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WHY ARE FRUITS ARE VEGETABLES BEYOND THE
BUNDLE OF VITAMINS AND MINERALS?
Vanisha S. Nambiar (MSc. PhD)
Department of Food and Nutrition,
(A WHO collaborating Center for Nutrition Research in anemia control and
Chronic degenerative diseases)
The Maharaja SayajiRao University of Baroda, Vadodara - 390 002, Gujarat, India.
Email: [email protected]
INTRODUCTION
Fruits and vegetables have long been recognized as healthy foods and valuable sources of vitamins and
minerals (Nambiar and Seshadri, 1998; Seshadri and Nambiar 2003). However, recent research has
shown that through overlapping or complementary effects, the complex mixture of minerals, vitamins
as well as phytochemicals in fruits and vegetables, act as antioxidants and provide a better protective
effect on health than single nutrient/phytochemical. These active ingredients are found as are natural
colorants characterized by their distinctive colors — the deep red color of cherries, the red color in
tomatoes, the orange color in carrots, and the yellow color of corn, mangos and saffron. The best
known “phytos” are carotenoids, flavonoids, and isoflavones. Carotenoids include yellow, orange, and
red pigment in fruits and vegetables. Dark, green, leafy vegetables are rich in the carotenoid, beta
carotene, but the usual yellow color is masked by the chlorophyll, the green pigment in the vegetables.
Flavonoids are reddish pigments, found in red grape skins and citrus fruits, and isoflavones can be
found in peanuts, lentils, soy, and other legumes.
Several fields of science, including epidemiology, human medicine, and nutrition, suggest that fruit
and vegetable antioxidants play an important role in reducing the risk of degenerative diseases such as
cardiovascular disease, various cancers, stroke and neurological diseases (Ames et al 1993).
A study conducted by Joshipura and coworkers (2001) have recommended an intake of 6 servings
daily of fruits and vegetables as this is associated with a 30% reduction in the risk of ischemic stroke
among men and women. The study also controlled lifestyle confounders, and found out that green
leafy vegetables, cruciferous vegetables and citrus fruits and juice, in particular, were protective in
nature. A protective effect against death from coronary heart disease for both fruit and vegetables was
also reported in a large Finnish men and women. These researchers controlled for some potential
lifestyle confounders (age, gender, smoking status, obesity and energy intake), which suggested that
their findings was explained by those factors and thereby, strengthened their results (Knekt et al 1994).
In biological systems, ANTIOXIDANTS are defined as any substrate that when present at low
concentrations compared to those of an oxidizable substrate delays or prevents oxidation of that
substrate like lipids, proteins, DNA and carbohydrate. The body produces several enzymes including
Superoxide dismutase, catalase and glutathione peroxidase, which neutralize many types of free
radicals. In addition to enzymes, many vitamins and minerals act as antioxidants in their own right,
such as vitamin C, vitamin E, ß- carotene, lutein, lycopene, vitamin B2, and co –enzyme Q10 and
cysteine along with certain non-nutrients such as polyphenols/flavonoids. Free radicals are believed to
play a role in more than 60 different health conditions, including the aging process, cancer and
arteriosclerosis.
Antioxidants work in several ways: they reduce the energy of the free radicals, stop the free radical
from forming in the first place or interrupt an oxidizing chain reaction to minimize the damage caused
by free radical. Antioxidants are thought to protect our cells from damage by cancer-causing agents in
several ways, interrupting one or several metabolic processes that can lead to cancer.
-
Inhibit formation of carcinogen.
-
Block the initiation of carcinogen.
-
Suppress the progression and proliferation of tumor.
-
Inhibits the lipid oxidation.
ANTIOXIDANTS IN FRUITS AND VEGETABLES--- NUTRIENTS:-
Food or diet contains large number of antioxidants, both nutritive and non-nutritive. The antioxidants
in fruits and vegetables include vitamin C, vitamin E, carotenoids and flavonoids, dietary fiber, folic
acid, phytoestrogens and other phytochemicals, potassium, magnesium and many other which may be
responsible for their protective effects (Eberhardt et al 2000; Halliwell 1994).
Vitamin C: - Fruits are rich sources of vitamin C (citrus fruits-amla, guava, oranges, grapes, pears).
Vitamin C there by plays a role of a powerful antioxidant in the body, one of the cofactor for
hydroxylase enzymes, recycles vitamin E, acts as an anti inflammatory agent and decreases the
incidence of asthma symptoms.
Vitamin E: - Tocopherols found in fruits are of high biological value and play a key role in preventing
oxidation of beta carotene and vitamin A as it is as a chain breaking antioxidant, prevents lipid
peroxidation of PUFA in cells and maintains integrity of cell membranes (Halliwell, 1994). Singhal et
al in 2001 interpreted from the study on antioxidant effects of vitamin E, vitamin C and Vitamin A and
fruit intervention in patients with CHD that all the antioxidant vitamins and fruits decrease the degree
of lipid peroxidation in CHD patients and the fresh fruit is the best choice out of all as it also favorably
modifies the lipid profile in such patients.
Carotenoids: - Carotenoids are a class of molecules that give fruits their bright colors. Some of the
carotenoids serve as precursors of vitamin A. beta-carotene is a dietary anticarcinogenic agent and
protects against heart disease. They act as antioxidants- scavenges singlet oxygen generated with the
interaction of light with chlorophyll. Carotenoids react with free radicals particularly the peroxyl
radicals and with the singlet molecular oxygen.
GLV’S are now recognized as rich sources of omega- 3fatty acids and several antioxidants such as
polyphenols and flavonoids and small molecular compounds like glutathione (Simopoulos et al, 1995;
Nambiar et al, 2005, Krinsky et al, 1979), which play a protective role against many degenerative
diseases.
Lycopene, one of the carotenoids, is a potent antioxidant. It has been associated with a reduced risk for
many cancers, especially prostate cancer, and protection against heart attacks, though research
continues on other potential health benefits. Tomato-based products have the most concentrated source
of lycopene. Cooked tomato sauces are associated with greater health benefits, compared to uncooked,
because the heating process makes all carotenoids (including lycopene) more easily absorbed by the
body. Green leafy vegetables like spinach and kale and brightly colored fruits and vegetables like
mangoes, oranges and cantaloupes contain phytochemicals called lutein and zeaxanthin that may
reduce the risk for macular degeneration.
Dietary Fiber: - Fruits and vegetables are rich sources of dietary fiber especially, pectin, lignin,
hemicellulose, etc. these fibers entrap cholesterol and food there by lowers the digestion time in body.
The fibre acts as hypocholesterolemic and hypoglycemic agent (Antia 1996). Isolated dietary fibers
from fruits and vegetable sources, particularly pectins have been shown to lower hypercholesterolemic
action in humans. The addition of pectin and fibre containing foods to experimental diets also reduce
plasma cholesterol (Lampe et al 1999). Increase excretion of
fecal bile acids and neutral steroids.
Alter ratios of primary and secondary bile acids. Indirect effects, like high fiber foods replacing fat and
cholesterol containing foods. Fiber also increases fecal cholesterol and fatty acid excretion. A diet high
in fibre prevents CHD. Eating fruits and vegetables high in the soluble fibre pectin has been linked
with reduced cholesterol levels (Perry, 1998)
Rai et al 1987 conducted a study to see the effect of Ocimum Sanctum (Tulasi) leaves on the blood
lipoproteins, glycated proteins and total amino acids in patients with NIDDM. All the patients were on
hypoglycemic drugs. One gm of powder was given to the patients for 1 month. After 1 month of
supplementation, a significant lowering of the blood glucose (20.8%), glycated proteins (11.2%), total
amino acids (13.5%) and uronic acid (13.7%) was observed. A significant reduction was also noticed
in the levels of TC (11.3%), LDL-C (14.0%), VLDL-C (16.3%) and TG (16.4%). No appreciable
change was noticed in HDL-C.
A study was carried out by Iyer et al, 1990 to study the effect of curry leaves powder supplementation
(12 gm providing 2.5 gms fibre) was given to 30 NIDDM patients for a period of 1 month. There was
a transient reduction in fasting and post-prandial blood sugar level at 15-day period with no
appreciable changes in serum glycosylated protein levels, glycosylated LDL-C fraction, serum lipids,
lipoprotein cholesterol levels, uronic acids and total amino acids.
Folic acid: - This B vitamin is especially found in green leafy vegetables and citrus fruit. It is much
publicised as preventing certain spine malformations in the fetus, but it also has a very likely role in
prevention of coronary heart disease (by lowering the blood level of homocysteine), may well help
prevent some cancers, and it is critical for all cell multiplication in the body. Unfortunately it is easily
destroyed by heat in its natural form (but not the synthetic kind used in food fortification), so such
foods should best be eaten either raw or only lightly cooked, preferably by microwaving or steaming.
It plays a role in methionine metabolism. The deficiency of folic acid leads to production of
homocysteine, which is linked, with increased risk of CVD (Morrison, 1996).
Potassium: - They contain high amounts of potassium that is responsible for electrolyte and fluid
balance i.e. osmotic balance to keep body cells intact.
Magnesium: - It is present in small concentrations and is required for cellular metabolism. It is also
implicated to have a role in CVD (Gopalan, 1996)
NON-NUTRIENT ANTIOXIDANTS IN FRUITS AND VEGETABLES
Non-Nutrient antioxidants are consumed at concentrations far exceeding nutrient antioxidants
(1g/day). These compounds are mainly polyphenolics especially falvonoids, phenolic acids,
anthocyanidins etc.
Polyphenols are receiving increasing interest from consumers and food manufacturers for several
reasons. Epidemiological studies have suggested associations between the consumption of polyphenolrich foods or beverage and the prevention of disease. Flavonoids are natural plant products that
provide color, texture and taste to plant foods. An important effect of flavonoids is scavenging of
oxygen-derived free radicals.
Flavonoids, a group of > 4000 polyphenolics, are products of plant metabolism and naturally occurring
polyphenolics present in fruits and vegetables and play an integral part in human diet. Although 5,000
plant phytochemicals have been identified, a large proportion remains unknown.
The chemical structure of polyphenols will affect their biological properties, bioavailability,
antioxidant activity, specific interactions with cell receptors and enzymes and other properties.
Some foods, which contain significant amounts of these phytochemicals, have been investigated in
human studies. These include garlic (allicin), cocoa (polyphenols, soy (isoflavones) and red wine
(anthocyanins). These foods are known to favorably alter some of the CV risk factors & thereby
decrease the incidence of CVD. Vinson et al (2001) developed the database on the total polyphenols in
fruits as catechin equivalents on the basis of serving size. The order of the top 10 fruits was:
Cranberry > pears>red grape>apple>blueberry>watermelon>banana= strawberry> white grape >
plum.
The flavonol quercetin is one of the most abundant dietary flavonoids and has been one of the most
frequently studied flavonoids.
Quercetin is actually the molecular backbone for the citrus bioflavonoids rutin, quercetin and
hesperidin. Quercetin has also been found to inhibit the growth of human prostate cancer cells and
human breast cancer cells. Quercetin has antiviral activity against several types of viruses.
Two potential mechanisms for quercetin’s anti-cancer effects include
- Inhibition of tumour growth by interacting with estrogen binding sites.
- Promotion the process of programmed cell death, called apoptosis, in damaged cells.
Quercetin and kaempferol belong to a subclass of flavonoids called flavonols. Both have antihistamine
activity. They both inhibit the release of histamine from immune cells called mast cells, which are
involved in the pathogenesis of asthma & allergic reactions.
Quercetin is generally found in all plant products (fruits, vegetables, cereals, leguminous plants, fruit
juices, tea, red wine, etc), whereas others are specific to particular foods (flavanones in citrus fruit,
isoflavones in soya, phloridzin in apples). The red, blue and purple pigment found in fruits and
vegetables, tea and herbs are chiefly due to myricetin, kaempferol,quercetin,hesperidin and narigenin.
They are considered to have antioxidant, anticlotting, antihistamine, anti-inflammatory, antitumor and
vascular effects (Catapano, 1997).
Other distinct groups of polyphenols known as falvan- 3 ols includes anthiocyanidins,
proanthocyanidins, catechins and tannins. They have been extensively studied for their antioxidant,
anticancer, antitumor and cardioprotective effects (Catapano1997).
Nambiar et al 2005 have identified the presence of phenolic acids such as vanillic acid, melilotic acid
and p-coumaric acid and flavonoids such as quercetin, kaempferol and acacetin in drumstick leaves
Several of these flavonoids have been reported to have a positive impact in decreasing LDL-C and
increasing HDL-C and helping the CVD patients achieve a desirable L/H ratio. Therefore, this leaf
holds a promising health benefit.
The best-described property of almost every group of flavonoids is their capacity to act as
antioxidants. The flavones and catechins seem to be the most powerful flavonoids for protecting the
body against reactive oxygen species. Body cells and tissues are continuously being threatened by the
damage caused by free radicals and reactive oxygen species, which are produced during normal
metabolism or are induced by exogenous damage (Grace et al 1994).
Certain flavonoids that occur in strawberries, including quercetin, kaempferol and anthocyanins, have
been shown to inhibit platelet aggregation, an abnormal clumping of the blood particles responsible for
clotting. These flavonoids appear to slow the clotting process, thereby decreasing the tendency to form
thrombi and reducing the risk of stroke.
Phytoestrogens: - Fruits and vegetables are storehouses of phytoestrogens that act as anticarcinogenic
agents.
DISCUSSION
Extensive study of phytochemicals in cell-culture systems and animal model has provided a wealth of
information on the mechanisms by which a diet rich in fruits and vegetables may lower the risk of
chronic disease in humans.
Scientific evidence strongly supports a causal relationship between fruit and vegetable intake and
CVD and cancers. A number of national and International bodies advocate an increase in the intake of
fruits and vegetables to 400-5—g/day (WHO, 1990). However, a worldwide global survey of fruit and
vegetable consumption pattern by sex and age reported very low intake in several countries such as
South America, Europe, South East Asia (including India) and Africa (Lock et al, 2004). Since fruits
and vegetables have a positive effect on health not only to combat micronutrient malnutrition (VAD,
IDA, folate etc) but also macronutrient malnutrition (obesity, CVD, cancer), the present review
suggests that each nation should develop and implement a National fruit and vegetable promotion
policy through integrated approaches involving various sectors including the health as well as
agriculture.
Increasing individual consumption of fruits and vegetables to an optimal level of intake could thus,
reduce the worldwide burden of disease and disability adjusted years. This would inevitably reduce the
government’s expenditure on health and medicine. It is therefore advisable therefore that nutrition be
given due importance on the policy agenda in order to address the overall health of the individuals
worldwide!
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HEALTH EFFECTS OF FRUITS AND VEGETABLES
Decrease
in
Platelet
Aggregation
Modulation of
Steroid Hormone
Concentrations
and Hormone
Metabolism
Alteration
In
Cholesterol
metabolism
Blood
Pressure
reduced
Antioxidant
Activity
Modulation
Of
Detoxification
enzymes
Stimulation
of the
Immune
System
Antibacterial
and
Antiviral
Activity
PICTURES 1 & 2 : ADVOCATE THE CONSUMPTION OF FRUITS AND VEGETABLES BY
INVOLVING THE FAMILY MEMBERS AND THE COMMUNITY