| Objects:This study aims to find out molecular mechanisms of how resistant starch (RS) controls weight, to determine the path by which RS plays its role, and to discover the target on which RS acts, thereby providing a scientific basis for developing RS foods.Methods:70Sprague Dawley rats (weighted100±10g) were selected as subjects and divided randomly into7groups each of which consists of5male and5female rats. One of the groups was selected as control group, and rats in this group were fed with normal foods. Rats in the other6groups were fed with high-fat foods for7weeks. The rats whose weights increased and were equal to or greater than the sum of the average weight of the rats in the control group and1.4times the standard deviation were referred to as "diet-induced obese (DIO) rats"; those rats whose weights increased but were equal to or less than the sum of the average weight of the rats in the control group and the standard deviation and whose total energy intakes were greater than that of the rats in the control group were referred to as "diet-induced obesity resistant (DIO-R) rats". The DIO rats were divided into five groups. One group was fed with high-fat foods, and other groups were fed respectively with high-fat foods that contain5%RS,10%RS,15%RS, and10%RS plus butyric acid as inhibitor for5weeks. Then, levels of short-chain fatty acids (including acetic acid, propionic acid and butyric acid) in the blood of those DIO rats, changes of their intestine areas, and changes of pH values of their intestine contents were detected. Also, influences of RS on the expressions of the uncoupling protein2(UCP2) gene were measured with the use of polymerase chain reaction (PCR).Results:1. Establishment of animal models:After being fed with high-fat foods for7weeks,45rats of the same weight at the initial stage were found to have weights greater than the sum of the average weight of the rats in the control group and1.4times the standard deviation, and7rats were found to have weights less than the sum of the average weight of the rats in the control group and the standard deviation. Compared with the rats in the control group, both the DIO and DIO-R rats showed statistical significance (p<0.01) in terms of weight.2. Impacts of RS on the weights of rats:After the rats were fed respectively with high-fat foods containing5%RS,10%RS and15%RS, for5weeks, their weights decreased. Compared with the high-fat control group, the decrease in weight was statistically significant. Moreover, the amount of the added RS was found to be negatively correlated with the decrease in rat weights, that is, the weights of the rats fed with15%RS-containing food decreased most obviously. The weights of the rats fed with the food containing butyric acid also decreased, but compared with the high-fat control group and the5%RS group, the decrease was not statistically significant.3. The kidney, heart, liver, thymus, spleen and other organs of the rats fed with RS-containing food did not change significantly in comparison with the rats in the high-fat control group and DIO-R group (p>0.05).4. The intestine areas of the rats fed with RS-containing food became larger as the content of RS increased. The increases in caecum areas of the5%RS,10%RS and15%RS groups were18.735±2.884,18.901±3.380, and22.605±6.258, respectively. Among them, the15%RS group was significantly different from the high-fat control group (p<0.05).5. RS can reduce the pH value of contents in caecum:The pH values of the5%RS,10%RS and15%RS groups were6.808±0.124,6.782±0.101, and6.764±0.105, respectively, showing differences of statistical significance. As can be seen, the pH values dropped more remarkably with the content of RS increasing. Addition of butyric acid led to a slight increase in the pH value, i.e.6.923±0.174, which was almost the same as that of the high-fat control group.6. Impacts of RS on short chain fatty acids in the blood: As the amounts of RS in the food increased, the contents of acetic acid, propionic acid and butyric acid in the blood all obviously increased, showing a statistical significance in comparison with the high-fat control group (p<0.01).7. Impacts of RS on the expressions of the UCP2gene: The expressions of the UCP2gene for the5%RS,10%RS and15%RS groups were1.065±0.046,1.088±0.041, and1.094±0.114, respectively. Compared with the high-fat control group, the10%RS and15%RS groups showed statistical significance. This suggested that the expressions of the UCP2gene increased with the amount of RS increasing, and that the expressions were correlated negatively with rat weights (r=-0.514). The addition of butyric acid did not result in obvious differences in the expressions of the UCP2gene, as compared with the high-fat control group.Conclusions:This study showed that RS had some weight loss effect on obese rats. That may be because that RS shortened both the transfer time of foods in the intestines and the residence time of foods and their residues in the guts, and that it reduced energy absorption in the intestines to some extent. RS contributed to increase the amounts of short-chain fatty acids in the blood, which might be relevant to the increase in the expressions of the UCP2gene. The rise of the expressions of the UCP2gene might make energy be released in the form of heat, and thus less energy was stored in the form of fat. The mechanism of RS’s effect on weight loss and its optimum dose needs further research.. |
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