Abstract
The rising prevalence of obesity, accompanied by increased risk of metabolic syndrome (MetS) is raising a worldwide alarm. One of the major factors is the western lifestyle including an unhealthy diet with high fat and refined carbohydrate contents. Dietary fiber (DF) intake has been proved to have health beneficial properties such as modulating digestion processes, improving microbiota profile, and short chain fatty acid (SCFA) production, which are linked to a lower risk of MetS including cardiovascular disease and type 2 diabetes. Some dietary proteins have insulinotropic effects, especially the abundant branched chain amino acids of whey protein have been shown to be efficient in promoting postprandial insulin and incretin, therefore improving the glycemic and insulin responses.
In this PhD thesis, the effects of dietary strategies based on low or high DF meals rich in arabinoxylan (AX) and low or high protein contents by addition of whey protein hydrolysate on metabolic responses and fermentation profile were studied using an obese Gӧttingen Minipig model. Before the DF and protein intervention, forty-three minipigs were fed a high fat high fructose diet for 20 weeks to induce obesity. After that, the minipigs were assigned to one of four diets for 8-week ad libitum feeding. Metabolic responses of blood and urine samples taken in the fasting and non-fasting states were determined, gene expression of liver, muscle and adipose tissues, carbohydrate, SCFA and microbiota in gut content were analyzed. In another study, the effects of DF ingredients on digestion and fermentation processes as well as SCFA absorption were investigated by feeding a rye bran (RB) diet high in AX to conventional pigs (n = 20) to make a comparison with a refined wheat fiber (Control) diet high in cellulose (n = 10). Half of the pigs fed the RB diets was treated with antibiotics to study if it would modify the effects of the RB diets on macronutrient digestibility, DF degradation, SCFA production and absorption.
The first experiment showed that a high DF content reduced weight gain and improved the C-peptide secretion of obese minipigs in the non-fasting state without alleviating mild tissue inflammation. However, a high dietary protein content increased weight gain, and unfavorably altered metabolic biomarkers and gene expression related to carbohydrate metabolism. AX in the high-DF diets was degraded until the mid colon, stimulated the abundance of butyrogenic genera, slightly increased intestinal butyrate production and circulating butyrate levels. High dietary protein also contributed to intestinal SCFA production, decreased circulating succinate levels, but did not show prebiotic effects, and proteolytic fermentation was attenuated by high DF. Overall, the modulated fermentation profile could be linked with the potential mechanisms of the effects of DF and protein on metabolic responses separately, and a combination of high DF and protein did not have a synergistic effect on
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metabolic health in this study. The second experiment showed that the RB diets slowed down and decreased the protein degradation in the gut. AX in the RB diets was mainly degraded in the cecum and proximal colon, showed higher butyrate production - but not absorption - compared with the Control diet. Cellulose in the Control diet was slowly degraded along the large intestine and increased the production and absorption of total SCFA, acetate and propionate, which influenced the plasma lipid profile. Although the use of antibiotics did not show noticeable change in the degradation process, it led to a reduction in butyrate production. Collectively, the study demonstrated that the intestinal degradation and fermentation patterns were closely associated with the DF ingredients, which resulted in different profiles of SCFA production and absorption.
In conclusion, the results in this PhD study show how DF and protein influence the metabolic responses by associating them with the intestinal degradation and fermentation patterns, and provide a greater understanding regarding the mechanisms of dietary strategies to modulate MetS.
In this PhD thesis, the effects of dietary strategies based on low or high DF meals rich in arabinoxylan (AX) and low or high protein contents by addition of whey protein hydrolysate on metabolic responses and fermentation profile were studied using an obese Gӧttingen Minipig model. Before the DF and protein intervention, forty-three minipigs were fed a high fat high fructose diet for 20 weeks to induce obesity. After that, the minipigs were assigned to one of four diets for 8-week ad libitum feeding. Metabolic responses of blood and urine samples taken in the fasting and non-fasting states were determined, gene expression of liver, muscle and adipose tissues, carbohydrate, SCFA and microbiota in gut content were analyzed. In another study, the effects of DF ingredients on digestion and fermentation processes as well as SCFA absorption were investigated by feeding a rye bran (RB) diet high in AX to conventional pigs (n = 20) to make a comparison with a refined wheat fiber (Control) diet high in cellulose (n = 10). Half of the pigs fed the RB diets was treated with antibiotics to study if it would modify the effects of the RB diets on macronutrient digestibility, DF degradation, SCFA production and absorption.
The first experiment showed that a high DF content reduced weight gain and improved the C-peptide secretion of obese minipigs in the non-fasting state without alleviating mild tissue inflammation. However, a high dietary protein content increased weight gain, and unfavorably altered metabolic biomarkers and gene expression related to carbohydrate metabolism. AX in the high-DF diets was degraded until the mid colon, stimulated the abundance of butyrogenic genera, slightly increased intestinal butyrate production and circulating butyrate levels. High dietary protein also contributed to intestinal SCFA production, decreased circulating succinate levels, but did not show prebiotic effects, and proteolytic fermentation was attenuated by high DF. Overall, the modulated fermentation profile could be linked with the potential mechanisms of the effects of DF and protein on metabolic responses separately, and a combination of high DF and protein did not have a synergistic effect on
IV
metabolic health in this study. The second experiment showed that the RB diets slowed down and decreased the protein degradation in the gut. AX in the RB diets was mainly degraded in the cecum and proximal colon, showed higher butyrate production - but not absorption - compared with the Control diet. Cellulose in the Control diet was slowly degraded along the large intestine and increased the production and absorption of total SCFA, acetate and propionate, which influenced the plasma lipid profile. Although the use of antibiotics did not show noticeable change in the degradation process, it led to a reduction in butyrate production. Collectively, the study demonstrated that the intestinal degradation and fermentation patterns were closely associated with the DF ingredients, which resulted in different profiles of SCFA production and absorption.
In conclusion, the results in this PhD study show how DF and protein influence the metabolic responses by associating them with the intestinal degradation and fermentation patterns, and provide a greater understanding regarding the mechanisms of dietary strategies to modulate MetS.
| Original language | English |
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| Qualification | PhD |
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| Award date | 4 Nov 2020 |
| Place of Publication | Aarhus |
| Publisher | |
| Publication status | Published - 4 Nov 2020 |