What is Resistant Starch (RS)?
RS is a type of plant fibre that is a newly recognized health food for both humans and animals. It refers to the portion of starch and starch products within the fibre that resist digestion as they pass through the gastrointestinal tract. The properties of the starch itself have been found to be beneficial to health by improving the population of gut microbiota and triggering cell signalling pathways associated with anti-inflammation, anti-diabetes and anti-obesity.
There are two basic types of dietary fibre: (1) insoluble fibre and (2) soluble fibre. Each group helps your body in different ways. Soluble fibre dissolves in water and forms a gel in the gut. It helps to keep stools soft, making them easier to pass, and is fermented by the colon’s bacteria. Conversely, insoluble fibre does not dissolve in water but bulks up the stools and makes waste move more quickly through the digestive tract. However, it can also be sub-divided into: fermentable and non-fermentable fibre. Non-fermentable insoluble fibre is known primarily as a bulking agent, whilst fermentable insoluble fibre – such as RS – can produce similar positive effects on colonic bacteria that soluble fibre can. One important difference between the two fibres is that soluble fibre tends to slow digestion, whilst insoluble fibre speeds up digestion.
RS and Prebiotics
Nutritional compounds that have the ability to promote the growth of specific beneficial (probiotic) gut bacteria are termed prebiotics. Prebiotics can be defined as “a selectively fermented ingredient that allows specific changes, both in the composition and/or activity in the gastrointestinal microflora that confers benefits upon the host well-being and health”. While many nutritional compounds meet this definition, only two groupings of nutritional compounds, at present, meet the requisite functional criteria: inulin-type prebiotics (oligofructose, fructo-oligosaccharides (FOS)) and galactooligosaccharides (GOS). Although RS exhibits prebiotic-type effects, currently it does not fulfil the requisite functional criteria, and so cannot formally be termed a ‘prebiotic’, although this might change in the future as the research in this area is promising.
What is Starch?
Starches are one of the main forms of dietary carbohydrates (the others being sugars), which act as a major energy source for all living cells. Starchy foods are derived from plant sources, such as potatoes and cereal products (e.g. breads and grains) and are a staple of the British diet. In plants, starch occurs as granules that provide an economical means of storing carbohydrate in an insoluble and tightly packed manner. The size and shape of these granules varies among plant species and also cultivars of the same species.
Chemically, starches are polysaccharides, i.e. they are composed of a number of monosaccharides or single sugar (glucose) molecules linked together. Two main structural types of starch exist: (1) amylose, which s is a linear molecule and typically constitutes 15-20% of starch; and (2) amylopectin, a larger branched molecule that is a major component of starch. Structurally, there are three types of crystalline structures, which contain differing proportions of amylopectin. Type A is found in cereals, Type B is found in tubers and Type C, which is a mixture of both A and B, is found in legumes. Generally, digestible starches are broken down (hydrolysed) by the enzymes alpha-amylases, glucoamylase and sucrose-isomaltase in the small intestine to yield glucose that is then absorbed.
Nutritional Classification of Starch
The nutritional property of starch is related to its rate and extent of digestion and absorption in the small intestine. It can be classified into 3 categories:
- Rapidly digestible starch (RDS) – causes a sudden increase in the blood glucose level after ingestion (within 20 minutes).
- Slowly digestible starch (SDS) – is digested completely in the small intestine at a slower rate compared with rapidly digestible starch. Digestion time is around 20-120 minutes.
- Resistant starch (RS) – is not absorbed in the small intestine of healthy individuals but is fermented in the large intestine. Digestion occurs after 120 minutes.
The ‘RS’ name was so coined because the starch resisted digestion in the stomach and small intestine. Later, they were found to act as a substrate for microbial fermentation in the large intestine, the end products beings hydrogen, carbon dioxide, methane and short chain fatty acid (SCFA). One of the most important chemical features of these different starch molecules is that high amylose content and specific structures of amylopectin are necessary for the production of resistant starch, determining both its biochemical and nutritional properties. Based on the physiological functionality of RS (rather than it’s physical or chemical characteristics), it has been further categorized into four sub-types:
- RS1 – physically inaccessible to digestion by being bound within the fibrous cell walls of plants.
- RS2 – un-gelatinised starch, which is starch in its raw state and is protected by its physical structure. Gelatinisation is a process that breaks down the starch molecule in the presence of water and heat.
- RS3 – retrograded starch. Non-granular starch-derived materials that are formed during the retrogradation of starch granules. Retrogradation is a reaction that takes place when the amylose and amylopectin chains in cooked, gelatinised starch realign themselves as the cooked starch cools.
- RS4 – chemically modified starch, also called starch derivatives. Prepared by physically, enzymatically or chemically treating starch to change its properties.
Although RS is found naturally in all starch-containing foods, factors which can influence the amount of RS present include: the initial quantity and type of starch present, how the starchy food is processed, cooked and stored and how it is ingested. Furthermore, physiological factors can impact the amount of RS in food, such as increased chewing or individual variations in stool transit time; whilst additives, such as phosphorous can bind to the starch making it more or less susceptible to digestion.
|RS Type||Description||Food Sources||Resistance Reduced By|
|RS1||Physically protected||Whole or partly milled grains & seeds, legumes, pasta||Milling, chewing|
|RS2||Ungelatinised resistant granules||Raw potatoes, green bananas, plantains some legumes, high amylose starches (such as maize)||Food processing & cooking|
|RS3||Retrograded starch||Cooked & cooled potatoes, bread, grains, food products with prolonged &/or repeated moist heat treatment||Processing conditions.|
|RS4||Chemically modified starches||Some fibre-drinks, certain breads & cakes. Used a thickening agent, stabilizer or emulsifier||Less susceptible to digestibility|
Nugent A P. British Nutrition Foundation Bulletin 2005, 30: 27-54.
Physiological Effects of RS
By escaping digestion in the small intestine, RS has few interactions with other components of the upper gastrointestinal tract. It is fermented in the large intestine resulting in the production of carbon dioxide, methane, hydrogen, organic acids (e.g. lactic acid), and short-chain fatty acids (SCFA). However, RS is believed to result in only a modest production of these gases compared with other non-digestible oligosaccharides and lactulose. The SCFAs produced include butyrate, acetate and propionate and it’s these SCFAs that are thought to mediate the effects of RS, rather than RS exerting a physical bulking effect.
A number of physiological effects have been ascribed to RS. Evidence from both animal models and humans show the role of RS in improving metabolic features. It has been found to improve glycaemic status, endotoxaemia and markers of oxidative stress in patients with type-2 diabetes; decrease fatty acid intake and synthesis and increase fatty acid oxidation; decrease energy intake, waist circumference, systolic blood pressure and HbA1c to improvements in blood glucose control and insulin sensitivity; and is associated with cardiovascular risk reduction through multiple mechanisms. The table below lists some of the known physiological effects.
|Physiological Effects||Conditions Where a possible Protective Effect|
|Improved glycaemic & insulinaemic response||Diabetes, impaired glucose & insulin responses, the metabolic syndrome.|
|Improved bowel health||Constipation, diverticulitis, inflammatory bowel disease, ulcerative colitis, colorectal cancer.|
|Improved blood lipid profile||Cardiovascular disease, lipid metabolism, metabolic syndrome.|
|Prebiotic effects||Colonic health.|
|Increased satiety & reduced energy intake||Obesity|
|Adjunct to oral rehydration therapies||Chronic diarrhoea, cholera.|
|Synergestic interactions with other dietary components, e.g. dietary fibres, proteins, lipids||Improved metabolic control & enhanced bowel health.|
Nugent A P. British Nutrition Foundation Bulletin 2005, 30: 27-54.
Short Chain Fatty Acids (SCFA)
SCFA are the metabolic products of anaerobic bacterial fermentation of polysaccharides, oligosaccharides, protein, peptide and glycoprotein precursors in the large intestine, including those derived from dietary fibre and RS. The principal SCFA are butyrate, propionate and acetate, although other SCFA are also produced in a lesser amount. SCFA are the preferred respiratory fuel of the cells lining the colon (colonocytes). They increase colonic blood flow, lower luminal pH and help prevent the development of abnormal colonic cell populations. They are mainly found in the proximal colon where fermentation is greatest and the amount mirrors the supply of carbohydrates in the diet.
Levels of SCFA fall during the passage of digestion through the colon; this is due to the uptake and utilisation by the colonocytes and bacteria. The abundance of SCFA is normally acetate > propionate > butyrate, although butyrate is the favoured fuel of the colonocytes. Depending upon diet, total SCFA concentrations are usually between 70-140 mM in the proximal colon and 20-70 mM in the distal colon. Hence, much lower quantities are found in the distal colon, which is normally the site of many colonic diseases and most colon cancers. Diet and colon transit time are both variables that are known to influence the concentration and types of SCFA found in the colon.
In general, increased SCFA production is associated with improved colonic health, including lower pH, lower production of ammonia and phenol, decreased secondary bile acid secretion, reduced cytotoxicity of faecal water, reduced transit time and altered bacterial activity. A lower pH is thought to depress the conversion rate of primary to secondary bile acids and lower their carcinogenic potential; whilst in combination with a high concentration of SCFA is thought to prevent the overgrowth of pH-sensitive pathogenic bacteria. Phenol and ammonia are products of protein fermentation and reduced concentrations indicate a decreased reliance on protein from colonic fermentation and possibly a shortened transit time. Furthermore, the reduced activity of certain bacterial enzymes (e.g. B-glucuronidase) depresses the formation of toxic and carcinogenic metabolites from dietary and endogenous compounds.
Unique Functions of RS on the Microbiome
The Microbiome or the “Microbiota” is the term used to describe the community of microorganisms (bacteria, viruses and fungi) that normally live in or on a given organ of the body. The microbiota contain roughly one quadrillion cells, at least ten times as many cells as does the body itself. Hundreds of bacterial species make up the intestinal microbiota and their composition affects our immune responses and susceptibility to infection by intestinal pathogens, as well as the development of allergic and inflammatory bowel diseases. The microrganisms possess a far greater range of degradative enzymes and metabolic capabilities than we do ourselves.
Certain dominant species, notably among the bacteroidetes, are known to possess very large numbers of genes that encode carbohydrate active enzymes and can switch readily between different energy sources in the gut depending on availability. Nevertheless, more nutritionally specialized bacteria appear to play critical roles in the community by initiating the degradation of complex substrates such as plant cell walls, starch particles and mucin. In particular, a beneficial function of RS is associated with the increase of butyrate in the large intestine. Butyric acid facilitates the maintenance of epithelial integrity, regulating inflammation and influencing gene expression in colonocytes. However, to increase butyric acid, the critical factor was found to be the presence of special bacteria to degrade RS.
Consistent with the finding of gene expression regulation, one such animal study demonstrated that resistant starch effected a change in mucosal gene expression related to energy metabolism, as well as microbiota composition. Whilst in humans, a randomised cross-over study in healthy middle-aged subjects found that resistant starch in whole grain cereal foods affected the release of gut hormones and improved appetite and glycaemic control. It is clear from this study that RS increased the levels of gut hormones involved in appetite regulation, metabolic control and maintenance of gut barrier function, as well as improved markers of glucose homeostasis. Further studies show that a diet high in RS modulates microbiota composition, short-chain fatty acids concentrations and host gene expression.
Microbial fermentation of complex non-digestible dietary carbohydrates in the gut has important consequences for health, including the ability of certain dominant species, such as the Bacteriodetes, to encode carbohydrate active enzymes that can switch readily between different energy sources in the gut depending upon availability. In particular, microbial alterations induced by RS have been associated with increased abundance of butyrate producers, including Incertae sedis XIV, Lachnospiraceae, and Ruminococcaceae.
RS Sub-Types and Gut Microbial Impact
Research into the differing effects of the RS sub-types on types of gut bacteria is still in its infancy and currently is not yet fully elucidated. In one human study the effects of RS2 and RS4 were compared, which revealed that the specific RS type induced specific shifts in the microbial community. RS2 promoted Eubaceterium rectale, a species associated with high butyrate, a trait that could be especially beneficial in the prevention of inflammation. In contrast, RS4 reduced the amount of Firmicutes in favour of Bacteriodetes and bifidobacteria. Such a shift in the gut microbiota could be especially beneficial in the prevention of obesity and related metabolic disorders because a mirobiome enriched in Firmicutes has been associated with an increased capacity for energy harvest and obesity. Furthermore, bifidobacteria have been linked to metabolic and immunological improvements related to type 2 diabetes.
The functional differences found in this study could imply that starches with different chemical structures could potentially selectively target specific bacterial populations. However, this study also demonstrated individualised responses to the starch and these individualised responses will pose a hurdle to developing universal dietary recommendations. More personalised strategies that target the gut microbiome might be required. Further research is needed in this area.
RS and Insulin and Glucose Metabolism
Insulin is the hormone that enables glucose uptake by muscle and adipose tissue, which lowers blood glucose levels. It also inhibits the use of stored body fat and together with an array of other physiological signals can modulate appetite and satiety signals. RS-rich foods release glucose slowly, which will lower the insulin response and enable a greater access to and use of stored fat and, potentially, a muted generation of hunger signals. Such conditions would help with the management of clinical conditions like diabetes and impaired glucose tolerance but also possibly in the treatment of obesity and in weight management.
There have been numerous studies examining the effects of various forms of doses of RS on glucose (glycaemic) and insulin (insulinaemic) responses. Most human studies have focused on post-prandial glycaemic and/or insulinaemic responses and have varied in quality and results. Although some studies have reported improvements in these markers, others have not and there was a lack of consensus regarding the precise effects of RS on insulin and glucose at the time of the studies (which were mainly mid 1990s-2005).
Difficulties arose in comparing the respective studies because the composition of the test and control meals often varied in terms of amount of digestible starch, total dietary fibre and macronutrients present. Most food sources also contain digestible starch as well as RS, yet often the content of digestible starch was overlooked. However, it is important to note that since then the cell signalling pathways that are influenced by RS have been identified. In particular, recent studies have shown that RS can stimulate the secretion of GLP-1 (glucagon-like peptide 1) and PYY (peptide YY), which are gut-secreted hormones with anti-obesity and glucose tolerance effects.
Glycaemic Index, Glycaemic Response and Glycaemic Load
The glycaemic index (GI) is a physiological concept used to classify carbohydrate-containing foods. It is closely tied in with the term ‘glycaemic response’. Both refer to the ability of a particular food to elevate postprandial blood glucose concentrations. Foods with a high GI value release glucose rapidly into the blood (i.e. elicit a rapid glycaemic response), while foods with a low GI value release glucose more slowly into the bloodstream and result in improved glycaemic and insulinaemic responses. It is known that dietary fibre may contribute to an improved (i.e. slower more controlled) glycaemic response and, in general, high-fibre foods are assigned a lower GI value. However, it is important to note that for foods enriched with RS, a reduced glycaemic response may simply result from a lack of available digestible starch, rather than any specific physiological effects per se and that any readily digestible starch present in the food would be absorbed as normal. Nonetheless, there will be a physiological effect as a result of lowering the content of digestible starch by replacing it with RS.
In reality, though, people eat meals containing a mixture of foods and generally carbohydrate-containing foods are eaten alongside food containing protein and/or fat. In addition, the total carbohydrate content (quantity) varies between foods. To account for this, the concept of glycaemic load (GL) was developed, which considers both the carbohydrate content per serving of food and its GI value, i.e. the quantity and the type of carbohydrate present. Using GL, it’s easier to account for a range of foodstuffs and also portion size. It is possible to lower GL by replacing the carbohydrate content with protein, fat or other lower GI carbohydrates. As RS has a low glycaemic response, adding it as an ingredient to foods will help lower the overall GL value of the food (particularly if it is replacing existing readily absorbed forms of carbohydrate).
Cell Signalling Pathways related to Physiological Effect of RS
Multiple studies have reported anti-inflammatory effects of RS. It has been found to increase the expression of IL-10 (anti-inflammatory cytokines), T-regulatory cells (immune suppressor cells), IFNγ (innate and adaptive immunity cells) and PPARγ (energy pathways regulator) to suppress gut inflammation. The interaction between a disturbed microbial composition, the intestinal mucosal barrier and the mucosal immune system plays an important role in inflammatory bowel disorders, such as ulcerative colitis and Crohn’s disease. Oral intake of RS has been found to counteract such inflammatory bowel diseases in relation to intestinal inflammation and weight loss.
Studies also show that RS can stimulate the secretion of GLP-1 (glucagon-like peptide 1) and PYY (peptide YY), which are gut-secreted hormones with anti-obesity and glucose tolerance effects. GLP-1 decreases blood sugar levels by enhancing insulin secretion, whilst PYY helps reduce appetite and limit food intake. Hence, increased GLP-1 and PYY play an important role in the effect of RS on body fat accumulation. It’s important to note that ingestion of sodium butyrate does not have the same effects on GLP-1 and PYY, suggesting that localisation in the gut rather than in the blood is very important in initiating the cell-signalling pathway by secreting GLP-1 and PYY. It has been further found that RS stimulates GLP-1 and PYY secretion in a substantial day-long manner, independent of meal effect or changes in dietary glycaemia; and that it is the effects of fermentation of RS in the gut that is the primary mechanism for increased endogenous secretions of GLP-1 and PYY.
Potential Side Effects
Several studies have investigated the possibility of any side effects of RS. No adverse effects were observed or evidence found of altered incidence or severity of pathological changes in any organs or tissues. Nor have any cases of allergic reaction been reported following supplementation with more traditional forms of RS, such as those made from high amylose maize. In addition, it appears to be more readily acceptable than other forms of dietary fibre (e.g. wheat bran) at high levels in the human diet. Currently, non-modified RS is considered safe under existing food classifications and legislations in the US and Europe. However, it is noteworthy that current EU legislation restricts the labeling of health claims with any food substance or supplement unless that claim is supported by scientific factual evidence.
Nonetheless, caution is advised in cases of suspected cases of SIBO (small intestinal bacterial overgrowth) or where there is any gastrointestinal distress after ingestion. SIBO is the most common cause of IBS, which affects around 20% of the UK population. It results from an overgrowth of normal bacterial flora in the small intestine, which should otherwise have low bacterial counts. The issue in SIBO is the location of the bacteria and not the type of bacteria. By being up high and in a part of the intestine not designed for them, bacteria eat the host’s food, especially carbohydrates, leading to carbohydrate malabsorption and high gas production. Because carbohydrate reactions vary between individuals with this condition, there are no ‘wrong’ carbohydrates to eliminate – it really does depend upon what triggers the symptom in that individual. Any symptomology suffered after consuming RS or other carbohydrates should be referred to a health care practitioner for further investigation.
Chufas (Tiger Nuts) as a Source of RS
The evidence clearly indicates potential health benefits of adding RS to your diet. Some common forms have already been discussed earlier on. However, a very old but not very well-known food in the UK is potentially a really interesting source of RS. Tiger nuts (Cyperus esculentus), or chufas in Spanish, are grown wild all over the world. They are a typical food product of Spain (but are also popular in Africa) where they are used to make a healthy refreshing non-alcoholic milk drink called ‘Horchata de Chufa’, which is used to cool down on hot summer days or post workout, although it can be used all year round. The milk can also be used to make ice-cream, whilst the fibre from which the milk is extracted can be used as an important dietary component in other foods, such as bread making and other baked goods.
What are Chufas (Tiger Nuts)?
Chufas are not actually nuts but tubers that grow under the ground, much like a potato. Once you actually get to the nuts, they’re about the size of a chickpea and taste mildly sweet and nutty, almost like a caramel flavour. They can be eaten raw or roasted or have their juices extracted as milk, like almonds or hazelnuts. They are the oldest cultivated plants in Ancient Egypt but pre-existed such Ancient civilisations. Based on a recent study, they possibly made up 80% of the early human diet, making it close to a true “paleo” food. ‘Paleo diets’ are a more recent dietary trend and hark back to the caveman days of our ancestors. The foods include anything that could have been ‘hunted or gathered’ during that period. Such diets have arisen in response to the modern diet, which is increasingly linked with chronic health complaints.
Chufas are vegan and free from nuts, gluten and soy, making them suitable for anyone with such food allergies/intolerances. The UK Food Standards Agency estimates that 1-2% of adults and 5-8% of children in the UK have a food allergy – that’s over 6.5 million people but doesn’t include those who have an intolerance, which is far more difficult to detect and, arguably, more prevalent. In response to the current levels of food allergies/intolerances, recent dietary trends have given rise to the demand for gluten-free flour – making chufa flour an excellent gluten-free and nut-free alternative for wheat flour, especially as it can be used as 1:1 replacement for wheat flour in most recipes. However, the most traditional chufa recipe is the milk beverage of ‘Horchata de Chufa’, which is made by blending the milky extract with water and a sweetener (typically dates) in the same process as nut milks.
In addition to having a low glycaemic load on account of the high RS content, chufas are also classified as a low FODMAP food. FODMAP is the acronym used to describe short-chain carbohydrates and alcohols that are poorly absorbed by the intestines. It stands for “Fermentable Oligo-Di-Mono-saccharides and Polys’. Such foods can cause digestive problems – such as excess gas, bloating and pain in sensitive people – especially those suffering from IBS (Irritable Bowel Syndrome) like symptoms, which is the most common gastrointestinal disorder in the world. Considering around 20% of the UK population suffers from IBS that equates to over 13 million people who would benefit from the introduction of a low FODMAP food such as chufa.
Nutritional Properties of Chufas (Tiger Nuts)
The nutritional composition of chufas is very high and similar to human breast milk, which might explain its popularity among our Paleolithic ancestors. These nutritional attributes include the following:
|Starches & Fibre||Rich in starch, especially high levels of RS – similar levels to that of maize (which is very high and has shown a wide range of health benefits, such as lowering the glycaemic index and promoting colon health). 33% fibre and – gram for gram – they have almost 6 times as much fibre as sweet potatoes as and more than 3 times the sugar, yet still have a low glycaemic index.|
|Fats||Unlike most starchy vegetables, such as potatoes, they are rich in beneficial fats. They consist of 73% monounsaturated fats in the form of oleic acid (which is very anti-inflammatory), 18% saturated fat and 9% polyunsaturated fat in the form of linoleic acid (Omega-6). This fatty acid profile is very close to olive oil (which has multiple health properties, including its favourable effects on inflammation and weight reduction).|
|Amino Acids||The principal one is arginine, which optimises blood flow by helping the body to make nitric oxide, which is a vasodilator. Arginine also helps liberate hormones that produce insulin. Good levels also of glutamic acid, important for neurotransmitters and brain health, and aspartic acid, which is necessary for cellular energy metabolism. Although the full range of the 8 essential amino acids is present, like other plant foods, they do not contain a complete protein profile because the levels of the essential amino acid are all below the World Health Organisation’s guidelines – with the exception of tryptophan and threonine. Tryptophan is very high (80% higher) and is important for mood and sleep, whilst threonine (47% higher) helps maintain protein balance and prevents fatty build up by metabolising fats.|
|Vitamins & Minerals||Rich in magnesium, calcium, potassium, iron, phosphorus, zinc, copper, manganese and vitamins C and E. Vitamins B1, B2, B3, B6 and folic acid are also found at trace levels.|
|Polyphenols||Relatively high levels of polyphenols at 1.7 mg per gram. Polyphenols are antioxidants that help protect the body from damage against free radicals. Strong associations now found between polyphenol consumption and the prevention of disease.|
|Enzymes||Contain the digestive enzymes lipase (fats), amylase (carbohydrates) and catalase (hydrogen peroxide). The latter is very important in protecting cells from oxidative damage by free radicals.|
Commercial Application vs Home Extraction
Chufas have huge important potential in today’s food market because of their high nutritional quality and their distinctive nutritional profile. They contain about 50% digestible carbohydrates, 25% oil resistant to peroxidation, 9% crude fibre and 4% protein. However, its potential in the commercial food market is limited by its short shelf-life, which is caused by the high starch content. However, such a short shelf-life can be overcome by home extraction using a simple processing device, such as the ChufaMix. This is incredibly quick taking only 1-2 minutes to extract the milk, which will be naturally free from preservatives and artificial flavourings, and can then be stored in the fridge for up to 5 days. The fibre that remains is composed of mainly insoluble fibre (99.8%), which can then be used as flour to make baked goods.
Foods containing high levels of RS offer the potential to confer multiple health benefits with regular consumption. RS has been shown to produce prebiotic-like effects in the digestive system as a result of microbial fermentation in the large intestine producing, in particular, SCFA of which the most beneficial is butyrate (the preferred fuel of the colonocytes). It is thought that it is these SCFA that mediate the effects of RS, rather than RS exerting a physical bulking effect. However, the critical factor was found to be the presence of special bacteria to degrade the RS. The presence of RS appears to change multiple parameters within the gut in addition to SCFA production. These include: a change in the microbiota composition and mucosal gene expression related to energy metabolism; stimulation of gut hormones involved in appetite regulation, metabolic control and maintenance of the gut barrier; and improvement of markers of glucose homeostasis.
Current research has identified certain cell signaling pathways that are affected by RS. In particular, its anti-inflammatory effects are mediated via the increased expression of IL-10 (anti-inflammatory cytokines), T-regulatory cells (immune suppressor cells) and IFN-gamma (innate and adaptive immunity cells). Whilst it’s anti-diabetes and anti-obesity effects are mediated via the increase secretion of the gut hormones GLP-1 and PYY. GLP-1 decreases blood sugar levels by enhancing insulin secretion, whilst PYY helps reduce appetite and limit food intake. These signaling pathways explain why RS has been found to be beneficial in gut related inflammatory conditions (such as IBD, UC and diverticulitis) as well as metabolic conditions (such as obesity, diabetes and cardiovascular conditions).
Chufas (Tiger Nuts) have emerged as a potentially good source of RS with a low glycaemic load; owing to their RS content being similar to maize (a well-known high RS food). However, it’s the unique nutritional composition of chufas that turns them into a potential ‘super-food’ over and about their RS content. In particular, the high concentrations of oleic acid (the main component of olive oil and the traditional Mediterranean diet) make it stand out as a health food, even without its high RS content. Furthermore, it will appeal to those on a specialized diet by virtue of it being vegan, paleo, low-allergenic (free from gluten, nuts and soy) and low FODMAP. Our Ancient ancestors managed to thrive on this food, perhaps now is the time for us to incorporate a health lesson from the past.
References Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Roberfroid M. Prebiotics: the concept revisited. J Nutr 2007;137:830S-837S  Kelly D ND. Insulin-type prebiotics – A review. Alternative Medicine Review 2008, 13(4): 315-329.  Kelly D ND. Insulin-type prebiotics – A review. Alternative Medicine Review 2008, 13(4): 315-329.  Imberty A, Buléon A, Tran V & Pérez S. Recent Advances in knowledge of starch structure. Starch 1991; 43: 375–84.  Baghurst PA, Baghurst KI & Record SJ. Dietary fibre, nonstarch polysaccharides and resistant starch – a review. Supplement to Food Australia 1996; 48 (3): S3–S35.  Nugent A P. Health properties of resistant starch. Review. British Nutrition Foundation Nutriton Bulletin, 2005; 30: 27-54.  Topping DL & Clifton PM. Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides. Physiological Reviews 2001; 81 (3): 1031–64  Englyst H, Wiggins HS, Cummings JH: Determination of the non-starch polysaccharides in plant foods by gas-liquid chromatography of constituent sugars as alditol acetates. Analyst 1982;107:307–318.  Nunes FM, Lopes ES, Moreira AS, Simões J, Coimbra MA, Domingues RM: Formation of type 4 resistant starch and maltodextrins from amylose and amylopectin upon dry heating: A model study. Carbohydr Polym 2016;141:253-262  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Brown I .(Complex carbohydrates and resistant starch. Nutrition Reviews 1996; 54 (11): S115–19.  Nugent A P. Health properties of resistant starch. Review. British Nutrition Foundation Nutriton Bulletin, 2005; 30: 27-54.  Christl SU, Murgatroyd PR, Gibson GR et al. Production, metabolism, and excretion of hydrogen in the large intestine. Gastroenterology 1992; 102: 1269–77.  Topping DL, Fukushima M & Bird AR. Resistant starch as a prebiotic and symbiotic: state of the art. Proceedings of the Nutrition Society 2003; 62: 171–6.  Bindels LB, Walter J, Ramer-Tait AE: Resistant starches for the management of metabolic diseases. Curr Opin Clin Nutr 2015;18:559-565  Karimi P, Farhangi MA, Sarmadi B, Gargari BP, Zare Javid A, Pouraghaei M, Dehghan P: The Therapeutic Potential of Resistant Starch in Modulation of Insulin Resistance, Endotoxemia, Oxidative Stress and Antioxidant Biomarkers in Women with Type 2 Diabetes: A Randomized Controlled Clinical Trial. Ann Nutr Metab 2016;68:85-93.  Sun Y, Yu K, Zhou L, Fang L, Su Y, Zhu W: Metabolomic and transcriptomic responses induced in the livers of pigs by the long-term intake of resistant starch. J Anim Sci 2016;94:1083-1094.  Messina V: Nutritional and health benefits of dried beans. Am J Clin Nutr 2014;100:437S-442S.  Bernstein AM, Titgemeier B, Kirkpatrick K, Golubic M, Roizen MF: Major cereal grain fibers and psyllium in relation to cardiovascular health. Nutrients 2013;5:1471-1487.  Andoh A, Tsujikawa T & Fujiyama Y (2003) Role of dietary fibre and short-chain fatty acids in the colon. Current Pharmaceutical Design 9 (4): 347–58.  MacFarlane S & MacFarlane GT (2003) Regulation of short-chain fatty acid production. Proceedings of the Nutrition Society 62 (1): 67–72.  Topping DL & Clifton PM. Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides. Physiological Reviews 2001; 81 (3): 1031–64.  Topping DL & Clifton PM (2001) Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides. Physiological Reviews 81 (3): 1031–64.  Schwiertz A, Lehmann U, Jacobasch G et al. Influence of resistant starch on the SCFA production and cell counts of butyrate-producing Eubacterium spp. in the human intestine. Journal of Applied Microbiology 2002; 93 (1): 157–62.  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Topping DL & Clifton PM. Short-chain fatty acids and human colonic function: roles of resistant starch and nonstarch polysaccharides. Physiological Reviews 2001; 81 (3): 1031–64.  Young GP & Le Leu RK. Resistant starch and colorectal neoplasia. Journal of the Association of Official Analytical Chemists International 2004; 87 (3): 775–86.  Young GP & Le Leu RK. Resistant starch and colorectal neoplasia. Journal of the Association of Official Analytical Chemists International 2004; 87 (3): 775–86.  Haenen D, Zhang J, da Silva CS, Bosch G, van der Meer IM, van Arkel J, van den Borne JJ, Gutiérrez OP, Smidt H, Kemp B, Müller M: A diet high in resistant starch modulates microbiota composition, SCFA concentrations, and gene expression in pig intestine. J Nutr 2013;143:274-283.  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Roeselers G, Ponomarenko M, Lukovac S, Wortelboer HM: Ex vivo systems to study host–microbiota interactions in the gastrointestinal tract. Best Pract Res Clin Gastroenterol 2013;27:101-113.  Flint HJ, Scott KP, Duncan SH, Louis P, Forano E: Microbial degradation of complex carbohydrates in the gut. Gut microbes 2012;3:289-306.  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Venkataraman A, Sieber JR, Schmidt AW, Waldron C, Theis KR, Schmidt TM: Variable responses of human microbiomes to dietary supplementation with resistant starch. Microbiome 2016;4:33.  Venkataraman A, Sieber JR, Schmidt AW, Waldron C, Theis KR, Schmidt TM: Variable responses of human microbiomes to dietary supplementation with resistant starch. Microbiome 2016;4:33.  Lange K, Hugenholtz F, Jonathan MC, Schols HA, Kleerebezem M, Smidt H, Müller M, Hooiveld GJ: Comparison of the effects of five dietary fibers on mucosal transcriptional profiles, and luminal microbiota composition and SCFA concentrations in murine colon. Mol Nutr Food Res 2015;59:1590-1602.  Nilsson AC, Johansson-Boll EV, Björck IM: Increased gut hormones and insulin sensitivity index following a 3-d intervention with a barley kernel-based product: a randomised cross-over study in healthy middleaged subjects. Br J Nutr 2015;114:899-907.  Haenen D, Zhang J, da Silva CS, Bosch G, van der Meer IM, van Arkel J, van den Borne JJ, Gutiérrez OP, Smidt H, Kemp B, Müller M: A diet high in resistant starch modulates microbiota composition, SCFA concentrations, and gene expression in pig intestine. J Nutr 2013;143:274-283  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Valcheva R, Hotte N, Gillevet P, Sikaroodi M, Thiessen A, Madsen KL: Soluble Dextrin Fibers Alter the Intestinal Microbiota and Reduce Proinflammatory Cytokine Secretion in Male IL-10–Deficient Mice. J Nutr 2015;145:2060-2066.  Martinez I et al. Resistant starch types 2 & 4 have different effects on the composition of the fecal microbiota in human subjects. PLoSOne 2010, 5(11):e15056.  Flint HJ, Duncan SH, Scott KP, Louis P. Interactions and competition within the microbial community of the human colon: links between diet and health. Environ Microbiol 2007; 9: 1101–1111.  Scheppach W, Sommer H, Kirchner T, Paganelli GM, Bartram P, et al. Effect of butyrate enemas on the colonic mucosa in distal ulcerative colitis. Gastroenterology 1992; 103: 51–56.  Turnbaugh PJ, Ley RE, Mahowald MA, Magrini V, Mardis ER, et al. An obesity-associated gut microbiome with increased capacity for energy harvest. Nature 2006; 444: 1027–1031  Cani PD, Delzenne NM. Interplay between obesity and associated metabolic disorders: new insights into the gut microbiota. Curr Opin Pharmacol 2009; 9: 737–743  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Champ MJ. Physiological aspects of resistant starch and in vivo measurements. Journal of the Association of Official Analytical Chemists International 2004; 87 (3): 749–55.  Hira T, Ikee A, Kishimoto Y, Kanahori S, Hara H: Resistant maltodextrin promotes fasting glucagon-like peptide-1 secretion and production together with glucose tolerance in rats. Br J Nutr 2015;114:34-42.  Jenkins DJ, Kendal CW, Augustin LS et al. High-complex carbohydrate or lente carbohydrate foods? American Journal of Medicine 2002; 113: 30S–37S.  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Bassaganya-Riera J, DiGuardo M, Viladomiu M, de Horna A, Sanchez S, Einerhand AW, Sanders L, Hontecillas R: Soluble fibers and resistant starch ameliorate disease activity in interleukin-10–deficient mice with inflammatory bowel disease. J Nutr 2011;141:1318-1325.  Hartog A, Belle FN, Bastiaans J, de Graaff P, Garssen J, Harthoorn LF, Vos AP: A potential role for regulatory T-cells in the amelioration of DSS induced colitis by dietary non-digestible polysaccharides. J Nutr Biochem 2015;26:227-233.  Hira T, Ikee A, Kishimoto Y, Kanahori S, Hara H: Resistant maltodextrin promotes fasting glucagon-like peptide-1 secretion and production together with glucose tolerance in rats. Br J Nutr 2015;114:34-42.  Zhou J, Martin RJ, Raggio AM, Shen L, McCutcheon K, Keenan MJ: The importance of GLP‐1 and PYY in resistant starch’s effect on body fat in mice. Mol Nutr Food Res 2015;59:1000-1003.  Vidrine K, Ye J, Martin RJ, McCutcheon KL, Raggio AM, Pelkman C, Durham HA, Zhou J, Senevirathne RN, Williams C, Greenway F: Resistant starch from high amylose maize (HAM‐RS2) and Dietary butyrate reduce abdominal fat by a different apparent mechanism. Obesity 2014;22:344-348  Zhou J, Martin RJ, Tulley RT, Raggio AM, McCutcheon KL, Shen L, Danna SC, Tripathy S, Hegsted M, Keenan MJ: Dietary resistant starch upregulates total GLP-1 and PYY in a sustained day-long manner through fermentation in rodents. Am J Physiol Endocrinol Metab 2008;295:E1160-1166.  Yang X et al: Resistant starch regulates gut microbiota: structure, biochemistry and cell signaling. Cellular Physiology & Biochemistry 2017; 42: 306-318.  Goldring JM. Resistant starch: safe intakes and legal status. Journal of the Association of Official Analytical Chemists International 2004; 87 (3): 733–9  Ferguson LR, Zhu S & Kestell P. Contrasting effects of nonstarch polysaccharide and resistant starch-based diets on the disposition and excretion of the food carcinogen, 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), in a rat model. Food Chemistry and Toxicology 2003; 41: 785–92.  https://www.gov.uk/government/publications/nutrition-and-health-claims-guidance-to-compliance-with-regulation-ec-1924-2006-on-nutrition-and-health-claims-made-on-foods. [Accessed 30.07.17].  http://www.ibscentre.co.uk/aboutibs.html. [Accessed 01.01.17].  Macho G A. Baboon feeding ecology informs the dietary niche of paranthropus boisei. PLoS One 2014, https://doi.org/10/1371/journal.prone0084942.  www.drhardick.com. Tigernuts: respectworthy tuber or another food fad? [Accessed 01.01.17].  FSA (2013). Food allergy & intolerances. An overview. www.food.gov.uk. [Accessed 01.08.17].  www.drhardick.com. Tigernuts: respectworthy tuber or another food fad? [Accessed 01.01.17].  www.drhardick.com. Tigernuts: respectworthy tuber or another food fad? [Accessed 01.01.17].  http://www.ibscentre.co.uk/aboutibs.html. [Accessed 01.01.17].  www.drhardick.com/tigernuts-tuber-or-food-fad. [Accessed 30.07.17].  Sanchez-Zapata E et al. Tiger Nut (Cyperus esculentus) Commercialisation: Health aspects, composition, properties and food applications. Comprehensive Reviews in Food Science & Food Safety 2012; DOI: 10.111/j.1541-4337.2012.00190.x  www.tigernuts.com. [Accessed 30.07.17].  https;//freetheanimal.com/2014/01/tigernuts-tuber-tubery.html.  Soriano del Castillo, J M (2014). Docton en Farmacia and Prof. Nutrition y Bromatologia, Universitat doe Valencia.  Sajilata, M. G., Singhal, R. S., & Kulkarni, P. R. Resistant starch – A review. Comprehensive reviews in Food Science and Food Safety, 2006; 5, 1–17.  Basu A et al. Dietary factors that promote or retard inflammation. Arteriosclerosis, Thrombosis & Vascular Biology 2006; 26:995-1001.  Schroder H et al. Adherence to the traditional Mediterranean diet is inversely associated with body mass index and obesity in a Spanish population. J Nutr 2004; 134(12):3355-61.  Scalbert A & Williamson G. Dietary intake and bioavailability of polyphenols. J Nutr 2000; 130(8):20735-20855.  Cortés, C., Esteve, M.J., Frígola, A. and Torregrosa, F. Physical and chemical properties of different commercially available types of horchata de chufa. Ital J Food Sci 2004; 16, 113–121.  Salem, M.L., Zommara, M. and Imaizumi, K. Dietary supplementation with Cyperus esculentus L (tiger nut) tubers attenuated atherosclerotic lesion in apolipoprotein E knockout mouse associated with inhibition of inflammatory cell responses. Am J Immuno 2005;l 1, 60–67.  Cortés, C., Esteve, M.J., Frígola, A. and Torregrosa, F. Physical and chemical properties of different commercially available types of horchata de chufa. Ital J Food 2004; Sci 16, 113–121.  Sanchez-Zapeta E et al. Preparation of dietary fibre powder from tiger nut (Cyperus esculentus) milk (“Horchata”) byproducts and its physiological chemical properties. J AGric Food Chem 2009, 57(17): 7719-25.