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Declining Nutrition of Fruits and Vegetables
Government Analysis Indicates Many Minerals Less Abundant
Results from research into Americans' diet habits haven't been good. We're consuming more calories than ever, many of them from unsaturated fats, and as a result, we're getting fatter, and probably unhealthier.
But if a person should decide to improve his or her diet and eat the foods doctors and dieticians recommend for better health, would it be enough? Actually, there is some evidence that the fruits and vegetables available to most people today don't contain the nutritional value they had about 40 or 50 years ago.
In 2004, a University of Texas research team headed by biochemist Donald Davis, Ph.D., analyzed a U.S. Department of Agriculture report on 43 common garden fruits and vegetables and found that almost half of the substances containing minerals important to good health had lost some nutritional value.
Davis said in a university news release that at first, his team didn't evaluate individual fruits and vegetables but found the nutritional declines in the plants as a group. "Considered as a group, we found that six out of 13 nutrients showed apparently reliable declines between 1950 and 1999," he said.
The nutrients Davis's team identified as losing at least some measurable value were protein, calcium, phosphorus, iron, riboflavin and ascorbic acid. The declines ranged from 6 percent for protein to 38 percent for riboflavin.
Specific Produce Identified as Losing Nutritional Value
Why did this happen? As best as Davis can determine, the nutritional value in some produce was diluted through faster methods major agro-farm companies employed to grow high-yield crops to meet consumer demand.
Davis continued studying what he termed the "genetic dilution effect" and was able to identify specific high-yield crops that had declines in nutrients.
Mother Earth News reported in its June/July 2009 edition that Davis had used the USDA report to find the following declines in nutritional value of broccoli:
According to U.S. Department of Agriculture (USDA) nutrient data, calcium content of broccoli which averaged 12.9 milligrams per gram of dry weight in 1950, had declined to only 4.4 mg/g dry weight in 2003
And in a study of much longer duration, Davis reported that in wheat and barley crops, protein concentrations declined by 30 to 50 percent between the years 1938 and 1990.
DID YOU KNOW?
According to the Centers for Disease Control and Prevention (CDC),
only 11% of Americans meet the USDA’s guidelines for eating 5-9 servings of fresh fruit and vegetables daily. CDC data indicates:
Which Foods are the Most Nutritious?
There is no single food group that contains more nutrients than another, according to the U.S. Department of Agriculture. But the USDA lists the following foods as having the most nutrient value in specific vitamins and minerals:
- Calcium -- spinach and calcium-fortified juices, dairy products
- Fiber -- apples, lentils, lima beans, pears, spinach, raspberries
- Folate -- asparagus, broccoli, chickpeas, lima beans
- Iron -- lentils, spinach
- Magnesium -- almonds, Brazil nuts, pinto beans, spinach (1/2 cup cooked)
- Potassium -- banana, broccoli, sweet cherries, chickpeas, Kiwi fruit, lentils potato, tomato
- Sodium -- low sodium: artichoke, bell pepper, broccoli, carrot, celery, radish, sweet potato; very low sodium: Brussels sprouts, green cabbage, cantaloupe, cauliflower, chickpeas, dried figs, grapes, lentils, iceberg lettuce, leaf lettuce, Lima beans, green onion, mushrooms, tomatoes
- Vitamin A -- cantaloupe, carrot, grapefruit, leaf lettuce, Romaine lettuce, mango, spinach, sweet potato, tomato, watermelon
- Vitamin C -- bell pepper, broccoli, Brussels sprouts, green cabbage, cantaloupe, cauliflower, grapefruit, Kiwi fruit, lemon, lime, honeydew melon, onion, orange, pineapple, potato, radish, spinach, summer squash, strawberries, sweet potato, tangerine, tomato, watermelon
- Protein -- red meat, chicken, soy, fish, legumes, eggs and dairy
You can find further information on good sources nutrition at the USDA Web site.
When to Consider Adding Dietary Supplements?
Jane Higdon, Ph.D., LPI Research Associate at Oregon State University's Linus Pauling Institute, reports that multivitamin supplements appear to have beneficial qualities.
Don't confuse a multi-vitamin pill or capsule as a replacement for prescription medicine. And it's important to remember to consult with your physician about any substances you might want to take -- both over-the-counter and prescription.
"Although it hasn’t been proven that a daily multivitamin supplement containing 100 percent of the Daily Value of most vitamins and essential minerals will lead to better health for well-nourished people," she writes, "recent research indicates that several of the nutrients found in standard multivitamin supplements play important roles in chronic diseases.”
"A daily multivitamin supplement ensures an adequate intake of several micronutrients that are not always present in the diet in optimal amounts," Dr. Higdon concludes. In her report, she identifies key vitamin and nutrient elements considered necessary for maintaining good health:
Increased folic acid intakes can lower homocysteine levels, and high homocysteine levels are associated with increased risk of some chronic conditions.
Since it is only found in animal products, strict vegetarians also need to get vitamin B12 from a supplement or fortified foods.
In many parts of the world, there is insufficient ultraviolet light for vitamin D synthesis in the skin during winter. Using sunscreen and avoiding sun exposure to prevent skin damage also prevents vitamin D synthesis. Vitamin D synthesis in the skin declines with age.
Iron deficiency is the most common micronutrient deficiency worldwide and is a significant problem in the U.S. Although uncommon in men and postmenopausal women, iron deficiency is still common in children, adolescents, and premenopausal women.
Omega-3s are also important, as they regulate many of the body’s functions, and balance the high-level of omega-6 fats found in the meat and animal fats found many American’s diets. Fish-oil, flax seed, and walnuts are good sources of omega-3s.
Tips to Preserve the Nutrients in Your Produce
Cooked vs Raw: High heat and water can destroy up to 30 percent of nutrients found in raw fruits and vegetables. Sautéing, steaming or even microwaving healthy produce can minimize nutrient loss. In fact, in some instances, cooking increases the potency of nutrients by aiding in the break down the cell walls of the plant. Cooking increases the availability of antioxidants typically found in carrots, spinach and tomatoes.
Fresh vs Frozen: When it comes to superior taste and nutrition, fresh fruits and vegetables from the garden are always best. But by the time your "fresh" produce reaches your local grocer, it has had plenty of exposure to air, heat and light -- enough time to diminish its nutritional value. Frozen produce, which is usually flash-frozen quickly after picking, can be just as nutritious and can last for about a year.
Canned produce is the least favorable option as most of the produce vitamin content is destroyed by high temperatures used in processing or lost in the water in the can. Canned fruit packed in in high calorie syrup should also be avoided.
Get more tips to maximize the healthfulness of your produce here.
- University of Texas news release, Dec. 1, 2004.
- Journal of the American College of Nutrition, Changes in USDA Food Composition Data for 43 Garden Crops, 1950 to 1999,Vol. 23, No. 6, 669-682 (2004).
- Mother Earth News, Industrial Farming is Giving us Less Nutritious Food, June/July 2009.
- HealthDay News Service, Vitamin D Good for Breast Cancer Patients, Oct. 9, 2009.
- U.S. Department of Agriculture Food Pyramid and nutrition content; Jane Higdon, Ph.D., LPI Research Associate Linus Pauling Institute Research Report, Oregon State University.
- Consumer Reports on Health, Preserve Your Nutrients, October 2009.