Can Milk Fat be Beneficial to Your Health?
by A. Denise Beaulieu and James K. Drackley
TAKE HOME MESSAGE
- Milk fat has a negative image with many consumers
- Conjugated linoleic acid (CLA), a component of milk fat, has potential health
- The content of CLA in milk fat has been shown to change under certain dietary
- Our research will investigate if milk CLA content can be increased by feeding
soybean oil to cows.
Whole milk consumption in the US has declined dramatically in the past 20 years.
This has been attributed to health concerns about the content and composition
of milk fat. The public has been exposed to negative messages about milk fat,
specifically regarding the low ratio of poly-unsaturated to saturated fatty
acids. However, this is an oversimplification. Hydrogenated vegetable oil, which
has a favorable polyunsaturated: saturated ratio, may contain 50 percent trans
fatty acids. Linoleic acid, a major polyunsaturated fatty acid of
vegetable oils, has been linked to increased risk for some cancers. Moreover,
some minor components of milk fat, notably CLA, sphingomyelin, butyric acid,
and ether lipids have beneficial effects on health, especially as anticarcinogens.
Research at the University of Illinois is presently focusing on one of these
compounds, CLA. This report briefly describes some previous research investigating
health benefits of CLA (references available upon request ) and the strategies
of our research program.
What is CLA and where does it come from?
The acronym CLA stands for conjugated linoleic acid. It is found
in milk and meat products of ruminant origin because it is synthesized in the
rumen during the biohydrogenation of linoleic acid. It is not an end-product
of this reaction and is quickly metabolized to other compounds. However, research
has shown that it is possible to influence the extent of ruminal biohydrogenation
and the concentration of CLA absorbed and incorporated into milk fat.
What are the health benefits of CLA?
The anticarcinogenic activity of CLA was discovered when researchers
who were investigating tumor-causing compounds in cooked meat noticed that one
of the components exhibited anticarcinogenic activity. This compound was later
identified as CLA. Since that research was published the health benefits of
CLA have garnered a great deal of attention. The research summarized in Table
1 is only a representative sample. Although it has been necessary to conduct
this research using animal and cell culture models, the mechanisms of action
are applicable to humans. CLA has been identified in human plasma and breast
milk in concentrations that are influenced by diet.
Table 1 illustrates two important points. First, the potential
health benefits are diverse and many have only recently been investigated. Second,
CLA is effective at very low concentrations in the diet. It has been estimated
that a human consuming about 3.5 grams CLA/day is ingesting an amount comparable
to a rat consuming 0.1% CLA in the diet. The CLA content of milk fat was 18
mg CLA/g lipid when cows consumed a diet containing sunflower oil (high in linoleic
Table 1. Health benefits of CLA
|Chemically induced mammary tumorigenesis
||CLA, 0.05% to 0.5% of the diet
||dose dependent9in mammary tumor yield
|Chemically induced stomach tumors in mice
||CLA, 0.8 ml in olive oil, administered
||CLA-treated mice developed only 50% as
|Chemically induced skin tumors in mice
||CLA up to 1.5% of the diet
||9 in tumors with 1% dietary CLA
|Chemically induced colon cancer in rats
||CLA, (0.5% of the diet) by gavage
||CLA inhibited the formation of aberrant
crypts in the colon
||CLA, 0.5 g/rabbit/day for 12 weeks
||9 in total and LDL cholesterol, 9 in atherosclerotic
plaques in the aorta
|Pregnant and lactating rats
||CLA, 0.25% or 0.5% of the diet
||CLA improved postnatal growth and feed
efficiency of pups born to CLA-supplemented dams
|Chicks, rats, and mice
||CLA, 0.5% of the diet
||9 in body fat and 8 in lean body mass and
|Chicks and rats injected with endotoxin
||CLA, 0.5% of the diet
||9 in post-injection weight loss
A 12-ounce glass of this milk, if it contained 3.5% milk fat,
would contain about 225 mg of CLA. It is evident that if the CLA content of
ruminant products is increased a consumer may select a diet containing a beneficial
amount of CLA.
Can the CLA content of dairy products be increased?
There is limited work examining factors which specifically affect
the concentration of CLA synthesized in the rumen, and/or transferred to milk
fat. It was shown more than 30 years ago that the conjugated diene (probably
CLA) concentration of Canadian milk fat exhibited seasonal variation, most likely
due to dietary changes. When cows were fed sunflower oil (5.3% diet DM), which
is high in linoleic acid, the CLA content of the milk fat was 18.1 mg/g, almost
double the 9.9 mg/g lipid produced by cows consuming peanut oil (low in linoleic
acid). A change in the forage: concentrate ratio from 50:50 to 35:65 resulted
in CLA content of the milk fat increasing from 6.6 to 11.3 mg/g lipid.
In research at the University of Illinois, we will be take advantage
of factors described above by dietary supplementation with oils high in linoleic
acid (soybean oil) and a high-grain ration that depresses rumen pH. We will
monitor the synthesis of CLA in the rumen and its incorporation into milkfat.
The overall objective of this work is to utilize the rumen microbes to synthesize
a beneficial compound, CLA, from linoleic acid that is found in soybean oil.
This work has the potential to benefit both the consumer and the dairy industry.
Watch for results to be presented in a future edition of the Illinois Dairy