is a common cancer in many western countries. Research
suggests that a diet that is high in meats, refined grains, and sugar and that
is low in vegetables and fiber may increase the risk of colorectal cancer. Results
of epidemiological studies indicate that a diet rich in vegetables may lower
the incidence of colorectal cancer. This research study focuses on the cancer
deaths and occurrences in various countries.
In particular, this study compares the colorectal cancer deaths and
occurrences in developed countries to less developed nations. The study is
designed using existing international databases to understand the effect of
vegetable/fruit consumption over meat consumption on colorectal cancer rates.
Data were analyzed to calculate the correlations between colorectal cancer and
vegetable/fruit consumption over meat consumption. The results indicated that
diet with high meat to vegetable/fruit consumption in developed countries plays
a significant role in the higher amount of colorectal cancer over the
developing counties. Using data for
over 50 countries, the results also indicate that there is a significant
association between higher vegetable and fruit consumption over meat
consumption on colorectal cancer rate.
is the second leading cause of deaths in the Unites States. The cancer of the
colon or the rectum, together known as colorectal cancer, is the third most
frequently occurring cancer among both men and women and is the cancer that has
the second highest rate of killing infected patients (Preventcancer.org, 2003). The American Cancer Society estimates that
there will be about 105,500 new cases of colon cancer and 42,000 new cases of
rectal cancer in 2003 in the United States. Combined, they will cause about
amount of research indicate significant effects of nutrients on cancer rates.
This study is aimed at vegetable/fruit consumption over meat consumption in
more than fifty countries and its effect on colorectal cancer incidence
colon and the rectum together form the large intestine, where the colon is the
first six feet of the large intestine and the rectum is the last 8-10 inches
(U.S. National Cancer Institute, 2003). Indigestible waste fluids and certain
minerals enter the large intestine, where much of the water and the minerals
are reabsorbed. The remaining solid feces that contain millions of bacteria
finish passing through the intestine before exiting through the anal canal
cancer begins from a small polyp. Polyps, or small bumps along the lining of
the intestine, form when there is a build-up of cells. Polyps are common
especially in men and women who are at least 50 years of age. Although one
third of polyps are harmless, the other two-thirds are adenomas, which have a five
percent chance of progressing into cancer.
It normally takes a polyp 5-10 years to transform into cancer in adults
regular examination of the large intestine for polyps is a sure way to prevent
this cancer. Symptoms include cramps, gas pains, bloating, and changes in bowel
habits such as constipation and diarrhea, chronic tiredness, and dark or bright
red blood in the stool (Winawer, 1995).
diet and diseases
For a very long
time, scientists have analyzed foods.
To begin with, scientists introduced factors for calculating caloric
value for foods. They measured the amount of food that people ate and
calculated what these amounted to in protein, carbohydrate, and energy. Atwater and Benedict (1899) showed that the
available energy produced by food eaten by an individual equaled the energy
lost by the individual in heat. They
compiled the chemical composition of American food materials (Atwater, 1906).
Hopkins discovered vitamins, scientists realized that vitamins helped human
body to grow and maintain health. Then
research was directed to analyze how nutrients help reduce risks associated
with certain diseases. Rickets was most
likely the first disease that pointed directly to a deficiency of vitamins in the
body, and cod liver oil was used to cure the disease as early as the 18th
century. Szent-Gyorgyi (1928) showed
that a certain substance extracted from ox suprarenal glands protected guinea
pigs against scurvy. Later on, King and
Waugh (1932) identified that substance as Vitamin C.
Mendel (1913) showed that green vegetables, known to contain yellow pigments
carotene and xanthophylls, were effective as a source of fat-soluble A, and
Steenbock (1919) later demonstrated that the carotene was the active
pigment. Chick, et al. (1923)
discovered that provitamin 7 dehydrocholestrol and ultraviolet rays formed
Vitamin D3 and D2 in the skin to cure rickets along with cod liver oil. Vitamin B was found to cure beriberi by
Smith and Hendrick (1926). Rickes et
al. (1948) isolated vitamin B12 and showed that B12 was active in the treatment
of pernicious anemia (West, 1948).
nine of the trace elements that include iodine, iron, zinc, copper, chromium,
selenium, molybdenum, manganese, and cobalt, have been reorganized in humans
(Sandstead, 1984) in addition to cadmium and methyl mercury. In the same study, it has been pointed out
that nickel, arsenic, and boron are now known to be required.
that iodine cured goiter and the suggestion that goiter might be caused by a
deficiency of iodine was made by French physicians in the early 1890s. The necessity of Zinc for proper nuclear
acid and protein synthesis, cell division and hypertrophy, tissue growth,
maturation, cellular and humoral immunity, and metabolism of carbon dioxide and
superoxide, had been discovered by then (Prasad, 1982 and Valle, 1983). Zinc deficiency is common among poor
populations that subsist on cereals and other foods of vegetable origin and
those who do not eat red meat, organ meats, and certain crustaceans and
shellfish (Sandstead, 1982).
deficiency is the most widespread nutrition deficiency in the world. Research has focused on a diagnosis as well
as on the effects of anemia, iron metabolism, and iron bioavailability
(Edgerton, 1982). The central nervous system is influenced by iron nutrition
(Pollitt, 1982). Copper has been
recognized as being important to cardiovascular health. Experimental copper
deficiency has been shown to debilitate glucose utilization (Klevay, 1982) and
elevate serum cholesterol (Klevay, 1980).
supplements corrected impaired glucose and amino acid utilization, poor
responsiveness to exogenous insulin, weakness, and weight loss in a patient
(Schroeder, 1970). Discovery in China
showed that in a certain province children exhibited cardiomyopathy and death
because of selenium deficiency (Ge, 1982).
These findings from China demonstrate that humans who consume foods from
a limited geographic area have a potential risk of deficiencies of essential
elements similar to farm animals (Sandstead, 1984).
toxins such as lead, cadmium, and methyl mercury need to be monitored carefully
as pointed out by research (Mahaffee, 1982).
Some epidemiological studies seemed to find a decreased risk of colon
cancer associated with eating certain cruciferous vegetables (Armijo,
1981). Selenium and Fiber have been
long researched in this topic.
It is difficult
to pinpoint a direct influence of a specific genotoxin in the customary food
supply in Western Countries. Their
concentrations are generally low and are usually monitored in United States.
Substances found in food such as N-nitroso compounds, hydrazines, safrole,
cycasin or pyrrolizidine alkaloaids have been found to be carcinogenic in
animals. Some of these compounds occur in U.S. diet in very small amounts
compounds (nitrosamines) are an important class of environmental carcinogens
that have caused tumors in experimental animals. Exposure to nitrates, nitrites, and N-nitroso compounds comes
from various sources. Nitrate and
Nitrite may occur as a result of food processing (Wynder, 1984). Some vegetables and fruits naturally contain
large amounts of nitrate; however, they have ascorbic acid, which is an
inhibitor of nitrosation. Nitrate and
nitrite in soil and drinking water may be associated with an increased
incidence of stomach and esophageal cancer (Cuello, 1976). Because chemicals that cause mutations have
a higher probability of being initiators of carcinogenesis, mutagens need to
isolated and tested for carcigogenicity in animals.
In a study,
observations were made that milk and several vegetables have been consumed with
less frequency by colorectal cancer cases than by controls (Bjelke, 1978).
Dietary lifestyle and colorectal cancer
cancers that are known to us, we focus on colorectal cancer in this study. The lifetime probability of developing
colorectal cancer is 1 in 17 for men and 1 in 18 for women (Curry, 2003). A personal history of colorectal polyps, or
chronicinflammatory bowel disease, or a family history of hereditary colorectal
cancer syndrome places individuals at higher risk for these types of cancer
(American Cancer Society, 2002).
The ways in which
diet might affect cancer are as follows:
- Ingestion of carcinogens:
a. In Natural foodstuffs
Produced in cooking
Produced in stored food by
- Affecting formation of carcinogens in
a. Providing nitrates and secondary amines
in the body
b. Altering intake or excretion of
cholesterol and bile acids
c. Altering bacterial flora of the
- Affecting transportation,
activation/deactivation of carcinogens
Altering concentration in or
duration of contact with feces
b. Altering transport of carcinogens to
c. Induction or inhibition of enzymes
d. Deactivation or prevention of
formation of short-lived intracellular species by use of vitamins, trace
metals and other antioxidants.
- Affecting promotion of cells
a. Vitamin A deficiency
b. Retinal binding protein
- Over nutrition
Of the various
factors discussed above, we are focusing on Items 2 and 3 from the
above-mentioned list in this study.
Substrates for the formation of carcinogens in the body
compounds are among the most powerful chemical carcinogens in laboratory
animals, and this is a sign that it may be powerful even when produced in small
amounts in humans. These compounds can be found in gastric juice, the digestive
tract, or even in the infected bladder by products of a reaction between
nitrites and certain nitrosable compounds. This nitrosation can be inhibited by
the presence of antioxidants such as vitamin C in the stomach.
The problem with
nitrites and nitrosable compounds is the fact that neither can be easily
avoided in a diet. The compounds are abundant in fish and meat, but they may
also be ingested as pesticide residues or drugs. In addition, nitrosable
compounds may be formed in the colon from amino acids. Nitrite found in food
may be derived from preservative color or a color and flavor enhancer. Nitrite
may be formed in the salivary ducts, the hypoacid stomach, the infected
bladder, and on nitrates or nitrogen in the gut by its bacterial action on
nitrates. The most important source of nitrite is from nitrate, which is
ingested in vegetables and also in water, but to a smaller extent.
evidence has supported it, there is no definite answer as to whether certain
types of cancer, such as cancer of the esophagus and stomach, correlates with nitrosamine
formation (Armijo, 1981). Studies have shown that dietary nitrates, found
mainly in vegetables, may actually protect the body against the development of
certain types of cancer (Reddy, 1979).
intake or excretion of cholesterol and bile acids
fats might contribute to the production of carcinogens in the body by
increasing the amounts of bile acids and cholesterol metabolites that encounter
with the gastrointestinal tract. One study that compared the diets of Asians
and Africans with the diet of people in the Western Hemisphere showed that
larger amounts of the bile acids and cholesterol metabolites, especially
deoxycholic and lithocholic acids, are found in those on a Western-type diet,
and that, in comparison to Africans and Asians, colon cancer is also more
common in Westerners (Curry, 2003). The amount of lithocholic and deoxycholic
acids in humans can be increased by a high-fat, high-meat diet. When such a
diet was tested on laboratory animals, there was an increase in the fecal
excretion of bile acids and an increase in the incidence of colon cancer that
was induced by various colon carcinogens, including methylnitrosourea. One
study showed that bile acids fed or administered intrarectally for a long
period to animals have a synergistic effect with small doses of carcinogens on
the incidence of large intestine tumors (Greenlee, 2001).
epidemiological data demonstrate a correlation between fecal bile acid
metabolites and the risk for colon cancer in diverse populations (Reddy,
1980). Such studies have shown that
patients with colon cancer have a higher concentration of these metabolites in
their feces than control patients. A
high intake of certain dietary fibers such as wheat bran and whole grain
cereals which are rich in cellulose and hermicellulose leads to an increased
stool bulk thereby diluting the colonic concentration of certain bile acids
that accompany high levels of fat intake (Reddy, 1979).
Doll and Peto
(1981) examined the degree to which cancer incidence and mortality rates could
be reduced in the United States. Their
choice of method stemmed from the observation that the cancer incidence rate
among migrants tends to be found in the country to which they migrated,
indicating that differential cancer incidence rates are due in part to
environmental factors such as diet, exercise, occupational exposures, and
smoking habits, and that the cancer does not arise exclusively because of
genetic factors. A follow-up study
recognized the fact that given the major shift toward the regulation of
occupational exposures to known carcinogens and the active surveillance of
workers previously exposed to many of the carcinogens, the most modifiable
component of cancer risk remains lifestyle factors (Monson, 1997). The American
Cancer Society has certain risk factor assumptions on diet. These risk factors
assume that prevalence of low levels of fruit and vegetable consumption will be
reduced to 47-58% by 2010 and prevalence of high fat intake reduced to 9-15% by
2010 (Byers, 1999).
evidence of a relationship between diet and cancer has been related to the
benefit of consumption of least five servings of fruits and vegetables per day.
The probability of evidence is moderate for colon cancer. Most of the research has focused on the
effects of specific agents contained in fruits and vegetables such as carotenoids, selenium, folic acid, fiber, and
Vitamins C and E. A study (Steinmetz, 1991) suggests that fruits and vegetables
contain an anti-carcinogenic cocktail of substances, including both recognized
nutrients and non-nutritive constituents. Together they inhibit the formation
of carcinogens, reduce the capacity of transformed cells to proliferate, and
act as antioxidants.
In studies, green
vegetables and cruciferous vegetables seemed beneficial. However, the prospective cohort studies to
examine this relationship have yielded less conclusive findings (Voorips,
2000). Vegetables contain so many
beneficial vitamins and nutrients that it is difficult to identify which ones
might be responsible for the possible association with colon cancer. Fiber has received the most attention so far
because of the proposed mechanism, i.e., fiber can help waste push through the colon
more quickly so that colon is less likely to come into contact with the
carcinogens. However, recent study
failed to support a link between fiber intake for over three years and the risk
of the occurrence of colon polyps, the precursor lesion for colon cancer
(Alberts, et al., 2000).
cancer, while being a fervent killer, can be prevented with the right diet.
Numerous studies have shown that a diet consisting of certain key nutrients
plays a key role in preventing colorectal cancer. The three important factors
of diet that include fiber, antotoxidants, and phytochemicals are present in
vegetable and fruits. We consider vegetables and fruits in this study as an
important portion of food consumption.
the structural part of plants that is indigestible by humans, is an element
that can be found in grains, legumes, and fruits and reduces the risk of colon
cancer. In 1989, researchers at the New York Hospital – Cornell Medical Center
discovered that adding fiber to the diet could shrink pre-cancerous polyps that
may have already begun to form in the colon.
Fiber has many advantageous uses to prevent cancer: it prevents
chemicals form harming the colon’s lining; sweeps carcinogens through the
intestines; and discourages the growth of harmful bacteria that could
potentially lead to cancer, while encouraging the growth of good bacteria (U.S.
National Cancer Institute, 2003). A study was conducted in India to compare the
frequency of people infected with colon cancer and the amount of fiber people
ate. North Indians tend to consume more fiber— roughage, cellulose, and
vegetable fiber, in comparison to the South Indians. The studies also showed
that the frequency of colon cancer was lower among the North Indians in
comparison to the South Indians (Shamberger, 1984).
are two types of fiber— soluble and insoluble fiber. While the soluble is
useful in lowering blood cholesterol, the insoluble fiber is what studies have
shown protects against colon cancer. This type of fiber can be found in fruits,
vegetables, grains, and legumes. Two types of dietary fiber in general are
known to help reduce colonic intraluminal pressure: cellulose and hemicellulose
A and B. These sources of fiber are found especially in citrus fruits, carrots,
and bran (Shamberger, 1984). Rich sources of fiber include whole wheat and bran
cereals, bread, and pasta; legumes such as kidney beans, lima beans, and pinto
beans; and fruits such as dried fruits and blackberries. Almost all other
fruits, vegetables, and legumes like almonds and peanuts have a moderate amount
of fiber. Fruits should be eaten with the skin in order to maximize the amount
of fiber consumed (Winawer, 1995).
fat is known to promote colorectal cancer. No reason has been formally
established in the role that fats play in relation to colorectal cancer, but
many explanations have been offered. One such explanation states that fat
increases the level of bile salts in the colon, which damage the lining of the
colon and promote excessive cell growth that can lead to cancer. In order to prevent
the occurrence of this cancer, it is most advisable to consume fat in
moderation (Winawer, 1995).
are a group of nutrients that counter the effects of molecules called free
radicals, which are highly reactive substances that are byproducts of certain
body functions and the body’s exposure to radiation, smoke, etc. Free radicals
can lead to cancer by attacking a cell’s membrane and harming the DNA inside of
the cell. They also interact with certain other substances in the body and turn
those substances into carcinogens. Among the antioxidants, beta-carotene and
Vitamine C are specific nutrients that help the body against colorectal cancer.
Beta-carotene and Vitamin A specifically offer protection against colon cancer.
They reduce the probability that altered cells will successfully change into a
tumor (Shamberger, 1984). These nutrients are abundant in carrots, diary
products, green and yellow vegetables and fruits such as peaches, mangoes,
cantaloupes, and tomatoes. Vitamin C is believed to help protect the body
against rectal cancer. It also strengthens the immune system, detoxifies
compounds in the liver, and blocks the formation of nitrosamines in the
digestive tract. Vitamin C is abundant in citrus fruits, potatoes, peppers,
peas, kiwi fruits, spinach, asparagus, and strawberries (Winawer, 1995).
D is another vitamin that may reduce the risk of colon cancer. It enables the
body to absorb calcium, which is believed to inhibit colon cancer. Vitamin D is
found in salmon, tuna, dairy products, and many fortified breakfast cereals
are substances that help the natural defense system against cancer. Among these
that directly help fight colorectal cancer are selenium and calcium. Calcium
abundant in dairy products helps to neutralize the damage that bile and other
cancer promoters may cause to the body. It also protects the colon’s lining
from certain damaging substances in the stool. Studies have shown that people
in Finland have a low rate of colorectal cancer cases particularly because of
their high intake of dairy products.
Phytochemicals are abundant in fruits and vegetables such as those in
the cabbage family (broccoli, cauliflower, brussel sprouts), garlic, onions,
soybeans, and nuts (Winawer, 1995).
and fruits contain the three dietary items discussed above that include fiber,
antitoxidants, and phtochemicals, we will consider the effect of vegetables and
fruits over meat consumption on colorectal cancer.
Effects of vegetables over meat
on colorectal cancer in developed countries
Developed countries (DC) according the definition from the United Nations
Web page are countries that generally have a per capita GDP in excess of
$10,000. Less developed counties (LDC)
are mainly countries and dependent areas with low levels of output. Living
standards, and technology; per capita GDPs are generally below $5,000 and often
less than $1,500; however, the group also includes a number of countries with
high per capita incomes, areas of advanced technology, and rapid rates of
growth; includes the advanced developing countries, developing countries, Four
Dragons (Four Tigers), and newly industrializing economies.
Even thought the food consumption patterns are different in these
countries, there is a difference in the purchasing power of these
countries. Since meat is costlier than
vegetables and fruits, developed counties generally have more access to meat
and may therefore consume more meat than less developed countries. Since much
of the research that we have identified in this study concerns the effects of
vegetables and fruits on colorectal cancer, we will hypothesize the following:
H1. The effect of cancer incidence rates is positively associated with
the affluence of a country.
H2. The effect of vegetable and
fruit consumption over meat consumption is negatively associated with cancer
The sample was drawn from various data sources. The research question addresses how much vegetable, fruit, and
meat consumption play a part in the cancer incidence rates in developed and
less developed countries. We collected
sample data for 52 countries from the 150 developed and less developed
countries. This was after dropping countries that did not have complete data
available. The cancer incidence rates were drawn from GLOBOCAN2000 database.
The population facts of countries were collected from the United Nations and
World Factors and Figures Web site. The food consumption was drawn from the food
balance sheet database from the United Nations Food and Agricultural
Organization. All data have been taken
as an average between the years 2000 and 2001.
To determine the cancer effects of vegetable/fruit to meat consumption,
the dependent variable CANCR was computed as cancer incidence rates, i.e., the
number of cancer incidences per population in various countries. The vegetable and fruit consumption was
compared to the meat consumption in various countries. The ratio of total vegetable and fruit
consumption per population to meat consumption per population was included as
the variable VFMEAT. The total
consumption of food TFC in these countries was also included as one of the
independent variables. To understand
the effects on the developed and less developed counties, we controlled the
analysis by using the variable GDP that is the Gross Domestic Product per
Certain preliminary steps were taken in order to assure that a linear
regression test could be conducted. A scatter plot and residual plot were
observed. The scatter plot for the first hypothesis tested, where CANCR was the
dependent variable and GDP was the independent variable, had a correlation
value of 0.846. Although the data does have some outliers, the 0.846
correlation shows that the linear relationship between the two variables is
positive and very strong. Similarly, a scatter plot between the CANCR and
VFMEAT variables shows a strong, negative correlation value of –0.634. By
looking at the residual plots for both tests, one can see that variation about
the 0 is approximately even throughout the given data, and that no detectable
pattern is present. All of this supports a linear regression test being
After the linear tests were conducted, the results for the first test
comparing CANCR and GDP showed an R2 value of 0.716 and a p-value of
0.009. The R2 value is high, simply stating that 71.6% of the
variation in the variable CANCR is explained by the regression. For this
experiment, an alpha level of 0.05 was chosen, and the p value of 0.009 is less
than that alpha level. Because it is smaller than the noted significance level,
the p-value is significant. This means that such an extreme value as what was
tested cannot occur due to chance alone. The results for the second test
comparing VFMEAT and CANCR had a R2 value of 0.744 and a p-value of
0.029. This R2 value is also high, where 74.4% of the variation in
the dependent variable CANCR is explained by the regression. The p-value of
0.029 is less than our chosen alpha level of 0.05, thus making it a significant
The means, standard deviations, and correlations are reported in Table 1.
The p-values of 0.009 and 0.029 are less than the standard 0.05 value, and so
there is enough evidence to accept our hypotheses. We find a positive
association between cancer incidence rates and the affluence of a country and a
negative association between vegetable and fruit consumption over meat
consumption and cancer incidence rates.
Therefore, we can conclude that the more developed
countries have a higher rate of colorectal cancer and that as the ratio between
vegetable and fruit consumption over meat consumption increases, the cancer
rate in a population decreases. This concurs with the research discussed
Descriptive Statistics and Correlations
Food Consumption per population
and Fruits to Meat Consumption
These results are in concurrence with the overall subjective view that
vegetable and fruit consumption helps to reduce the effects of cancer. This also acknowledges that higher vegetable
and fruit consumption compared to meat consumption reduces cancer incidence
We highlight several implications for future research. This study needs to be extended to the rest
of the developed and less developed countries as well. We have considered average values for food
consumption and cancer incidence rates.
Further research can use values for a number of years and analyze the
effects. The study can be extended to
the least developed countries as well.
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