Chapter 1: Functional Foods for Health: Evidence and Insights Free

For centuries, cultures worldwide have recognised the strong association between food and health. From traditional Chinese medicine to Ayurveda, food has been utilized not just for nourishment but also for therapeutic purposes. Ancient societies know the power of herbs, spices and plant-based remedies in treating illnesses, balancing bodily systems and improving general health. These practices laid the groundwork for what we now call functional foods. This reinforces the enduring belief that “let food be thy medicine and medicine be thy food.” For instance, peppermint tea (Mentha piperita) has long been utilized for digestive issues. The effectiveness of peppermint oil can be attributed to its spasmolytic compounds, which interfere with calcium channels in smooth muscle and thus alleviate symptoms of digestive discomfort.¹  Similarly, cranberry juice (Vaccinium macrocarpon) has been traditionally used to prevent urinary tract infections. In general, cranberry polyphenols may help prevent urinary tract infections (UTIs) by inhibiting the adherence of pathogens to uroepithelial cell receptors, which leads to these infections.² 

Herbs and spices have historically been added to food not only to enhance flavor but also to prevent spoilage. Many of these ingredients, recognized for their medicinal properties, are classified as functional foods. For example, thyme (Lamiaceae spp.) is known to be a powerful antiseptic that is commonly used in mouthwash, hand sanitizers and various acne medications.³  Additionally, thyme has been used to treat inflammatory diseases and research showed that thyme extracts reduced the production and gene expression of proinflammatory mediators such as tumor necrosis factor (TNF)-α and interleukins (IL-1β and IL-6) in a dose-dependent manner, while simultaneously increasing the secretion of the anti-inflammatory cytokine IL-10 in activated macrophages.⁴  Additionally, ginger (Zingiber officinale) root, cinnamon (Cinnamomum spp.) bark, and licorice (Glycyrrhiza glabra) root are common in both Chinese herbal medicine and Western folk remedies to treat digestive issues.⁵  Ginger is rich in various chemical constituents, such as phenolic compounds, terpenes, polysaccharides, lipids, organic acids and dietary fibers. Its health benefits are primarily attributed to phenolic compounds like gingerols and shogaols. In general, research has shown that ginger has a broad spectrum of biological activities, including antioxidant, anti-inflammation, antimicrobial, anticancer, neuroprotection, cardiovascular, and respiratory protective effects, as well as benefits for managing obesity, diabetes, nausea, and vomiting.⁶  In traditional medicine, cinnamon is used to balance the body’s Yang energy by mitigating inflammation, restoring energy flow, relieving coldness, reducing discomfort, and promoting smooth energy circulation through the body’s meridians. It is widely utilized to address a range of conditions such as erectile dysfunction, coldness in the uterus, cold-induced pain in the lower back and knees, kidney deficiency, respiratory issues, Yang deficiency, dizziness, eye redness, cold-related heart and abdominal discomfort, diarrhea caused by cold, hernia, abdominal pain, and painful menstruation.⁷  In traditional Chinese medicine (TCM), Glycyrrhiza glabra, commonly known as licorice, is regarded as a herbal remedy. TCM practitioners often say that “licorice is present in nine out of ten formulas,” emphasizing its widespread use.⁸  Licorice is highly valued for its ability to reduce toxicity and enhance the effectiveness of other herbs when combined in treatments. Additionally, due to its “medicine food homology” properties, licorice can also be consumed as a health food product and natural sweetener.⁸ 

In modern times, the scientific community has started to investigate and validate these age-old claims. Researchers have shifted their focus to how certain foods can serve not only as sources of basic nutrition but also actively promote health and potentially mitigate the risk of disease. Examples of foods that go beyond basic nutrition to actively support health and potentially reduce disease risk include fatty fish like salmon, which are rich in omega-3 fatty acids that are known for their heart-protective benefits. Blueberries are abundant in antioxidants and have been linked to reducing inflammation and improving brain function. Turmeric contains curcumin, a compound with strong anti-inflammatory and anticancer properties. In addition, oats are recognized for their ability to lower cholesterol, while garlic is known to boost immune function and help regulate blood pressure. These foods illustrate the growing focus on dietary components as functional agents in health promotion and disease prevention.

As the market for functional foods expands, they are increasingly seen as a health investment. Consumers and healthcare professionals alike are recognizing their potential to prevent and mitigate chronic diseases, making them critical elements in public health promotion. Functional foods are not just about nutrition—they offer tangible, scientifically supported health benefits, and their popularity continues to grow as the scientific principle and clinical evidence of their effectiveness accumulate.

The definition of functional foods has evolved over time. Various international organizations in dietetics and nutrition, such as the International Life Sciences Institute, the European Commission, and the Academy of Nutrition and Dietetics, acknowledge that functional foods offer health benefits that go beyond basic nutrition. However, there is no universal consensus on whether categories like medical foods, foods for special dietary use, or food supplements qualify as functional foods. Functional foods can be understood as whole foods, as well as fortified, enriched, or enhanced foods, that provide potentially beneficial effects on health when consumed regularly as part of a varied diet at effective levels.⁹ 

To further refine this definition, functional foods are characterized by several key attributes:

1. Found in conventional food forms

2. Contain functional components: they are not consumed at medicinal or therapeutic levels but are present in amounts that contribute to overall health.

3. Scientifically proven benefits: these foods have been shown to confer measurable health benefits when consumed as part of a regular diet but not in pill or isolated forms.

4. Safe for long-term consumption: they must be proven safe for the intended population when consumed over an extended period.

5. Functional components present or added: they may be naturally occurring nutrients or phytochemicals, or they may be added to enhance the food’s health properties.

6. Used to prevent or treat certain diseases: these foods play a role in health maintenance or disease prevention and management.

Building on this operational definition, functional foods are generally categorized into three classes based on their preparation: conventional foods, modified foods, and food ingredients. Conventional foods, such as fruits, vegetables, fish, dairy, and grains are whole, unmodified foods that naturally contain bioactive compounds beneficial to health. Modified foods, on the other hand, have been enriched, fortified, or enhanced with functional components like calcium-fortified fruit juices or iodine-enriched salt.⁹  Food ingredients include inulin-type fructans, which act as prebiotics to promote gut health. Prebiotics are compounds that positively influence the gut microbiome, particularly in the colon. Examples of prebiotics include beta-glucans found in oats and fructans.¹⁰ 

Functional foods are becoming increasingly popular as part of a proactive approach to health promotion. The global focus on reducing public health costs has further fuelled interest in these foods. Products like cranberries for UTI prevention, garlic for heart health, and green tea for ulcer prevention demonstrate the variety of ways functional foods can be integrated into daily diets to support well-being. On the other hand, common functional foods like yoghurt, cereals, and protein bars are easily accessible options that offer specific health benefits, making them valuable tools for managing and preventing chronic diseases.

The concept of functional foods emerges from the observation that certain foods and beverages offer health benefits that extend beyond their basic nutritional content, such as macronutrients, vitamins, and minerals. All foods contribute to our health by providing nutritional benefits. For instance, fruits, vegetables, grains, and proteins are staples that provide essential nutrients that are vital for maintaining health.

However, functional foods are distinguished by their additional benefits derived from specific bioactive compounds that contribute to improved physiological or cognitive functions, or to help prevent disease. This added value goes beyond basic nutrition and is supported by scientific evidence. The challenge lies in differentiating foods that provide basic nourishment from those offering additional health benefits. This distinction is crucial for understanding the specific advantages that functional foods can offer, which might not be evident in conventional foods.

The definition and regulation of functional foods vary globally. They are often influenced by historical, cultural, and regulatory factors. The functional food terminology in Japan and Australia typically applies to foods that are specifically modified to enhance health benefits. In these regions, the focus is often on foods that are altered or fortified to offer additional health benefits beyond their traditional nutritional value. On the other hand, in China, Europe and North America, these areas have a broader interpretation of functional foods. They include any natural or preserved foods that enhance physiological functions or prevent disease. This approach encompasses both unmodified and modified foods that offer health benefits beyond basic nutrition.

In most countries, functional foods must be consumed in their natural food or beverage form, rather than as medications. If ingredients are presented in pills, sachets, or other dosage forms, they are categorized as dietary supplements or nutraceuticals, not functional foods.

An area of debate is whether modified foods, such as vitamin or mineral-enriched products (e.g., folate-fortified flour or calcium-fortified orange juice), should be considered functional foods. Some definitions emphasize the presence of non-nutritive components, such as fiber or polyphenols, as key indicators of functional foods. However, there is a lack of international consensus on this matter.

All in all, understanding these definitions and regulatory differences helps clarify what qualifies as a functional food and ensures that claims about their health benefits are substantiated by scientific evidence. This distinction is essential for consumers seeking to make informed choices about foods that may contribute to their overall health and well-being.

Traditional knowledge has long recognized the health benefits of certain foods and natural products. Many modern functional foods have their origins in these practices, where foods were used not only for nutrition but also for their therapeutic properties. Traditionally, Lemongrass (Cymbopogon citratus), a fragrant plant from the Poaceae family, was used to treat the nervous system as well as gastrointestinal and metabolic disorders.¹¹  Research has shown that Lemongrass contains essential oils (including citral, nerol, geraniol, citronellal, and terpinolene) and polyphenolic compounds (such as luteolin and its glycosides, isoorientin 2′-O-rhamnoside, quercetin, kaempferol, apigenin, elimicin, catechol, chlorogenic acid, caffeic acid, and hydroquinone) that have antimicrobial, anthelmintic, anti-inflammatory, antioxidant, antiproliferative, antidiabetic, and antihyperlipidemic properties.¹²  Similarly, green tea has been consumed in Asia for thousands of years and is valued for its ability to promote longevity and overall health. Scientific research has demonstrated that green tea is rich in catechins, particularly epigallocatechin gallate (EGCG), which has potent antioxidant properties and may reduce the risk of various chronic diseases, including cardiovascular disease and certain cancers.¹³  In another example, ancient Indian, Greek, and Egyptian civilizations used Moringa leaves and fruits to maintain skin health and mental fitness.¹⁴  In fact, ancient Indian Maurian warriors were given Moringa leaf extracts for pain relief, stress reduction, and added energy during battles. Furthermore, the seeds of Moringa were prized for producing Ben oil, a pleasant-tasting edible oil used by Greeks, Romans, and Egyptians for skincare and perfume-making since 3000–2000 BC.¹⁴  Recent research has shown that moringa contains flavonoids, isothiocyanate and triterpenoids, which are known to possess anti-bacterial, antimicrobial and neuroprotective effects.¹⁴ 

These examples highlight how traditional wisdom often precedes scientific discovery. In many cases, traditional uses of certain foods have paved the way for modern scientific research, which seeks to understand and validate these ancient practices.

While traditional knowledge has provided a rich foundation for identifying potential functional foods, it is important to recognize the gap between anecdotal evidence from traditional practices and the scientific rigor required to validate these claims. Modern science relies on well-designed studies, including randomized controlled trials (RCTs), to establish the efficacy and safety of functional foods and their bioactive compounds. The functional effects of foods can be demonstrated through human intervention studies, whereby the efficacy of functional food is compared to a placebo that does not provide the same benefits. These studies can also evaluate whether the effects are dose-dependent. Randomized controlled trials are regarded as the gold standard because they can clearly establish the link between the consumption of functional foods and the resulting health benefits.¹⁵  Traditional practices are often based on anecdotal evidence that can be influenced by a variety of factors, such as cultural beliefs, placebo effects, and individual variability. Therefore, it is difficult to generalize these findings to larger populations. The gap between traditional claims and scientific evidence can lead to the proliferation of “snake oil” products—those marketed with exaggerated health claims but lack credible scientific support. For example, green coffee bean extract has been promoted as a weight loss product based on limited and poorly designed studies. Similarly, products like colloidal silver, once touted for a range of health benefits, were reported to have little therapeutic value and significant safety concerns.¹⁶  This indicates that the validation of traditional knowledge through modern scientific methods can be challenging. Some traditional practices involve complex mixtures of compounds or rely on effects that are difficult to replicate in controlled studies. Additionally, the dose, preparation, and form of the functional food used in traditional contexts may differ significantly from those tested in scientific studies.

To bridge the gap between traditional wisdom and modern science, an integrative approach is needed—one that respects and incorporates traditional knowledge while applying scientific methods to ensure efficacy and safety. Ethnopharmacology, the study of traditional medicines and their use, offers a valuable approach to identifying promising candidates for functional foods. In general, researchers can gain insights into traditional uses and preparation methods by collaborating with traditional healers and communities. In fact, combining insights from multiple disciplines (nutrition, biochemistry, pharmacology, and anthropology) can provide a more comprehensive understanding of how functional foods work. For example, studying the bioavailability and metabolism of curcumin in turmeric can help optimize its formulation for improved efficacy in reducing inflammation. In general, developing functional foods based on both traditional knowledge and scientific evidence ensures that products are not only effective but also safe for consumption.

All in all, traditional wisdom provides a rich foundation for the development of functional foods by offering insights into the potential health benefits of various natural products. However, it is crucial to apply scientific rigor to validate these claims, ensuring that functional foods are both effective and safe for consumption. By bridging the gap between traditional practices and modern science, we can unlock the full potential of functional foods and their role in promoting health and well-being.

The study of bioactive compounds in foods has typically focused on isolating single compounds and understanding their individual effects on health. While this approach has provided valuable insights into specific nutrients and compounds, it often neglects the intricate interactions within whole foods and dietary patterns. This limited perspective is similar to the story of the elephant and the blind men—each man perceives only a part of the elephant, leading to an incomplete understanding. In the same way, focusing only on individual components of functional foods may result in an incomplete understanding of their health benefits.

To gain a more accurate understanding of the health benefits of functional foods, it’s essential to integrate both molecular (reductionist) and holistic approaches. The reductionist approach isolates single bioactive compounds, such as vitamins, minerals, or phytochemicals, and studies their effects under controlled conditions. While this method can identify mechanisms of action, it often overlooks how these compounds behave in the context of whole foods or mixed diets. For example, focusing on curcumin which is the active compound in turmeric, this compound has shown anti-inflammatory and antioxidative properties.¹⁷  However, when consumed with other diverse food products, its effects can be different due to interactions with other compounds.

On the other hand, the holistic approach considers the whole food matrix and dietary patterns and takes into account the synergistic effects of multiple bioactive compounds. For instance, the Mediterranean diet is studied not just for its individual components like olive oil or fish, but as a dietary pattern that includes a variety of nutrients working synergistically to reduce inflammation and improve cardiovascular health. A more comprehensive understanding of functional foods could be achieved by combining the two methods. This integrated approach involves identifying individual bioactive molecules and their mechanisms and understanding how these compounds interact within the food and with other foods in the diet to produce a cumulative health effect. Lastly, after consuming these diverse and nutrient-rich diets, the overall impact on health is evaluated.

Many functional foods exert their effects through mechanisms that are not solely dependent on their bioactive compounds. Factors such as the food matrix, bioavailability of compounds, and individual variations in metabolism can all influence the health outcomes associated with functional foods. It is important to note that traditional research methods may not fully capture these variables, leading to incomplete or misleading conclusions.

Synergy refers to the phenomenon whereby multiple compounds in a food or from various food products work together to produce a greater effect than any single compound alone. When multiple bioactives are consumed together, they can enhance each other’s effects. For example, the bioavailability of lycopene, a potent antioxidant found in tomatoes, is significantly increased when consumed with olive oil. The healthy fats in olive oil enhance the absorption of lycopene (fat-soluble), thus leading to greater antioxidant activity in the body.¹⁸  Similarly, curcumin in turmeric has poor bioavailability on its own, but when combined with piperine, a compound found in black pepper, curcumin’s absorption increases by up to 2000%.¹⁹  This synergistic combination enhances curcumin’s anti-inflammatory and antioxidant effects. Likewise, research has shown that green tea and black pepper can work together synergistically, enhancing the bioavailability of epigallocatechin gallate (EGCG), a key compound found in green tea.²⁰  However, it is crucial to recognize that phytochemicals can still exhibit cytotoxic effects. These toxic effects may be intensified at high dosages or during interaction with other compounds. Therefore, it is generally safer to consume bioactive compounds through whole plant-based foods, which provide lower doses of phytochemicals and are typically considered safe.²⁰ 

Bioavailability is the extent to which nutrients and bioactive compounds are absorbed and utilized by the body. Bioavailability can be influenced by several factors, including the food matrix, preparation methods, and the presence of other nutrients. For instance, the bioavailability of non-heme iron (found in plant-based foods) is low compared to heme iron (from animal sources).²¹  However, when consumed with vitamin C (ascorbic acid), the absorption of non-heme iron is enhanced.²¹  Another example is that when lemon juice (rich in vitamin C) is added to spinach (a source of non-heme iron), this leads to an increase in iron uptake.²²  Additionally, some compounds can inhibit nutrient absorption, such as oxalates found in spinach and beet greens, which can bind to calcium and reduce its bioavailability.²³  In order to prevent this, consuming calcium-rich foods like dairy with low-oxalate vegetables can ensure better calcium absorption. Likewise, lowering the oxalic acid content in spinach could improve its nutritional value by increasing the dietary bioavailability of calcium, other minerals, ascorbates, and vitamins.²³  This reduction would make spinach more palatable by reducing its bitterness, thus boosting consumer acceptance.

Overall, understanding the synergy and bioavailability of bioactive compounds is crucial for the development of functional foods and the creation of effective dietary recommendations. When bioactive compounds are combined in specific formulations, their synergistic effects can be significantly enhanced. For instance, adding prebiotics into functional food products like yogurt can help to promote gut health more effectively.²⁴  This synergy between bioactives not only enhances the efficacy of functional foods but also opens new avenues for innovative product development that maximizes health benefits.

In terms of dietary recommendations, this understanding shifts the focus from isolated nutrients or supplements to whole foods and balanced dietary patterns. Therefore, instead of emphasizing single nutrients, the dietary guidelines can promote the consumption of a variety of fruits, vegetables, whole grains, nuts, and seeds, which naturally combine the various bioactive compounds.

Personalized nutrition is another area whereby the integration of molecular and holistic approaches can have a significant impact. In general, it is possible to optimize the health benefits derived from functional foods by tailoring dietary recommendations to individual needs based on genetics, microbiome composition, and overall health status. This personalized approach ensures that individuals receive the maximum possible benefits from their diet, aligned with their unique biological makeup.

The use of omics technologies, such as genomics, proteomics, and metabolomics, plays a vital role in understanding how functional foods interact with biological systems at the molecular level. These technologies allow researchers to identify biomarkers and elucidate the mechanisms through which functional foods exert their health effects. For instance, metabolomics studies have shown how certain compounds in functional foods can influence metabolic pathways, contributing to specific health outcomes. This molecular insight is essential for advancing our understanding of functional foods and developing targeted nutritional interventions. Additionally, nutrigenomics emphasizes the need to consider how certain food components will affect gene expression when making food and diet choices, rather than solely relying on taste, culture, and tradition.²⁵  Researchers have identified various foods that can positively or negatively impact the genome by modulating gene expression. The core concept of nutrigenomics lies in identifying food components that can activate specific genes, thereby influencing the production of certain metabolites. This field enhances our understanding of how nutrition affects metabolic pathways and its connection to diet-related diseases. For instance, by understanding transcriptional regulators that influence the expression of disease-related genes and the identification of genome polymorphisms, medical researchers can uncover the causes of diet-related diseases and provide solutions to society. For instance, folate is essential to maintain genomic stability. Research has shown that a daily intake of folate above 200 µg is necessary to prevent chromosomal damage.²⁶  In general, moderate folate deficiency can cause DNA damage, which is comparable to high radiation exposure. In the future, healthcare may shift from treating diseases caused by genome or epigenome damage to focus on diagnosing and nutritionally preventing or reversing such damage. Nutrigenomics will drive the creation of new functional foods and supplements designed to support genome health, allowing for personalized nutrition that aligns with an individual’s genetic profile.²⁶ 

Microbiome research is another promising field in the study of functional foods. Diet plays a significant role in shaping the gut microbiota, which could influence overall health. This relationship has spurred the development of functional foods. These foods are digested and absorbed through a series of complex processes within the GI tract, during which the gut microbiota can modulate the effects of the functional food components. For instance, gut bacteria can metabolize dietary compounds and xenobiotics, while functional foods can also alter the composition and activity of the microbiota. An example of this interaction is the inhibitory effect of tea phenolics on certain gut bacteria species, such as Bacteroides and Clostridium, showcasing the bidirectional influence between diet and microbiota. Therefore, understanding the interactions between functional foods and gut microbiota is crucial to harness their health benefits. Metabolomics is the study of small-molecule metabolite profiles, which provides detailed information on how functional foods are processed by gut bacteria. Additionally, by utilizing techniques like gas or liquid chromatography–mass spectrometry, researchers can monitor these interactions and gain insights into how diet influences the gut microbiota and how the gut microbiota could affect health. For example, probiotics, prebiotics, and fermented foods are known to positively impact gut health. This is because probiotics introduce beneficial bacteria into the gut, while prebiotics serve as food for these microbes, enhancing their growth and activity. Together, they help balance the gut microbiota, supporting overall gut health and contributing to disease prevention.

The physicochemical properties and the structure of food also play a critical role in the bioavailability and efficacy of functional components. The way functional foods are processed, prepared, and consumed can significantly influence their health benefits. Therefore, understanding these matrix effects is crucial for optimizing the impact of functional foods, ensuring that their beneficial properties are fully realized.

Current research also focuses on long-term health outcomes. Researchers aim to better understand the sustained benefits of functional foods and their role in preventing chronic diseases by conducting longitudinal studies and gathering real-world evidence. These studies provide valuable insights into the long-term impact of dietary patterns and specific functional foods on health, helping to refine dietary recommendations and functional food development.

Finally, it is important to understand consumer preferences and educate the public about the benefits of functional foods. It is essential to look at the factors influencing consumer choices and to select the most effective strategies to communicate the health benefits of functional food. In general, it is possible to promote healthier eating habits and increase the consumption of functional food by educating the masses with scientific knowledge.

The advances in analytical methods, such as spectroscopy, liquid chromatography high-resolution mass spectrometry, and biomolecular techniques, along with computational tools like online libraries and in silico studies, have greatly enhanced the discovery of new compounds. These advancements have also progressed the analysis of their effects on human metabolism and specific pathways, such as those associated with inflammatory or oxidative-driven diseases, through both simulated in vitro conditions and in vivo studies. The use of molecular (biochemical assays, genomics, proteomics and metabolomics) and holistic approaches (observational studies, epidemiological research and traditional knowledge) allows for a multidimensional understanding and application of functional foods. In fact, by understanding the synergy and bioavailability of these bioactive compounds, researchers and healthcare professionals can better harness the health-promoting properties of foods. As a result, more effective dietary strategies will be developed, leading to the creation of functional foods that will enhance overall health and well-being.

Today, there is growing evidence supporting the use of functional foods for health promotion. Functional foods are increasingly recognized for their potential to prevent chronic diseases, support immune function, and enhance overall well-being. Research has shown that components such as probiotics, prebiotics, omega-3 fatty acids, and phytochemicals can positively impact human health. For example, fermented foods rich in probiotics have been linked to improved gut health and immune function, while omega-3 fatty acids are known to support cardiovascular health.

The complex interactions of bioactive compounds within food matrices and their collective impact on human health are not fully understood. This is because of the variability in individual responses to functional foods that are influenced by genetics, microbiome composition, and lifestyle factors. All these require more comprehensive research. As such, future studies should aim to capture the intricate relationships between diet and health by considering the synergies in food products.

In addition, it is crucial to integrate traditional wisdom with modern scientific research to develop functional foods that are not only effective but also safe and accessible to all. Traditional knowledge has long recognized the health benefits of certain foods, such as turmeric for inflammation or cranberries for urinary health. Therefore, by validating these traditional uses with scientific studies, we can ensure that the health claims of these functional foods are reliable. In conclusion, by combining the insights of traditional practices with cutting-edge scientific research, we can create a new generation of functional foods that are grounded in evidence and optimized for health promotion.