In these testing times of the pandemic (COVID-19), it is quite apt to say that “an ounce of prevention is like a pound of cure”. This realization has made people seek ways to take proactive steps for prevention of disease. The human body has its own defence system (innate immunity) that helps fight infections. And building a robust immune system is not a one day job. It is an effect of healthy dietary habits that we continue to have over a period of time. Since ‘immunity’ is of upmost concern in current times, the interest of people in foods, beverages, and supplements that benefit immune health has progressively increased.
For long, it has been said that immunity begins in the gut and this is because over three-fourth of the immune system components reside in the digestive system along with 100 trillion gut microbes that form the gut microbiota. The primary function of this microbiota is to protect the intestine from the harmful microorganisms and to enable the immune system in the gut to differentiate between harmless antigens, such as food and other health hazards. Optimally, the immune system – microbiota association manages the immunity in a way that selects, adjusts and terminates responses in the most suitable manner.
Gut microbiota influences many areas of human health from innate immunity to appetite and energy metabolism.
Thus, having a healthy gut microbiome by increased abundance of good gut bacteria is indeed a good strategy to boost immunity. A healthy diet, inclusive of dietary fibres, is one of the best ways to promote a healthy microbiota4,5. The gut microbiota thus adapts to the dietary habits and patterns of an individual. However, changing environmental conditions as well as intake of anti-biotics may harm the same.
Foods rich in fiber, in particular fermentable fibres as fructo-oligosaccharides, help to achieve this purpose of maintaining gut-health and improving the beneficial bacteria in the gut. Dietary fiber is that part of plant-based foods that the body cannot break down. It passes through the body undigested and reaches the gut to be metabolized by the resident gut bacteria. Whole grains and pulses, fruits and vegetables, nuts, and beans contain reasonable amounts of dietary fiber (Table 1).
|Table 1: Dietary fibre content of some fibre-rich foods7|
|Food||Dietary Fibre (g/100g)|
|Red gram whole||22.84|
|Soya bean (brown)||21.55|
|Nuts and seeds|
Some of these fibres are fermented (also known as fermentable dietary fibres) by the bacteria in the gut and are classified as prebiotic fibres. Some foods containing such prebiotic fibres are bananas, garlic, onions, chicory root, sugar cane, asparagus, acacia gum, beetroot, cabbage, apple, custard apples, peaches and Jerusalem artichokes. These prebiotic fibres selectively stimulate the growth and activity of certain bacteria (such as lactobacillus and bifidobacteria) in the colon, and thus improve host health.
|Table 2: Clinical studies showing different dietary Fibres with prebiotic effects|
|Wheat Dextrin||Increased Bacteroides; Decreased Clostridium perfringens|
|Polydextrose||Increased lactobacillus and bifidocacterium|
|Gum Arabic||Prebiotic efficacy; increased Bifidobacteria, Lactobacilli and Bacteroides|
Prebiotics are thus a type of dietary fibre that is not digested by the body but are selectively utilized by gut microbiota. Beneficial gut microbes break down prebiotic fibres into short-chain fatty acids like butyrate or acetate, which stimulate immune cell activity.
As a result, they help in the prevention of various immune-related, respiratory and digestive system disorders that occur due to inflammatory response pathways.
Recommended daily intake of fiber per day
The National Institute of Nutrition (NIN), India recommends the daily value for fiber as 40 grams per day on a 2,000-calorie diet for adults. However, this varies based on the lifestyle:
- Adult Sedentary worker male (requiring 2110 kcal per day): 42.2 grams
- Adult Sedentary worker female (requiring 1660 kcal per day): 33.2 grams
The NIN- ICMR, India and USDA has given detail recommendations as under:
|Age GroupCategory of Workbody weight (Kg)Energy RequirementFiber Requirement*MenSedentary65211042.2 Moderate271054.2 Heavy347068.2WomenSedentary55166033.2 Moderate213042.6 Heavy272054.4 Pregnant55+10+35050.3 Breastfeeding0-6 months7-12 months–+600+52054.252.6Infants0-6 months6-12 months5.88.55506701113.4Children1-3 years4-6 years7-9 years12.918.325.311101360170022.227.224Boys10-12 years34.9202040.4Girls10-12 years36.4206041.2 13-15 years50.5286057.2 13-15 years49.6240048 16-18 years64.4332066.4 16-18 years55.7250050Source: National Institute of Nutrition, Indian Council of Medical Research, , India;*Values of the fiber intake calculated considering the requirement of 40 g of daily dietary fiber for a 2000 kcal diet|
People who are unable to eat fiber-rich foods to meet their Recommended Daily Intake of fiber can resort to having packaged foods that are enriched with dietary fiber such as prebiotic dietary fibers (FOS: fructo-oligosaccharides), and GOS: galacto-oligosaccharides).
In conclusion, the ability of prebiotics to modify the composition of gut microbiota is appealing for the modulation of immunity. In other words, the gut microbiota should be considered as a significant body organ which if fed properly with prebiotics can become stronger and healthier, which, in turn, can lead us to a healthy life.
 Rachul C et al, et al. COVID-19 and ‘immune boosting’ on the internet: a content analysis of Google search results. BMJ Open 2020;10:e040989. doi:10.1136/bmjopen-2020-040989
 Wu HJ, Wu E. The role of gut microbiota in immune homeostasis and autoimmunity. Gut Microbes. 2012;3(1):4-14. doi:10.4161/gmic.19320
 Ley RE, Peterson DA, Gordon JI. Ecological and evolutionary forces shaping microbial diversity in the human intestine. Cell. 2006 Feb 24;124(4):837-48. doi: 10.1016/j.cell.2006.02.017. PMID: 16497592.
 Belkaid Y, Hand TW. Role of the microbiota in immunity and inflammation. Cell. 2014 Mar 27;157(1):121-41.
 Valdes AM et al. Role of the gut microbiota in nutrition and health. BMJ. 2018 Jun 13;361:k2179. doi: 10.1136/bmj.k2179. PMID: 29899036; PMCID: PMC6000740.
 Tandon et al. A snapshot of gut microbiota of an adult urban population from Western region of India. PLoS ONE, 2018; 13(4): e0195643
 Longvah T et al. Indian Food Composition Tables. National Institute of Nutrition. Indian Council of Medical Research,2017.
 Lefranc-Millot C et al. Impact of a resistant dextrin on intestinal ecology: how altering the digestive ecosystem with NUTRIOSE®, a soluble fibre with prebiotic properties, may be beneficial for health. J Int Med Res. 2012;40(1):211-24. doi: 10.1177/147323001204000122. PMID: 22429361.
 Fanaro S et al. Galacto-oligosaccharides are bifidogenic and safe at weaning: a double-blind randomized multicenter study. J Pediatr Gastroenterol Nutr. 2009 Jan;48(1):82-8. doi: 10.1097/MPG.0b013e31817b6dd2. PMID: 19172129.
 Elli M et al. Evaluation of prebiotic potential of refined psyllium (Plantago ovata) fiber in healthy women. J Clin Gastroenterol. 2008 Sep;42 Suppl 3 Pt 2:S174-6. doi: 10.1097/MCG.0b013e31817f183a. PMID: 18685505.
 Jie Z et al. Studies on the effects of polydextrose intake on physiologic functions in Chinese people. Am J Clin Nutr. 2000 Dec;72(6):1503-9. doi: 10.1093/ajcn/72.6.1503. PMID: 11101478.
 Calame W et al. Gum arabic establishes prebiotic functionality in healthy human volunteers in a dose-dependent manner. Br J Nutr. 2008 Dec;100(6):1269-75. doi: 10.1017/S0007114508981447. Epub 2008 May 9. Erratum in: Br J Nutr. 2009 Aug;102(4):642. PMID: 18466655.
 Tandon D et al. A prospective randomized, double-blind, placebo-controlled, dose-response relationship study to investigate efficacy of fructo-oligosaccharides (FOS) on human gut microflora. Sci Rep. 2019 Apr 2;9(1):5473. doi: 10.1038/s41598-019-41837-3.
 Nutrient requirements for Indians. Recommended Dietary Allowances and Estimated Average Requirement