Chinese Intake Of Resistant Starch And Effects Of Resistant Starch On AOM-induced Colorectal Tumorigenesis In Rat

Background:Because of the rapid developing in economy and changing food habits,there was an increasing trend yearly at colorectal cancer(CRC)incidence in our country. It is an effectively preventive method to tumor by ingesting natural food that has anticancer effect.At present,the relationship of resistant starch(RS)and colon cancer is being paid close attention at home and abroad.A number of food,such as cereals,legumes,tubers,green banana have been shown to contain various amounts of RS.The published information on the RS content of Chinese food and the daily intake in Chinese population were less.And there was no reference reported about the effect of resistant starch on colon cancer in animal.Objective:1.To report the RS contents of typical starchy foods used frequently by Chinese population.2.To study the effect of processing to RS content by comparing the results of RS content in raw food materials and cooked food products.3.Based on the RS values measured in the present study and food consumption data obtained from the dietary survey,RS intake(g/per capita/day)was estimated by individual.4.The key sources of RS in Chinese foods were also identified.This will supply the basic science information for the study of dietary guidance and colon cancer prevention.5.To determine the effects of RS at different levels on the carcinogen (azoxymethane,AOM)-induced colonic preneoplastic aberrant crypt foci(ACF) and tumor at different stage(pre-initiation,initiation and promotion stages)of AOM exposion,to observe the regulation function of RS on colonic luminal environment in rats and to analyse its antitumous effect and mechanism of action. The results will supply useful proof for prevention and treatment of colon cancer. It is also significant for guiding Chinese diets and depression the tendency of increasing incidence in CRC and other chronic disease caused by changing food habits in China.6.To study the effect of resistant starch on serum lipids and glucose in normo-glucose and normo-lipid rat.Methods:1.Dietary survey:in order to estimate the daily RS intake in the Chinese population,food consumption data from a dietary survey was used.Population was Choosed randomly from city and country(Shandong,China)by the method of cluster sampling.All subjects were asked to complete an estimated dietary record for 3 consecutive days of food items and liquids each individual consumed.2.Determining of resistant starch:to collect the typical starchy foods(raw material and cooked food)used frequently by Chinese population and to determine RS content of before and after processing by an in vitro method that mimicked gastrointestinal conditions.3.Estimating the Chinese intake of RS:based on the RS values measured in the present study and food consumption data(g/per capita/day)obtained from the dietary survey,RS intake was estimated by individual.The main sources of RS in foods were also explained.RS intake was also divided according to the food from which it originated(i.e.tuber,legume or cereals).In addition,data reported from references were used for estamiting the intake of different area.4.Experiment study in Animal:for inducing colonic tumorigenesis,rats received chemical carcinogen(AOM)injections by intraperitoneal once a week for two consecutive weeks.Rats consumed different doses of RS diets(0%,7.6%,15.2%,22.8%)before,meanwhile and after exposure to AOM,respectively.At 13 weeks after the first injection,part of the rats per group was killed using CO₂ asphyxiation.Colons of rats were removed and the total numbers of ACF as well as the number of crypts per focus were scored using a light microscope at low magnification after staining with 0.5%methylene blue solution.At 32weeks after the first injection,the surplus rats were killed to observe the tumor number,size and distribution in the big bowel and to examine the tumor in histological by staining with H&E.During the experiment,some parameters such as short chain fatty acid(SCFA)concentration in the fecal and cecal content,intestinal transit time,fecal output and pH,fecal bacterial were also determined.In addition, biochemical indicators were analyzed used kits for approaching the effects of RS on blood glucose and serum lipids in normal rats.Results:1.Resistant starch content in food:the contents of RS largely varied with plant source.In general,tubers,tuber vegetables and legumes had more RS than cereals. Among the selected samples of raw material,potato showed high amount of RS. The pure potato starch and cassava starch had the highest RS content.Among the food products,roasted and cooled potato had the highest RS content.The following were sweet potato starch noodle,mung bean starch noodle and Sweet potato starch jelly sheet.The content of RS in cooked foods was lower than raw food material in general.Deep-fried and roasted foods have more RS than general braised foods.Commercially processed starch products were found to have higher RS content compared with general cooked products.2.Chinese intake of resistant starch:the daily RS intake of Shandong population was estimated to be 14.9±9.1g,which were 16.2±8.8g/d in male and 14.2±9.3g/d in female.And the value was 14.1±7.5g/d in population who live in the city and 15.9±10.7g/d in population who live in the country.The range of intake was 2.9g～49.0g/d.Obviously,RS intake varied considerably among individuals.The average intake of Chinese population was 9.0g/d.3.The key RS sources in the Chinese diet:the key RS sources in the Chinese diet are wheat products,rice products and starch products.Other important sources of RS are tubers and legume products,followed by corn products and other cereals, nuts and seeds.Vegetables and banana contribute fewer amounts of RS to the Chinese diet.4.The number of colonic ACF:the number of ACF was fewer in rats fed RS than control and there was a dose-response effect in the promotion group.In initiation group,the number had no significant difference comparing with control fed rats. However,rats fed RS had more ACF than that of the control fed rats in the prevention and a significant dose-response effect was observed between enhancement of ACF formation and dietary RS amount.5.Colon cancer:the colon cancer incidence was 33～100%in rats treated with AOM. It was 100%in control dietary group.The incidence was lower(33～86%)in RS groups and there was statistic significance in promotion groups compared to control group.Average number of tumor per bearing-tumor rat had no difference among groups.The size of tumor was also no significantly different.Comparing with control group,early cancer was more and infiltrating cancer was fewer in the RS treatment rats.6.Body weight alteration of rat:before 13 week,the body weights of rats in RS groups were lower that control and there was a dose-dependent in lower weight and high RS level.After 13 week,the weight had no significant difference between RS groups and control.And the individual variation among group was obviously.7.The fecal excreting habit:Addition of RS to the diet significantly increased fecal output and water content.In the three groups of RS fed rats,further increase in fecal output and water content were seen with the concentration of RS.The intestinal transit time was shortened by addition of RS and high-RS group had a more markedly effect.8.Concentration of SCFA in fecal and cecal content:total SCFA concentration were elevated(p＜0.01)in RS groups in a dose-dependent relationship,especially butyrate.The SCFA concentrations in the cecal contents were approximately twice those of the feces.9.Intestinal tract pH:the addition of RS to the diet significantly decreased fecal and cecal pH and the value were lower in fecal than in cecal content. 10.Feces flora of rats:the numbers of bifidobacteria were more and enterococcus were fewer in RS groups than control.11.Serum lipids and glucose:the values of FBG,TG,TC,LDL-C in RS groups and control had no statistical difference.However,HDL-C level were higher in RS groups than control and high-RS had significant different(p＜0.05).Conclusion:1.This method mimics physiologic conditions preferably adopted by the overseas laboratory widely these days.Not only is it usable for low-content(＜1%)starchy foods but also for high-content starchy foods,with its good recurrence,low price and high analytic efficiency.2.The contents and pattern of resistant starch in different kinds of food were largely varied.Different processing of food material was another important factor influencing the content of RS.The content of RS in cooked foods decreased obviously.Deep-fried and roasted foods have more RS than general braised foods. It could come to the conclusion that rough processing is propitious to retain high amount of RS.In addition,the content of RS increased generally in the cooked food after preservation.3.Findings from this study suggest that the estimated intake of RS by Chinese population is approximately 9.0g/d on average.Comparing with the values reported abroad,the level was higher than American and European but lower than African.It might be a factor that CRC incidence was lower in China than European.The estimate of RS intake provides a valuable reference for researchers and food and nutrition professionals.4.The more intake of carbohydrate,the more amounts of RS.Therefore,it could be suggested that population increase RS intake by ingesting more carbohydrate as foundation.Cereals are the Chinese staple food and the most fundamental source of RS.Tubers are the optimal source of RS.It would be prudent to increase consumption of tubers,legumes and cereal grain products. 5.Rats reacted differently to AOM-induced colonic tumorigenesis when given RS at different stages of AOM exposure.In the promotion group,dietary RS dose-dependently suppresses ACF formation.There was a clear dose response in suppression of ACF formation with increasing levels of RS.It also showed that RS significant reduced the incidence of colon cancer in long-term consumption. In the initiation group,RS did not affect ACF formation at short-term ingesting. However,there was a tendency that RS decreased the cancer incidence by long-term consumption.When the RS diet was administered prior to AOM exposure(the prevention group),the results indicated the RS diets promote the formation of ACF and there was also a dose response in enhancement of ACF and total AC formation with increasing levels of dietary RS.However,it also decreased incidence of cancer by long term consumption.It was hinted by these findings that RS might affect the early events of colonic tumorigenesis and did not affect advancement on happened tumor.And therefore,colon tumorigenesis may be highly sensitive to dietary intervention.Adults who have preneoplastic lesions in their colon may therefore benefit from dietary RS.This suggests the usefulness of RS as a preventive agent for individuals at high risk for colon cancer development.However,adults who are tumor patient would avoid ingesting RS because.its fermentation products not only furnish normal intestinal epithelial cell, but also stimulate growth of tumor cell.6.Dietary RS retarded the body weight gain to rat.Therefore it may be an effective natural approach to the treatment of obesity.7.Dietary RS shorten the GTT and increase the weight of cecal content,fecal output and moisture.These effects on excreting habit might be beneficial for eliminating toxic substrates timely.Dietary RS increase the luminal SCFA concentration, decrease intestinal tract pH.In addition,RS diet increase the number of colonic bifidobacteria and decrease the number of enterococcus.Bifidobacteria are thought to have beneficial effects to the human host.All these findings showed that RS favourably influence the colonic luminal environment8.Dietary RS do not affect the blood serum concentrations of FBG,TC,TG,LDL-C in normal rat,but increase the level of HDL-C.It is hinted that RS might prevent the formation of atherosclerosis and this suggests the usefulness of RS as a preventive agent for coronary artery disease.