In Inulin-Type Fructans: Functional Food Ingredients, Dr. Marcel Roberfroid provides a scholarly and comprehensive review of inulin and inulin-like substances as functional foods, principally in their capacity as "colonic foods." He defines functional foods as naturally occurring substances in food ingested as part of the normal diet that provide health benefits beyond basic nutrition and may reduce the risk of chronic disease. This concept must be distinguished from dietary supplements and nutraceuticals, which are concentrated food components (e.g., lycopene) that are ingested like pharmaceutical products. In an era when the public is better informed about what constitutes a healthy diet and lifestyle, and is also disenchanted with standard forms of medical care, a better understanding of the role of diet in health is needed as an alternative. In addition, the excessive and inappropriate use of antibiotics in animals and humans over the last several decades has resulted in an ever increasing microbial resistance to treatment, resulting in the likelihood of life-threatening diseases, including food-borne infections, particularly in hospitalized young (infants) and elderly patients.
In a recent review in the New England Journal of Medicine, Jean-Francois Bach describes the impact of changes in public health worldwide over the last fifty years. He shows that the major infectious causes of death (hepatitis, AIDS, tuberculosis, malaria, etc.) have declined dramatically in developed countries due to public health measures such as improved sanitation, use of vaccines, antibiotics and sterile hospital settings. However, over the same time period, there has been a steady "mirror-image" increase in allergy and autoimmune diseases (e.g., asthma, type 1 diabetes, Crohn's disease). This change in disease prevalence has been explained by the so-called "hygiene hypothesis" which suggests that these public health measures, while reducing life-threatening infection, have actually decreased the microbial burden during development resulting in an increased incidence in immune-mediated disease. The implication is that an appropriate microbial stimulation to the developing immune system with proper initial colonization of the gut is necessary for lifelong health. Inulin-like fructans can function as "prebiotics" to stimulate the increased proliferation of health-promoting colonic bacteria (e.g., bifidobacteria, lactobacilli). Marcel Roberfroid, in conjunction with Glenn Gibson in an article in the Journal of Nutrition, coined the term prebiotic. Prebiotics are large molecular weight carbohydrates (e.g., oligosaccharides) which are not digested in the small intestine and enter the colon intact as "colonic food" to be fermented by resident bacteria. Because of fermentation producing short-chain fatty acids and an acid milieu, bifidobacteria and other health-promoting organisms (lactobacilli, etc.) proliferate to stimulate active immune function and to prevent infectious diseases. For proper development of mucosal immune responses, this process must occur during infancy. What allows prebiotics to be effective is that these functional foods stimulate the proliferation of resident endogenous flora rather than an artificial colonization of the gut with nonresident flora, which occurs with the use of probiotics. Early colonization is necessary to stimulate the development of a balanced mucosal immune response.
Dr. Marcel Roberfroid has an encyclopedic knowledge of this field and is well-trained professionally to understand the basic research involved. In this text, he carefully reviews the evidence to support which complex carbohydrates can be considered as prebiotics as well as the experimental evidence to support their function and utility in humans as functional foods. Since the field of prebiotics is relatively new (since 1995), large clinical trials have not been completed to definitively establish their long-term stimulus of endogenous flora. It is known that bifi-dobacteria and other health-promoting bacteria increase in the colon shortly after ingestion of inulin-type fructans and that their levels decrease with the cessation of their use. However, it would be important to determine whether the prebiotic stimulus can last for extended periods of time (years rather than months) or, instead, whether colonic bacteria can adapt by fermentation occurring with other less desirable bacteria using short-chain fatty acids as food, thus negating the long-term prebiotic effect. In addition, it is presumed that prebiotics, by stimulating proliferation of bifidobacteria and lactobacilli, have the same effect as if those organisms were given as probiotics. However, not knowing their secondary effect is the same as the use of these organisms as probiotics to prevent/treat disease. Additional multicenter trials are needed to confirm this concept.
In addition to the prebiotic effect of inulin-type fructans, these non-digestible oligosaccharides have been shown to have other primary effects (e.g., promote calcium and other mineral absorption, improve elimination of colonic waste, modify lipid metabolism towards a healthier profile, etc.). Again, large additional multicenter trials are needed to support preliminary clinical observations suggesting this effect. Marcel Roberfroid, as Chairman of the ORAFTI scientific group (a nonprofit group of scientists meeting semiannually to review the field of prebiotics) has been committed to filling in the gaps in our knowledge, particularly our clinical knowledge, with regard to the use of inulin-type fructans as functional foods. These activities, along with in-depth knowledge of the subject that appears in this text, provide the basis for what should be considered to be the definitive review of this topic in the field.
Conrad Taff Professor of Nutrition Harvard Medical School Cambridge, Massachusetts
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