What is CLA?
CLA is a newly discovered good fat called "conjugated linoleic acid"
that may be a potent cancer fighter. In animal studies, very small amounts
of CLA have blocked all three stages of cancer: 1) initiation, 2) promotion,
and 3) metastasis. Most anti-cancer agents block only one of these stages.
What's more, CLA has slowed the growth of an unusually wide variety of tumors,
including cancers of the skin, breast, prostate, and colon. (1)
Human CLA research is in its infancy, but a few studies
have suggested that CLA may have similar benefits in people. A recent survey
determined that women with the most CLA in their diets had a 60 percent reduction
in the risk of breast cancer. (2)
Where do you get CLA? Many people take a synthetic version
that is widely promoted as a diet aid and muscle builder. New research shows
that the type of CLA in the pills may have some potentially serious side effects,
including promoting insulin resistance, raising glucose levels, and
reducing HDL (good) cholesterol. (3)
Few people realize that CLA is also found in nature, and
this natural form does not have any known negative side effects. The most abundant
source of natural CLA is the meat and dairy products of grassfed animals. Research
conducted since 1999 shows that grazing animals have from 3-5 times more CLA
than animals fattened on grain in a feedlot. Simply switching from grainfed
to grassfed products can greatly increase your intake of CLA. (4)
Click here to find a
local supplier of grass-fed meat and dairy products—all naturally rich
in the healthy form of CLA.
BEYOND THE BASICS
On the molecular level, CLA resembles another type of fat called
"linoleic acid" or LA. (Both CLA and LA have 18 carbon atoms and
two double bonds holding the chain together. The main difference is in the
placement of those bonds.) However, CLA and LA appear to have opposite effects
on the human body. For example, LA promotes tumor growth but CLA blocks it.
There are 28 possible types (isomers) of CLA, each one
with a slightly different arrangement of chemical bonds. The type most commonly
found in meat and dairy products has double bonds between the 9th and 11th
carbon atoms and is referred to as
"cis 9, trans-11 CLA" or "rumenic acid."
From Eatwild's News and News Archives...
Three Times More CLA in a Grass-fed Hamburger
A lean hamburger from grass-fed
cattle has two and a half times more conjugated linoleic acid (CLA) than
an equally lean hamburger from cattle raised in a feedlot. CLA (conjugated
linoleic acid) is a healthy fat that has been shown to fight obesity, cancer,
and diabetes in lab animals. Human studies are now underway.
“A literature Review of the Value-Added Nutrients
Found in Grass-Fed Beef Products.” Nutrition Journal, June 2006
Milk from Grass-Fed Cows Higher in Vitamin E
Cows that get all their nutrients from grazed grass—their
natural diet—produce milk with 86 percent more vitamin E (alpha-tocopherol)
than cows fed a standard dairy diet, according to a recent study.
The standard dairy diet consists of large amounts of “concentrate,” which
is typically a dry mixture of corn and soy. Some organic dairies raise their
cows on pasture and supplement them with organic concentrate; others keep their
cows indoors and feed them organic concentrate and stored grasses. The more
freshly grazed grass in a cow’s diet, the more vitamin E, omega-3 fatty
acids, and CLA. Organic Valley is a nation-wide organic dairy that emphasizes
Leiber, F., M. Kreuzer, et al. (2005). Lipids 40(2):
Alpine milk may be the healthiest of all
Milk from one hundred percent grass-fed cows is healthier
than milk from grain-fed cows because it contains more of a number of key nutrients,
including omega-3 fatty acids, beta-carotene, and conjugated linoleic acid
or CLA. New research shows that cows that graze at relatively high altitudes
may produce the healthiest milk of all. Compared with lowland grazers, milk
from high altitude grazers (3700-6200 ft) has even more omega3s and CLA and
significantly less saturated fat.
Why? Plants growing in higher altitudes
have more omega-3 fatty acids, fats which solidify at lower temperatures
than other fats and therefore act as a form of anti-freeze. The cows eat
this enriched pasture and pass the nutrients on to their milk.
Hauswirth, C. B., M. R. Scheeder, and J. H. Beer.
"High Omega-3 Fatty Acid Content in Alpine Cheese: The Basis for an Alpine
Paradox." Circulation 109, no. 1 (2004): 103-7.
Natural CLA from grazing animals superior to pills
Tens of thousands
of people who want to lose weight or reduce body fat have been taking a
synthetic version of conjugated linoleic acid or CLA. A new study shows
that the pills may cause more harm than good. After reviewing 13 randomized
studies, a group of researchers concluded that the pills do not reduce
body weight or body fat to a significant degree. Unfortunately, the promising
results seen in animal studies do not seem to apply to humans.
Worse yet, the researchers
found that a kind of CLA found in the pills (CLA (t10, c12) may cause serious
health complications, including an enlarged liver, lower levels of HDL (good)
cholesterol, and insulin resistance.
Meanwhile, the main type
of CLA found in meat and dairy products (c9, t11 or "rumenic acid")
has been given a clean bill of health. Once again, a natural product has
been found to be superior to its synthetic counterpart.
Larsen, T. M., S. Toubro, et al. (2003). "Efficacy
and safety of dietary supplements containing conjugated linoleic acid (CLA)
for the treatment of obesity-evidence from animal and human studies." J
Latitude and altitude —
hidden factors that influence omega-3 and CLA levels in milk
The amount of beneficial CLA and omega-3 fatty acids in
a cow's milk is influenced by a host of factors in addition to diet, including
her breed, individual genetics, age, and even the time of year. Now one more
factor has been added to the list: prevailing temperatures. Milk and cheese
from alpine grazers or cows raised in colder climates appear to have the omega-3
and CLA edge.
The reason? It has to do with plant antifreeze. Omega-3
fatty acids stay fluid at colder temperatures than other, more saturated fats.
A plant that has to withstand the cold needs more of this natural antifreeze
to keep its cell membranes fluid. Cows that graze on this cold climate grass
ingest more omega-3s, which they then convert to another good fat—CLA.
In a recent study, cows that grazed in alpine meadows had more than twice the
amount of CLA in their milk as similar cows that grazed down in the valley.
"Composition of milk fat and
correlation with fodder plants" Marius Collomb, Jacques-Olivier
Bosset, Ueli Bütikofer, Robert Sieber, Hans Eyer,
Natural CLA from milk products is a better cancer-fighter
than CLA pills
Many people are not aware that there are many types of
the cancer-fighting fat CLA, depending on minute differences in molecular structure.
It now appears that, in test tube studies, the kind of CLA found in butter
and animal fat is the most potent cancer-fighter. Human breast cancer cells
were incubated in milk fat high in CLA or in an isolated form of CLA without
any milk fat. The high CLA milk fat decreased cancer growth by 90 percent but
the isolated CLA decreased it by only 60 percent. When the cells were incubated
in linoleic acid, the kind of fat that is most abundant in grain and grain-fed
animals, cell growth increased by 25 percent.
Milk products from 100 percent grassfed cows are as much
as seven times higher in cancer-fighting CLA than ordinary milk and far lower
in cancer-promoting linoleic acid.
(Cancer Letters 1997;116:121-130)
Autumn milk has more CLA
Valerie Dantoin from Full Circle Farm in Seymour, Wisconsin,
has gone the extra mile to verify that her Northern Meadows cheddar cheese
is high in CLA—she's had samples of the milk tested at the University
of Wisconsin throughout the grazing season.
As you can see from the graph below, there is a marked
difference in the CLA levels of the milk from month to month. The cows were
turned out to pasture in May and remained on pasture for the remainder of the
study period. The CLA content in April (before the cows started grazing) is
similar to the amount found in ordinary supermarket milk. By September, the
CLA content was three times higher than at the start of the grazing season.
(In addition to the pasture, the cows were supplemented with 15 pounds of high-moisture
corn, 5 pounds of corn silage and 4 pounds of added protein from soybean meal
and roasted beans. Milk from cows given no additional supplement is even higher
in this cancer-fighting fat.
Seasonal variation in CLA levels
To learn more about Full Circle Farm and to purchase their
cheese, visit Valerie's website at http://www.fullcirclefarm.net/
CLA in North American hunter/gatherer diets
CLA, the cancer-fighting fat, has been found in North American
game animals, suggesting that CLA has been a part of the human diet since the
first spear was thrown. Deer, elk, and moose have about the same amount of
CLA as cattle. Surprisingly, mountain lions and black bears have more (7 and
9 mg/g of fat, respectively) even though they are not herbivores.
Now, when is someone going to test and publish the CLA
levels of free-range bison?
A welcome source of high CLA butter
To our knowledge, there are no American farms or cooperatives
that are currently marketing butter from 100% grassfed cows. Although cheese
from all grassfed cows is available from many suppliers on the Eat
Wild Pastured Products directory, grassfed butter cannot be found. Restrictive
government regulations and lack of consumer awareness keep small-scale butter
operations from being profitable.
Until a US supplier gets up and running, it is possible
to purchase excellent butter imported from Ireland by the Kerrygold company.
The butter is made from cows that are raised on pasture or grass silage, making
it five times higher in CLA and also higher in vitamin E and beta carotene
than commercial butter, whether organic or non-organic. It costs about twice
as much as ordinary butter and about the same as organic butter. It is yellower
than butter from cows raised in confinement, melts at a lower temperature,
and has a terrific taste. Look for Kerrygold butter in up-scale supermarkets
and specialty stores. To see if there's a store in your neck of the woods, search
Kerrygold for "where to buy." You can also order their butter
and cheese on-line from http://www.foodireland.com (Once
at the site, go to the "Irish Deli" section.) You may be able to
convince your local supermarket to stock it, eliminating the high cost of shipping.
more about Kerrygold...
Lab animals fed CLA-rich butterfat have stronger bones
Animal studies suggest that CLA enhances bone formation.
Chicks and rats fed CLA-rich butterfat had greater bone growth than animals
fed other fats. Researchers attribute the stronger bones to CLA's ability to
block excess production of an inflammatory substance called PGE2. Grassfed
dairy meat and dairy products have from 2-5 times more CLA than ordinary products.
Watkins, B. A. and M. F. Seifert (2000). "Conjugated
linoleic acid and bone biology." J Am Coll Nutr 19(4):
Wild game has CLA, too
CLA, a type of healthy fat found in the meat and milk of
ruminants, is found in wild game as well, according to researchers Larry Cordain
and Bruce Watkins. They discovered that CLA levels are especially high in the
bone marrow. This finding is significant because there is evidence to suggest
that our hunter/gatherer ancestors sought out bone marrow to add calories and
fat to their lean diet. Thus, although CLA is new to modern science, it may
have played a key role in human nutrition for eons.
Cordain et al, "A Detailed Fatty Acid Analysis
of Selected Tissues in Elk, Mule Deer, and Antelope." Food Composition 670.1-670.6
Two new studies suggest that
grassfed meat and dairy products may reduce the risk of breast cancer
CLA (conjugated linoleic acid) is
a cancer-fighting fat that is most abundant in grassfed products. Two new European
studies link a diet high in CLA with a lower risk of breast cancer. In Finland,
researchers measured CLA levels in the serum of women with and without breast
cancer. Those women with the most CLA had a significantly lower risk of the
disease. Meanwhile, French researchers measured CLA levels in the breast tissues
of 360 women. Once again, the women with the most CLA had the lowest risk of
cancer. In fact, the women with the most CLA had a staggering 74% lower risk
of breast cancer than the women with the least CLA.
The most natural and effective way to increase your intake
of CLA is to eat the meat and dairy products of grassfed animals.
A. Aro et al, Kuopio University,
Finland; Bougnoux, P, Lavillonniere F, Riboli E. "Inverse relation between
CLA in adipose breast tissue and risk of breast cancer. A case-control study
in France." Inform 10;5:S43,
Milk from grassfed cows has hidden
Until recently, all of the experiments demonstrating the
cancer-fighting properties of CLA (conjugated linoleic acid) have used synthetic
CLA. To see whether the CLA that occurs naturally in cow's milk has similar
cancer-fighting properties, researchers recently compared the two. They fed
one group of rats butter that was high in CLA and fed another group of rats
an equivalent amount of synthetic CLA. As one would expect, the natural CLA
proved to be just as effective in blocking tumor growth as the man-made variety.
(In both cases, cancer yield was reduced by about 50 percent.) However, the
high CLA butter had an added benefit: the rats eating the butter accumulated
even more CLA in their tissues than the rats fed an equivalent amount of synthetic
CLA. The reason? Researchers believe that the rats were converting another
"good" fat found in the butter, trans-vaccenic acid or TVA, into
CLA, giving them a second helping of this cancer-fighting fat. (Click here
for more information about TVA.)
(Ip, C., S. Banni, et al. (1999). "Conjugated
Linoleic Acid-Enriched Butter Fat Alters Mammary Gland Morphogenesis and
Reduces Cancer Risk in Rats." J Nutr 129(12):
Feedlot cattle fattened on stale
Some commercial feedlots feed stale candy to cattle in
an effort to reduce costs. According to a recent review, milk chocolate and
candy "are often economical sources of nutrients, particularly fat. They
may be high in sugar and/or fat content. Milk chocolate and candy may contain
48% and 22% fat, respectively. They are sometimes fed in their wrappers. Candies,
such as cull gummy bears, lemon drops, or gum drops are high in sugar content." The
article recommends that
"upper feeding limits for candy or candy blends and chocolate are 5 and
2 lb. per cow per day, respectively."
As long as beef producers are not accountable for the ultimate
nutritional value of the meat, they will continue to formulate feedlot diets
on a least cost basis and American consumers will continue to eat meat that
is artificially high in fat and low in vitamin E, beta carotene, omega-3 fatty
acids, and CLA.
Feedstuffs in Dairy Cattle Diets in the Upper Midwest."
Randy D. Shaver, Ph.D.
Associate Professor, Extension Nutritionist, Department of Dairy Science,
College of Agricultural and Life Sciences, University of Wisconsin)
Feed them grass, not grease!
In yet another short-sighted experiment, researchers at
Washington State University are feeding recycled restaurant grease to feedlot
cattle in an attempt to raise the CLA levels of their
meat. Although grease will indeed enhance CLA levels, it cannot compete with
grass when the total nutritional value of the meat is taken into consideration.
Meat from cattle raised on grass and legumes is not only five times higher
in CLA than meat from feedlot cattle, it is also higher in vitamin E, beta
carotene, and omega-3 fatty acids. Also, restaurant grease is high in a type
of fat called "linoleic acid"
or LA that is known to stimulate tumor growth.
Although grease-fed cattle will have more of the cancer-fighting CLA, they
will also have higher levels of the cancer-promoting LA, perhaps canceling
out the anticipated benefits.
Comments: As long as researchers
focus on artificial ways to raise CLA levels in
animals, we will continue to have beef that is nutritionally inferior in other
areas. We will also be plagued with all the problems linked with the feedlot
industry including nutrient leaching, odor, diseased animals, and the indiscriminate
use of growth promoting hormones and antibiotics.
New findings on CLA clarify
the benefits of meat and dairy products
Conjugated linoleic acid or CLA has demonstrated a multitude
of benefits in animal studies, including fat reduction, increase in lean muscle
mass, reduced risk of diabetes, reversal of arteriosclerosis, and a marked
reduction in tumor growth.
Many people do not realize, however, that there are 16
different types of CLA, each with a slightly different molecular shape. New
research reveals that each type of CLA has a different set of benefits. The
type of CLA most abundant in meat and dairy products (referred to by chemists
as "cis-9, trans-11, CLA") appears to be the champion cancer fighter.
Compared with another common type of CLA (trans 10, cis 12, CLA) it was a third
more effective in blocking the growth of human cancer cells. (78% versus 58%
But the type of CLA found in meat and dairy products does not appear
to reduce fat or increase lean muscle mass in humans. (That property is linked
with trans 10, cis 12, CLA)
It will be some time before researchers match each type
of CLA with its particular benefits.
(Information gleaned from abstracts
presented at the 91st American Oil Chemists Society April 25-28, 2000 annual
meeting. Special supplement to Inform, vol 11,
no 5, 2000)
French cheese has more CLA than ordinary American cheese
French cheeses are among the most carefully crafted and
coveted in the world. Now there's another reason to seek them out: they're
especially high in cancer-fighting CLA . A 1998 survey found that CLA levels
in French cheese range from 5.3 to 15.8 mg/g of fat. American cheese from conventional
dairies has half this amount, with levels ranging from 2.9 to 7.1. The reason?
Typically, American dairies raise their cows in confinement and feed them a
grain-based diet. French dairies are more likely to raise their cows on pasture,
resulting in naturally high levels of CLA
Fortunately, cheese from American pasture-based dairies
has the same CLA advantage as French cheese. Search the Eat
Wild Pastured Products Directory for cheese suppliers and treat yourself
to an extra helping of CLA.
(JAOCS 75, 343352 (1998))
TVA — yet another good fat in grassfed products?
Evidence is mounting that dairy products from grassfed
cows supply yet another "good" fat to our diet---trans-vaccenic acid
or TVA. Technically, TVA is classified as a "trans-fatty acid,"
a type of fat nutritionists tell us to avoid. But TVA appears to behave differently
from the man-made fat that comes from the hydrogenization of vegetable oil.
Unlike the trans-fatty acids found in fast foods and margarine, TVA is not
linked with an increased risk of cardiovascular disease and may help inhibit
tumor growth and obesity.
Interestingly, TVA may perform these feats by being converted
into CLA in our own bodies. In fact, dairy scientist David Schingoethe from
South Dakota State University suggests that eating diary foods high in TVA
may be a more effective way to increase CLA levels than ingesting CLA itself.
Schingoethe and colleagues are experimenting with increasing
TVA in dairy cows by feeding them fish meal and soybeans. But raising cows
on fresh pasture and withholding all grain may prove just as effective. In
fact, grassfed cows produce milk that is naturally high in both CLA and TVA,
a potentially lifesaving combination. Stay tuned!
(To learn more, read "Making
Milk Better," by Jamie Lammers.)
The Irish are making the most of their "unfair" advantage
Milk from grassfed Irish cows is 2–3 times higher
in conjugated linoleic acid (CLA) than milk from grainfed American cows. Experiments
are underway in Ireland to increase this CLA advantage. Recent experiments
show that feeding oilseeds to grassfed dairy cows boosts their CLA production
even more. Rapeseeds (the seeds that make canola oil) increase the CLA content
of the milk an extra 60%. (To read more, refer to "Milk
and Dairy Products for Better Human Health," by D. McDonagh, et al.)
The Irish get added health benefits from their grassfed
beef as well, according to a soon-to-be-published study. Compared with animals
fed supplemental grain, meat from cattle raised on pasture alone was lower
in saturated fat, but higher in the "good fats," including monounsaturated
fats, omega-3 fats, and CLA. Commented the researchers,
"These data indicate that many Irish beef producers, due to their grass-based
production systems, have a natural advantage in producing beef that is more
beneficial to human health than beef produced from concentrate-based systems."
(For study details, refer to R&H
Hall Technical Bulletin Issue No. 4 ~1999)
(French, P., Stanton, C., Lawless,
F., O'Riordan, E.G., Monahan, F., Caffrey, P.J. and Moloney, A.P. 1999a.
Fatty acid composition, including conjugated linoleic acid, of intra-muscular
fat from steers offered grazed grass, grass silage or concentrate-based diets. Journal
of Animal Science. Submitted)
Some types of cheese have more CLA than others
The way that cheese is made influences its CLA (conjugated
linoleic acid) content. In general, the longer cheese is aged, the lower the
CLA. Thus, hard cheeses such as Parmesan and Romano tend to have less CLA than
softer cheeses such as cream cheese, cottage cheese, feta, farmer's cheese,
ricotta, and Brie. In addition, cheese that is aged through "bacterial
surface ripening" (Brick and Muenster) has more CLA than cheese that does
not go through this process. Finally, a serving of high-fat cheese will have
more CLA than a similar serving of low-fat cheese. (The CLA is measured in
terms of grams of CLA per gram of total fat; the more total grams of fat in
a serving of cheese, the more CLA it will have Reduced fat swiss is an anomaly,
for unknown reasons..)
The table below shows CLA levels in cheese purchased at
a grocery store in 1992. In all likelihood, the milk came from confinement
dairy operations. If the milk had come from grassfed animals, the CLA content
would have been five times higher.
|TYPE OF CHEESE
||CLA (mg/gram of fat)
|Reduced Fat Swiss
(Chin et al, "Dietary
Sources of Conjugated Dienic Isomers of Linoleic Acid, a Newly Recognized
Class of Anticarcinogens." J. of Food
Composition and Analysis 5:185-197 1992)
Red clover increases CLA levels in the milk of grassfed
The type of grasses and legumes growing in a pasture can
influence the amount of CLA in cow's milk. When dairy cows grazed pasture that
contained 20 percent red clover, they produced 50 percent more cancer-fighting,
fat-busting CLA than cows that grazed on grasses alone. (Search for the study
titled, "Paddocks containing red clover compared to all grass paddocks
support high CLA levels in milk.")
Sheep are the CLA winners
Dr. Gerhard Jahreis from the Institut Ernaehrung und Umwelt
in Germany has studied the CLA content of human milk and milk from a variety
of animals. He reports that horses have the lowest CLA content and sheep the
highest. Human milk is in the middle. (Mare's milk <
sow's milk < human milk < goat's milk < cow's milk < ewe's milk.)
There are fewer than 100 sheep dairy farms in the United
States (we imported 66 million pounds of sheep's milk cheese in 1994, valued
at $118 million.) With this new finding about CLA, perhaps more US farmers
will consider milking sheep.
(Jahreis, G. et al, The potential
anticarcinogenic conjugated linoleic acid in milk of different species: cow,
goat, ewe, sow, mare, woman." Nutr Res 1999. 19:1541-9.)
Soft cheese has more CLA than aged cheese
All cheese made from the milk of grassfed cows is rich
in conjugated linoleic acid (CLA). However, the cheese making process itself
can increase or decrease this amount. In a comprehensive survey, the highest
amounts of CLA were found in soft cheeses aged approximately three months.
Longer aging periods reduced this highly desirable fat.
(Chin, S. F. et al (1992)). "Dietary Sources
of Conjugated Dienoic Isomers of Linoleic Acid, a Newly Recognized Class of
Anticarcinogens." J of Food Composition 5: 185-97.)
Turkeys make CLA, too
CLA (conjugated linoleic acid) is highest in products from
grazing animals on a diet of fresh pasture, and it is very low in non-ruminants
such as chickens and pigs. But turkeys appear to be an exception, having about
2.5 mg of CLA per gram of fat. (For comparison, chickens have 0.9 and pigs
0.6 mg. per gram of fat.) To date, no one has tested the CLA content of turkeys
raised on pasture rather than in confinement, an experiment that begs to be
done. It is possible that turkeys with a significant amount of greens in their
diet will have even more CLA.
(Chin, S. F. et al. (1992)).
"Dietary Sources of Conjugated Dienoic Isomers of Linoleic Acid, a Newly
Recognized Class of Anticarcinogens)
Cows that graze on "ecologically managed" pasture
may have more CLA
Raising dairy cows on fresh pasture instead of a standard
dairy diet increases the CLA content of their milk five-fold. Now there is
some evidence that grazing on organic pasture may boost the CLA even further.
In a study conducted in Germany, cows on organic pasture had almost twice as
much CLA as those grazing on a nearby, non-organic farm. More research is needed.
(Jahreis, G. et al. (1997).
"Conjugated linoleic acid in milk fat: high variation depending on production
system." Nutrition Research 17(9): 1479-1484.)
Learn more about the health
benefits of products from pasture-raised animals.
1. Ip, C., J. A. Scimeca, et al. (1994). "Conjugated
linoleic acid. A powerful anticarcinogen from animal fat sources." Cancer
74(3 Suppl): 1050-4.
Conjugated linoleic acid (CLA) is a mixture of positional
and geometric isomers of linoleic acid, which is found preferentially in dairy
products and meat. Preliminary studies indicate that CLA is a powerful anticarcinogen
in the rat mammary tumor model with an effective range of 0.1-1% in the diet.
This protective effect of CLA is noted even when exposure is limited to the
time of weaning to carcinogen administration. The timing of this treatment
corresponds to maturation of the mammary gland to the adult stage, suggesting
that CLA may have a direct effect in reducing the cancer risk of the target
organ. Of the vast number of naturally occurring substances that have been
demonstrated to have anticarcinogenic activity in experimental models, all
but a handful of them are of plant origin. Conjugated linoleic acid is unique
because it is present in food from animal sources, and its anticancer efficacy
is expressed at concentrations close to human consumption levels.
2. Aro, A., S. Mannisto,
I. Salminen, M. L. Ovaskainen, V. Kataja, and M. Uusitupa. "Inverse
Association between Dietary and Serum Conjugated Linoleic Acid
and Risk of Breast Cancer in Postmenopausal Women." s 38,
no. 2 (2000): 151-7.)
3. Riserus, U., P. Arner, et
"Treatment with dietary trans10cis12 conjugated linoleic acid
causes isomer-specific insulin resistance in obese men with the
metabolic syndrome." Diabetes Care 25(9): 1516-21.
OBJECTIVE: Conjugated linoleic acid
(CLA) is a group of dietary fatty acids with antiobesity and antidiabetic
effects in some animals. The trans10cis12 (t10c12) CLA isomer seems
to cause these effects, including improved insulin sensitivity.
Whether such isomer-specific effects occur in humans is unknown.
The aim of this study was to investigate whether t10c12 CLA or
a commercial CLA mixture could improve insulin sensitivity, lipid
metabolism, or body composition in obese men with signs of the
metabolic syndrome. RESEARCH DESIGN AND METHODS: In a randomized,
double-blind controlled trial, abdominally obese men (n = 60) were
treated with 3.4 g/day CLA (isomer mixture), purified t10c12 CLA,
or placebo. Euglycemic-hyperinsulinemic clamp, serum hormones,
lipids, and anthropometry were assessed before and after 12 weeks
of treatment. RESULTS: Baseline metabolic status was similar between
groups. Unexpectedly, t10c12 CLA increased insulin resistance
(19%; P < 0.01) and glycemia (4%; P < 0.001) and reduced
HDL cholesterol (-4%; P < 0.01) compared with placebo,
whereas body fat, sagittal abdominal diameter, and weight decreased
versus baseline, but the difference was not significantly different
from placebo. The CLA mixture did not change glucose metabolism,
body composition, or weight compared with placebo but lowered HDL
cholesterol (-2%; P < 0.05). CONCLUSIONS: These results reveal
important isomer-specific metabolic actions of CLA in abdominally
obese humans. A CLA-induced insulin resistance has previously been
described only in lipodystrophic mice. Considering the
use of CLA-supplements among obese individuals, it is important
to clarify the clinical consequences of these results,
but they also provide physiological insights into the role of specific
dietary fatty acids as modulators of insulin resistance in humans.
4. Dhiman, T. R., G.
R. Anand, et al. (1999). "Conjugated linoleic acid
content of milk from cows fed different diets." J Dairy Sci
Conjugated linoleic acid in milk was
determined from cows fed different diets. In Experiment 1, cows
were fed either normal or high oil corn and corn silage. Conjugated
linoleic acid was 3.8 and 3.9 mg/g of milk fatty acids in normal
and high oil treatments, respectively. In Experiment 2, cows consumed
one-third, two-thirds, or their entire feed from a permanent pasture.
Alfalfa hay and concentrates supplied the balance of feed for the
one-third and two-third pasture treatments. Conjugated
linoleic acid was 8.9, 14.3, and 22.1 mg/g of milk fatty acids
in the one-third, two-third, and all pasture treatments, respectively.
Cows grazing pasture and receiving no
supplemental feed had 500% more conjugated linoleic acid in milk
fat than cows fed typical dairy diets.