Similarly, the Iowa Women's Health Study found that skimmed milk-but not whole milk-was significantly associated with an increased risk of cancer of the ovaries (Am J Epidemiol, 1999; 149: 21-31).
What's the verdict?
Just as there are often two sides to every story, there are findings that don't support the 'low fat = bad, high fat = good' hypothesis. In one study, for example, whole milk resulted in a threefold increase in ovarian-cancer risk, while low-fat milk reduced the risk (Am J Epidemiol, 1990; 132: 871-6).
These, however, were case-control studies, which are retrospective and, therefore, tend to be less reliable.
Indeed, a recent meta-analysis, which pooled together the data from a number of studies, found that case-control studies on milk and ovarian-cancer risk are conflicting, whereas
the more reliable prospective, cohort studies-which record relevant data before the disease develops-were consistent. And these prospective studies showed that low-fat milk, but not whole milk, was associated with an increased risk of ovarian cancer (Int J Cancer, 2006; 118: 431-41).
Ditching low-fat milk
One of the more worrying elements of these findings is that low-fat milk is so popular. In the Physicians' Health Study, for instance, skimmed milk was the most-consumed dairy product, accounting for 48 per cent of all dairy (Am J Clin Nutr, 2001; 74: 549-54).
And yet, there are so many reasons to stop drinking the stuff.
As if prostate cancer, infertility and ovarian cancer weren't bad enough, scientists have also noted a connection between low-fat milk and acne. Taking data again from the Nurses' Health Study, retrospective evaluation found that women who frequently consumed low-fat dairy such as reduced-fat milk, skimmed milk and cottage cheese as high-school teenagers were more likely to suffer from severe, physician-diagnosed acne at the time.
Skimmed milk showed the strongest association, leading the researchers to speculate that changes in milk composition during the fat-extraction process could aggravate acne. Altering the balance of the hormones in milk, for example, might be an explanation. The addition of whey proteins-added to low-fat and skimmed milk to simulate the consistency of whole milk-could also have a role to play (J Am Acad Dermatol, 2005; 52: 207-14).
The final nail in the coffin, though, is delivered by NASA's Dr Grant, in his summary of the mounting evidence that non-fat milk is a major player in bringing on heart disease. The report points out that non-fat milk, which contains substantial amounts of dairy protein, is very low in B vitamins. The body's attempts to metabolize all this protein in the absence of B vitamins contributes to the build up of homocysteine, a known marker for heart disease.
Not surprisingly, Grant's statistical analysis of the dietary influences on coronary heart disease (CHD) across 32 countries found non-fat milk to have the highest association in men aged 45 and over, and in women aged 75 and over-more than any other dietary factor, including saturated fats (Altern Med Rev, 1998; 3: 281-94).
Evidently, the idea of removing fat from milk to protect the heart is not only putting both men and women at risk from a number of serious health problems, it is also seriously flawed.
The milky way forward
Many researchers are now calling for a revision of current dietary guidelines for dairy intake-which are similar in the US and UK. For example, Dr Jorge Chavarro, research fellow in the Department of Nutrition at Harvard School of Public Health, and lead author of the dairy and infertility study, says that the current dietary guidelines for Americans-that adults consume three or more servings of low-fat milk or equivalent dairy products per day-"may be deleterious for women planning to become pregnant". His advice to women wanting to conceive is to change their diet. "They should consider changing low-fat dairy foods for high-fat dairy foods; for instance, by swapping skimmed milk for whole milk and eating ice cream, not low-fat yoghurt."