However, new research suggests that low-fat milk could actually be doing us more harm than good, increasing the risk of serious health problems-from infertility to prostate cancer.
Worse, scientists hypothesize that stripping the fat from milk-to make the drink supposedly healthier-could be the very reason for its toxic effects.
Two major studies have discovered that a high-dairy diet increases the risk of prostate cancer-but the real culprit could be the multibillion-pound low-fat industry built upon the belief that animal fats cause heart disease (see WDDTY vol 17 no 11). Scientists now suspect that the real problem is processed, low-fat dairy foods that have been stripped of their protective and health-giving qualities.
The two separate studies-both published in February-have confirm-ed growing suspicions of a link between dairy and prostate cancer. One is the CLUE II study, involving nearly 4000 men in Washington County, Maryland; this found that those who consumed five or more servings a week of dairy foods were more likely to suffer from prostate cancer than those who ate a serving of one or less (Cancer Causes Control, 2007; 18: 41-50).
Similarly, the other study, an analysis of over 29,000 Finnish men taking part in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (ATBC Study), found that the more dairy consumed, the higher the risk of prostate cancer (Int J Cancer, 2007 Feb 2; Epub ahead of print).
These findings deal a double blow to the dairy industry, yet the link between dairy and prostate cancer is not new. As far back as 1975, scientists noted a strong correlation between milk intake and prostate cancer deaths (Am J Clin Nutr, 2005; 81: 1147-54).
Since then, many more reports have confirmed an increased cancer risk from dairy foods-particularly milk, the most common form of dairy consumed.
Initial explanations for such an association blamed saturated dairy fat (Salud Publ Mex, 1997; 39: 298-309), but mounting evidence suggests that the truth could be quite the opposite: that removing the fat from milk may be responsible for the carcinogenic effects.
An American prospective study involving more than 3600 men and 10 years of follow-up-for the first National Health and Nutrition Examination Epidemiologic Follow-up Study (NHEFS)-found that those with the highest intakes of dairy were more than twice as likely to develop prostate cancer than men with the lowest intakes.
However, when the researchers looked at the individual dairy products consumed, they found that the risk was higher only with low-fat milk-and not for whole milk or any other dairy. In fact, whole milk had a slight-albeit statistically not significant-protective effect (Am J Clin Nutr, 2005; 81: 1147-54).
Harvard's Physicians' Health Study arrived at a similar conclusion. This study, involving over 20,000 men and 11 years of follow-up, found that the increased risk of prostate cancer associated with dairy intake was attributable primarily to skimmed milk. Of the five dairy foods investigated (milk in cold breakfast cereal, whole milk, skimmed milk, cheese and ice cream), only skimmed milk showed a significantly positive relationship when men consumed one or more servings per day (Am J Clin Nutr, 2001; 74: 549-54).
Similar results were found in a prospective study of more than 25,000 Norwegian men (Int J Cancer, 1997; 73: 634-8) and, in an analysis of milk-drinking and diet in 41 countries, Dr William B. Grant, of the NASA Langley Research Center in Virginia, found that non-fat milk had the highest association with prostate-cancer death rates (Altern Med Rev, 1999; 4: 162-9).
Thus, rather than being a healthy choice, low-fat milk-and possibly other low-fat dairy items-may, in fact, be detrimental to men's health. But why should this be so?
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 anticarcinogenic 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 (Anticancer Res, 1990; 10: 1307-11).
Indeed, a recent study from Harvard showed that a high calcium intake-whether from diet or supplements-was associated with reduced levels of calcitrol and a higher risk of prostate cancer (Cancer Epidemiol Biomarkers Prev, 2006; 15: 203-10). The above-mentioned Finnish study also suggested a connection between calcium and prostate cancer (Int J Cancer, 2007 Feb 2; Epub ahead of print).
While the suppressive effects of calcium from whole milk may be countered by higher levels of vitamin D, such a reversal of calcium effects may not occur with low-fat milk as fat-reduced milk tends to contain little, if any, vitamin D. And even if the vitamin is added to skimmed milk, as it is in the US, it may still be less well-absorbed from fat-reduced milk.
This has been confirmed in studies looking at different types of milk that have shown that calcium from low-fat or skimmed milk is associated with a greater risk of prostate cancer, while calcium from whole milk is not (Am J Clin Nutr, 2005; 81, 1147-54; Am J Clin Nutr, 2001; 74: 549-54).
So, it appears that, far from being good for us, calcium-when separated from the fat in milk-can be toxic to the body.
The CLA connection
Another possible explanation is that stripping the fat from milk also removes other important cancer-protective 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 anticarcinogen. In the lab, 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 58 per cent up to 90 per cent (Br J Nutr, 2003; 90: 877-85; Anticancer Res, 2000; 20: 3591-601).
Although modern milking methods and processing affect the CLA content of milk, 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 effect. The researchers attributed the results to CLA, although they noted that other potentially anticancer components, such as sphingomyelin and ether lipids, may have also played a role (Am J Clin Nutr, 2005; 82: 894-900).
CLA may protect against prostate cancer by cancelling out the effects of the potentially carcinogenic growth factors found in milk, such as insulin-like growth factor-1 (IGF-1). This occurs naturally-and in identical forms-in both cows and humans. Because cows are milked during and after pregnancy-when growth factors are at their highest-scientists are concerned that consuming milk and dairy could raise IGF-1 levels in humans-perhaps by crossing the gut wall-and trigger an abnormal res-ponse leading to, for example, certain cancers.
Indeed, elevated IGF-1 levels have recently been linked to an increased risk of gastrointestinal and breast cancers (Int J Health Serv, 1996; 26: 173-85; Lancet, 1998; 351: 1393-6), lung cancer, childhood cancers, melanoma, and cancers of the pancreas and prostate (Ann NY Acad Sci, 1995; 766: 402-8; J Natl Cancer Inst, 2000; 92: 1910-7).
The association with the prostate appears to be particularly strong. In one study, men with the highest levels of IGF-1 had more than four times the risk of prostate cancer compared with those who had the lowest levels (Science, 1998; 279: 563-6).
Whether the IGF-1 in milk is the real culprit is not yet known. What is clear is that milk stripped of its natural fat is more likely to promote cancer, and the more of its natural fat-and CLA content-that milk retains, the more anticancer benefits it will have.
But it's not only men who are at risk from the hazards of low-fat milk, and the problem isn't just cancer. Harvard scientists recently confirmed a link between low-fat dairy in the diet and an increased risk of infertility due to lack of egg release-also known as 'anovulatory infertility'.
This study monitored 18,555 American women aged 24 to 42, without a history of infertility, who were trying to become pregnant or had become pregnant between 1991 and 1999. It showed that women who ate two or more servings of low-fat dairy foods a day, such as skimmed milk or yoghurt, increased their risk of anovulatory infertility by more than
85 per cent compared with women who ate less than one serving of low-fat dairy a week.
Of the low-fat dairy foods, women who consumed one or more servings per week of skimmed or low-fat milk had a significantly higher risk of anovulatory infertility compared with those having less than one serving per week.
In contrast, adding a daily serving of whole milk reduced the risk of infertility by more than 50 per cent. Other high-fat dairy products, such as ice cream, were also associated with a lower risk.
Previous research has suggested that lactose, the sugar found in milk, might be involved in anovulatory infertility, but the present study found no such connection. Instead, the researchers believe that the presence of a fat-soluble substance, which improves ovarian function, might explain the lower risk of infertility from high-fat dairy foods. As with the prostate-cancer studies, there appears to be a substance vital for healthy ovaries that requires the presence of fat for it to be properly absorbed (Hum Reprod, 2007 Feb 28; Epub ahead of print).
This may also explain why studies that have looked at dairy intake and rates of ovarian cancer have found that only low-fat milk and skimmed milk, but not whole milk, were associated with an increased cancer risk. In the Brigham and Women's Hospital Nurses' Health Study, based on more than 80,000 women, those who consumed one or more servings of skimmed or low-fat milk daily had a 32-per-cent higher risk of any type of ovarian cancer-and a 69-per-cent higher risk of serous ovarian cancer, the most widespread form-compared with women who had three or fewer servings a month. Whole milk, on the other hand, had no such effect (Int J Cancer, 2004; 110: 271-7).
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."
Considering the other negative health effects linked to low-fat milk, should we all heed this advice?
Sadly, it's not that simple. While whole milk seems to be a healthier option than low-fat or skimmed milk, it, too, is subjected to processing that destroys some of its nutrients. Pasteurization typically involves heat-ing milk for 30 seconds at 63 degrees C, which destroys beneficial bacteria as well as all the important enzymes that aid milk digestion. Essential vitamins and proteins are also damaged or destroyed.
Homogenization, a process that passes milk through a fine filter, causes other problems by reducing the size
of fat globules by a factor of 10 or more. When protein molecules become attached to these smaller fat globules, this piggy-backing allows the proteins to bypass digestion in the stomach, which may lead to their incomplete digestion and allergies.
Processed milk also contains a host of undesirable components (see box, page 8), which might explain why it's not just low-fat milk that has been linked to a rash of illnesses, but other sorts of dairy in general.
So, other than avoiding all dairy products altogether, a more sensible option would be to consume milk in its most natural state-raw, unprocessed and full-fat.
For more information on raw milk and where you can get it, visit the website: www.realmilk.com.