The risk of
IRS developing in overweight individuals over 10 years was found
to reduce dramatically with increased dairy product consumption
(72% reduction in risk between lowest and highest categories). After
adjustment for the healthy propensity score the reduction in risk
was 63% and was still clearly statistically significant. Other adjustments
presented did not significantly alter the results. Increased dietary
fibre was found to be associated with a substantial reduction in
risk, exceeding that associated with dairy product intake but largely
independent of it.
change driving categorisation of IRS was obesity, with elevated
fasting glucose and blood pressure also changing notably and lipid
abnormalities playing a minor role. It should be noted that IRS
is a proxy for heart disease and diabetes risk rather than a direct
measure of such risk.
these results, it is useful to place them in the context of other
results on diabetes and heart disease risk.
risk of type II diabetes: the roles of fat and carbohydrate",
FB Hu et al., Diabetologia (2001) 44:805-817 reviews diet and diabetes
with some interesting conclusions:
unhydrogenated unsaturated fats (such as those in natural vegetable
oils, nuts and seeds) for saturated fat (such as those in animal
products) and trans-fat (such as those in vegetable shortening and
hard margarine) could substantially lower the risk of Type II diabetes
as well as other chronic diseases. Substituting minimally processed
whole grain products for refined grains would also have substantial
benefits on these diseases."
(amount of carbohydrate times relative effect on glucose levels
over two hours) was also associated with increased risk of diabetes,
particularly in overweight individuals, but increased consumption
of whole grains was associated with lower risk of diabetes.
Looking at dairy
products in this context, one would expect increased dairy product
consumption to be associated with lower glycaemic load (dairy products
have little carbohydrate and what carbohydrate they do have has
modest effect on glucose over two hours). As the apparent adverse
effect of glycaemic load is largely limited to overweight individuals
and the observed beneficial association of dairy products is also
limited to this group, this provides a plausible mechanism for the
observed association. If this is the case, it should be noted that
the same benefit would be expected from consuming wholemeal spaghetti
with vegetable sauces rich in olive oil. In contrast to dairy products,
this alternative approach would also capitalise directly on the
observed benefit of whole grains and of unsaturated fat vs saturated
fat as well as providing other beneficial nutrients such as lycopene,
folate and fibre. Surprisingly, the JAMA paper by Pereira et al.
did not attempt adjustment of the results for glycaemic load although
the protective associations observed between dairy intake and fibre
intake and IRS could both be related to this mechanism.
to consider is what foods were displaced from the diet by dairy
foods. If dairy products were displacing refined carbohydrates and
hard margarines high in trans-fats, then a beneficial effect is
more likely to be observed. No adjustment was made for trans-fat
consumption in the paper by Pereira et al.
If dairy food
consumption were associated with consumption of other foods associated
with a benefit, then these associated foods might also explain the
apparent benefit. As noted above, there was a marked association
between dairy intake and certain healthful behaviours. It is plausible,
therefore, that the observed beneficial association was significantly
influenced by other changes in diet and behaviour associated with
but not directly linked to dairy consumption.
A similar pattern
of risk factors is found for heart disease as for diabetes: replacing
saturated fats with unsaturated fats is beneficial, as is reducing
glycaemic load if overweight and increasing whole grain consumption.
increased calcium consumption reduces blood pressure and may thereby
reduce heart disease risk. However, several studies have found that
the apparent benefit of increased calcium on heart disease risk
is reversed if the calcium source is full fat dairy products. Calcium
can be readily obtained from non-dairy sources, such as green leafy
vegetables, which are not associated with increased saturated fat
in the food supply.
In a typical
(poor quality) Western diet, increased dairy consumption can be
expected to reduce glycaemic load and reduce blood pressure and
thereby contribute to reduced risk of diabetes and heart disease,
particularly in overweight individuals. However, dairy product use
will also increase saturated fat in the food supply and thereby
contribute to increased risk of heart disease and diabetes in the
population. All the beneficial components in milk can be readily
obtained within a plant-based diet without the harmful components.
It is plausible that adding dairy products to certain diets (low
in calcium or high in refined carbohydrates) could be beneficial,
but they have no place in an ideal diet based on current scientific
is the UK Vegan Society spokesperson on Nutrition and Health