pathways. However, special populations should adjust their intake accordingly. For example, older adults should choose softer, potassium-rich fruits such as bananas and mangos, which are beneficial for people with cardiovascular disease, and for people with metabolic syndrome, their diets should focus on high-fiber, low-GI choices such as berries and apples. A balanced and varied fruit intake provides synergistic benefits for immunity, digestion and chronic disease prevention, whereas fruit juice intake should be limited due to its higher glycemic impact. Future research should explore personalized fruit combinations based on gut microbiota profiles.

4. Conclusion

This study comprehensively elucidates the critical role of dietary fruit intake in promoting human health through diverse physiological mechanisms and molecular pathways. The findings demonstrate that fruits exert systemic benefits by delivering essential nutrients and bioactive compounds that address oxidative stress, inflammation, and metabolic dysfunction. At the molecular level, flavonoids and carotenoids directly scavenge reactive oxygen species, enhance endogenous antioxidant defenses via Nrf2 activation, and suppress pro-inflammatory signaling through NF-κB and NLRP3 inflammasome inhibition. Simultaneously, fruit-derived dietary fibers, particularly pectin and resistant polysaccharides, reshape gut microbiota composition, elevating butyrate-producing bacteria and improving metabolic parameters such as insulin sensitivity and endotoxemia reduction. Epidemiological evidence further corroborates these mechanistic insights, revealing that regular consumption of 200g of fruit daily correlates with a 12% lower cardiovascular disease risk and 7% reduced type 2 diabetes incidence, with berries and citrus fruits exhibiting the most pronounced protective effects. Short-term interventions highlight the rapid efficacy of specific fruits—kiwifruit for immune enhancement, papaya for digestive improvement, and mixed berries for gut inflammation attenuation—underscoring their therapeutic potential in targeted health contexts. The significance of this research lies in its translational integration of molecular, clinical, and population-level evidence, providing a scientific foundation for precision nutrition strategies. By delineating how distinct fruit categories (citrus, berries, tropical) address specific health risks, the study advances beyond generic "five-a-day" recommendations toward personalized dietary frameworks. However, limitations include variability in individual responses due to genetic polymorphisms, microbiota heterogeneity, and bioavailability differences among fruit matrices. Additionally, most clinical trials focus on acute effects, warranting longer-term studies to validate sustained benefits. Future research should prioritize first, biomarker-driven interventions to match fruit bioactive with individual health profiles. Then, advanced processing techniques to optimize nutrient retention and investigation of synergistic effects between fruit compounds and pharmaceuticals. Embracing these directions will unlock the full potential of fruits as functional foods, bridging nutrition science with preventive medicine to combat the global burden of chronic diseases.