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Conjugated Linoleic Acid (CLA)
Concentrations
found in Grass Fed Beef:
C.A. Daley1, A. Abbott1, M. Basursto1, G. Nader2, and S. Larson2
College of Agriculture, California State University, Chico1
University of California Cooperative Extension Service2
Conjugated Linoleic Acid (CLA):
The term conjugated linoleic acid and its acronym CLA is a
group of polyunsaturated fatty acids found in beef, lamb,
and diary products that exist as general mixture of positional
and geometric conjugated isomers of linoleic acid (Sehat et
al., 1999). These compounds are produced in the rumen of cattle
and other ruminant animals during the microbial biohydrogenation
of linoleic and linolenic acids by an anaerobic rumen bacterium
Butyrivibrio fibrisolvens. (Pariza et al., 2000).
 Nine
different positional and geometrical isomers result from this
process, of which, cis-9, trans-11 is the most abundant and
is the biologically active form. Cis-9, trans-11 makes up
75% or more of the total CLA in beef (Ip, et al, 1994; Chin
et al., 1992; Parodi, 1997).
Over the past two decades numerous health benefits have been
attributed to CLA in experimental animal models including
actions to reduce carcinogenesis, atherosclerosis, onset of
diabetes, and body fat mass.
The anti-atherosclerotic evidence was first reported in CLA
treated mice by Clement Ip in 1994. Ip and coworkers showed
CLA levels as low as 0.05 percent of the diet can have a beneficial
effect in mice. A level of 0.5 percent reduced the total number
of mammary tumors by 32 percent. These results also demonstrated
that CLA administered through a dietary route was effective
in providing protection against cancer (Ip et al., 1994).
In a 1996 supplemental feeding study, Carol Steinhart showed
a lower level of LDL ("bad") cholesterol in both
rabbits and hamsters treated with oral CLA, resulting in significantly
less plaque formation in the aortic artery of treated animals
(Steinhart, 1996). Presumably this reduction in plaque formation
would therefore reduce the incidence of heart disease. Likewise,
David Kritchevsky demonstrated that CLA levels as low as 0.1
percent of the diet can have beneficial effects by inhibiting
atherogenic activity in rabbits (Kritchevsky et al., 2000).
This particular study also showed a 30 percent regression
of established atherosclerosis with a CLA level of 1 percent
of the diet.
There is a plethora of data to demonstrate that CLA modulates
body composition by reducing the accumulation of adipose tissue,
primarily in experimental animals. In mice, rats, pigs, and
now humans, dietary CLA has been shown to reduce adipose tissue
depots (Dugan et al., 1999; Park et al., 1997; Sisk et al.,
2001; Smedmen et al., 2001) Although there is some controversy
within the human data, it is likely that dose, duration, isomeric
composition, age and gender influence the outcome of CLA supplementation.
For instance, lower doses (3g/day: Blankson et al., 2000)
had little effect while larger doses (3.4 - 6.0 g/day) significantly
reduced fat mass in humans (Zambell et al., 2000). These ultra
high doses of synthetic CLA reportedly do not produce ill
side-effects, indirectly demonstrating that the compound is
in fact safe. Little is known of upper toxicity levels because
there doesn't appear to be an unsafe dose. |
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CLA
is found naturally in a variety of ruminant meats (French,
et al, 2000) and dairy products (Dhiman, et al, 1999), due
to the anaerobic activity of the rumen bacterium Butyrivibrio
fibrisolvens. This rumen organism is responsible for the biohydrogenation
of linoleic and linolenic acids into the conjugated isomers
referred to as CLA. Because linoleic and linolenic acid is
a precursor, diets rich in these compounds increase the concentration
of the CLA within the fat depot of the animal. Lush green
forages are high in this precursor, therefore, grass-fed ruminant
species have been shown to produce 2 to 3 times more CLA than
ruminants fed in confinement on concentrate-only diets (French,
et al, 2000; Duckett, et al, 1993; Rule, et al, 2002; Mandell
et al, 1998).
| Conjugated
Linoleic Acid (g/100g or g/3.50oz.) |
| Study |
Feedlot/Concentrate |
Range/Grass |
Amount Increased |
| French,
2000 |
.37z |
1.08w |
2.92X |
| Duckett,
1993 |
.82c |
2.2d |
2.69X |
| *Rule,
2002 |
.26e |
.41c |
2.04X |
Table 1. Comparison of beef raised on grass-based diets vs.
concentrate-based diets.
To achieve biological effects, the average human would need
to consume approximately 5 grams CLA/day. On average, a single
3.5 oz. serving of grass-fed beef provides 1.23 grams of CLA,
25% of the daily requirement for a biological effect. Conversely,
conventional beef provides 0.48 grams in a 3.5 oz. serving,
providing 9.6% of the CLA needed for positive physiological
effects.
Grass-fed beef, coupled with the consumption of grass-fed
dairy products could provide higher daily doses of CLA from
dietary sources, providing the concentration of CLA needed
for a positive healthful effect.
References
Contact information: C.A.Daley, Associate Professor, College
of Agriculture, California State University, Chico, Chico
CA 95929, cdaley@csuchico.edu. |
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