SCIENTIFIC UPDATE

Dairy product consumption is increasing worldwide, even in countries such as China where dairy products were not a traditional part of the diet. As we face a global epidemic of obesity, scientists are questioning the effect of increased dairy product use on the risk of obesity. Some researchers have suggested that dairy products can promote weight loss, although this claim has been questioned. A recent meta-analysis rigorously examined the results of 29 studies which investigated the impact of dairy products on weight loss.

Overall, dairy product use was not associated with weight loss. In studies where subjects followed low calorie diets, the use of dairy products was associated with greater weight loss over the short term but was not associated with weight loss in longer term studies, lasting at least a year. In studies where subjects did not reduce calories, the use of dairy products was not associated with short-term weight loss and was actually associated with weight gain in studies lasting a year or longer. As the authors of the study state, "A long-term and sustained weight loss is of greater public health and clinical significance than a short-term weight loss is, and the results of this meta-analysis do not support increasing dairy consumption as an effective way for long-term weight control." It seems clear that dairy products are not an essential part of a weight reduction diet and that wide-scale introduction of dairy products is not a solution to the problem of obesity.

Omega-3 fatty acids, namely EPA and DHA, are typically found in fish and fish oil and are the reason many people take fish oil supplements. Vegetarians can get alpha-linolenic acid, another omega-3 fatty acid, from foods including flaxseeds, flaxseed oil, walnuts, and canola oil. Alpha-linolenic acid can be converted to EPA and DHA in our bodies to a limited degree. Vegetarians can use microalgae supplements to get the same omega-3 fatty acids as are found in fish. Use of foods or supplements containing omega-3 fatty acids has been promoted to the general public because these fats are believed to have benefits in terms of reducing the risk of heart disease.

Some have questioned whether or not vegetarians need to use fish oil supplements to reduce their risk of heart disease (you can read more about this issue on our website at http://www.vrg.org/journal/vj2005issue1/2005_issue1_hotline.php). A recent meta-analysis raises significant questions about the role of omega-3 fatty acids in heart disease in the general population. Twenty studies of a total of 68,680 people were included in the meta-analysis. Researchers examined the effects of supplements of omega-3 fatty acids on heart attacks, strokes, and deaths from heart disease.

Omega-3 supplements (typically fish oil capsules) did not decrease the risk of heart attack, stroke, or of dying from heart disease. These results call into question the widespread use of fish oil supplements to reduce the risk of heart disease or stroke.

The American Academy of Pediatrics has concluded that the mother's avoidance of tree nuts or peanuts during pregnancy does not reduce the risk of her infant developing an allergy to one or both of these products (Pediatrics. 2008; 121:183-191). A recent study looked at a related issue — whether or not avoiding nuts during pregnancy can affect the risk of asthma. Many vegetarian women who rely on nuts and peanuts as convenient foods will be interested in these results. The study was conducted in Denmark and included more than 60,000 subjects. Maternal nut and peanut intake was assessed at the mid-point of pregnancy using a questionnaire. When infants were 18 months old, their mothers were asked if they had been diagnosed with asthma or had symptoms, such as a wheeze. The mothers were also asked about their children's symptoms and diagnoses when the children were 7 years old.

Higher maternal peanut or tree nut intake during pregnancy (once or more a week as compared to never) was associated with a lower risk of asthma in 18-month-old and 7-year-old offspring. This study found no increased risk of asthma with peanut and tree nut consumption during pregnancy. Higher use of tree nuts and peanuts was actually associated with a lower risk of wheezing. These results suggest that women can eat peanuts or tree nuts when they are pregnant without having to worry about increasing their child's risk of developing asthma or wheezing.

Dried beans such as kidney beans, chickpeas, and lentils are typically high in fiber and protein. They are described as 'low-glycemic index' foods, which means that after people eat beans, their blood sugar levels don't go up that much. These characteristics make beans a potentially important food group for people with diabetes. A recent study assigned people with type 2 diabetes, the most common kind of diabetes, to one of two groups. Half were encouraged to increase their intake of cooked dried beans by at least one cup a day. The other half was encouraged to increase their fiber intake by eating more whole wheat products. The study lasted 3 months. Blood tests showed that blood sugar levels were better controlled in the group eating beans. This group also lost slightly more weight and had a larger drop in waist circumference.

In addition, the group eating beans had lower blood pressure and a lower heart rate. Estimated heart disease risk was lower in the group eating beans compared to the group eating fiber from wheat. These results indicate that beans can play an important role in diets of people with type 2 diabetes.

Dried beans are a traditional food for many cultures, including some Native Americans, Latin Americans, and Asian Indians. As diets of these groups have changed to include more animal products and processed foods, rates of type 2 diabetes have soared. A return to the use of dried beans may help to reduce the risk of developing type 2 diabetes.

A recent meta-analysis combined the results of seven studies where vegetarians' health was compared to non-vegetarians' health. More than 120,000 participants were included. Study participants were from the UK, Germany, the Netherlands, Japan, and California. The 'vegetarian' group included lacto-ovo vegetarians and vegans, as well as participants who ate meat or fish less than once a week. The risk of death from heart disease was 29% lower in the 'vegetarian' group than in non-vegetarians. This reduced risk was seen in those who had followed a vegetarian or near-vegetarian diet for more than 5 years. There was not a significant difference between the groups in the risk of dying from a stroke. The incidence of cancer was 18% lower in the 'vegetarian' group. This difference did not appear to be due to a difference in cancer incidence in any one of the major cancer sites, such as breast, lung, prostate, or colon, but was in overall cancer incidence.