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

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Milk and dairy products in human nutrition
lower cholesterol levels enough to change a person’s risk of CVD from a high-risk
category to a lower risk category. 45 Parodi (2009) examined the risk factors for
CHD with emphasis on total- and LDL-cholesterol levels and reported that epidemiological
studies do not supply convincing evidence for an association between
SFA intake and CHD risk. The author concludes that the evidence “that shows
the major cholesterol-raising SFA, C12:0, C14:0 and C16:0 concomitantly elevate
antiatherogenic high-density lipoprotein (HDL)-cholesterol levels”. Overall, the
effect of SFA on serum lipoproteins suggests that they may be “atherogenically
neutral” (Parodi, 2009). Similarly, Lecerf and de Lorgeril (2011) reported that epidemiological
data do not support a link between dietary cholesterol and CVD, but
the authors also remarked that there is an absence of clinical trial data and there are
limitations to the epidemiological approach. As aptly stated by Astrup et al. (2011),
“the effect of diet on a single biomarker is insufficient evidence to assess CHD risk.
The combination of multiple biomarkers and the use of clinical endpoints could
help substantiate the effects on CHD”. Furthermore, the effect of particular foods
on CHD cannot be predicted solely by their fatty-acid profile and the content of
total SFAs, as individual SFAs may have different cardiovascular effects.
Conjugated linoleic acid
Conjugated linoleic acid (CLA) refers to a family of positional and geometric
isomers of linoleic acid (an n-6 omega fatty acid) predominantly found in the
milk and meat of ruminants. There are opposing opinions on its classification as a
trans fat. For labelling purposes, the United States Food and Drug Administration
(FDA) and Codex Alimentarius exclude CLA from the definition of TFAs but
the United States National Academy of Sciences Institute of Medicine includes all
TFAs whether conjugated or non-conjugated (USDHHS and FDA, 2003; FAO and
WHO, 2004).
While there are 28 different isomers, or types, of CLA, the cis-9, trans-11 isomer
accounts for 75–90 percent of total milk-fat CLA (Stanton et al., 2003), while trans-
10, cis-12 CLA accounts for a much smaller proportion. These isomers have been
linked to health-promoting activities, including an ability to inhibit various types
of cancer, hypertension, atherosclerosis and diabetes and improve immune function
and body composition (Pariza, Park and Cook, 2001; Nagao and Yanagita,
2005; Beppu et al., 2006; Bhattacharya et al., 2006; Kelley, Hubbard and Erickson,
2007; Silveira et al., 2007; Watras et al., 2007; Mitchell and McLeod, 2008; Benjamin
and Spener, 2009; Churruca, Fernández-Quintela and Portillo, 2009). However, the
proposed beneficial health effects of CLA are mostly derived from animal studies.
McCrorie et al. (2011) recently reviewed the scientific evidence available for
human health effects and found that three human studies that involved consuming
CLA-enriched dairy products reported no effect on body weight or body mass
index (BMI).
In an intervention study, cis-9, trans-11 was shown to modestly improve blood
lipid profiles in healthy normolipidemic males (Tricon et al., 2004). In another study
45 The relationship between milk and dairy consumption and CVD is discussed in detail in Chapter 4.