“It’s the healthiest gift you can give your body,” was my grandmother’s
breakfast message about the oatmeal she served me 50 years ago.
She would be amused to know that the last 10 years of medical science have given
proof to her intuition about the value of whole oats. Grandma would also chuckle
that I am still following her breakfast advice with added ingredients like fresh
or frozen berries.
Oatmeal and berries have a health value in common; they are not only nutritious
in multiple ways but are also related as great fiber sources with important
health benefits now recognized by the US Food and Drug Administration, Health
Canada and European Medicines Evaluation Authority.
The FDA lists whole oats, barley and psyllium seed husk as excellent sources of
dietary fiber that can reduce cancer risk via regular dietary intake.
Health Benefits of Fiber in the Diet
Consumed as long as people have eaten plants, dietary fiber has recently come
into the view of governments, nutrition advisory groups and the public as one of
our most important dietary macronutrients.
However, nutritionists have estimated that Canadians and Americans consume less
than 50% of the required daily fiber amount to maintain intestinal health and
its multiple other benefits.
Consistent intake of fiber through foods like whole grains, berries and other
fresh fruit, vegetables, seeds and nuts is now associated with reduced risk of
some of the world’s most prevalent diseases including:
· Several types of cancer
· Type 2 diabetes
· High blood cholesterol
· Cardiovascular disease
· Numerous gastrointestinal disorders (constipation, inflammatory bowel
disease, ulcerative colitis, Crohn’s disease, diverticulitis and colon cancer)
Fiber Health Benefits
Recent medical research has proven several physiological benefits of consuming
fiber, among which are:
Improved absorption of calcium, magnesium, and iron
Reduction of blood cholesterol and triglyceride levels
Stabilization of blood glucose levels after a meal, i.e., a low glycemic index
Maintenance of an optimal intestinal environment
Stimulation of immune responses
Over the past 30 years, government agencies around the world have undertaken
analyses and definitions of fiber to more accurately describe this dietary
nutrient. Among some 32 reports filed, the most universally accepted definition
is one by the American Association of Cereal Chemists. The AACC focused on the
physiological and metabolic significance of fiber, defining it as:
“…[T]he edible parts of plants or similar carbohydrates resistant to digestion
and absorption in the human small intestine with complete or partial
fermentation in the large intestine.”
Recognizing these facts, advisories now exist in several countries for
increasing adult intake of dietary fiber to 30 grams per day, double the current
intake levels. Achieving this goal has been difficult because high-fiber foods
do not always taste good and may lack other qualities needed to attract
Resistant Starch and Fermentation Provide Health Benefits
Let’s review some properties of how our bodies use fiber. “Resistant starch”
(same as “resistant carbohydrates”) is a term sometimes used to refer to fiber
sources resistant to complete digestion in the small intestine. These fiber
sources need to pass through to the large intestine perhaps only attracting
water along the way. In the large intestine they undergo fermentation by the
We should remember that fermentation of fiber is normal and healthy, even if
fiber products sometimes cause minor gastric discomfort when the user has not
previously had sufficient fiber in their diet.
“Fermentation” is one normal biological process many people never consider when
they eat healthy foods like fresh berries or vegetables. Fermentation simply is
the breakdown of soluble, resistant starch comprised mainly of carbohydrate
molecules in the large intestine, yielding gases and further useful chemicals
like short-chain fatty acids. A typical property of soluble fibers is to bind
water forming a viscous gel having numerous health benefits during passage
through the digestive system.
Other dietary fiber sources include polysaccharides (starch or sugar chains of
dozens to many hundreds or thousands of units), oligosaccharides (short-chain
sugars, usually 2-20 units long), monosaccharides, lignins and “insoluble” fiber
sources such as cellulose, plant waxes and collagens. Insoluble fiber sources,
however, do not undergo fermentation, but are nevertheless valuable for their
water-attracting properties that aid bowel regularity.
Some of the soluble fiber sources you may see in public news and a variety of
functional foods are:
o Pectins, a seed-like component common in berries, fruits, legumes
o Cellulose from brans and many vegetables
o Beta-glucans in whole oats and barley
o Plant waxes from many edible species
o Polyfructoses from inulin and oligofructans
o Gums and mucillages from tree exudates, fermentation of corn syrup
(xanthan gum), algae (agar, carageenan) and grain seeds (e.g., psyllium seed
Should fiber be new to your diet, add sources of fiber to your diet gradually
over a month. This will allow your intestinal system to adjust slowly until the
30 grams per day of fiber become your normal intake. Drink plenty of water. If
you have persistent discomfort from using fiber sources, speak with your doctor
or a nutritionist.
Fiber Fermentation and Prebiotic Nutrient Value
The process of intestinal fermentation involves action by natural bacteria,
sometimes called flora, residing in our large intestine (primarily the colon).
These bacteria require soluble fiber as fuel and as sources for fermentation to
produce valuable chemicals and health benefits.
Since the fiber serves as food for the bacteria already in the intestine, this
is called a “prebiotic” nutrient value, meaning that before the bacteria can
serve their main purpose in digestion–producing enzymes that digest food–they
must be fed with a substrate they prefer (i.e. fermentable fibers). The main
intestinal flora are bifidobacteria and lactobacilli that are essential for our
Berry pectins, inulin, psyllium and xanthan gum, all mentioned in the above
list, are sources of soluble fibers that provide this prebiotic function in the
normal fermentation process.
The Rubus berries such as the blackberry (Rubus nigra) and red raspberry (Rubus
idaeus) have the highest density of dietary fiber per gram than any other
published food source.
Fermentation is a metabolic process involving the use of one organic source to
create others, such as enzymes to digest food that then release new elements.
Among products of fermentation are gases (methane, carbon dioxide, hydrogen,
nitrogen) and short-chain fatty acids, which result as new molecules clipped
from the more complex digested fiber and food compounds.
Short-chain fatty acids such as butyric acid, acetic acid, propionic acid and
valeric acid make up about 90% of the total fatty acid yield from fermentation
in the human body. Collectively, these fatty acids have several beneficial
physiological effects in the large intestine worth repeating from above.
Enhance absorption of calcium, magnesium and iron (thus are important to bone
and blood health)
Contribute to lowering blood cholesterol and triglyceride levels
Promote colon health by raising acidity levels that improve nutrient
absorption and lower risk of colon cancer
Act as anti-inflammatory mediators
Stimulate immune protection through an array of intermediate effects within
the intestinal system, including cytokine production
Appear to inhibit appetite, leading to reduced calorie intake and weight gain.
Insoluble fiber sources from plants, such as cellulose, typically undergo no
fermentation so do not contribute new elements. Rather, they bind water
effectively, making them valuable in digestion as stool softening agents with
the essential benefit of promoting bowel regularity.
Including more fiber in your diet is a crucial step towards a healthier
lifestyle. From oatmeal to berries the combination of ways to creatively
include this nutrient are countless. Why wait?
Wong JM, de Souza R, Kendall CW, Emam A, Jenkins DJ. Colonic health:
fermentation and short chain fatty acids. J Clin Gastroenterol. 40:235-43, 2006.
Kendall CW, Emam A, Augustin LS, Jenkins DJ. Resistant starches and
health. J AOAC Int. 87:769-774, 2004.
Tungland BC, Meyer D. Nondigestible oligo- and polysaccharides
(dietary fiber): their physiology and role in human health and food., Compreh
Rev Food Sci Food Safety 1:73-92, 2002.