Scientific Update

New Study Shows Benefits of Lower Dietary Sodium

Almost one quarter of adults in the United States have hypertension. Less than half of US adults have what is considered to be optimal blood pressure (below 120/80). Many factors influence blood pressure, including obesity, sodium intake, and alcohol use. In 1997, we reported that a dietary approach using generous amounts of fruits, vegetables, and lowfat dairy products with reduced saturated and total fat was effective in reducing blood pressure. This diet was called the DASH diet. DASH stands for Dietary Approaches to Stop Hypertension. Of course, we don't know whether or not a diet that did not contain any animal products would have been even more effective. A follow-up to this study found that reducing sodium intake from the high level typical of American diets to a low level of sodium in conjunction with the DASH diet had a significant effect on blood pressure. This effect, in those study participants with hypertension, was the same as or greater than the reduction that would be seen with blood pressure medication. The combination of the two dietary changes, namely more fruits and vegetables and less red meat along with a reduction in sodium, led to the greatest effect on blood pressure. The diet and sodium reduction worked to lower blood pressure in people with hypertension and in people without hypertension, in men and women, in African-Americans and caucasians. Even in people who did not use the DASH diet, a significant reduction in blood pressure was seen when sodium was reduced. Currently, the average level of sodium intake in the United States is 3.5 grams (3,500 milligrams) per day. This is the equivalent of almost 9 grams or 1.5 teaspoons of salt. The majority of this salt comes from prepackaged foods and not from salt added in cooking. To achieve a reduction in sodium to either 2.3 grams (good) or 1.2 grams (better), food manufacturers will need to produce more low-sodium foods. Vegetarians typically have lower blood pressure than non-vegetarians, possibly for dietary reasons or because vegetarians tend to have lower weights. Nevertheless, many vegetarian convenience foods are quite high in sodium. Consumers can contact manufacturers and request that they reduce sodium in their products. If we don't ask for it, chances are they won't produce it!

Sacks FM, et al. 2001. Effects on blood pressure of reduced dietary sodium and the dietary approaches to stop hypertension (DASH) diet. New Engl J Med 344: 3-10.

Greenland P. 2001. Beating high blood pressure with low sodium DASH. N Engl J Med 344: 53-55.

New Regulations Released For Organic Foods

On December 20, 2000, the USDA announced the final national standards for the production, handling, and processing of organically-grown agricultural products. When organic standards were first proposed, there was a tremendous outcry because the proposed standards allowed genetically engineered foods, irradiated foods, and foods grown with sewage sludge to be defined as organic. More than 275,000 public comments were received by USDA (including comments from The Vegetarian Resource Group) protesting the proposed standards. The final standards incorporate many of the comments and prohibit the use of genetic engineering, ionizing radiation, and sewage sludge in organic production. New labeling regulations for organic products have been developed. In order for a product to be labeled “100 percent organic” it must contain only organically produced ingredients (with the exception of water and salt). A product labeled “organic” must contain at least 95% organically produced ingredients and any remaining ingredients must be not commercially available in organic form. Products containing at least 70% organic ingredients can be labeled “made with organic ingredients” and the remaining ingredients cannot be genetically engineered, irradiated, or use sewage sludge. Products that contain less than 70% organic ingredients cannot have anything on the display part of the label that says “organic.” The ingredient list on the label can identify ingredients that are organically produced. Products that are labeled “100 percent organic” or “organic” may use a special seal from the USDA that identifies the product as “USDA Organic.” These rules will be fully implemented by mid-2002, at which point we will begin to see USDA's seal on organic products.

National Organic Program, www.ams.usda.gov

Protein and Bone Health

Dietary protein from different sources may have different effects on bone. Researchers at the University of California, San Francisco, studied 1,035 women over the age of 65 years. Protein intake was determined by asking the women what they had eaten over the past year, and bone mineral density was measured. Women whose diets were highest in animal protein and lowest in plant protein lost more bone than did women whose diets had lower amounts of animal protein and higher amounts of plant protein. Higher losses of bone increase risk of osteoporosis and fracture. However, the amount of animal protein did not appear to be related to bone density, suggesting that bone loss due to animal protein may not occur until later in life. Women with a high intake of animal protein had almost 3 times more risk of fracturing a hip than did women with low intakes of animal protein. While adequate protein intake is important to bone health, the use of more vegetable protein sources and less animal protein appears to also be important in older women.

Sellmeyer DE, Stone KL, Sebastian A, et al. 2001. A high ratio of dietary animal to vegetable protein increases the rate of bone loss and the risk of fracture in postmenopausal women. Am J Clin Nutr 73: 118-122.

New Research on Iron and Vitamin C

Most of us know that the form of iron found in plants (called non-heme iron) is not absorbed as well as heme iron, found in animal products. Vegetarians are often taught that vitamin C improves the absorption of non-heme iron so that to maximize iron absorption from vegetarian meals, meals should include orange juice, tomato products, or other good sources of vitamin C. There is a great deal of variation from one individual to another in the amount of iron that is absorbed. A recent study found that this individual variability accounts for more than half of the variability in iron absorption, while vitamin C accounts for only about 8% of the variability. However, food sources of vitamin C can still improve iron absorption, although perhaps not as much as was once believed. Because of the benefits of both substances, it is still important for vegetarians to include good sources of both iron and vitamin C in their diets.

Cook JD, Reddy MB. 2001. Effect of ascorbic acid intake on nonheme-iron absorption from a complete diet. Am J Clin Nutr 73: 93-98.

Do Vegetarians Need to Be Concerned About Vitamin A?

The Institute of Medicine recently released new recommendations for a number of vitamins and minerals, including vitamin A. Their report concluded that fruits and vegetables provide the body with half as much vitamin A as previously thought. Some newspaper reports warned that vegetarians might need to eat more dark-colored fruits and vegetables if they rely on these foods for vitamin A and don't get vitamin A from meat, fish, eggs, or vitamin A-fortified milk. This is a strange warning since vitamin A deficiency is very rarely reported in the United States, even among those relying on fruits and vegetables for vitamin A. Is this something to be concerned about? Probably not. Dark-colored fruits and vegetables like carrots, sweet potatoes, and apricots are quite high in beta-carotene, which our bodies make into vitamin A. Even if these foods are only half as effective at supplying vitamin A as we thought, they are still great sources. For example, the new RDA for vitamin A is 900 micrograms per day for men and 700 micrograms per day for women. Since 12 micrograms of beta-carotene are needed to provide the equivalent of 1 microgram of vitamin A, if you only used foods containing beta-carotene to meet your vitamin A requirements, a safe level of beta-carotene would be 8,400 micrograms (700 x 12) for women and 10,800 micrograms (900 x 12) for men. Please note that these are micrograms of beta-carotene, NOT vitamin A. A half-cup of cooked carrots provides 6,252 micrograms of beta-carotene, while one medium raw carrot provides 5,390 micrograms. A half-cup of sweet potatoes provides 9,488 micrograms of beta-carotene, two apricots provide 1,788 micrograms, and a half-cup of broccoli has 959 micrograms. As you can see, eating a couple of servings of dark green vegetables or deep-orange fruits and vegetables daily can easily provide all the vitamin A you need. In addition, some brands of soymilk are fortified with vitamin A. Do vegetarians need to be concerned about vitamin A? No, as long as we eat a variety of fruits and vegetables regularly. We'll have more about the new recommendations for iron and zinc in the July/August issue of Vegetarian Journal.

Food and Nutrition Board, Institute of Medicine. 2000. Dietary Reference Intakes for Vitamin A, Vitamin K,Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press. www.nas.edu.