Altering the composition of ruminant-derived foods for improved human
health
Kevin J. Shingfield1, Sirja Viitala2, Heidi Leskinen1 and Johanna Vilkki2
1Animal Production Research, MTT Agrifood Research Finland, Jokioinen FI-31600,
Finland
2Biotechnology and Food Research, MTT Agrifood Research Finland, Jokioinen FI-
31600, Finland
Clinical trials and biomedical studies in animal models have provided evidence that
nutrition plays an important role in the development of chronic diseases in the human
population including cancer, cardiovascular disease (CVD), insulin resistance and
obesity (Shingfield et al. 2008). Direct and indirect costs of CVD have been estimated
to cost the 25 member states of the EU €169 billion per annum (Leal et al. 2006). In
order to reduce the economic and social burden of chronic disease public health
policies in developed countries have placed greater emphasis on the development of
diets or specific dietary components that enhance or with the potential to improve
human health as part of an overall strategy for disease prevention.
Studies in human subjects have indicated that saturated fatty acids (SFA) and trans
fatty acids (TFA) in the diet increase CVD risk, with emerging evidence that excessive
intakes of SFA may also be associated with lowered insulin sensitivity which is a key
factor in the development of the metabolic syndrome. Even though it is generally
accepted that SFA raise plasma total and low-density lipoprotein (LDL) cholesterol
concentrations, atherogenic effects are confined to the medium-chain fatty acids,
lauric (12:0), myristic (14:0) and palmitic acid (16:0). Furthermore, cell culture and
biomedical studies have provided evidence to suggest that isomers of conjugated
linoleic acid (CLA) may have important physiological roles with respect to
mutagenesis, CVD, diabetes, bone formation, nutrient partitioning and immunity
(Shingfield et al. 2008). For industrialised countries, milk and dairy products are the
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major source of 12:0 and 14:0 in the human diet, while ruminant-derived foods are
the principle source of CLA and also make a major contribution to total 16:0 and TFA
consumption (Givens and Shingfield, 2006). However, developing public health policies
promoting a decrease in the consumption of milk, cheese, butter, lamb and beef
ignores the value of these foods as a versatile source of nutrients. Altering the fatty
acid composition of ruminant meat and milk fat more in line with public health
recommendations, rather than simply promoting a population-wide decrease in the
consumption of these foods would enable SFA intakes to be reduced and the supply of
CLA in the human food chain to be increased without requiring changes in consumer
eating habits, whilst at the same time maintaining the potential benefits associated
with the macro and micro nutrients in these foods.
Nutritional regulation of milk and meat fatty acid composition has been the subject of
intense research during the last few decades. Considerable progress has been made
towards understanding the role of diet on enhancing the nutritional value of ruminantderived
foods while more recent studies have attempted to elucidate the molecular
mechanisms underlying the changes in milk and tissue lipid fatty acid composition in
ruminants. Diet is the major environmental factor influencing the CLA content of
ruminant milk whilst the effects of genotype, stage of lactation and parity are
relatively minor (Palmquist el al. 2005). Concentrations of CLA in ruminant meat are
dependent on diet, gender, slaughter weight and breed with evidence of variable
enrichment between tissues. Increases in the proportion of dietary energy derived
from fresh forage or inclusion of plant oils, oilseeds or marine lipids in the diet can be
used to enhance the CLA content of ruminant milk and meat, but also result in an
inevitable increase in TFA concentrations. Nutritional and management strategies can
be used to enhance the CLA content of ruminant milk (range 0.5-10.1 g/100 g fatty
acids) and meat (4-134 mg/100 g muscle). Furthermore, estimates of heritability of
Δ-9 desaturase in the bovine indicate the potential to further enhance CLA in ruminant
milk and meat through genetic selection.
Milk fat is comprised of triacylglycerides (96-98% of total milk lipids) and contains
more than 400 individual fatty acids, but quantitatively SFA of chain lengths from 4 to
18 carbon atoms, 16:1 cis-9, 18:1 cis-9, trans 18:1 and 18:2n-6 are the most
abundant (Shingfield et al. 2008). Fatty acids secreted in milk fat are derived from two
sources, uptake of preformed fatty acids from peripheral circulation and fatty acid
synthesis in mammary secretory cells. Fatty acid synthesis de novo contributes to ca.
40% by weight or 60% on a molar basis to total fatty acid secretion in milk. Long
chain fatty acids containing 16 or more carbon atoms are known to lower mammary
de novo fatty acid synthesis due to direct inhibitory effects on acetyl-CoA carboxylase
(E.C. 6.4.1.2; Barber et al., 1997) with the effects being more potent for fatty acids
containing a longer carbon chain and/or higher degree of unsaturation. Decreases in
the secretion of fatty acids synthesized de novo are associated with a reduction in the
activity and transcript abundance of acetyl-CoA carboxylase and fatty acid synthetase
(E.C. 2.3.1.85) in mammary tissue (Bernard et al., 2008). Altering the relative
contribution of preformed fatty acids and fatty acid synthesis de novo is central to
nutritional strategies to decrease concentrations of 12:0, 14:0 and 16:0 in milk fat.
Concentrations of medium chain SFA can be decreased by increasing the proportion of
energy from fresh forages and inclusion of plant oils or oilseeds in the diet. Changes in
milk fatty acid composition to lipid supplementation are dependent on i) the amount of
oil included in the diet, ii) fatty acid profile of the lipid supplement, iii) form of lipid in
the diet and/or processing of oilseeds and iv) composition of the basal diet (Chilliard et
al. 2007). Cultivation of different forage species may also assist in attempts to alter
milk fat composition, but the overall impact is related to forage conservation method,
the proportion of forage in the diet and composition of concentrate supplements
(Dewhurst et al., 2006; Chilliard et al., 2007). Milk fatty acid composition is known to
vary between cows fed the same diet suggesting a genetic component in the
regulation of milk fatty acid composition (Palmquist et al., 2005) Polymorphisms for
several lipogenic genes have recently been identified in the bovine confirming the
existence of genetic variation and highlighting the potential of genomic selection to
enhance the nutritional quality of ruminant milk.
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