Dietary intake of nutrients and non-nutritive compounds directly impacts the immune system and its corresponding segments, such as the gut microbiome and the physical, innate, and adaptive immune systems. Eating a largely plant-based, balanced diet positively affects the immune system just as nutrient-poor diets negatively impact it.

The reverse scenario also is true—that is, immune system function has a direct effect on nutrient metabolism. Specifically, when functioning properly, the immune system positively affects nutrient metabolism. Thus, immune function and nutrient intake are forever dependent on one another to maintain host health. 

Correctly fermented dairy products, such as yogurt, kefir, and other cultured dairy, as well as fermented vegetables (sauerkraut and kimchi) are rich in live, colony-forming probiotic microorganisms (the microbiota). When combined with increased intake of prebiotic dietary fiber, they build a diverse, functional gut microbiome. Prebiotic fibers are the preferred food components that stimulate growth and/or activity of beneficial gut bacteria in the colon, resulting in improved health.

It has been well established that long-term nutritional imbalance due to low-fiber diets leads to increased incidence of noncommunicable diseases, such as heart disease, diabetes, gut dysbiosis, cancer, metabolic syndrome, allergies, inflammatory bowel disease, obesity, and autoimmune diseases. 

Fiber force

Dietary fibers (including gums and resistant starches) have both direct and indirect impacts on immunity. As fibers, they provide bulk, decrease transit time in the digestive tract, help lower serum cholesterol, and reduce the risk of certain cancers. They also contribute to balanced blood sugar levels and increased satiety, thus helping to lower the risk of heart disease, cancer, and other diseases. Other benefits are weight management and reduced inflammation.

Studies in both humans and animals have reported improvements in immune function as a result of increased dietary fiber intake. The predominant fibers in use today include oligosaccharides, such as fructo-oligosaccharides (FOS), fructans (longer-chain FOS, such as inulin), galacto-oligosaccharides (GOS), galactomannan-oligosaccharides (such as guar gum), xylo-oligosaccharides (XOS), acacia gum (gum Arabic), pectins, arabinoxylan hydrolysates, beta-glucans, lignins, celluloses, and other carbohydrate compounds.

While most prebiotic compounds are derived from plants, some, such as beta-glucans, exist in high concentrations in yeast and mushrooms. Another type, exopolysaccharides, are polysaccharides secreted by bacteria and include compounds such as lentinan, xanthan, dextran, and curdlan.

All these have been shown, to varying degrees, to have immune functions that are multifaceted due to their diverse physicochemical characteristics, potent bioactive compounds, and abundance of functional groups. Their properties upregulate the immune system by increasing cytokine production, promote maturation of dendritic cells, increase activation of neutrophil secretion of interleukins while delaying neutrophil breakdown, improve T-cell immune response, decrease pro-inflammatory cytokines, improve activity of natural killer (NK) cells, rebalance the gut microbiome, improve epithelial cell barrier integrity, and modulate secretion of innate immune-response compounds. They also trigger activation of immune receptors.

Chain gang

Recent research has indicated that these compounds resist digestion in the upper g.i. tract and ferment in the lower gut. There, they produce post-biotic compounds involved in immunomodulation, such as short-chain fatty acids (SCFAs).

SCFAs have an impressive range of activity. They influence multiple segments of the immune system, including increasing secretion of interleukins, regulating immune cell proliferation and tumor suppression, modulating bone marrow function, reducing oxidative DNA damage, improving gut epithelial barrier integrity, regulating cytokine production, reducing chronic inflammation, and inhibiting mast-cell degranulation.

These diverse influences result in reported decreases in the incidence and severity of noncommunicable diseases such as colitis, inflammatory arthritis, asthma, respiratory syncytial virus (RSV) infection, allergic airway inflammation, and food allergies.

Fibers benefit the immune system in several ways. By feeding the gut microbes, fermentable fibers reduce epithelial barrier destruction, promote gut biodiversity, and strengthen the innate gut microbiome. This, in turn, further increases production of SCFAs and antimicrobial peptides. These are protein fractions that actively target harmful bacteria in the gut, broadly reducing the establishment of opportunistic pathogens.

Multifunctional workers

Fibers, gums, and resistant starches are versatile workhorses in the food and beverage industry. Non-starch polysaccharides are present in beer, providing viscosity and turbidity while reducing haze. Gums and pectins modify texture and stability, providing a thickening or gelling function while simultaneously stabilizing the product. Cellulose and hemicellulose provide a non-digestible substrate for gut bacteria. There are a variety of polysaccharide compounds, each with their specific applications in food and beverage products and a resulting impact on the immune system.

Beta-glucans are naturally present in the cell walls of some bacteria, yeast, algae, and fungi, and in grains such as oats, rye, wheat, and barley, with barley and oats having the highest content. They are soluble and fermentable, with immune-modulating activities that include increasing cytotoxic activity of macrophages, circulating B cells, and NK cells.

Many countries allow a heart health statement on products that include oat beta-glucans. This is based on the effect beta-glucans have on reducing cholesterol and managing blood sugar response. Oat beta-glucans are also soluble, yet provide a favorable mouthfeel in dairy and dairy-alternative beverages, smoothies, and powdered drink mixes.

Resistant starch is a starch that is unique for behaving like a fiber in the body, but like a starch in foods and beverages. Whole grains, legumes, potatoes, slightly underripe bananas, and nuts and seeds are sources of resistant starch. Resistant starch improves glucose metabolism, insulin resistance, and reduces cholesterol and triglyceride levels. It is highly versatile and is perfect for food and beverage applications due to its solubility, neutral flavor, and heat tolerance. In baking, resistant starch slightly increases volume of risen products.

Gum acacia, or gum arabic, is another common additive used as an emulsifier, stabilizer, thickener, and texture enhancer without altering the flavor of a food or beverage. It is a natural, soluble gum made from the sap of the Acacia tree (Acacia senegal). Used for decades in food production, it was discovered to be fermentable by the gut microbiome and to have strong prebiotic effects—so much so that it recently earned FDA approval as a dietary fiber.

Gum acacia reduces intestinal inflammation, blocks opportunistic pathogens, lowers serum cholesterol and triglycerides, and even exhibits antioxidative capacity. Further aiding the immune system, it increases production of SCFAs, promotes maturation of dendritic cells, improves cardiovascular health, increases cytokine secretion, and has been used in the treatment of chronic renal failure.

Gum acacia is employed extensively in water emulsions found in sodas and carbonated beverages but is also used to an extent in bakery products, pet foods, and confections. Due to its functional properties, it is a beneficial component of functional beverages and prebiotic beverages such as prebiotic smoothies. It even has applications in food extrusions due to its lubrication capabilities. Gum acacia is a popular ingredient in lactose-free and vegan dairy products to improve the consumer mouthfeel experience. It also improves the quality of plant-based milks, and emulsifies and stabilizes sauces and condiments through its bulking capacity.

Pectins have a long history in food production as texturants, especially for gelling. But research has also revealed their healthful attributes. During digestion, pectin binds to cholesterol and smaller carbohydrates. Studies have also confirmed the prebiotic effect of pectins and their stimulation of SCFA production. Although apples and citrus are primary sources, an emerging star in the pectin family is carrot-derived rhamnogalacturonan (cRG-1).

A recent clinical study found that cRG-1 accelerated immune responses in subjects suffering from a common cold virus, reducing severity and duration of symptoms. Moreover, the ingredient has minimal g.i. side effects and is effective in smaller amounts—as low as 300mg/day, and feeds a widespread variety of probiotic bacteria. As a bonus, cRG-1 is highly sustainable, made from upcycled carrot processing waste.

Fiber alphabet

Fructo-oligosaccharides are soluble, fermentable short-chain polymers found largely in fruits and vegetables. FOS support immune function due to an increase in calcium-binding protein expression that boosts solubility of minerals such as calcium, improving circulatory micronutrient availability. In enhancing the gut microbiome, FOS further stimulate the immune system by decreasing inflammation through reduction in pro-inflammatory cytokines, improving immunomodulation by increasing immunoglobulin secretion, and reducing oxidative stress while supporting cytokine expression.

In foods and beverages, FOS add a slight natural sweetness in a healthier, low-calorie option. They also provide a bulking action that has fat-mimetic qualities to improve texture and mouthfeel, adding a creaminess to products. FOS work best in thicker, dairy or dairy-alternative beverages, smoothies, dressings, confections, and baked goods. 

GOS and XOS provide bulking in the g.i. tract to prevent constipation, reduce cholesterol, improve mineral absorption, and enhance immune modulation. Derived primarily from milk, GOS help reduce allergy symptoms and skin problems. They also have the same positive effects on immune function as FOS, making them ideal for use in infant formula and prebiotic drinks. GOS do not affect flavor and are stable in baked goods, snacks, and yogurts. 

XOS are non-digestible, fermentable sugar oligomers that are temperature- and acid-stable. They reside in plant cell walls and are effective prebiotics. XOS improve gut microbial diversity, immune regulation, and antioxidant capacity, and they have a positive impact on gut barrier function. Derived from plants, XOS are well suited for baked products due to their temperature stability but are also popular as sugar-reducers in beverages. Similar to the other oligosaccharides in mouthfeel, sweetness, and prebiotic capacity, XOS are popular in beverages ranging from smoothies to alcohol drinks.

There are endless applications that can include these compounds, individually or in combination. Crafting products with the right fiber profile can be a simple and effective adjustment that allows consumers to easily include these ingredients in a healthy lifestyle.

Dana McCurdy, PhD, is an analytical chemist, nutrition biochemist, and fermentation scientist with industry experience. Her expertise is in fermented dairy, nutrition-mediated immunity, and the application of live bioactive cultures in food and beverage formulation with a focus on fermentation process development and product innovation and development. She can be reached at danamccurdy@hotmail.com. 

A Question of Balance

Not Quite a Fiber, but…

Isomaltulose is a polysaccharide known for reduction of body weight, blood glucose control, and cardiovascular health improvement based on its beneficial effect on metabolic parameters. Primary of these is the expression of glucagon-like peptide (GLP-1). GLP-1 is a hormone that enhances the production of insulin and helps reduce appetite. Even though isomaltulose is a disaccharide isomer of sucrose and has 4kcals/g, it boasts a low glycemic index and has about half the sweetness of sugar.

 Your Daily Fiber

Recommended daily dietary fiber intake varies between men and women. Adult men should consume 34g/day, and adult women should consume 28g/day. Children from ages 1-8 need 20-25g/day, and those from ages 9-18 require about 25-30g/day for girls and 30-38g/day for boys.

 Synchronicity

Microbiota in the gut are in a complex, multifaceted relationship that only becomes more complicated as species diversity increases. An increase in gut microbe diversity is directly linked to improved overall health and a lower incidence of non-communicable diseases. A reduction in fiber intake, soluble and insoluble, leads to a reduction in species diversity and richness, decreasing the efficiency of fiber usage by disrupting cross-feeding and food webs of a robust gut microbiome.

Fiber Network

Mycelia are the branching, thread-like root system of mushrooms and other fungi. Research has revealed compounds in mycelia fiber that increase immune function. In traditional medicine, mushrooms and their roots have been used to treat infectious disease, cancer, and other diseases and dysfunctions. This history is likely due to the complex variety of polysaccharides in mycelia. These include not only beta-glucans but also proteoglycans, heteroglucans, and chitin. They also contain a wealth of other non-fiber bioactive compounds in different varieties of mushrooms and their corresponding mycelia. Mushroom-derived ingredients have been appearing increasingly in food and beverage formulations promoted as supporting an improved innate immune response, including antitumor ability via stimulation of interleukins and tumor necrosis factor. Mycelia can be a healthful extender in plant-based meat alternative products, as well as in broths, bread, fermented beverages, cheeses, and sauces. The most recent application of mycelia has been in coffees, teas, and other hot beverages.