Читать книгу Whole Grains and Health - Группа авторов - Страница 68

Much about the notion of carbohydrate quality of whole grains is centered on the idea that whole grain foods have a low GI compared to refined grain foods. In this case, low GI is equated with a slow digestion property of starch that moderates and extends glycemic response. Low GI foods (GI<55) are considered to be beneficial to health by preventing or therapeutically addressing obesity and associated metabolic diseases (Ludwig 2002; Livesey 2005; Fabricatore et al. 2011). High GI foods (GI >75), which have been associated with consumption of refined grain products (Ludwig et al. 1999). Thus, whole grain foods with starch of the same chemical structure can generate different nutritional outcomes based on their digestion profile or carbohydrate quality property. A positive correlation between GI and RDS‐derived glucose (Englyst et al. 1999) and a negative correlation between RDS and SDS (Zhang et al. 2008) indicate that SDS is the structural basis for cereal‐based low GI foods. It should be noted that whether there remains a controversy regarding the relationship between GI and health, though a recent international consensus report supports that low GI or glycemic load foods in diets reduce certain chronic metabolic diseases such as diabetes and heart disease (Augustin et al. 2015).

Although SDS is defined by an in vitro starch digestion method (Englyst et al. 1992), studies on raw corn starch, which is a naturally pure source of SDS, showed it to produce a prolonged and sustained low postprandial glycemic and insulinemic responses similar to those of low GI foods (Seal et al. 2003; Wachters‐Hagedoorn et al. 2006). Indeed, the health benefits of SDS are also assumed to be similar to low GI foods (Lehmann and Robin 2007). Literature reports have shown metabolic and physiological effects of SDS consumption. SDS epigenetically caused a shift of the gene expression peak of SGLT1 from the upper jejunum to ileum (Shimada et al. 2009), leading to an increased glucose transporters in the ileum (Woodward et al. 2012), and consumption of SDS in the form of raw normal corn starch resulted in sustained release of incretin hormone of GLP‐1 (Wachters‐Hagedoorn et al. 2006), which is important for body weight regulation and insulin sensitivity (Larsen 2008). Our recent animal study (Hasek et al. 2018) using a slowly digestible starch‐entrapped microsphere that digests starch into the ileum showed reduced food intake behavior and decreased expression of hypothalamic orexigenic neuropeptides NPY and AgRP, which are appetite stimulators. Thus, SDS not only generates a modulated postprandial glycemic response, but also influences a variety of processes that may be important to human health.

The making of efficacious healthy SDS materials requires an understanding of the in vivo process of starch digestion related glycemic response, and also to physiological response. Our group has pursued a path of research relating location of digestion and glucose release in the ileal region of the small intestine to activation of the gut‐brain axis and ileal brake (Hasek et al. 2018; Lee et al. 2013; Romijn et al. 2008). Yet, not all SDS materials necessarily digest into the ileum, and this is also true with digestion of starch in whole grain foods. For instance, using a pig model, normal corn starch, which is a standard SDS material, was nearly all digested in the duodenum and upper jejunum with little measurable amount of starch getting to the ileum (Hasjim et al. 2010). More research needs to be done on the factors that moderate starch digestion in whole grain foods and, in particular, the role of whole grain matrices in digestion.