Milk: from healthy to harmful

Nothing is more terrible than ignorance in action.

Johann Wolfgang von Goethe

Part 2

Why more cancers with low-fat dairy?

But why should low-fat milk have such an effect? One theory is that removing the fat from milk strips it of certain nutritional components that are vital to health. Fat is found in milk for a reason. It contains vitamins A and D, both of which are necessary for the uptake and use of the calcium and protein elements in milk. Without these vitamins, milk protein and calcium are more difficult to absorb and can even become toxic to the body.

Calcium, particularly in large amounts, seems to have a specific adverse effect: it suppresses the formation of calcitrol, the hormonal form of vitamin D. Because calcitrol has anti-cancer effects on prostate cells, scientists have postulated that a reduction in the amount of calcitrol in the circulation could increase the risk of prostate cancer.^[10]

The CLA connection

Another possible explanation is that stripping the fat from milk also removes other important anti-cancer components such as conjugated linoleic acid (CLA). CLA was identified as a component of milk and dairy products over 20 years ago, and studies have shown it to be a powerful anti-cancer agent. In the laboratory, when human breast and colon cancer cells were bathed in high-CLA milk fat from cows raised on pastureland, the number of cancer cells was reduced by between 58% and 90%.^[11,12]

And women who consumed four or more servings a day of high-fat dairy foods were half as likely to develop colorectal cancer as women who ate less than one serving a day. Low-fat dairy had no such protective effect.^[13]

Low-fat milk and infertility

Low-fat milk doesn't just increase the risk of cancers. A study conducted at Harvard University Medical School monitored 18,555 American women aged 24 to 42 between 1991 and 1999 and found that the risk of anovulatory infertility, a form of infertility due to lack of egg release from the ovaries, was also increased in women who drank low-fat milks.^[14] The women studied, who were pregnant or trying to become pregnant, did not have a history of infertility. Nevertheless, the study showed that women who ate two or more servings of low-fat dairy products such as skimmed milk or low-fat yoghurt a day, increased their risk of anovulatory infertility by more than 85% compared with women who ate less than one serving of low-fat dairy a week. And women who ate one or more servings per week of skimmed or low-fat milk had a significantly higher risk of anovulatory infertility compared with those who ate less than one serving per week. Adding a serving of whole milk per day reduced the risk of infertility by more than 50%.

The authors of this study suggested that there might be a substance, vital for healthy ovaries, that requires the presence of fat for it to be properly absorbed. This would explain the lower risk of infertility from high-fat dairy foods. It might also explain the results of the prostate cancer studies.

Low-fat milk and acne

As well as more serious conditions, scientists have also noted a connection between low-fat milk and acne. Data, again from the Nurses' Health Study, also showed that women who frequently consumed low-fat dairy such as reduced-fat milk, skimmed milk and cottage cheese as teenagers were more likely to suffer from severe acne at the time.^[15]

As skimmed milk showed the strongest association, the researchers 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.

Low-fat milk and coronary heart disease

Ironically, coronary heart disease, the very disease against which all the work was aimed, also seems to be made worse by low-fat milk. In 1998, William Grant published a review of all the epidemiological evidence concerning diet and heart disease, and also carried out his own researches, examining heart disease and dietary habits in 32 countries.^[16] He found a correlation between low-fat milk, as well as calcium and milk sugars, with heart disease in both sexes.

The review 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.

References

10. Schwartz GG, Hulka BS. Is vitamin D deficiency a risk factor for prostate cancer? (Hypothesis). Anticancer Res 1990; 10: 1307-1311.
11. Miller A, et al. Conjugated linoleic acid (CLA)-enriched milk fat inhibits growth and modulates CLA-responsive biomarkers in MCF-7 and SW480 human cancer cell lines. Br J Nutr 2003; 90: 877-885.
12. O'Shea M, et al. Milk fat conjugated linoleic acid (CLA) inhibits growth of human mammary MCF-7 cancer cells. Anticancer Res 2000; 20: 3591-3601.
13. Larsson SC, et al. High-fat dairy food and conjugated linoleic acid intakes in relation to colorectal cancer incidence in the Swedish Mammography Cohort. Am J Clin Nutr 2005; 82: 894-900.
14. Chavarro JE, et al. A prospective study of dairy foods intake and anovulatory infertility. Hum Reprod 2007; 22: 1340-1347.
15. Adebamowo CA, et al. High school dietary dairy intake and teenage acne. J Am Acad Dermatol 2005; 52: 207-14.
16. Grant WB. Milk and other dietary influences on coronary heart disease. Altern Med Rev 1998; 3: 281-94.

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