Soy Protein for Weight Control
Also known as: Daidzein, Genistein, Glycine Max, Isoflavone,
Protein [Soy], Soya
What is it?
Soy, a staple food in many Asian countries, contains valuable constituents, including
protein, isoflavones, saponins, and phytosterols. Soy protein provides essential amino acids. When eaten with rice, soy provides protein comparable with that found
in animal products. Soy is low in fat and cholesterol-free.
Why do dieters use it?*
Some dieters say that soy protein
- provides a source of low-fat, cholesterol-free
protein.
What do the advocates say?*
Protein is necessary for rebuilding tissue, which is especially important for bodybuilders.
All types of protein provide the body with amino acids.
From an athletic point of view, soy is just another type of protein. Choosing soy protein
over other types of protein adds variety to the protein choices available. However, because
soy lowers cholesterol, it is an excellent choice for those also trying to lower their
cholesterol levels.
Soy is a common ingredient in many meal replacements that are designed to provide a large
amount of nutrients in a minimal amount of calories.
How much is usually taken by dieters?
Animal and human studies have suggested that when soy is used as a source of dietary
protein, it may have several biological effects on the body that might help with weight
loss.1 A preliminary study found that people trying to lose weight using a
meal-replacement formula containing soy protein lost more weight than a group not using any
formula.2 However, controlled studies comparing soy protein with other protein
sources in weight loss diets have not found any advantage of soy.3 4
5 When soy protein is used for other health benefits, typical daily intake is 20
grams per day or more.
Are there any side effects or interactions?
Soy products and cooked soybeans are safe
at a wide range of intakes. However, a small percentage of people have allergies to soybeans and thus should avoid soy
products.
Soy isoflavones have been reported to reduce thyroid function in some people.6 A
preliminary trial of soy supplementation among healthy Japanese, found that 30 grams (about
one ounce) per day of soybeans for three months, led to a slight reduction in the hormone that
stimulates the thyroid gland.7 Some participants complained of malaise, constipation, sleepiness, and even goiter. These symptoms resolved within a month of
discontinuing soy supplements. However, a variety of soy products have been shown to either
cause an increase in thyroid function8 or produce no change in thyroid
function.9 The clinical importance of interactions between soy and thyroid function
remains unclear. However, in infants with congenital hypothyroidism, soy formula must not be added, nor
removed from the diet, without consultation with a physician, because ingestion of soy may
interfere with the absorption of thyroid medication.10
Most research, including animal studies, report anticancer effects of soy extracts,11
though occasional animal studies have reported cancer-enhancing effects.12 The
findings of several recent studies suggest that consuming soy might, under some circumstances,
increase the risk of breast cancer.
When ovaries have been removed from animals—a situation related to the condition of
women who have had a total hysterectomy—dietary genistein has been reported to
increase the proliferation of breast cancer cells.13 When pregnant rats were
given genistein injections, their female offspring were reported to be at greater
risk of breast cancer.14 Although
premenopausal women have shown decreases in
estrogen levels in response to soy,15 16 pro-estrogenic effects have
also been reported.17 When pre-menopausal women were given soy isoflavones, an
increase in breast secretions resulted—an effect thought to elevate the risk of
breast cancer.18 In yet another trial, healthy breast cells from women previously
given soy supplements containing isoflavones showed an increase in proliferation
rates—an effect that might also increase the risk of breast cancer.19
Of 154 healthy postmenopausal women who received 150 mg of soy isoflavones per day for five
years, 3.9% developed an abnormal proliferation of the tissue that lines the uterus
(endometrial hyperplasia). In contrast, none of 144 women who received a placebo developed
uterine hyperplasia.20 Although no case of uterine cancer was diagnosed during the
study, endometrial hyperplasia is a potential forerunner of uterine cancer. The amount of
isoflavones used in this study is two to three times as much as that used in many other
studies. Nevertheless, the possibility exists that long-term use of isoflavones could cause
uterine hyperplasia, and women taking isoflavones should be monitored appropriately by their
doctor.
Soy contains a compound called phytic acid,
which can interfere with mineral absorption.
Are there any drug
interactions?
Certain medicines may interact with soy. Refer to
drug interactions for a list of those medicines.
*Dieters and weight-management advocates may claim benefits for soy
protein based on their personal or professional experience. These are individual opinions and
testimonials that may or may not be supported by controlled clinical studies or published
scientific articles on soy protein. For more complete and detailed information, including
references and safety information, see Soy as a
nutritional supplement.
References:1. Bhathena SJ, Velasquez MT. Beneficial role of dietary phytoestrogens
in obesity and diabetes. Am J Clin Nutr 2002;76:1191–201 [review].
2. Allison DB, Gadbury G, Schwartz LG, et al. A novel soy-based meal
replacement formula for weight loss among obese individuals: a randomized controlled clinical
trial. Eur J Clin Nutr 2003;57:514–22.
3. Bosello O, Cominancini L, Zocca I, et al. Short- and long-term effects
of hypocaloric diets containing proteins of different sources on plasma lipids and apoproteins
of obese subjects. Ann Nutr Metab 1988; 32:206–14.
4. Yamashita T, Sasahara T, Pomeroy SE, et al. Arterial compliance, blood
pressure, plasma leptin, and plasma lipids in women are improved with weight reduction equally
with a meat-based diet and a plant-based diet. Metabolism 1998;47:1308–14.
5. Jenkins DJ, Wolever TM, Spiller G, et al. Hypocholesterolemic effect
of vegetable protein in a hypocaloric diet. Atherosclerosis 1989;78:99–107.
6. Divi RL, Chang HC, Doerge DR. Antithyroid isoflavones from soybean.
Biochem Pharmacol 1997;54:1087–96.
7. Ishizuki Y, Hirooka Y, Murata Y, Togashi K. [The effects on the
thyroid gland of soybeans administered experimentally in healthy subjects.] Nippon
Naibunpi Gakkai Zasshi 1991;67:622–9. [in Japanese].
8. Forsythe WA. Soy Protein, thyroid regulation and cholesterol
metabolism. Forsythe WA. Soy protein, thyroid regulation and cholesterol metabolism. J
Nutr 1995;125:619S–23S.
9. Bennink MR, Mayle JE, Bourquin LD, Thiagarajan D. Evaluation of soy
protein in risk reduction for colon cancer and cardiovascular disease: Preliminary results.
Second International Symposium on the Role of Soy in Preventing and Treating Chronic
Disease. September 15–18, 1996. Brussels, Belgium.
10. Jabbar MA, Larrea J, Shaw RA. Abnormal thyroid function tests in
infants with congenital hypothyroidism: the influence of soy-based formula. J Am Coll
Nutr 1997;16:280–2.
11. Messina MJ, Persky V, Setchell KD, Barnes S. Soy intake and cancer
risk: a review of the in vitro and in vivo data. Nutr Cancer
1994;21:113–31.
12. Rao CV, Wang C-X, Simi B, et al. Enhancement of experimental colon
cancer by genistein. Cancer Res 1997;57:3717–22.
13. Barnes S. The chemopreventive properties of soy isoflavonoids in
animal models of breast cancer. Breast Cancer Res Treat 1997;46:169–79
[review].
14. Hilakivi-Clarke L, Cho E, Onojafe I, et al. Maternal exposure to
genistein during pregnancy increases carcinogen-induced mammary tumorigenesis in female rat
offspring. Oncol Rep 1999;6:1089–95.
15. Lu L-JW, Anderson KE, Grady JJ, Nagamani M. Effects of soya
consumption for one month on steroid hormones in premenopausal women: implications for breast
cancer risk reduction. Cancer Epidemiol Biomarkers Prev 1996;5:63–70.
16. Nagata C, Takatsuka N, Inaba S, et al. Effect of soymilk consumption
on serum estrogen concentrations in premenopausal Japanese women. J Natl Cancer Inst
1998;90:1830–5.
17. Hargreaves DNF, Potten CS, Harding C, et al. Two-week dietary soy
supplementation has an estrogenic effect on normal premenopausal breast. J Clin Endocrinol
Metab 1999;84:4017–24.
18. Petrakis NL, Barnes S, King EB, et al. Stimulatory influence of soy
protein isolate on breast secretion in pre- and postmenopausal women. Cancer Epidemiol
Biomarkers Prev 1996;5:785–94.
19. McMichael-Phillips DF, Harding C, Morton M, et al. Effects of
soy-protein supplementation on epithelial proliferation in the histologically normal human
breast. Am J Clin Nutr 1998;68(suppl):1431S–6S.
20. Unfer V, Casini ML, Costabile L, et al. Endometrial effects of
long-term treatment with phytoestrogens: a randomized, double-blind, placebo-controlled study.
Fertil Steril 2004;82:145–8.