Diet and melanoma: a literature review plus some additional thoughts
While
investigating alternative therapies after being diagnosed with melanoma, I
began wondering why cancer is so prevalent in our time. Could it be increased
exposure to carcinogens and other toxins in our environment? In the case of
melanoma, it is possible that exposure to the carcinogen – the sun’s rays – may
be greater now as a result of our outdoor lifestyle choices and thinning of the
ozone layer that formerly more effectively limited the amount of ultraviolet
light hitting the earth. Or could it be that our diets these days consist of
fewer of the foods with cancer fighting properties? From the literature I have
come across, it seems that the answer may be a bit of both. Rogue cells have
always been part of our existence – but it is conceivable that an increasing
exposure to environmental toxins and a decrease in our bodies’ ability to deal
with cellular changes caused by these toxins because of poor diet and
compromised immune systems might be playing a role in the current high rates of
cancer.
One relatively recent study suggested that diet
is second only to tobacco as a risk factor for cancer, accounting for about 30%
of cancers in developed countries1. It may not be so much the bad
things we eat, but the good things that are missing from our diets. With the
popularity of processed snack foods, many of us are not getting the recommended
number of daily servings of fruits and vegetables containing natural plant
phytochemicals. These phytochemicals have interested cancer researchers for
some time and include phytoestrogens (such as isoflavones, coumestans, and
lignans), isothiocyanates, and polyphenols such as flavonoids (i.e. catechins)
and flavenols (i.e. quercetin). The risk of melanoma has been shown to be lower
in people who get more vitamin D, alpha carotene, beta-carotene, cryptoxanthin,
lutein, and lycopene in their diets2. [An informative website for
learning about these compounds and ways to incorporate them into your diet (including
recipes) can be found at:
http://www.cancerproject.org/medicine/phytochemicals.html.]
In addition to the quantity of fruits and
vegetables, the quality of these foods as cancer fighters may also no longer be
what they used to be3. A research group from U.C. Davis recently
discovered that organically or sustainably grown food crops contained a
significantly higher concentration of phenolic compounds and vitamin C than the
same crops grown conventionally4. Phenolics are potent antioxidants
and are thought to have anti-cancer activity5, and the role of
vitamin C in cancer prevention has also generated interest6.
Phenolics are among the naturally occurring chemicals found in plants that also
provide protection from being eaten by herbivore pests. When growing plants are
nibbled on, a signal is sent that results in a plant changing the mix of
compounds produced to reduce palatability7,8.
The maximum concentration of these compounds therefore tends to occur only with
pest pressure. When induced, some of the energy of the plant that might
otherwise go to growth goes instead to defensive compounds. Potentially
partially as a result of such trade-offs, crop yields of organically grown food
might not be as high, but this study is one of the first that shows how organic
foods might be better for our health.
Some other changes
to vegetable and fruit quality are more deliberate. Many of the plant compounds
that have both interested cancer researchers and repel plant pests are bitter,
acrid, or astringent. Consumers do not generally appreciate these qualities. It
also had been assumed that natural chemical insect repellants in plants are
toxic to us – in all concentrations.
However, recent research is revealing that some compounds that are toxic
in high concentrations may actually be beneficial at lower levels. Many modern
crop varieties have been purposefully selected by plant breeders to contain
reduced amounts of such compounds9. Not only are the blander tasting
highly bred crop varieties possibly not as good for us, they may also be less
able to ward off attack by plant pests, leading an increased reliance on
chemical pesticides to produce them. The loss of beneficial plant chemicals
also occurs after crops are harvested, as the food industry removes still more
through de-bittering agents during food processing10. While aversion
to excessive bitterness is to us an important cue for avoiding poisonous
plants, by removing any hint of bitterness, we may have gone too far. Like most
things about food, moderation seems to be the key. Humans can surely tolerate
more bitterness and other unusual flavors than exists in most of our food
today.
These issues have
changed my thinking about diet and cancer. In order to increase the chances of
my own body being able to destroy remaining melanoma cells that might still be
floating around and also to possibly help prevent formation of any additional
skin cancers, I am eating more of foods shown to have anti-cancer properties. I
am also eating as much organic produce I can find – the more holes chewed by
bugs the better - and am attempting to eat wilder foods that have not been
extensively altered by plant breeders and therefore maintain more of their
natural phytochemicals – for example, black walnuts instead of English walnuts,
flax seeds (this crop was bred mostly for fiber – the content of the seeds is
more a byproduct), assorted leafy greens like collards, mustard greens, or
dandelion leaves, and wild berries.
Below is a list of foods I am incorporating into
my diet and some of the reasons why the particular food might be beneficial.
Wherever possible, I have included foods that have been studied in relation to
melanoma, but many have also generated interest for the prevention or treatment
of other cancers as well.
Soybeans contain an abundance of phytoestrogens,
including isoflavones, which are believed to protect against certain cancers.
In a study on mice, adding soy protein to the diet dramatically reduced the
extent of melanoma metastasis11. Mice were intravenously injected
with live melanoma cells and some were fed a diet high in soy protein while
others received regular mouse food. After a period of time on this diet, it was
discovered that 80 percent of the standard diet/control mice had more than ten
distinct areas of melanoma growing in their lungs, while only 22 percent of the
soy fed mice contained more than ten metastases. In addition, the median number
of tumors in mice where soy protein comprised 0%, 10%, 15% and 20% of their
diet was 53, 2, 2, and 1, respectively. A follow up study where mice were fed
the soybean isoflavones genistein and daidzein showed a similarly dramatic
reduction in tumor number and size12.
How much soy to eat? It is hard to say since the
same studies that have been done on mice have so far not been done on humans.
What works for mice may not work for us. However, the amount that was shown to
be effective in mice would equate to a lot of soy. While tofu and soymilk are
good sources of isoflavones, I am also trying to eat soy products that are less
processed, such as edamame or soynuts. Both make great snacks.
Flax seed is a rich source of lignans, a natural
plant phytoestrogen compound with cancer fighting properties. Lignans are found
in many plants, but the concentration in flax is particularly high. Researchers
have investigated the effect of dietary supplementation of flax on mice with
melanoma, finding a substantial reduction in tumor occurrence compared to mice
not fed flax13. The median number of tumors in mice fed diets
supplemented with 2.5%, 5%, and 10% flax was 32%, 54%, and 63% lower than that
of mice fed no flax, respectively. The addition of flaxseed to the diet also
resulted in reduced tumor size and volume.
Flax seed oil is
convenient and widely available, but not all of the good things about flax end
up in the oil - lignans are most abundant in the hulls of flax seed. Some flax
seed oil blends include plenty of hull particles. But because oils can change
chemically with processing and storage, I am also grinding whole fresh seeds into
a coarse meal using a coffee grinder and adding them to cereal and smoothies.
The whole raw seeds make an interesting nutty-tasting snack on
their own. Eating the whole seeds requires quite a bit of chewing
though… without chewing, the whole seeds mostly pass through the body
undigested.
Carotenoids such as beta-carotene and lycopene
that are found in many yellow and red vegetables are powerful antioxidants that
protect cells from free radicals that can damage DNA and lead to cancer. The
beneficial effects of beta-carotenes to the skin are shown by studies that have
linked beta-carotene consumption with reduced reactions to sunburns14.
In addition, one recent study showed that mice with melanoma fed a diet
supplemented with beta-carotene had 71% fewer tumors than mice not fed
beta-carotene15. Some carotenoids are vitamin A precursors and
vitamin A supplements have also been shown to reduce melanoma tumor size and
extent of metastases in mice16. [Note: vitamin A supplements can be
very toxic when taken in large amounts – so be careful.]
One great way of ingesting a large quantity of
beta-carotene (and vitamin A precursors) is by drinking lots of fresh carrot
juice. When making juice, I sometimes also add a beet, celery stalks, a few collard green leaves, or even broccoli stalks and kale stems
that might otherwise be thrown away, to the mix.
Lycopene -another
type of carotenoid that gives tomatoes their red color - has been shown to reduce
the risk of prostrate cancer. A diet consisting of one tomato product serving a
day or five servings a week has been recommended for protection against
prostate cancer and other malignancies17.
Studies have
associated diets high in cruciferous vegetables with lower risk for breast,
lung, stomach, colorectal, prostate, and bladder cancers in humans18.
Isothiocyanates and other plant phytochemicals with cancer fighting properties
are very abundant in this vegetable group which includes broccoli, brussel
sprouts, cabbage, cauliflower, kale, bok choy, kohlrabi, collard greens,
mustard greens, turnips, and water cress. Several laboratory studies have
suggested that cruciferous vegetables help regulate a complex system of bodily
enzymes that defend against cancer. Isothiocyanate compounds have been shown to
arrest cell growth and even kill melanoma cells in culture in the laboratory19,20. In the
body, these compounds are thought to exert their anti-cancer effects by
activating detoxifying proteins that scavenge for cancer-causing molecules. The
more bitter the aftertaste may possibly mean the
better for you – mustard greens, collard greens, and brussel sprouts contain
among the highest levels of several of these beneficial compounds.
Many fruits contain phytochemicals including
flavonoids such as anthocyanins. Anthocyanins, like other antioxidants, help
neutralize the negative by-products of metabolism called free radicals, which
can damage DNA molecules and lead to cancer. Antioxidants also counteract
environmental carcinogens, protect against cardiovascular disease, fight sun
damage to skin and may thwart the effects of Alzheimer's and other age-related
diseases. Not all fruits are created equal. Wild blueberries apparently contain
some of the highest levels of anthocyanins of any fruit. One study showed that
isoprenoids found in fruits (and vegetables) actually suppressed the
proliferation of mouse melanoma cells21. A great way to get plenty
of fruit in the diet is to make smoothies using frozen and/or fresh fruit. To
enhance intake of phytoestrogens as well, I use soymilk when making smoothies
and add a few tablespoons of ground flax seed to the mix.
Green tea is rich in polyphenols such as
catechins that have generated considerable interest among cancer researchers.
Studies have linked regular green tea consumption with reduced cancer risk22
and there is some evidence that green tea might prove to be effective for
cancer treatment as well. Compounds found in green tea are believed to be
especially effective at preventing skin cancers. In one study, extracts of
green tea applied to the skin of rats inhibited the development of skin cancer
in response to exposure to carcinogens including ultraviolet light23.
Green tea has also been shown to inhibit some of the cellular changes that
result in melanoma metastases24, and even directly reduce the
incidence of lung metastases in mice25. Interestingly, some of the
same beneficial catechins are also found in dark chocolate, providing the
characteristic bitter aftertaste.
Whole grains are rich in antioxidants and
phytoestrogens and studies have shown that diets high in whole grains are
protective against cancer26, 27. In addition, the beta-glucan found
in whole grains such as barley and oats may play a role in enhancing immune
response by stimulating macrophages to attack foreign bodies such as viruses
and cancer cells. One study showed that treatment with beta-glucan increased
the survival of mice with metastatic liver disease28. Unfortunately, many of the grains we get in
our diet are highly processed and have reduced levels of beneficial compounds.
My sister passed a simple cereal recipe on to me which calls for putting ½ cup
of whole oat groats in a thermos, adding two cups of boiling water, closing the
lid and leaving overnight. Served with honey, it makes for a healthy and tasty
way to start the day.
It is believed that
vitamin E confers protection against some types of cancers29. Nuts
contain particularly high concentrations of this vitamin. In addition,
compounds found in black walnuts, such as ellagic acid and juglone have been
shown to reduce tumor growth rate in mice30. Almonds also contain
many phenolic compounds that act as antioxidants31.
The only “food” for
which I could find evidence about a positive association with melanoma was
alcohol2,32. In a study of a limited number
of Australian women, those consuming two or more drinks a day had 2.5 times the
risk of developing melanoma32. This was only an observational study
with many other possible confounding lifestyle factors. However, researchers
have hypothesized that alcohol reduces the bodies’ ability to repair certain
types of cell damage that can lead to cancer33. Heavy drinking is
probably something to avoid.
While many of the foods listed above are thought
to help prevent certain cancers, their efficacy as cancer treatment has not
been demonstrated, at least in humans. Studies on mice provide tantalizing
clues that at least some plant phytochemicals may eventually prove useful in
the treatment realm. Until much more is known, what we eat should be viewed as
a supplement to other medical treatment, and not a substitute. However, with the adjuvant therapies available for melanoma today
having only a limited apparent benefit to survival, the proportional impact of
eating the right foods, even if it not great, may still be important.
For me, changing diet to include different cancer fighting foods has also had a
powerful psychological impact. Doing something to assist in my own treatment
reduces the feeling of helplessness that can accompany a cancer diagnosis.
Besides, people who take an active role in their treatment and maintain an
optimistic outlook generally lead a better quality of life and may even have a
higher rate of survival34. Eating healthy certainly can’t hurt.
I compiled these
research findings, along with my own thoughts and ideas in case it might
inspire other melanoma patients to explore some different possibilities. Since
www.mpip.org posted the first version, melanoma patients from around the world
have contacted me with more great suggestions of foods to try, or asking for
advice and information. So, I feel it is important to disclose that although I
am a scientist, I am not a medical doctor and no expert in this field. The research I've read in the past year is
all new information to me too. Please also keep in mind that the foods I
summarized are by no means the only ones researchers are studying. Quite a few
folks who have written seem to also be interested in supplements… I did not
mention supplements due to my own biases that compounds in foods act
synergistically… and even the non-active substances within foods may be
important. I also really enjoy eating
LOTS of unusual vegetables and fruits… some others might feel they need
supplements to get the volume. Comments
or additional ideas welcome.
Good health and happy
eating! -Eric Knapp (eeknapp2000@yahoo.com)
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