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

Chapter 4 – Milk and dairy products as part of the diet 105
to systematic reviews/recommendations provided by other learned bodies, such as
the FAO/WHO 2010 expert consultation on fats and fatty acids (FAO and WHO,
2010); the FAO/WHO expert consultation on vitamin and mineral requirements
(FAO and WHO, 2002); WHO/FAO expert consultation on diet, nutrition and the
prevention of chronic diseases (WHO and FAO, 2003); the World Cancer Research
Fund/American Institute for Cancer Research report on food, nutrition, physical
activity and the prevention of cancer (WCRF and AICR, 2007); the European Food
Safety Authority (EFSA) Panel on Dietetic Products, Nutrition, and Allergies; the
United States National Cholesterol Education Program Expert Panel on Detection,
Evaluation, and Treatment of High Blood Cholesterol in Adults; and the World
Allergy Organization Diagnosis and Rationale for Action against Cow’s Milk
Allergy (DRACMA) guidelines (Fiocchi et al., 2010). This is particularly so for
areas such as Cardiovascular disease (Section 4.8) and Cancer (Section 4.9), where
we were compelled to depend on review studies rather than considering individual
studies because of the large amount of published literature on these topics.
4.1.1 Limitations of studies reviewed
In theory, only randomized control intervention studies can provide definitive
answers to questions about risks and benefits of milk consumption. For such studies
to show causation and a population health impact ideally they need to cover the life
span of the study subjects and involve large numbers of people. Such studies are
very costly and difficult to carry out for both ethical and methodological reasons
(Alvarez-León, Román-Viñas and Serra-Majem, 2006; Elwood et al., 2010; Givens,
2010). Thus, in reality, the best evidence on the present-day associations between
milk and dairy consumption and health and survival come from high-quality prospective
studies.
Public health decisions need to be based on epidemiological evidence and not
just on effects on selected markers of risk (Alvarez-León, Román-Viñas and Serra-
Majem, 2006; Givens, 2010; Mozaffarian, 2011) and results interpreted in the context
of all lifestyle issues such as dietary patterns (e.g. salt and fibre intake, consumption of
fruit and vegetables etc.), physical activity, and smoking (Givens, 2010; Mozaffarian,
2011). In addition, it is important to consider the foods that are replacing dairy in the
diets of people who choose to decrease dairy in their diets, i.e. the replacement foods
and nutrients. For example, while replacing SFAs in the diet with polyunsaturated
fatty acids (PUFAs) would be beneficial, replacing SFAs with refined carbohydrates
such as sugars and starch may increase CHD risk (Mozaffarian, 2011).
Many studies do not distinguish between high-fat and low-fat dairy consumption,
often because of inadequacies in the methods used to collect dietary data. Furthermore,
consumption patterns may change from high to low fat when studies take
place over long periods of time. Data from observational studies of consumption of
fat-free and full-fat dairy products may be difficult to interpret even when available
because people who choose to drink fat-reduced milk often adopt other “healthy”
behaviours, such as taking physical exercise, reducing smoking etc., which affects
their health status (Elwood et al., 2010). This is especially true for comparisons of
national food data with CHD incidence (German et al., 2009; Gibson et al., 2009).
Although these lifestyle factors are often controlled for in statistical models, there
may still be residual confounding factors (Tholstrup, 2006). Other discrepancies