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NATURAL TOXINS IN SPROUTED SEEDS: SEPARATING MYTH FROM
REALITY
By Warren Peary and William Peavy, Ph.D.
Natural toxins in food has become a hot and
controversial subject recently. In the last few years, some popular writers have
attacked sprouts (particularly alfalfa and legume sprouts) as containing natural
toxins. These writers may have heard something about a lathyrogen toxin,
saponins, canavanine, and maybe other nasty-sounding toxins, and concluded that
the sprouts of legumes are toxic in the raw state and so should not be eaten.
These statements are taken out of context.
LATHYROGEN TOXIN
One of the natural toxins that has been mentioned comes
from peas of the genus Lathyrus. It is blamed for causing a disease known as
lathyrism. Lathyrism causes paralysis in the legs in susceptible individuals and
is believed to be caused by a toxic amino acid. This sounds scary, but it's not,
because peas of the genus Lathyrus are NOT edible peas. The toxin is found only
in the seeds of certain Lathyrus species (L. sativus, L. cicera, L. clymenum).1
Edible peas and beans are of the genera Cicer, Glycine, Phaseolus, Pisum, and
Vigna. They DO NOT contain any such toxin.
Non-edible peas of the genus Lathyrus include sweet
peas, which are ornamentals grown for their scented flowers. In India, where
food is often scarce, some people have resorted to eating a non-edible pea known
as Lathyrus sativus. It is often called "chickpea" but is NOT the same chickpea
eaten in this country or any other developed country. The edible chickpea is of
the genus Cicer and in botany is known as Cicer arieti-num.
Outbreaks of lathyrism in India have been blamed on
eating large amounts of the non-edible chickpea without proper cooking.
Well-cooked, it is safe to eat. But it shouldn't matter to us at all because it
is considered an inedible species.
There are at least 1,500 species of legumes within one
of three subfamilies of the family Leguminosae (Latin for legume). Of these
1,500 species, only a few dozen are regularly used as human food. Of course
there are toxins in many of the raw legumes not usually used for human food;
that's why humans have learned not to eat them. This is the first mistake
sometimes made in warning about natural toxins - talking about a toxin that's
found in some non-edible species people don't or shouldn't eat to begin with!
SAPONINS
The second mistake often made in talking about natural
toxins is to call something toxic that, in the body, is not toxic at all but
rather, is beneficial. Such is the case with saponins.
Saponins are a compound found in legumes and legume
sprouts. They are toxic to red blood cells only in vitro (outside of the body in
a test tube) but harmless when ingested.2-3 In fact, Saponins appear to be
beneficial, being responsible for a major part of the cholesterol- lowering
effect of legumes.3 Perhaps it is more than coincidence that the increase in the
incidence of heart disease in the 20th century in the Western countries
coincides with a decline in the consumption of saponin-rich legumes. Saponins
also seem to be anticarcinogens; in one study they inhibited colon cancer.4
Even some of the most beneficial nutrients, such as
vitamin C, can be shown to be toxic under certain laboratory conditions. Vitamin
C is considered an important antioxidant, and substantial evidence shows that it
is involved in cancer prevention.5 Yet under the right experimental conditions,
in the presence of iron (Fe III) or copper (Cu II) ions, ascorbic acid can
actually cause the formation of harmful free radicals.6 Does this mean you
should try to avoid vitamin C? Absolutely not! These experimental conditions do
not appear to be relevant to what goes on in our bodies.
CANAVANINE
The third mistake made in warning about some natural
toxins is failing to say that the amount encountered in a food is so minuscule
that it is completely insignificant. Such is the case with a toxin called
canavanine, which is found in alfalfa seeds. While some writers may make
canavanine sound like a dangerous carcinogen - it isn't. Canavanine is a
non-protein amino acid that's toxic in high amounts. In the dry seed it serves
as a storage protein, a growth inhibitor, and a defense against natural
predators. As you might guess, as the sprout grows, canavanine falls rapidly to
insignificant levels.7 The text, Seed Physiology, clearly states that "Canavanine...is
non-toxic to mammals at low concentration."8 Canavanine is so irrelevant that
the 1980 text, Toxic Constituents of Plant Foodstuffs, doesn't even mention it.
A 150-pound human would have to consume 14,000 milligrams of canavanine all at
once for it to be toxic at the same level it is toxic in mice.9 This is an
incredible amount! It is doubtful that with a generous helping of alfalfa
sprouts, you would get more than a few milligrams. There is NO canavanine at all
in other legumes that are commonly used as human food.7, 10
Even in toxic amounts, canavanine has nothing to do
with cancer. In very high, toxic amounts it can cause a lupus-like anemia in
susceptible animals due to an alteration in the red blood cells. These studies
are not relevant to the human diet. The minute doses found in the diet are
completely irrelevant and harmless.
Just remember that most substances can show some kind
of toxic effect at a high enough dose. Vitamin A, selenium, copper, zinc, and
iron will all kill you at a high enough dose. So don't stop eating alfalfa
sprouts any more than you would any other food because of some minute toxin that
may be present. They are a good source of vitamin C, folic acid, and other
protective compounds.
ANTI-NUTRIENTS IN SPROUTED LEGUMES
As far as the sprouts of other edible legumes go, the
only other toxins for which any concern has been raised is for a class known as
anti- nutrients. These are sub-stances that bind enzymes or nutrients and
inhibit the absorption of the nutrients. The commonly alleged anti- nutrients
are protease inhibitors, amylase inhib-itors, phytic acid, and polyphenolic
compounds such as tannins. With proper soaking and germination, none of these is
anything to worry about.
Around the world, studies have been and are being
conducted on the use of germinated seeds as a low-cost, highly nutritive source
of human food. It is well-established that when legumes are properly soaked and
germinated, their nutritive value increases greatly, usually to levels equal to
or exceeding those of the cooked bean. (Nutritive value is the ability of food
to provide a usable form of nutrients: protein, carbohydrates, vitamins and
minerals). This has been shown for mung bean, 11-13 lentil,13-14 chickpea
(garbanzo bean), 15-17 cowpea (blackeye pea), 18 pigeon pea,19 fava bean,20-21
fenugreek seeds22-23 (a member of the pea family), green & black gram,15-17
kidney bean,24-26 moth bean,27 rice bean,28 soybean,13, 29-36 and legumes in
general.37-40
The increase in nutritive value in the raw sprouted
seed is due to an explosion of enzyme activity, which breaks down the
storage-protein and starch in the seed into amino acids, peptides, and simpler
carbohydrates needed for the seed to grow. The seed is literally digesting its
own protein and starch and creating amino acids in the process. Because of this
process, sprouted seeds are essentially a predigested food. At the same time,
the anti-nutritional factors such as enzyme inhibitors and other anti-nutrients
are greatly decreased to insignificant levels or to nothing.11, 20, 22, 33,
41-65
Soaking alone causes a significant decrease in
anti-nutrients, as the antinutrients are leached into the soak water. Soaking
for 18 hours removed 65% of hemag-glutinin activity in peas.66 Soaking for 24
hours at room temperature removed 66% of the trypsin (protease) inhibitor
activity in mung bean, 93% in lentil, 59% in chickpea, and 100% in broad bean.42
Then as germination proceeds, anti-nutrients are degraded further to lower
levels or nothing. Soaking for 12 hours and 3-4 days of germination completely
removed all hemagglutinating activity in mung bean and lentil.56 Soaking for 10
hours and germination for 3 days completely eliminated amylase inhibitor in
lentils.62 Normal cooking removes most or all of the anti-nutrients.
ANTI-NUTRIENTS AS PROTECTORS
Some of the substances commonly referred to as
anti-nutrients are actually powerful cancer-protecting phyto-chemicals. These
include protease inhibitors and tannins. The problem in most diets is that we
don't get enough of these substances.
Substantial research shows that protease inhibitors are
one of the most powerful anti-carcinogens we have in our arsenal. They have
proven to be particularly protective against cancer of the colon, breast, and
prostate. 67-72
Tannins have also been shown to give substantial
protection against cancer (including cancer of the stomach and lungs) when
ingested orally.72 Tannins and other polyphenols may play a role in fighting
tooth decay. Evidence shows that some tannins inhibit the growth of bacteria
that cause tooth decay.73
Phytates, like tannins, may also interact with
digestive processes in a beneficial way. Small amounts in food slow down the
absorption of sugars and regulate insulin levels. This is beneficial in the
prevention and treatment of diabetes and hyperlipidemia (high blood fats).74
Small amounts of protease inhibitors, tannins, and
phytates are beneficial and can be considered to be a normal part of our
nutritional ecology.
ENDNOTES
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Warren Peary is an investigative health journalist.
William S. Peavy holds a doctoral degree from Kansas State University in
horticultural science. They can be reached at 316 Horton Lane NW, Albuquerque,
NM 87114.
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