Often confused with sweet potatoes, yams
rarely appear in American markets, except in cities with large ethnic populations. This thick
tuber, grown on tropical vines, is a staple food in Africa, where it originated, and in
Indonesia, the Caribbean, China, Korea, and India. Yams are similar in size and shape to sweet
potatoes, but contain more natural sugar and have a higher moisture content.
Health benefits and concerns
Asthma
Vitamin C, present in fruits and
vegetables, is a powerful antioxidant and
anti-inflammatory. This anti-inflammatory activity may influence the development of asthma
symptoms. A large preliminary study has shown that young children with asthma experience
significantly less wheezing if they eat a diet high in fruits rich in vitamin C.
Athletic performance
Carbohydrate food is the most efficient fuel for energy production
and can also be stored as glycogen in muscle and liver, functioning as a readily available
energy source for prolonged, strenuous exercise. For these reasons, carbohydrates may be the
most important nutrient for sports performance. Depending on training intensity and duration,
athletes require up to 4.5 grams of carbohydrates per day per pound of body weight or 60 to 70
percent of total dietary calories from carbohydrates, whichever is greater. Including starchy
vegetables in the diet is one good way to obtain these carbohydrates.
Bruising
Many Americans eat insufficient amounts of foods containing vitamin
C; the disease caused by vitamin C deficiency, scurvy, causes easy bruising. While very few
people actually have scurvy, even minor deficiencies of vitamin C can increase the incidence
of bruising. People who experience easy bruising may want to try eating more fruits and
vegetables—common dietary sources of vitamin C.
Cancer
The strong association between increased intake of beta-carotene from food and a reduced risk of lung cancer does not necessarily mean that supplementation
with natural beta-carotene supplements would reduce the risk of lung cancer. Dietary
beta-carotene may be a marker for diets high in certain fruits and vegetables that contain
other anticancer substances that may be responsible for the protective effects. Until more is
known, some doctors advise smokers to avoid all forms of beta-carotene
supplementation—even natural beta-carotene.
Capillary fragility
Eating plenty of flavonoid- and
vitamin C-rich fruits and vegetables helps to support the structure of capillaries.
Cataracts
Some, but not all, studies have reported that eating more foods rich
in beta-carotene or vitamin A was associated with a lower
risk of cataracts. Synthetic beta-carotene supplementation has not been found to reduce the
risk of cataract formation. It remains unclear whether natural beta-carotene from food or
supplements would protect the eye or whether beta-carotene in food is merely a marker for
other protective factors in fruits and vegetables high in beta-carotene.
High homocysteine
A controlled trial showed that eating a diet high in fruits and
vegetables containing folic acid, beta-carotene, and
vitamin C effectively lowered homocysteine levels. Healthy people were assigned to either a
diet containing a pound of fruits and vegetables per day, or to a diet containing 3 1/2 ounces
(99g) of fruits and vegetables per day. After four weeks, those eating the higher amount of
fruits and vegetables had an 11 percent lower homocysteine level compared to those eating the
lower amount of fruits and vegetables.
Kidney stones
Potassium reduces urinary calcium
excretion, and people who eat high amounts of dietary potassium appear to be at low risk of
forming kidney stones. The best way to increase potassium is to eat fruits and vegetables. The
level of potassium in food is much higher than the small amounts found in supplements.
Macular degeneration
People who eat plenty of fruits and vegetables high in beta-carotene
appear to be at lower risk for macular degeneration than people who do not eat these foods.
However, another study found no association between age-related macular degeneration and
intake of antioxidants, either from the diet, from supplements, or from both combined. More
research is needed to reconcile these differences. In the meantime, beta-carotene-rich
vegetables continue to be part of a healthful diet.
Multiple sclerosis (MS)
In one survey, researchers gathered information from nearly 400
people (half with MS) over three years. They found that consumption of vegetable protein, fruit juice, and foods rich in vitamin C, thiamine, riboflavin, calcium, and potassium correlated with a decreased MS risk.
Night blindness
Low intake of fruits and vegetables containing beta-carotene, which
the body can convert into vitamin A, may contribute to a vitamin A deficiency.
Pap
smear
Most dietary studies have found that women receiving high amounts of
nutrients from fruits and vegetables have less risk of cervical dysplasia. Protective effects
may be especially strong from diets high in dark yellow and orange vegetables (carrots, winter
squash, etc.) and tomatoes.
Stroke
Researchers have found an association between diets low in potassium
and increased risk of stroke. However, the association of increasing dietary potassium intake
and decreasing stroke mortality only occurred in black men and hypertensive men in one study.
Others have found an association between increased risk of stroke and the combination of low
dietary potassium plus high salt intake. Increasing dietary potassium has lowered blood
pressure in humans, which by itself should reduce the risk of stroke; however, some of the
protective effect of potassium appears to extend beyond its ability to lower blood pressure.
Maintaining a high potassium intake is best achieved by eating fruits and vegetables.
Health benefits and
concerns for vegetables
Many health benefits and concerns associated with this food are applicable to other
vegetables. Read about health benefits and concerns
for vegetables for a full description.