Since May
1999, the Defining
Dietary Fiber on-line discussion group has served as a public forum for input
on the topic of defining dietary fiber. A number of individuals from academia,
government, and industry have submitted their opinions on the issue. This page
summarizes many of these comments along with responses from select members of
the AACC Committee to Define Dietary Fiber.
In terms of
nutritional/physiological parameters, many new carbohydrates not currently having
fiber labeling status, such as inulin and several naturally based
oligosaccharides, meet the general definition or concept of dietary fiber. They
are remnants of plants, they resist digestion by mammalian digestive enzymes,
reach the bowel intact, are fermented to short chain fatty acids by resident
microflora, and affect both the gastrointestinal tract and its function and
influence host systemic physiology.
While no unequivocal definition of dietary fiber exists internationally, where
national regulations make provision for a definition of dietary fiber, those
definitions usually correspond to one based on non-digestibility (i.e. on a
nutritional criterion). In some countries, additional analytical criteria are
required. The US has an analytical definition for dietary fiber classification
and labeling as defined in 21 CFR A7 101.9 requiring that dietary fiber
components must be analytically measured by FDA approved methods before being
included in the Nutritional Facts label.
Although for the purpose of food policy it may appear on the surface more
practical to apply a simple analytical definition, it is likely not be
satisfactory from a nutritional point of view. Understandably, the dietary
fiber concept and need for an increased consumption of dietary fiber is based
on the healthy effects the various entities making up the concept have on human
physiology, and not because of their analytical or physiochemical properties,
which in part defined their method of determination. Thus, if specific compounds
that represent the dietary fiber concept according to a nutritional definition
are not detected as dietary fiber by current applied fiber methods, other more
specific methods will likely be required for the analysis of such compounds.
Due to the increasing number of naturally-occurring carbohydrates that fit the
nutritional definition of fiber, many of which are not measured adequately in
current fiber methods because of their different physiochemical properties, it
becomes evident that no single analytical method can identify all types of
fiber with sufficient specificity, accuracy and precision. As such, it appears
reasonable to have several methods as standard for the measurement of differing
components of the dietary fiber concept and to further replace or supplement
existing methods by appropriately validated methods, if the new methods provide
closer agreement with the definition of dietary fiber.
Based on the complexity of defining the dietary fiber concept using analytical
terms, a nutritional or physiological definition rather than an analytical
definition would appear much simpler in terms of nutritional labeling,
feasibility for food policy, law enforcement and the possibility to supply
customers with foods that help achieve recommended levels of fiber intake.
Further, as was most evident in the recent article from the New England Journal
of Medicine, the current general definition of dietary fiber lends confusion,
as it provides no differentiation of insoluble, and soluble fiber types
(viscous soluble, non-viscous soluble). As such, misinformation regarding the
health benefits of various dietary fiber components can be the result.
Moreover, the current definition does not differentiate soluble dietary fiber
components of unlike chemical bond or make up and consequently differing
physiological effect and potential health benefit. By example, most viscous
soluble dietary fibers such as xanthan gum, pectin, guar gum (high water
binding carbohydrates) have influence on gastric emptying and have influence on
human metabolism and health, such as blood glucose effects and satiety through
this gut-based effect. In addition, their fermentation varies by chemical bond,
due to the specifics of the gut microflora population and activities of their
various fermentation enzymes. By contrast, several non-viscous carbohydrates,
such as inulin, have little effect on gastric emptying, but rather have
systemic physiological effects through regulation of metabolic pathways through
short chain fatty acids (SCFA) produced from their fermentation. Regarding
soluble fiber components, it is very important to differentiate the chemical
make up of the fiber component as the chemical bond (and the molecular chain
distribution) is critical to the fermentation pattern and ultimately the total
SCFA production and its profile. As the SCFA regulate key physiological
mechanisms differently, such as glycolysis, gluconeogenesis, lipid metabolism,
and mineral absorption, it is important that fermentation substrates be
selective for specific microflora that produce levels of SCFA that can provide
potential for better health, i.e. higher levels of propionate and butyrate
rather than acetate. Acetate being known for its contribution to
gluconeogenesis, while propionate for its positive effects on glycogen
formation, normalizing blood glucose and have effects on reducing cholesterol
formation. In addition, butyrate is utilized primarily as energy for colon
cells and is a strong differentiating agent, having implications for inhibiting
proliferation of colon cancer cells. Several differing soluble fiber components
have been shown in vitro using human fecal material to produce relatively high
propionate levels and moderately butyrate levels (inulin, beta- glucans, high
amylose pea starch), while producing relatively low acetate levels.
Combinations of these soluble fiber components are likely to produce desirable
health effects.
Thus, when defining the dietary fiber concept, it is important to differentiate
or categorize classes of fiber, in addition to specific types of soluble
dietary fiber having specific physiological effect.
Often a low cost insoluble dietary fiber component is used in a formulation to
increase the fiber label and marketing position of a food or nutritional
product. This practice undereducates, misinforms and misleads the consumer as
to the true health benefits of the active nutritional components they are
consuming. This practice is made possible by design of the current dietary
fiber definition.
Scientific definition and regulations need to be more specific and more fully
clarify the use of specific dietary components for health, i.e. insoluble fiber
(roughage), viscous soluble and non-viscous soluble each combined with a
specific chemical linkage and general physiological effect.
Mr. Bryan C. Tungland
Vice President, Scientific and Regulatory Affairs
Imperial Suiker Unie, LLC
Sugar Land, Texas
Committee Responses:
Inulin and some of the oligosaccharides appear to
have physiological impact, thus: 1.) Existing TDF methods should be modified to
include these components or 2.) New methods can be added to the TDF
procedure…maybe complete dietary fiber? However, I take issue with the concept
that low-cost IDF is not advantageous in food products. IDF increases stool
weight, etc. Less-refined materials such as brans and peels that are
essentially food processing by-products may contain important associated
compounds that act synergistically with fiber constituents to improve human
health. Fiber has multiple benefits and thus multiple sources of fiber are
useful to include in the diet. – Mary
Ellen Camire
Overall, a useful contribution highlighting inulin’s place in the dietary fiber
debate. – Stuart Craig
The statement “No single analytical method can identify all types of fiber with
sufficient specificity, accuracy, and precision” translates into “It’s unlikely
that a universal method can be developed for the determination of all types of
fiber.” This is not unique for fiber analysis. Nutritional and physiological
definition of dietary fiber have been based on epidemiological studies on foods
(fruits and vegetables), yet most of the animal or human studies employed
purified fiber sources, such as pectin, guar, cellulose, wheat bran, etc.
Differentiation of insoluble and soluble fiber types must depend on analytical
(specifically physicochemical) definition. Currently, the designation is
strictly method dependent. When the day comes that sequencing of
polysaccharides is as routine as for purified proteins, we should be able to
answer the questions regarding the true chemical makeup of the fiber components
as based on their chemical bonds. – Betty Li
I think the definition can be expanded beyond just
the physiological parameter of non-digestibility, but this could be
accomplished in a companion document to a simple definition or statement. This
companion document should offer a great deal of additional information. A
method or methods should not be the deciding factor in having a definition of
dietary fiber or limit the food components, which should be included as dietary
fiber. Additional methods should be available to recover and quantitate oligo-,
di- and mono-saccharides, which are non-digested and non-absorbed. It remains
to be decided how small an oligosaccharide (DP less than?) should be considered
a source of dietary fiber. At the present time, I favor including compounds
with DP values of three (3) and higher.
Based on the complexity of proposed dietary fiber components, there
appears to be more than one category for non-digestible and non-absorbable
carbohydrates in foods. There are dietary fiber components derived from plant
cells, those that are derived from plant cells but not recovered by current
methods for DF analysis, and those manufactured or isolated as
(poly)saccharides", "carbohydrate analogues", "dietary
fiber analogues" or "bulking agents". These many food
carbohydrates, non-digestible and non-absorbable, need to be adequately
described, and possibly in the accompanying document. For some of these
carbohydrates, additional verification of their physiological effect(s) will
explain why these compounds should be defined as dietary fiber. Does everyone
agree we have sufficient information to suggest a change in colon pH, an
accumulation of SCFA, and changes in intestinal microflora are advantageous and
benefit long term health? The current discussions on a definition of dietary
fiber will help review the available information on these important topics and
effects of dietary fiber. Do terms such as "laxation", "soluble
dietary fiber", "insoluble dietary fiber" and
"oligosaccharides" need to be included in the definition? Is the term
"health" or some variation of this term, such as "disease
prevention" implied in the definition of dietary fiber or should it be
clearly stated in any definition? - Dennis
Gordon
I
have a simplistic way of looking at fiber: any plant carbohydrate material (or
its equivalent) that cannot be converted into calories through digestion and
absorption. If oligosaccharides are absorbed and converted into calories, they
would be excluded by this definition, which can be summarized as
"calorically inert."
Marion Nestle
Department of Nutrition and Food Studies
New York University
Committee Responses:
Bacteria partly or completely hydrolize polysaccharides, yielding fatty acids
that provide some energy, thus these compounds are not really calorically
inert. Lignin is important – why exclude it? – Mary Ellen Camire
We must move beyond the “inert” concept towards physiological benefits. – Stuart Craig
This definition will exclude virtually all types of fiber except cellulose or
whatever can be recovered in the feces. – Betty
Li
I agree with Mary Ellen Camire that all dietary
fiber is fermented to some degree in the large intestine. (There are a few
exceptions.) There is a very good debate currently in progress as to the amount
of energy liberated through the fermentation of non-digestible and
non-absorbable carbohydrates. The debate centers on how much net metabolizable
energy (NME) is contributed to the host. This is an important topic for research
now and in the future. The fact any of these carbohydrates, including those
currently considered dietary fiber are fermented with energy loss through other
pathways or retained as NME may be the one criterion for including them as a
source of dietary fiber. Their fermentation leads to biochemical changes caused
by the bacteria in the intestine and subsequent physiological function(s). Are
these biochemical and physiological changes beneficial? – Dennis Gordon
Being familiar with the cell wall components from first hand experience, I feel
comfortable with the current definition of dietary fiber. Adding other
components would seriously dilute the meaning. Whatever is added is already
covered under "Additives" and I feel that it should remain there.
This includes synthetic polymers. Inclusion of oligosaccharides in the
definition would defeat the purpose. After all, these are mostly soluble, and
don't fit the definition of fiber. Fiber, from definition, means a long chain
or strand, for which the term 'oligo' does not qualify. If it would be long, it
would be 'poly'.
Geza Hrazdina
Professor of Biochemistry
Department of Food Science and Technology
Geneva, N.Y
Committee Responses:
This argument reminds me of the line from Romeo
and Juliet: “A rose by any other name….” Since the interest in fiber
derives from its health benefits, these properties should be included in the
definition. – Mary Ellen Camire
Nicely put, Mary Ellen. This comment captures the “traditionalist” view, which
requires serious debate over the next months. – Stuart Craig
This brings us to the question as to whether sugar alcohols, raffinose,
stachyose, etc. should be included in the fiber definition, as others have
suggested later on. – Betty Li
Why does dietary fiber only have to be a long chain
carbohydrate having a DP value of 10 or more? Many oligosaccharides may be
proven to be beneficial to the host. There is accumulating evidence that
oligosaccharides (DP < 10) are beneficial. See my earlier comment to B.
Tunglund. Exclusion of oligosaccharides because they cannot be recovered by a
current method of analysis should not be a reason for excluding them as a
source of dietary fiber. Again I agree with Mary Ellen Camire, the body will
recognize an oligosaccharide in nature the same as if it was synthesized in the
laboratory or produced through genetic engineering. I think we are all
interested in the "associated substances'" which are consumed along
with plant foods whether they provide polysaccharides or oligosaccharides.
Although there is accumulating evidence for many of the "associated
substances" in plant foods as to their importance to human health and
disease, we are discussing a definition of dietary fiber. Other definitions may
be needed for "associated substances". Yes, I acknowledge that it may
be the combination of dietary fiber and "associated substances" in
plant foods, which may be most effective in promoting health and preventing
disease. However, dietary fiber can stand-alone based on its physiological
importance to the body, thus a definition for dietary fiber would be helpful. –
Dennis Gordon
I believe that for the uses identified, the rather "classic"
definition will suffice. I feel that the issues surrounding resistant starch,
various oligosaccharides, etc cannot be resolved at this stage and can/should
be dealt with separately. Sometime in the future we may be able to add/include
additional compounds to the dietary fiber or "oligosaccharide" list.
Persons/manufacturers may still be able to identify the compounds included in
foods/supplements even if not "covered" in the definition.
Peter L. Beyer MS, RD
Associate Professor,
Dietetics and Nutrition,
University of Kansas Medical Center
Kansas City, Kansas
Committee Responses:
This comment does not explain how consumers will know that the compounds not
recovered in the AOAC TDF procedure behave in the body as fiber. – Mary Ellen Camire
Communication of the scientific evidence of physiological benefits is the best counter to this “do it later” argument. – Stuart Craig
The issues surrounding resistant starch, various oligosaccharides and others
are part of the objectives for a reexamination of the current definition(s) for
dietary fiber. Whether the issues can be resolved remains to be seen as we
consider all the comments received from individuals and open discussions at
various workshops, forums, and symposia planned for the remainder of 1999. – Betty Li
There may have to be more than one chemical
description of dietary fiber components as part of a new definition. How do we
both regulate and allow progress in the form of new "carbohydrate
analogues" or "dietary fiber analogues" into the food chain and
possibly onto the food label? There is an interesting precedent with the
approval and use of non-digestible and non-absorbable fat substitutes into the
food supply. Although they are fats, they are not included as part of the fat
content of a food on its Nutrition Facts panel. Added to this list of fat
substitutes in our diet are sterols added to margarine's to block the
absorption of dietary cholesterol. We have the opposite situation with some
carbohydrates proposed as dietary fiber. Can labeling allowances be made for
oligosaccharides, or "carbohydrates analogues" or "dietary fiber
analogues" or "bulking agents" especially if they are shown to
have positive physiological effects? How do we make allowances in the definition
of dietary fiber to be honest with the consumer, scientific community and
ourselves? – Dennis Gordon
Because of my educational background, research interests, and a certain
perspective on how fiber should be defined, I am quite comfortable accepting
FDA's/USDA's definition of dietary fiber as it stands now. As some synthetics
are also finding use in processed foods, it may be appropriate to broaden this
definition to include synthetics.
Gur Ranhotra, Ph.D.
Director, Nutrition Research
American Institute of Baking
and Adjunct Professor, Kansas State University
Committee Responses:
I agree with the inclusion of synthetic, but am curious about FDA/USDA
definition (??) – Mary Ellen Camire
“Synthetics” should have human clinical data to substantiate physiological benefits. Otherwise, we lose credibility. – Stuart Craig
We need guidance as to how we could broaden the
current definition to include “synthetics” and avoid the danger of including,
nondiscriminately, any food components which reach the colon. – Betty Li
There is no FDA/USDA definition of dietary fiber.
Current FDA rules, appearing in the CFR, pertain to what is measured and
reported on the Nutrition Facts panel. The FDA in their rules on health claims
refers to dietary fiber provided by whole cereals/grains, fruits and
vegetables. In making laws to incorporate the amount of dietary fiber on the food
label, the results obtained by approved AOAC methods has become the de facto
definition of dietary fiber in the United States. This dietary fiber is the
residue resulting after a food is treated with three hydrolytic enzymes, plus
the material precipitated in 70% ethanol. The project of evaluating the
historical definition and proposing a new definition for dietary fiber can be
forwarded to the FDA for their possible consideration. One of the big issues
today is that certain manufactures of "carbohydrate analogues",
"dietary fiber analogues", "(poly)saccharides" or
"bulking agents" would like their compound(s) classified as dietary
fiber. Instead of addressing the issue one carbohydrate at a time, this project
to review the definition of dietary fiber will help bring many similar
questions together which may have a common answer. – Dennis Gordon
I strongly believe that the definition of dietary fiber should not change to
reflect the changes in the diet because there are several compounds of high
molecular weight that resist the digestion by digestive enzymes of the human
digestive tract these compounds are produced through food processing or food
preparation or adding the compounds to perform certain function. I'll try to
give examples:
1.
Polydextrose
(cyclic)
2.
Fat
substitutes, olestra
3.
Scorched
or burnt food such as those resulted during barbecue fried breaded products
etc.
4.
Polymerized
fatty aldehydes which are produced as a result of breakdown of oxidized fat
5.
Polysorbates
which are used as emulsifiers or surfactants
6.
Cartilages
and hair etc. I hope these examples will help you not to change the definition.
Sami
M. Al-Hasani, Ph.D.
ConAgra Frozen Foods Analytical Laboratory
Columbia, Missouri
Committee Responses:
Actually, these examples had the opposite effect on me. Perhaps bacteria cannot
digest Olestra, but what shall we do with undigested fat that ends up in the
colon because the person has taken a chitosan supplement or the new
fat-absorbing drug Xenical? The lipid will surely nourish some bacteria. Do we
have any info on the utilization of lipids in the colon? – Mary Ellen Camire
Deeper into “Pandora’s Box”. – Stuart
Craig
These are diet constituents we need to give some serious considerations during
our discussion on defining dietary fiber. – Betty
Li
There are many non-digestible and non-absorbable
polymers-compounds in our food supply, albeit in small amounts, which are not
dietary fiber. These compounds should not be included as DF and for the most
part they are excluded. An analytical correction is made to exclude
nitrogen-containing compounds in most AOAC methods to measure dietary fiber. I
agree polyols and polysorbates should not be included in the definition of
dietary fiber. Resistant starch was found to be an artifact in the analysis of
dietary fiber. Now resistant starch is commercially produced and added to foods
as a source of dietary fiber and to lower its calorie content. Will the same
happen with Maillard products in the future? I hope not. Many compounds will
have to be individually reviewed to be included as a source of dietary fiber.
MEC mentions an interesting compound chitosan derived from chitin. Are these
two polymers dietary fiber? Issues raised by Al-Hasani need to be resolved. – Dennis Gordon
Although
there is no universal consensus on the definition of dietary fiber, the results
of the international survey by Prosky and Lee JAOAC, 78(1), 22-35(1995)) showed
that most respondents favored a definition based on both physiological and
chemical attributes, as opposed to the idea of fiber being the sum of remnants
of plant components resistant to digestive enzymes. However, there was no
discussion in the survey of either synthetic oligo- or polysaccharides being
incorporated into the definition of fiber. If synthetic oligosaccharides are to
considered as dietary fiber, then what is the molecular weight cut-off going to
be? n3D5, 10, 15, etc.? Since most components of fiber are polymers of high
molecular weight, I think it is questionable to include a synthetic component
of low molecular weight as dietary fiber, especially if it doesn't precipitate
under conditions of existing methods, i.e. 75% alcohol. The definition of
dietary fiber needs to be based on scientific analysis and consensus, not on
marketing concepts.
Bob Sapp
ConAgra Frozen Foods Analytical Laboratory
Columbia, Missouri
Committee Responses:
Good points. I think we selected DP3D10 as a cutoff. – Mary Ellen Camire
I have a problem with DP 10 as a cutoff. It’s just as arbitrary as 80% ethanol,
and analytically very difficult. FDA has an issue with low DP, but especially
mono- and disaccharide. These can be more easily quantified. So, is DP3 a more
reasonable cutoff? – Stuart Craig
As we know, the distinction between oligo- and polysaccharides is rather
arbitrary. The International Union of Pure and Applied Chemistry assigns
oligosaccharides to be DP3-DP9, and polysaccharides to be > 10. It is not
based on any specific physicochemical characteristics. – Betty Li
The latest definition agreed upon at the recent
AACC/ILSI workshop, June 2-3, includes the term (poly)saccharides. I think the
intent of this term was to include saccharide polymers above a DP-10 value
(poly), and to oligosaccharides below DP-10. There was no consensus as how low
a DP number should be included as a source of dietary fiber. This must be
resolved. Future discussions should provide an explanation or justification as
to what is included and excluded from any new definition. I initially agree
with SASC that a DP value of 3 could be a cut-off. Again, any method that
incorporates an arbitrary inclusion limit by precipitation in 70% ethanol
should not be a criterion in defining dietary fiber. If we consume FOS
naturally occurring in foods, our body physiologically considers this a form of
dietary fiber although it was not recovered in the AOAC assay. – Dennis Gordon
As we
walk the fine line of pharmaceutical (drug) ADA nutraceutical, functional food,
suplements, etc., it may behoove us to use the same "template" as
that of pharmacopoeia, i.e. structure-function to define those fibers (natural
and synthetic) that are resistant first to alimentary human enzymes
(non-digestible and/or non- absorbable) and secondly (and separately) to
fermentation while defining the microflora of relevance.
Robert Serrano
Grain Millers, Inc.
VP-Technical Operations
Eugene, Oregon
Committee Responses:
Good point. – Mary Ellen Camire
This gets us toward defining scientific criteria. – Stuart Craig
Drugs are well characterized compounds, whose structure-function can be tested.
No matter how we eventually define dietary fiber, it will remain a complex
entity. – Betty Li
I agree with the comments of Mary Ellen Camire and
Stuart Craig. Expanded comments like this should be included in the collateral
document to accompany a simple and useful definition. – Dennis Gordon
I have been doing some work with inulin, which some people would like to see
listed as a dietary fiber. Since it is not digested by enzymes but is fermented
it is difficult to find a place for it on a label. I think Canada may list it
as a fiber. It would be good to be consistent. In Europe inulin is used in more
products and there is a lot of interest here too. Nebraska is growing some
chicory and looking at it as a crop to rotate with sugar beets.
Marilynn Schnepf
University of Nebraska
Lincoln,
Nebraska
Committee Responses:
I agree that harmonization with Canada is important and that inulin has
benefits. – Mary Ellen Camire
Ditto. – Stuart Craig
This calls our attention to the question: Are we seeking a definition for
dietary fiber mainly for nutritional labeling, for diet/health relationship,
for nutritional research purposes, or for all of the above? – Betty Li
Yes, any definition agreed upon in the United States
must consider trade among all countries. Canada does have guidelines on novel
sources of dietary fiber. These guidelines can be found at this website.
The Canadian definition of dietary fiber, not included in their Food
Directorate's guidelines on novel dietary fiber is provided. This definition
was approved in the 1985 report of their Expert Advisory Committee on Dietary
Fibre. The Canadian definition of dietary fiber is: "Endogenous components
of plant material in the diet which are resistant to digestion by enzymes
produced by man. They are predominantly nonstarch polysaccharides and lignin
and may include, in addition, associated substances". – Dennis Gordon
Principles to use in defining dietary fiber:
1.
Dietary
fiber is a marker for plant foods in the diet.
2.
Dietary
fiber is chemically complex and hence the methods for are not digested by
enzymes of the mammalian small intestine.
3.
The
physical characteristics of dietary fiber components vary.
4.
The
term dietary fiber, in contrast to specific chemical composition, encompasses a
physiologic definition of fiber.
Primary characteristics of
dietary fiber:
1.
Predominately
of plant origin
2.
The
primary components are nonstarch polysaccharides and oligosaccharides. Polymers
that cannot be digested by enzymes from the mammalian small intestine
Issues that influence the
definition of dietary fiber:
1.
Analytical
methods are likely to include some additional non-digestible materials
such as lignan and Maillard reaction products. Although these compounds are not
categorized as carbohydrate, they are a part of the non-digested material in
the gut.
2.
Oligosaccharides
and resistant starch are carbohydrates, they are not digested in the small
intestine, and function like nonstarch polysaccharides as fermentable
carbohydrates. In this context they should be included in dietary fiber.
3.
Dietary
fiber is a generic term that encompasses the physiologic characteristics
of this food component. Alternatively this food component can be defined based
on chemical components (e.g. NSP, oligosaccharides, cellulose, resistant starch
etc.). In a sense this is analogous to considering chemical composition vs.
bioavailable nutrient (e.g. digestibility of proteins vs. N content,
equivalents for vitamins vs. isomers) both approaches are useful from a
nutrition perspective and not mutually exclusive.
4.
Sources
of fiber can be characterized according to physical characteristics such as
water holding capacity, viscosity, fermentability, and binding capacity.
Defined conditions are needed for determining these characteristics of
fiber.
Barbara
O. Schneeman, Ph.D.
College of Agricultural and Environmental Sciences
University of California at Davis
Committee Responses:
Excellent. – Mary Ellen Camire
Ditto. – Stuart Craig
This is a comprehensive listing of all the characteristics and issues concerning
dietary fiber. We should examine all the points thoroughly. – Betty Li
I would first agree that dietary fiber should be
restricted to carbohydrates, non-digested and non-absorbable. There are so many
different physiological functions associated with dietary fiber. Which are the
most important and should be stated or implied in a definition? How important
is fermentation in the definition of dietary fiber? Some people would like to
include the term "fermentation" in the definition. These comments
again suggest the need for a collateral document to expand in detail and list
categories of compounds to be included as dietary fiber. The term
"non-starch polysaccharides" is an appealing term to be used with the
definition of dietary fiber. This term is used in the United Kingdom and Canada
in their definitions of dietary fiber. If this term were used, it would imply
that any type of resistant starch or oligosaccharides should not be included in
the definition. – Dennis Gordon
Perhaps this is an opportunity to mesh chemical composition, analytical needs
and physiological function, and distinguish the various carbohydrates.
Undigestible, naturally occurring disaccharides (i.e. lactose),
oligosaccharides (stachyose, raffinose), and sugar alcohols (sorbitol,
mannitol), among others, elicit physiological responses that have been
inadequately recognized. Data on effects and functions of the different classes
of carbohydrates have accumulated over the past 25 years, and analytical
methodology for their analysis has continued to improve.
We may be in a position to use existing carbohydrate categories -
monosaccharides, disaccharides, polyols, oligosaccharides (DP 3-10) and polysaccharides
- to recognize that these other classes have beneficial properties, although
they are not dietary fiber, and at the same time, integrate function and
chemical composition.
Each
class of carbohydrates would contain digestible and undigestible categories
that could include natural and synthetic compounds.
Each class could be analyzed accurately (as well as reproducibly, as now is the
case for some of these components) for its chemical composition.
Each class would have to be characterized for other properties that precipitate
the physiological response to ingestion, i.e. laxation with polyols and
oligosaccharides; viscosity for the hypocholesterolemic mechanism of
action; laxation with non- or incomplete-fermentation; short chain fatty acid
pattern resulting from fermentation. Obviously, some of these
responses have been more thoroughly elucidated than others, and there is a need
for physiologically relevant measures. In this regard we have not made as much
progress.
Each category within a class of carbohydrates would elicit a specific set
of physiological responses.
It may be most appropriate to retain the term dietary fiber and the
current definition to identify the heterogeneous and naturally-occurring
mixture of polysaccharides and lignin that are present in foods.
The strengths of this approach include:
1.
Use
of the chemical classification of carbohydrates
2.
Characterization
of physicochemical properties
3.
Association
of function or physiological effect with composition and properties
4.
Recognition
of benefits of other carbohydrates, natural and synthetic
5.
Recognition
of the complex and variable component in the food supply we currently term
dietary fiber
The
limitations of this approach include:
1.
Lack
of laboratory methodology to predict physiological response
2.
Lack
of physiologically relevant measures of physicochemical properties.
Within
this framework, compounds would be correctly labeled and manufacturers would be
able to promote healthy benefits of their products.
Since processing may alter properties of naturally occurring materials,
there would need to be demonstration by manufacturer that response was the
same. An example that comes to mind is partial hydrolysis which can reduce
a hypocholesterolemic response. I believe that for many of the functions
that have been elucidated in the past 25 years, in vitro or analytical
tests that give physiologically relevant results can be standardized.
I have been uncomfortable for some time with several materials being
labeled dietary fiber, when in fact, they are an oligosaccharide or
polysaccharide.
Judith A. Marlett, Ph.D.
University of Wisconsin
Department of Nutritional Sciences
Committee Responses:
Very good points, but I wasn’t sure of how lignin and chitosan would fit in. – Mary Ellen Camire
How much can we fit on the nutrition label? Can we have “fiber” and another
term? Probably not. Increasing “fiber” content of foods by replacing digestible ingredients with non-digestible
carbohydrates leads to improved health. Therefore, it is more practical to
broaden the fiber term. – Stuart Craig
Along with Barbara Schneeman’s comment above, the
author has outlined a number of important factors to be considered during our
discussion on defining dietary fiber. – Betty
Li
I think the term dietary fiber should remain and the
term used on the Nutrition Facts panel of food packages. I agree with Marlett.
We now have the chance to categorize the many different compounds into common
physiological functions. – Dennis Gordon
I think that fiber should be defined from a physiological perspective, because
the effects of food processing can render starch or protein undigestible
therefore allow it to act as fiber.
Gabriel Keith Harris
USDA Fellow
Department of Food Science and Technology
Columbus, Ohio
Committee Responses:
Undigested protein has been overlooked in our discussions. I believe that the
USDA WRRC found that such protein can lower cholesterol. – Mary Ellen Camire
Pandora’s Box II. – Stuart Craig
Should we simply ignore those food components that are produced during
processing, even though they may possess certain physiological characteristics
attributable to dietary fiber? – Betty Li
I favor dietary fiber being restricted to
carbohydrates thus eliminating any type of polymerized fat or protein. I invite
Dr. Harris to submit a definition he feels would include more physiological
actions-perspectives of dietary fiber. The AACC Committee to Dietary Fiber is
looking for ideas on a definition that could include more on the physiological
action(s) of dietary fiber. – Dennis
Gordon
I don't have a problem with the present definition, although it is somewhat
arbitrary. It is probably useful to have additional ways to characterize
related characteristics of carbohydrates, but I would favor additional
adjectives or using other names until we know their relevance to physiology and
disease risk. For the most part, these are research issues.
Walter C. Willet, M.D., Dr. P.H.
Chair, Department of Nutrition
Harvard School of Public Health
Committee Responses:
I disagree that these issues are research-based. – Mary Ellen Camire
There is sufficient data to support broadening the definition. - Stuart Craig
This is a reasonable suggestion we should keep in mind. – Betty Li
I agree with MEC and SACS that additional research is
not needed now as we consider a definition for dietary fiber. Adequate
discussion with available information will go a long way in helping to possibly
propose and defend a new definition. If the present definition were arbitrary,
would inclusion of such terms as "(poly)saccharides" and
"carbohydrate analogues" be acceptable in a new definition. These
terms must be defined. – Dennis Gordon
I agree
with the need for a more accurate definition or description of dietary fiber.
The current definition is too narrow and contributes to limit our thinking
about the diverse chemical, physiological and physical properties of fiber.
Research indicates that the physicochemical action of fiber components are
diverse in different parts of the digestive system and impacts human health.
Although the current definition of dietary fiber has served us well as an
estimate of mass of materials and amount of soluble/insoluble, it
oversimplifies the role of fiber. The committee might consider a more detailed
compositional statement, such as nonstarch polysaccharides chemical
composition; sterols, waxes and other indigestible lipids; and phenolic
compounds. Also, I think the word fiber connotes plant polysaccharide materials
that exclude the other chemical classes.
Wallace Yokoyama, Research Chemist
USDA, WRRC
Albany, California
Committee Responses:
I agree. – Mary Ellen Camire
There’s a lot to consider. – Stuart Craig
Interesting point on the word fiber. Should we consider dropping that
altogether? Probably not. – Betty Li
Again, I think a simple statement of definition and
a supporting document will satisfy Yokoyama's suggestion. I also think Yokoyama
is correct in stating the term "dietary fiber" pertains to plant
foods, whole grains and cereals, fruits and vegetables. What are the best terms
to have in a definition to describe oligosaccharides (DP <10), isolated
sources of dietary fiber, and carbohydrate analogues? – Dennis Gordon
My
views are the following: The definition already accepted by the U.S. FDA and the
Department of Agriculture is, if a short definition is wanted, appropriate. Of
the alternative wording "hydrolysis" vs. "digestion." I
prefer the latter, since a substance or botanical component might not be
resistant to hydrolysis by human (digestive tract) enzymes but yet end to be
regarded as dietary fiber due to incompleteness of the hydrolysis, e.g.
affected by physical barriers or similar factor. In addition to the main
definition, a reconsideration of the subdivision of dietary fiber should be made
for the following reasons:
Yrjo
Malkki
Managing Director, Cerefi Ltd, a consulting company holding
industrial rights to patented and non-patented processes for
enrichment of oat dietary fiber. Affiliation formerly Director and
Professor, Food Research Laboratory of the Technical Research Centre
of Finland Author and co-author of 10 original research papers and 3
patents related to dietary fibre
Committee Responses:
FDA/USDA definitions…is this a pervasive industry belief? The criteria for
solubility are not strong and need to be carefully considered. – Mary Ellen Camire
Good points. – Stuart Craig
I agree completely with the preference of using “digestion” vs. “hydrolysis”
and with the statement that the definition and determination of soluble fiber
is not satisfactory as they stand now. Viscosity is one certain dietary fiber
constituents. – Betty Li
I am not sure we need to explain soluble and
insoluble dietary fibers in the definition. A discussion of these topics could
be included in the accompanying document. The comments of other suggest sources
of dietary fiber be categorized based on their chemical, physical and
physiological properties. Viscosity is just one of these properties. – Dennis Gordon
The Corn Refiners Association, Inc. (CRA) appreciates the opportunity to
provide these comments regarding the appropriateness of the current definition
for dietary fiber. Because of the growing importance of physiological function
ascribed to fiber fractions, the definition of dietary fiber and prescribed
analytical method should be carefully identified.
The CRA is the national trade association representing the corn wet milling
industry. Members of the Association produce starches, sweeteners, alcohol,
feed ingredients and vegetable oil using the corn wet milling process.
The dietary fiber analytical methodology needs to be improved to better support
the current structural/physiological definition. The present methodology has
resulted in confusion to consumers, food formulators and regulators, and has
impeded the development of new foods to assist the public in achieving national
nutrition goals like those promoted in the Dietary Guidelines for Americans.
Defining fiber in terms of more specific physiological function to encompass
all known health benefits of fiber and a formulated list would be unduly
restrictive. Rather, the analytical methodology should be broadened to
encompass both insoluble and soluble components of fiber. Specifically, we
believe the approved analytical method which is specific for insoluble fiber
should be broadened to include soluble fiber which is not currently recovered.
The following comments consider specific issues raised in this dicussion:
Should the definition include oligosaccharides and other saccharides That
are not recovered with the current AOAC method for measuring total dietary
fiber?
Yes. Oligosaccharides like polydextrose and other
saccharides, currently excluded with the current AOAC method for
measuring total dietary fiber, should be included in the definition. This is
provided they satisfy Trowell?s redefinition of dietary fiber, accepted by the
scientific community in 1976. The definition was broadened to include all
indigestible polysaccharides (mostly plant storage saccharides), such as gums,
modified celluloses, mucilages, oligosaccharides and pectins. However,
Trowell's definition retains the original physiological requirements of
edibility and digestion resistance. During the 1995 AOAC International
Workshop on the Definition and Analysis of Complex Carbohydrates and Dietary
Fiber, participants confirmed that the physiological definition of fiber does
indeed include digestion-resistant oligosaccharides.
How should synthetic polymers be considered
in any new and updated definition?
For synthetic polymers to be considered dietary fiber,
they should conform to the following requirements: Structural; polysaccharide
or lignin composition. Physiological; edible and digestion resistant.
Should
non-digestible and non-absorbable but fermentable oligosaccharides and
monosaccharides be included?
Digestion-resistant
oligosaccharides should be included in the definition of dietary fiber;
digestion-resistant monosaccharides appear to be outside the scope of any
reasonable definition. Given sufficient exposure (time and concentration)
to an energy source, lower bowel microbes will adapt to virtually any oligo- or
polysaccharide substrate and ferment it to some degree. Some fermentation
products provide significant health benefits.
Is
dietary fiber only obtained from edible plant cells?
No. As stated above, the chief determinants for
dietary fiber should be structural similarity to plant cell
polysaccharides or lignin, and the physiological requirements of edibility
and digestion resistance. There are components commonly used in foods
today that satisfy these determinants, are not directly obtained from edible
plant cells, but may be derived from plant materials.The definition should be
restricted to substances that are suitable for use as a food source. Materials
listed as food ingredients, GRAS substances and food additives all fall within
this definition. Fiber from microbial cells (e.g., yeast cell wall glucans) or
products from non-edible plants that are produced to meet FDA requirements as
legal food ingredients would be acceptable.
Should the definition include both a chemical
and physiological component?
Yes. Both are already included in the definition. If
both are not required, then classes of compounds allowed to be called
dietary fiber could conceivably be broadened to include hormones and other
biologically active molecules of non-saccharide or lignin origin.
In conclusion, the CRA supports broadening the
analytical methodology to include soluble dietary fiber. New food ingredients
are available to food formulators that show physiological benefits of dietary
fiber but are excluded because they are not recovered with the official
analytical method.
Jennifer Snyder, Director of Technical Affairs
Corn Refiners Association, Inc.
Committee Responses:
Good points. – Mary Ellen Camire
A nicely structured series of answers.
– Stuart Craig
These comments represent very thorough responses to some questions Dennis
Gordon has raised in his letter to colleagues. How we are going to define
soluble fiber remains a critical question. – Betty Li
Thank you for these excellent comments. – Dennis Gordon
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