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Wednesday, August 24, 2011

Are dairy products healthy?

Many books and articles contain health recommendations based on little or no scientific evidence. So when making personal decisions about how to maintain and improve one’s health, it is important to look for books and articles based on solid studies, especially large, well-controlled ones. A good example of science-based health information can be found in the July/August 2011 issue of the Nutrition Action Health Letter, published by the Center for Science in the Public Interest. It evaluates the pros and cons of consuming dairy products, Some of its key points:

We all know that milk is a major source of dietary calcium, which is needed to maintain bone density. Recently however, some health writers have contended that eating animal protein lowers bone density. Because protein contains amino acids, the alleged mechanism is increased acidity of the blood, prompting the body to respond by leaching calcium from the bones to neutralize the acid. Since milk is a protein source, it is implicated in bone loss. However, scientific study has refuted this contention. In actuality, bone mineral density is higher among people who eat more protein and lower among people who eat less protein. Radio isotope studies that tracked actual deposition and depletion of calcium have verified that consumption of dairy foods does not increase bone loss as we age.

Colon Cancer
A major analysis by the Harvard School of Public Health of 10 studies conducted in 5 countries, involving over 500,000 people concluded that people who drank at least one cup of milk per day had a 15% lower risk of colon cancer than those who drank less than 2 cups per week. Similarly, people treated for colon cancer who took 1200 mg of calcium per day and who had an above-average Vitamin D level had 15% less chance of recurrent colon cancer than those who didn’t take the calcium. Twenty-five percent of experimental animals fed a high-fat diet low in fiber, calcium, Vitamin D, and folic acid, developed colon tumors, but those supplemented with calcium and Vitamin D got none.

Prostate Cancer
There is some inconsistent evidence that high calcium consumption (in excess of 1500 mg/day) may increase the risk of prostate cancer. Milk increases the body’s level of insulin-like growth factor-1 (IGF-1), a hormone that stimulates the growth of both muscle and bone, but may also stimulate prostate-cancer growth. Even though a study of men receiving a 1200 mg calcium supplement daily showed no prostate cancer increase, the article recommended that men limit their calcium intake from food and supplements combined to 1000 mg/day if under 70 years of age and 1200 mg/day if over 70.

Blood Pressure
Adding 2 servings per day of low-fat dairy foods to a diet rich in fruits and vegetables, lowered blood pressure even further. In addition, a study of 28,000 women over 10 years showed that those consuming at least 2 cups/day of low-fat dairy foods reduced their risk of high blood pressure by 10%.

Weight Loss
When restricted to the same number of calories per day, women consuming more dairy products showed no difference in weight loss than those who consumed less dairy. However, when allowed to eat all they wanted at the end of the study, the dairy group consumed fewer calories. The implication is that dairy may help control appetite. While the weight-loss results were equivocal, the women in the low-dairy group lost bone density in their hips, while the high-dairy group did not. This is an important finding, considering that dangerous loss in bone density is common among both women and men as they age.

Lactose Intolerance
Lactose is the sugar found in milk. The following is the lactose content of some dairy products:
  • 8 oz cup of milk: 12 grams
  • 6 oz cup of yogurt - 10 grams
  • 1 oz hard cheese or cream cheese - 1 gram or less
  • ½ cup cottage cheese - 4-5 grams
  • ½ cup ice cream - 4-5 grams
Many people think they are lactose-intolerant, However, the article cites evidence that between one-third and three-quarters of people who think they are lactose-intolerant are actually not so. Many of them show none of the typical symptoms of gas or diarrhea when lactose is put in their non-dairy drinks without their knowledge. Many people’s digestive systems can adjust to lactose by building up intestinal bacteria over a period of time. So the authors recommend that people who think they are lactose intolerant try to adjust to lactose by:
  • Limiting lactose to 12 grams at a time (the amount in one 8 oz glass of milk).
  • Consuming lactose along with other foods to give it more time to be digested
  • Eating dairy foods regularly to maintain lactose-digesting bacteria
  • Other Health Issues Related to Dairy Products
A study of 200,000 people over 20 years showed that those consuming 3-5 servings per day of dairy products had a 14% lower risk of Type II diabetes than those consuming less than 1.5 servings per day. However, it is not known whether that is an effect of the dairy products or another factor common to people who consume more dairy products.

Breast and Ovarian Cancer
Eight studies of 350,000 women in several countries did not find any link between milk consumption and breast cancer. However, research on 500,000 women in the U.S. and Europe did show a weak and marginally significant increased risk of ovarian cancer for women who consumed more than 30 grams of lactose per day. However, two major cancer research organizations did not feel the evidence was conclusive.

Bottom Line
Dairy products made from skim or one-percent milk can be considered health-promoting foods. They contain large quantities of calcium necessary for maintaining bone-density as we age. Also, most are excellent sources of protein (except products made primarily from milk fat, such as cream cheese and butter). Milk appears to help control blood pressure and avoid colon cancer, and may also help control appetite. However, high milk consumption may increase the risk of prostate cancer among men and ovarian cancer among women. Therefore, men should limit calcium consumption from food and supplements combined to 1000 mg/day below age 70 and 1200 mg/day above age 70. Adequate Vitamin D intake is essential for healthy bone mineralization, even if calcium intake is adequate. Many people are deficient in Vitamin D because of low sun exposure. Current recommendations for daily Vitamin D supplementation are in the neighborhood of 1,000-2,000 IU.

Additional Note
The main type of saturated fat found in milk (myristic acid) is particularly potent in raising blood cholesterol, specifically the harmful low-density variety (LDL). Because of that, consumption of milk fat should be very limited. High proportions of milk fat are found in cream, butter, ice cream, cheese (especially cream cheese and soft cheeses like Brie), whole milk, and 2% milk. That is why non-fat and 1% fat milk products are preferable. Unfortunately, many dishes popular in the U.S., such as cheese burgers cheese ravioli, macaroni and cheese, and pizza, contain large amounts of cheese. The evidence indicates that the cardiovascular health of Americans would benefit from a reduction in cheese consumption.