Atrk
Menu
AAEFX Carbs Users Guide Free Download

Microbial degradation of whole-grain complex carbohydrates and impact on short-chain Fatty acids and health

Wheat

The consumption of whole-grain cereals has been associated with a reduced risk of numerous chronic diseases such as overweight-obesity, type-2 diabetes, and cardiovascular diseases, and some cancers. Last year, researchers from around the world attended the Dietary Whole-Microbiota Interactions: Insights into Mechanisms for Human Health symposium at Experimental Biology 2014 to discuss how whole-grains may influence health through the microbiome. Thankfully, Knud Erik Bach Knudsen from Denmark was kind enough to summarize the discussion for us.

The most notable component of whole-grains is their dietary fiber content. The health benefits of adequate fiber consumption are clear, there is no denying this, and whole-grains contain three primary categories of fibers: nonstarch polysaccharides (NSPs), resistant starch (RS), and oligosaccharides (mostly fructans). The NSPs are those we are most familiar with and are most prevalent in the cereal bran such as arabinoxylans, various glucans including our beloved β-glucan in oats, and cellulose. The starchy endosperm may also contain some fibers, but in a far lesser quantity. The overall amounts and distributions do differ among various grains, and the table below compares three of the most common – wheat, rye, and oats.

  Wheat Rye Oats
  Whole-grain Flour Bran Whole-grain Flour Bran Whole-grain Flour Bran
Starch (g/kg) 696 832 55 658 767 275 612 710 424

NSPs (g/kg)

Fructans

Cellulose

β-glucan

Arabinoxylans

Others

124

9

19

6

71

19

40

6

2

2

21

9

58

17

114

24

337

58

185

31

13

20

96

25

96

23

5

8

43

17

361

40

23

45

216

37

76

1

6

38

21

10

49

1

4

22

14

8

157

2

8

98

36

13

Dietary Fiber (g/kg) 139 40 622 202 98 412 96 56 187

Using individuals who have undergone an ileostomy, it becomes clear that the structure of the starch granule in cereal grains (20–30% amylose content) makes starch relatively easily accessible for digestion in the small intestine when provided as breads or breakfast cereals. Moreover, while fibrous bulk created by the soluble β-glucan and arabinoxylans may delay the digestion and absorption processes and thereby impede starch absorption, quantitatively this impediment is very little (~1.9% after a high-fiber diet). Nonetheless, there is still a significant amount of fiber that obviously cannot be digested by us, per se, and continues towards the large intestine and its bacterial powerhouse. In other words, cereal fibers feed the microbiome without impairing our ability to feed on the starch within the grains.

The primary bacterial phyla within the gut are Firmicutes, Bacteriodetes, and Actinobacteria, with lower amounts of Proteobacteria and Verrucomicroba. However, it should be emphasized that these categories are huge and contain literally countless species of bacteria within each. The microbial breakdown of carbohydrates follows a very hierarchic fashion: sugar residues = oligosaccharides > starch residues > soluble NSPs > insoluble NSPs. This is one reason why those with digestibility problems that allow starch and/or sugars to escape absorption in the small intestine suffer unbearable gas and bloating, because those sugars and starches are preferentially metabolized by the microbiome. Lactose intolerance is a perfect example of this.

The main by-product of bacterial metabolism of fiber that we are interested in is short-chained fatty acids (SCFAs). The cecum and proximal colon are the most active site for fermentation, with acetate accounting for about two-thirds of the SCFAs produced. The numbers of bacteria that produce butyrate are far more limited and actually utilize acetate to make butyrate, but we can increase its production with certain fibers. For instance, an arabinoxylan-rich cereal-based diet was found to stimulate the proliferation of butyrate-producing microorganisms, butyrate production in the large intestine, and the net portal absorption of butyrate to a larger extent than a diet with equal amounts of dietary fiber in the form of RS. Similarly, in patients with ulcerative colitis who daily consumed 60 g oat bran rich in b-glucan, it was found that the fecal butyrate concentration increased significantly, whereas the remaining fecal SCFA concentrations were unchanged.

The production of SCFAs is a central part of the health benefits of fibers. In addition to being an energy source for colonic epithelial cells, butyrate can induce changes in gene expression influencing the colonic function. It has also been recognized that the binding of SCFAs to receptors on colonic cells may be involved in controlling anorectic hormones including peptide YY and glucagon-like peptide 1 (GLP-1), which function to stimulate satiety. In fact, a diet with 10% β-glucan increased total SCFA content in the cecum, suppressed central neuronal activity in the hypothalamic appetite centers, and decreased food intake in mice. Studies in humans have also shown a satiating effect. Finally, SCFAs are signaling molecules between the gut and the rest of the body that may have implications for insulin sensitivity and glucose tolerance.

Bottom line

Cereal grains are a great source of fiber that is known to have health benefits. However, this is not saying that to be healthy the consumption of cereal grains is necessary. If increasing fiber intake is difficult for someone, then whole-grain cereals may be an easy route. Oats and oat bran are a favorite of mine and work for those who are gluten-free as well.

Network Affiliates

Internet-Radio.com
SHOUTcast.com
TrulyHuge.com
FitnessLinkPros.com
WorldFitness.org
CriticalBench.com
LiftForLife.com
LiveLongerLiveStronger.co.uk

Quick Links I

Our Location

SUPER HUMAN RADIO
2908 Brownsboro Rd
Suite 103
Louisville, KY 40206
(502) 690-2200

SHR Newsletter

Subscribe to our FREE newsletter
to receive the latest updates in your inbox!
SHR Newsletter