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In the Vegetarian & Vegan News...
   Stephen Walsh | VegSource Interactive, Inc.

Study: Does Dairy Consumption Prevent Diabetes and Heart Disease?
by Stephen Walsh, PhD

The recent study by Mark Pereira published in JAMA today "Dairy Consumption, Obesity and the Insulin Resistance Syndrome in Young Adults" (Vol 287, April
24, 2002)


finds that increased dairy products were associated with reduced risk of insulin resistance syndrome (IRS) in overweight individuals (BMI > 25). The 3157 individuals studied were between 18 and 30 at the start of the study in 1985 and follow up was over 10 years.

IRS was defined in this study as the presence of two or more of obesity, high blood pressure, elevated fasting blood glucose and low HDL cholesterol or high triglycerides. IRS cases found within the first year were excluded.

Overweight individuals were observed to consume dairy products less than normal weight individuals. Dairy consumption was positively associated with whole grain, fruit, vegetable and saturated fat intake, and inversely associated with sugar-sweetened soft drink intake. Whole grain consumption doubled and soda consumption halved between the lowest and highest categories of dairy intake. The authors constructed a healthy propensity score between 0 and 5 based on smoking, physical activity, fruit and vegetable intake, whole grain intake and soft drink consumption.

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.

The dominant 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.

In examining these results, it is useful to place them in the context of other results on diabetes and heart disease risk.

"Diet and 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:

"Substituting 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."

Glycaemic load (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.

Another factor 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.

In addition, 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 understanding..

Stephen Walsh PhD (stephenwalsh@vegans.fsnet.co.uk) is the UK Vegan Society spokesperson on Nutrition and Health


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