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VICUS.COM ( 31
May 2000) -- Isoflavones
appear to make a positive contribution to health, and soy foods offer
the best source of isoflavones. Soy also provides high-quality
protein, as well as being low in saturated fat, and a good source of
essential fatty acids. Although there is no recommended daily dose for
soy or isoflavones, for those who want to increase their intake of
soy-containing foods, here are some guidelines to consider.
How
much is enough?
Here is a
summary of the daily amounts of soy and isoflavones that have or are
being studied to prevent a range of diseases (Table 1).
Table
1. Daily amounts of
soy and isoflavones studied or being studied to prevent a range of
diseases.
|
Objective
|
Daily
dose
|
|
Cholesterol lowering
|
25-50 grams of soy
protein
|
|
Cancer (breast, prostate, colon) prevention
|
20-40 grams of soy protein
|
|
Hot flashes, reduction
|
45 g of soy flour/day
80-160 mg of isoflavones
|
|
Osteoporosis, post-menopausal women
|
40 grams of soy protein per day containing 90 mg total
isoflavones/day for 6 months had a positive effect on bone
density
|
Source: University of
Illinois at Urbana-Champaign, College of Agricultural, Consumer and
Environmental Sciences.
Sources
of soy and isoflavones
Isoflavones
are available in tablets, but these are not recommended as the primary
source of phytoestrogens. This is because it is not known if the
beneficial effects of isoflavones are due to the body's response to
isoflavones alone or a combined effect of isoflavones with other
nutrients. For example, in addition to isoflavones, soybeans contain
protease inhibitors, omega-3 fatty acids and phytosterols, all of
which are absent from isoflavones tablets. In addition, soybeans
contain other beneficial nutrients such as iron, protein and calcium,
as well as non-nutrients such as fiber.
Most manufacturers do not list the isoflavone
content of their packaged foods, but here is a partial list (Table
2) developed through a collaborative effort between the USDA and
the Department of Food Science and Human Nutrition of Iowa State
University. The USDA/Iowa State database reflects the isoflavone
content of foods produce in 1999. The year and place where the food
was grown will affect the isoflavone content of soybeans as well as
soy foods. However, this list and the charts that follow provide
guidelines for selecting foods that are rich in isoflavones.
All soybeans are
not equal…in isoflavones
Soy foods are the richest sources of isoflavones.
However, the average concentration of isoflavones varies according to
the source. For example, Taiwan soybeans have only about 40% of the
isoflavones found in soybeans from Korea, the richest source of
isoflavones from soybeans (Figure
1). Soy flour is even richer in isoflavones (Figure
2). Full fat, roasted soy flour has almost 200 mg of isoflavones
per 100 grams compared with defatted soy flour, which has about 40%
fewer isoflavones for the same weight.
Eating soybean seeds as a snack is a convenient
way to increase soy intake. They can be eaten in place of peanuts
(contain 0.26 mg isoflavones/100g) or dried sunflower seed kernels
(contain no isoflavones). The concentration of isoflavones in soybean
seed varies (from 12 to 153 mg/100 grams) depending on the maturity
and processing of the seed (Figure
3).
Other good sources of isoflavones are beans,
although compared with soybeans (Figure
1), their isoflavone content is rather low (Figure
4).
Some food processors have attempted to capitalize
on the growing interest in soy and isoflavones. The five examples in
Figure
5 reveal the wide differences in isoflavone content of franks,
links, patties, nuggets and adult formula.
A strategy for
increasing dietary isoflavones
In order to reach the daily amounts of
isoflavones that researchers suggest are needed for a positive impact
on health, it is logical to concentrate on soy-based foods. This might
include baking with soy flour (up to 177.89 mg isoflavone/100g),
drinking a soy beverage (109.51 mg/100g), or eating defatted soybean
flakes (125.82 mg/100g). Other good sources of isoflavones include
tofu, such as Mori-Nu silken firm (27.91 mg/100g) or dried-frozen
(67.491 mg/100g) and tempeh, either cooked (53.00 mg/100g) or burgers
(29.00 mg/100g).
Not all beans contain isoflavones. Those that do,
contain modest concentrations of isoflavones and should be eaten to
supplement a isoflavone-rich diet. Navy, pinto, red, fava, garbanza
and small white beans contain 0.10 to 0.74 mg/100g.
For people raised on meat and potatoes, it may
require significant (often pleasant) changes in cuisine to achieve the
intake reported in clinical studies, including eating miso, tofu
and natto. Contrary to popular belief, soya sauce (shoyu), the
most important Japanese condiment is a relatively poor source of
isoflavones (1.64 mg/100g).
Table
2.
An
abridged list of the isoflavone content in foods.
|
Food
|
Average
mg isoflavone/100g
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Bacon, meatless
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12.10
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Beans, kidney, all types, mature, seeds, raw
|
0.06
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Beans, navy, mature seeds, raw
|
0.21
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Beans, pinto, mature seeds, raw
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0.27
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Beans, red, mature seeds, raw
|
0.31
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Beans, small white, mature seeds, raw
|
0.74
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Broadbeans, fried
|
1.29
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Chickpeas (garbanzo beans, bengal gram), mature seeds, raw
|
0.10
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Clover sprouts, raw
|
0.35
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Frichick (meatless chicken nuggets), canned, cooked
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14.60
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GreenGiant Harvest Burger®, original flavor,
all vegetable protein patties, frozen
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9.30
(8.22 when prepared)
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Instant beverage, soy, powder, not reconstituted
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109.51
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Kala chana, mature seeds, raw
|
0.64
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Miso
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42.55
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Miso soup mix, dry
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60.39
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Mung beans, mature seeds, raw
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0.19
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Natto (soybeans, boiled and fermented)
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58.93
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Peanuts, all types, raw
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0.26
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Peas, split, mature seeds, raw
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2.42
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Pigeon peas (red gram), mature seeds, raw
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0.56
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Snacks, granola bars, hard, plain
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0.13
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Soybean butter, full fat, Worthington Foods, Inc.
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0.57
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Soy cheese, unspecified
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31.32
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Soy cheese, cheddar
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7.15
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Soy cheese mozzarella
|
3.00
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Soy cheese, parmesan
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6.40
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Soy drink
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7.01
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Soy cheese, parmesan
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6.40
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Soy drink
|
7.01
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Soy fiber
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44.43
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Soy flour, textured
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148.61
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Soy flour, defatted
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131.19
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Soy flour, full-fat, raw
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177.89
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Soy flour, full fat, roasted
|
198.95
|
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Soy hot dog, frozen, unprepared
|
15.00
|
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Soy meal, defatted, raw
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125.82
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Soymilk, fluid
|
9.65
|
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Soymilk, iced
|
4.71
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Soymilk skim, or film (Foo jook or yuba), raw
|
18.40
(50.70 if cooked)
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Soy noodles, flat
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8.50
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Soy paste
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31.52
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Soy protein concentrate, aqueous washed
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102.07
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Soy protein concentrate, produced by alcohol extraction
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12.47
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Soy protein isolate
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97.43
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Soy sauce made from hydrolyzed vegetable protein
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0.10
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Soy sauce made from soy and wheat (shoyu)
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1.64
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Soy-based liquid formula for adults, Ross,
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0.54
Enrich®, 0.34 Jevity Isotonic®
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Soybean chips
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54.16
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Soybean curd cheese
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28.20
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Soybean, curd, fermented
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39.00
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Soybean, Brazil, raw
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87.63
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Soybean, Japan, raw
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118.51
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Soybean, Korea, raw
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144.99
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Soybean, Taiwan, raw
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59.75
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Soybean, flakes,
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125.82
defatted (128.99 full-fat)
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Soybeans, immature, cooked, boiled, drained, no salt
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13.79
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Soybeans, immature, seeds, raw
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20.42
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Soybean, green, mature seeds, raw
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151.17
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Soybeans, mature seeds, dry roasted
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128.35
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Soybeans, mature seeds, raw (US, food quality)
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11.66
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Soybeans, mature seeds, raw (US, commodity quality)
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153.40
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Soylinks, frozen, Morning Star breakfast
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3.75
cooked (3.93 raw)
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USDA Commodity beef patties with VPP, frozen
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1.86
cooked, (1.14 raw)
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Worthington Foods, Loma Linda, Big Franks®,
meatless
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3.35
canned (3.75 prepared)
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Source:
USDA-Iowa State University Database on the Isoflavone Content of
Foods.
University of Illinois at
Urbana-Champaign, College of Agricultural, Consumer and Environmental
Sciences. Soy and Human Health. Last modified 2000 March
31. (Cited 2000 May 30) Available from URL: http://web.aces.uiuc.edu/faq/faq.pdl?project_id=5&faq_id=565
USDA-Iowa State University Database on the Isoflavone Content of
Foods. Released 1999 Jan 1. (cited 2000 May 30) Available from
URL: http://www.nal.usda.gov/fnic/foodcomp/Data/isoflav/isoflav.html
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