Emerging Benefits

There are several areas of benefits that do not yet have sufficient evidence to be established or verified.  It is not a coincidence that these areas are strongly correlated with type 2 diabetes and other aspects of metabolic syndrome. Existing evidence suggests that benefits exist in the following areas:

Kidney Health

Three clinical studies have shown improvements in biomarkers related to inflammation, oxidative stress in individuals with chronic kidney disease. This may occur because the nitrogen-containing compounds are captured by the bacterial mass and excreted through the intestines instead of being disposed through the kidneys. This may not present problems in healthy individuals, but is definitely problematic in individuals with kidney disease.

The first human study (Sirich CJ ASN 2014) suggested that resistant starch assists in reducing the blood levels of p-cresol sulfate and indoxyl sulfate, compounds believed to be toxic in individuals with impaired kidney function. The second human study (Tayebi Khosroshahi HI 2018) found that resistant starch significantly reduced inflammatory and oxidative biomarkers TNF-alpha, interleukin-6 (IL-6), malondialdehyde as well as serum urea and creatinine in hemodialysis patients. The third clinical showed reduced IL-6, thiobarbituric acid reactive substances plasma and indoxyl sulfate in individuals with chronic kidney disease. (Esgalhado FF 2018) Animal studies have also found the similar benefits. (Kiefer FASEB J 2015 and Vaziri PO 2014)

Two studies have shown that high levels of resistant starch protected kidney function and improved Vitamin D metabolism in the kidneys in animal models of type 1 and type 2 diabetes. As a result, circulating levels of serum 25-hydroxycholecalciferol (25-hydroxy Vitamin D) were significantly increased. Koh JN 2014, Smazal JN 2013

Inflammation

Two clinicals have shown reduced inflammation following very high levels of resistant starch consumption.  Animal studies are also beginning to examine the potential for resistant starch to assist in reducing or preventing inflammation through restoration of the gut barrier and other effects of resistant starch’s fermentation.

  • Dr. Stephen O’Keefe’s study included an entire diet swap, so the results cannot be isolated to one dietary component. While resistant starch was a major focus of the study, dietary fat and protein was also reduced in the two week diet swap. O’Keefe NC 2015 found reduced mucosal inflammation in the cells of the colon wall after African-Americans living in Pittsburgh ate a South African diet very high in resistant starch (38 grams/day). Reciprocally, South Africans eating the American diet had increased colonic inflammation after two weeks.
  • Dr. Denise Robertson’s study fed British adults with well-controlled type 2 diabetes high quantities of unmodified RS2 resistant corn starch (40 grams/day) and found a reduction in obesity-associated inflammation independent from any changes in body fat volume. Bodinham EC 2014.

In addition, new animal research from Baylor College of Medicine has shown that resistant starch prevented inflammation-induced hypertension. Their research focused on restoring the gut barrier and preventing bacterial translocation that has been implicated in the progression of this type of hypertension. Resistant starch also prevented loss of goblet cells in the intestinal crypts and TNF-alpha expression in the cecum and increased T-reg cells in the brain by 10-fold. The authors concluded that manipulation of the gut microbiota through prebiotics may serve as a novel therapy in the prevention of hypertension. Durgan H 2017, Durgan FJ 2017

Eye Health

Four animal studies from Allen Taylor and his colleagues at Tufts University compared the effects of resistant starch versus highly digestible starch on eye health in rodent models. They found significantly reduced age-related glycation end-products (AGEs) in the eyes. AGEs are a major biomarker for age-related macular degeneration. The early papers attribute the benefits to reduced glycemic index without seeming to consider the well-established fermentation metabolic effects but the later papers confirmed the importance of intestinal fermentation.  Uchiki AC 2012, Weikel IOVS 2012, Rowan IOVS 2014, Rowan PNAS 2017 and Rowan GM 2018 (review).

Metabolism

One animal study demonstrated that resistant starch changes the expression of more than 200 genes in the large intestine – some genes were up-regulated while others were down-regulated. Keenan JNN 2015  While the function of some of these genes is not known, resistant starch changed the expression of genes involved in digestive health and disease (cell growth, proliferation and differentiation of the gut tissues, and apoptosis), immunity (cytokines and lysosome) as well as overall metabolism (insulin sensitivity, hunger and satiety hormones) in animal as well as human studies. Keenan JNN 2015, Zhou IJBM 2015, Sun FM 2015, Malcomson AJCN 2017, Zybaylov B 2018.  Further work has also demonstrated changes in genes expression in the hypothalmus region of the brain (Shen O 2009), fat tissue (Robertson JCEM 2012), and liver (Kieffer JN 2016).

There is a tremendous amount of research underway in this area.  This demonstrates the potential of nutrigenomics and is very promising.

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