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.