THESIS

1.2 Nutritional and health relevance of resistant Starch
Starch is a major dietary component of most diets around the world. Its
digestion and metabolism therefore has physiological ramifications. Disparities in the
prevalence of diseases related to consumption and digestion of complex carbohydrates
such as starch and dietary fiber have been widely described. Epidemiological studies
indicate that diets with slowly digestible, less available starch protect against diseases
such as type 2 diabetes, colorectal cancer and other diet-related chronic diseases.
Differences in levels of starch consumption as well as modes of food processing are
certainly of some significance. Muir et al. (1996) established the relationship between
dietary fiber intake in Japan and occurrence of colon polyps, colon cancer and
diverticulosis, further establishing dietary fiber metabolism in the colon as having a
primary role in disease prevention. The role of resistant starch was highlighted by
observations that fermentation products in the colon surpassed expected amounts from
available dietary fiber, indicating that another significant fermentation substrate was
probably present (Topping and Clifton, 2001). This was established to be resistant
starch.
1.2.1 Resistant starch and colonic function
Resistant starch has been shown to be protective against colorectal
cancer. Ahmed et al. (2000) attributed low rates of colorectal cancer in a black South
African population to high levels of resistant starch in the diet. This population
consumes processed maize products as staples, particularly fermented maize porridge.
Experimental data in human subjects showed that stale maize porridge (high resistant
starch) resulted in higher fermentation in the colon, and subsequently higher levels of
short-chain fatty acids and a significant lowering of stool pH. Short-chain fatty acids
levels were significantly higher in healthy subjects who consumed stale maize
porridge than in subjects who consumed fresh porridge (low resistant starch).
Bingham et al. (2003) reported that in populations with a low to average intake of
dietary fiber (measured as non-starch polysaccharides), doubling of fiber intake could
reduce the risk of colorectal cancer by up to 40%.
7