What Is Conjugated Linoleic Acid (CLA)?
Conjugated Linoleic Acid (CLA) occurs naturally in whole milk
and red meat. A collective term used to designate a mixture of
positional and geometric isomers of the essential fat linoleic acid. It
is actually a fat, derived from linoleic acid (an essential fatty
acid). Studies have shown that CLA can increase lean body mass and
decrease fat, inhibit the growth of tumors and enhance immune function.
CLA is found naturally in beef, cheese and whole milk.
The role of diet in the development of cancer has been the focus of
much scientific research during the past decade. Researchers now know
that high intakes of certain naturally occurring dietary chemicals
increase our risk of cancer. Such chemicals include benzo(a)pyrene
(found in charcoal-broiled meat), aflatoxin (found in peanuts), and
certain hydrazines (found in edible mushrooms). But scientists studying
the chemical makeup of the human diet have also identified some
naturally occurring anticancer chemicals. One looks especially
promising.
New results on the physiological properties of conjugated linoleic
acid have been published by several working groups, especially showing
the effects of single conjugated linoleic acid isomers on
carcinogenesis and body composition. Recently, other studies have shown
that conjugated linoleic acid has an influence on diabetes mellitus,
platelet aggregation and the immune system.
Conjugated linoleic acid has been shown to inhibit carcinogenesis
and therosclerosis, enhance immunologic function while protecting
against the catabolic effects of immune stimulation, affect body
composition change (reducing body fat gain while enhancing lean body
mass gain), and stimulate the growth of young rats. We discuss possible
biochemical mechanisms that underlie these physiological effects. We
emphasize the importance of considering the effects, both individually
and combined, of the two CLA isomers (cis-9, trans-11 CLA and trans-10,
cis-12 CLA) that have been shown to exhibit biological activity and
which appear to exert their effects via different biochemical
mechanisms.
The optimum approach to conquering cancer is prevention. Although
the human diet contains components which promote cancer, it also
contains components with the potential to prevent it. Recent research
shows that milk fat contains a number of potential anticarcinogenic
components including conjugated linoleic acid, sphingomyelin, butyric
acid and ether lipids. CLA inhibited proliferation of human malignant
melanoma, colorectal, breast and lung cancer cell lines. In animals, it
reduced the incidence of chemically induced mouse epidermal tumors,
mouse forestomach neoplasia and aberrant crypt foci in the rat colon.
In a number of studies, conjugated linoleic acid, at near-physiological
concentrations, inhibited mammary tumorigenesis independently of the
amount and type of fat in the diet. In vitro studies showed that the
milk phospholipid, sphingomyelin, through its biologically active
metabolites ceramide and sphingosine, participates in three major
antiproliferative pathways influencing oncogenesis, namely, inhibition
of cell growth, and induction of differentiation and apoptosis. Mice
fed sphingomyelin had fewer colon tumors and aberrant crypt foci than
control animals. About one third of all milk triacylglycerols contain
one molecule of butyric acid, a potent inhibitor of proliferation and
inducer of differentiation and apoptosis in a wide range of neoplastic
cell lines. Although butyrate produced by colonic fermentation is
considered important for colon cancer protection, an animal study
suggests dietary butyrate may inhibit mammary tumorigenesis. The dairy
cow also has the ability to extract other potential anticarcinogenic
agents such as -carotene, -ionone and gossypol from its feed and
transfer them to milk. Animal studies comparing the tumorigenic
potential of milk fat or butter with linoleic acid-rich vegetable oils
or margarines are reviewed. They clearly show less tumor development
with dairy products.
In this review of the effects of trans fatty acids, oleic acid, n-3
polyunsaturated fatty acids, and conjugated linoleic acid on mammary
carcinogenesis in animals, the goal is not to provide an exhaustive
survey of all the publications on these topics; such a Herculean effort
has been accomplished by previous reviews, which are cited in the text.
Instead, the emphasis is on the consistency or lack of consistency of
information regarding each of the above fatty acids, confounding
factors that may help to reconcile discrepancies in the database, a
perspective of the history of the research, and certain unique or
exciting opportunities that are worthy of special attention in
evaluations of the relations between specific fatty acids and cancer.
This review arrives at four conclusions:
There is little evidence that trans fatty acids have an adverse effect on carcinogenesis.
The
data on cancer protection by oleic acid are not convincing. An
inhibitory effect attributed to an increased intake of oleic acid could
be due to an inadequate supply of linoleic acid.
Although a
suppressive response to n-3 polyunsaturated fatty acids is observed in
most cases, the availability of linoleic acid is likely to be a
confounding factor in determining the final outcome.
Conjugated
linoleic acid is unique in the sense that concentrations of less or =
1% are sufficient for producing significant cancer protection and that
this effect seems to be independent of the other fatty acids.
CLA may also prevent diabetes, according to a research team from
Purdue and Pennsylvania State universities. This information could lead
to new drugs to help fight diabetes, or to improved dietary strategies
to manage diabetes, the researchers say. The study found that
conjugated linoleic acid can prevent the onset of diabetes in
laboratory animals, at least in the short term. The researchers say CLA
appears to work as well as a new class of diabetes-fighting drugs, the
thiazolidinediones, or TZDs. Martha Belury, Purdue assistant professor
of foods and nutrition, says: "If you inherit a genetic predisposition
to adult-onset diabetes and you're obese and inactive, then you may
well develop this disease. Our study suggests that CLA may help
normalize or reduce blood glucose levels and prevent diabetes."
Conjugated Linoleic Acid (CLA) occurs naturally in whole milk
and red meat. A collective term used to designate a mixture of
positional and geometric isomers of the essential fat linoleic acid. It
is actually a fat, derived from linoleic acid (an essential fatty
acid). Studies have shown that CLA can increase lean body mass and
decrease fat, inhibit the growth of tumors and enhance immune function.
CLA is found naturally in beef, cheese and whole milk.
The role of diet in the development of cancer has been the focus of
much scientific research during the past decade. Researchers now know
that high intakes of certain naturally occurring dietary chemicals
increase our risk of cancer. Such chemicals include benzo(a)pyrene
(found in charcoal-broiled meat), aflatoxin (found in peanuts), and
certain hydrazines (found in edible mushrooms). But scientists studying
the chemical makeup of the human diet have also identified some
naturally occurring anticancer chemicals. One looks especially
promising.
New results on the physiological properties of conjugated linoleic
acid have been published by several working groups, especially showing
the effects of single conjugated linoleic acid isomers on
carcinogenesis and body composition. Recently, other studies have shown
that conjugated linoleic acid has an influence on diabetes mellitus,
platelet aggregation and the immune system.
Conjugated linoleic acid has been shown to inhibit carcinogenesis
and therosclerosis, enhance immunologic function while protecting
against the catabolic effects of immune stimulation, affect body
composition change (reducing body fat gain while enhancing lean body
mass gain), and stimulate the growth of young rats. We discuss possible
biochemical mechanisms that underlie these physiological effects. We
emphasize the importance of considering the effects, both individually
and combined, of the two CLA isomers (cis-9, trans-11 CLA and trans-10,
cis-12 CLA) that have been shown to exhibit biological activity and
which appear to exert their effects via different biochemical
mechanisms.
The optimum approach to conquering cancer is prevention. Although
the human diet contains components which promote cancer, it also
contains components with the potential to prevent it. Recent research
shows that milk fat contains a number of potential anticarcinogenic
components including conjugated linoleic acid, sphingomyelin, butyric
acid and ether lipids. CLA inhibited proliferation of human malignant
melanoma, colorectal, breast and lung cancer cell lines. In animals, it
reduced the incidence of chemically induced mouse epidermal tumors,
mouse forestomach neoplasia and aberrant crypt foci in the rat colon.
In a number of studies, conjugated linoleic acid, at near-physiological
concentrations, inhibited mammary tumorigenesis independently of the
amount and type of fat in the diet. In vitro studies showed that the
milk phospholipid, sphingomyelin, through its biologically active
metabolites ceramide and sphingosine, participates in three major
antiproliferative pathways influencing oncogenesis, namely, inhibition
of cell growth, and induction of differentiation and apoptosis. Mice
fed sphingomyelin had fewer colon tumors and aberrant crypt foci than
control animals. About one third of all milk triacylglycerols contain
one molecule of butyric acid, a potent inhibitor of proliferation and
inducer of differentiation and apoptosis in a wide range of neoplastic
cell lines. Although butyrate produced by colonic fermentation is
considered important for colon cancer protection, an animal study
suggests dietary butyrate may inhibit mammary tumorigenesis. The dairy
cow also has the ability to extract other potential anticarcinogenic
agents such as -carotene, -ionone and gossypol from its feed and
transfer them to milk. Animal studies comparing the tumorigenic
potential of milk fat or butter with linoleic acid-rich vegetable oils
or margarines are reviewed. They clearly show less tumor development
with dairy products.
In this review of the effects of trans fatty acids, oleic acid, n-3
polyunsaturated fatty acids, and conjugated linoleic acid on mammary
carcinogenesis in animals, the goal is not to provide an exhaustive
survey of all the publications on these topics; such a Herculean effort
has been accomplished by previous reviews, which are cited in the text.
Instead, the emphasis is on the consistency or lack of consistency of
information regarding each of the above fatty acids, confounding
factors that may help to reconcile discrepancies in the database, a
perspective of the history of the research, and certain unique or
exciting opportunities that are worthy of special attention in
evaluations of the relations between specific fatty acids and cancer.
This review arrives at four conclusions:
data on cancer protection by oleic acid are not convincing. An
inhibitory effect attributed to an increased intake of oleic acid could
be due to an inadequate supply of linoleic acid.
suppressive response to n-3 polyunsaturated fatty acids is observed in
most cases, the availability of linoleic acid is likely to be a
confounding factor in determining the final outcome.
linoleic acid is unique in the sense that concentrations of less or =
1% are sufficient for producing significant cancer protection and that
this effect seems to be independent of the other fatty acids.
CLA may also prevent diabetes, according to a research team from
Purdue and Pennsylvania State universities. This information could lead
to new drugs to help fight diabetes, or to improved dietary strategies
to manage diabetes, the researchers say. The study found that
conjugated linoleic acid can prevent the onset of diabetes in
laboratory animals, at least in the short term. The researchers say CLA
appears to work as well as a new class of diabetes-fighting drugs, the
thiazolidinediones, or TZDs. Martha Belury, Purdue assistant professor
of foods and nutrition, says: "If you inherit a genetic predisposition
to adult-onset diabetes and you're obese and inactive, then you may
well develop this disease. Our study suggests that CLA may help
normalize or reduce blood glucose levels and prevent diabetes."
- Michael W. Pariza, Yeonhwa Park and Mark E. Cook.
Mechanisms of Action of Conjugated Linoleic Acid: Evidence and
Speculation - Food Research Institute, Department of Food Microbiology
and Toxicology, University of Wisconsin-Madison - Peter W.
Parodi. Cows' Milk Fat Components as Potential Anticarcinogenic Agents
- Human Nutrition Program, Dairy Research & Development
Corporation, Glen Iris, Victoria 3146 Australia - American
Journal of Clinical Nutrition, Vol 66, 1523S-1529S - Review of the
effects of trans fatty acids, oleic acid, n-3 polyunsaturated fatty
acids, and conjugated linoleic acid on mammary carcinogenesis in animals - Purdue News 1998 - Compound in meat prevents diabetes, study suggests
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