Milk-and-Dairy-Products-in-Human-Nutrition-FAO

Chapter 5 – Dairy components, products and human health 211
in healthy males, consumption of this CLA isomer failed to lower LDL-cholesterol
when consumed in amounts exceeding that currently present in dairy foods (Tricon
et al., 2006). Furthermore, the anti-atherosclerotic effects of CLA demonstrated in
animal studies may not be the result of its effect on lipids, but rather may be related
to another mechanism, for example an anti-inflammatory effect (McCrorie et al.,
2011). Similarly, the anti-diabetic properties of CLA cannot be fully determined
from current epidemiological evidence, considering that few studies undertook rigorous
measures of insulin resistance. Combined with small sample sizes and other
study limitations, overall results show no effect of CLA on glucose and insulin
(McCrorie et al., 2011). Studies on animal models have shown that CLA has antiinflammatory
properties and may play a role in the management of chronic inflammation,
such as inflammatory bowel disease and rheumatoid arthritis. However,
similar to the other health outcomes described in this section, results from human
studies investigating the effect of products that are naturally enriched with CLA on
inflammation have been mixed (McCrorie et al., 2011). The promising beneficial
effects seen in some animal models have not yet been reflected in human studies.
Indeed, FAO and WHO recently stated that there are insufficient data to provide a
recommendation regarding CLA and cancers (FAO and WHO, 2010a).
Trans fatty acids
Ruminant trans fatty acids (rTFAs) are found naturally in dairy and meat products
and are structurally different from industrial TFAs (iTFAs), which are predominantly
a by-product of industrial processing, usually in the form of partially-hydrogenated
vegetable oils (PHVO) (FAO and WHO, 2010a). Vaccenic acid constitutes
the main TFA in milk fat and it can be partially converted into CLA in humans.
In light of the potential health benefits of CLA, studies have attempted to increase
vaccenic acid in milk fat (Cruz-Hernandez et al., 2007, and references therein). The
justification for this would need to be supported by conclusive evidence that CLA
has a positive impact in humans and that vaccenic acid from ruminant sources is not
a risk factor for CVD (Givens and Gibbs, 2008).
FAO and WHO (2010a) found convincing evidence that iTFA increases CHD
risk factors and CHD events and probable evidence of an increased risk of fatal
CHD, sudden cardiac death, metabolic syndrome and diabetes from iTFA. Similarly,
Bendsen et al. (2011) recently concluded that iTFA may be positively related
to CHD while rTFA may not be, although the authors note that it is not feasible to
make a firm conclusion based on current evidence. In relation to cancer, FAO and
WHO (2010a) stated that “there is not a large body of evidence to suggest either
a deleterious or a beneficial effect of trans fats on cancers” but there is a possible
increased risk of prostate cancer.
The quantity of trans fats consumed may also be a factor in the disease risk.
Present knowledge on TFA intakes in most countries is not robust. Estimates of
the intake of TFAs are generally obtained from dietary assessment surveys and the
use of food composition tables which may have incomplete TFA data (Stender,
Astrup and Dyerberg, 2008; Uauy et al., 2009). There are large variations in the
TFA content of snack and convenience foods (FAO and WHO, 2010a). The concentration
of TFAs in ruminant fats varies with season and animal feed. The total
intake of TFAs was investigated in the Transfair study in a number of European