Soy - Interactions

What Are "Star" Ratings?

a7_3star Reliable and relatively consistent scientific data showing a substantial health benefit.

a7_2star Contradictory, insufficient, or preliminary studies suggesting a health benefit or minimal health benefit.

a7_1star For an herb, supported by traditional use but minimal or no scientific evidence. For a supplement, little scientific support.

Our proprietary “Star-Rating” system was developed to help you easily understand the amount of scientific support behind each supplement in relation to a specific health condition. While there is no way to predict whether a vitamin, mineral, or herb will successfully treat or prevent associated health conditions, our unique ratings tell you how well these supplements are understood by the medical community, and whether studies have found them to be effective for other people.

For over a decade, our team has combed through thousands of research articles published in reputable journals. To help you make educated decisions, and to better understand controversial or confusing supplements, our medical experts have digested the science into these three easy-to-follow ratings. We hope this provides you with a helpful resource to make informed decisions towards your health and well-being.

This supplement has been used in connection with the following health conditions:

Used for	Amount	Why
High Cholesterol	25 grams soy protein per day	Soy supplementation has been shown to lower cholesterol. Soy contains isoflavones, which are believed to be soy’s main cholesterol-lowering ingredients.
High Cholesterol 25 grams soy protein per day Soy supplementation has been shown to lower cholesterol in humans.¹ Soy is available in foods such as tofu, miso, and tempeh and as a supplemental protein powder. Soy contains isoflavones, naturally occurring plant components that are believed to be soy’s main cholesterol-lowering ingredients. A controlled trial showed that soy preparations containing high amounts of isoflavones effectively lowered total cholesterol and LDL (“bad”) cholesterol, whereas low-isoflavone preparations (less than 27 mg per day) did not.² However, supplementation with either soy³ or non-soy isoflavones (from red clover)⁴ in pill form failed to reduce cholesterol levels in a group of healthy volunteers, suggesting that isoflavone may not be responsible for the cholesterol-lowering effects of soy. Further trials of isoflavone supplements in people with elevated cholesterol, are needed to resolve these conflicting results. In a study of people with high cholesterol levels, a soy preparation that contained soy protein, soy fiber, and soy phospholipids lowered cholesterol levels more effectively than isolated soy protein.⁵ Learn More

Used for	Amount	Why
Hypertension	10 grams soy protein or 16 ounces soy milk twice per day	Supplementing with soy protein may significantly lower blood pressure.
Hypertension 10 grams soy protein or 16 ounces soy milk twice per day In a double-blind study of postmenopausal women, supplementing with 10 grams of soy protein twice a day for six weeks significantly reduced diastolic blood pressure by an average of 5 mm Hg, compared with a diet not containing soy protein.⁶ In another study, men and women with mild to moderate hypertension consumed 500 ml (approximately 16 ounces) of soy milk or cow's milk twice a day for three months. After three months, the average systolic blood pressure had decreased by 18.4 mm Hg in the soy group, compared with 1.4 mm Hg in the cow's milk group. The reductions in diastolic blood pressure were 15.9 mm Hg with soy milk and 3.7 mm Hg with cow's milk.⁷ In another study of people with hypertension who were consuming a low-protein, low-fiber diet, supplementing with a combination of soy protein and psyllium (a fiber source) lowered systolic blood pressure by an average of 5.9 mm Hg.⁸ The blood pressure reduction with soy protein alone or with fiber alone was less pronounced than that with combination treatment. Other research has also shown a blood pressure–lowering effect of soy protein.⁹ ^{, 10} Learn More

Used for	Amount	Why
Athletic Performance and Exercise Recovery	33 to 40 grams daily	In one study, elderly men participating in a strength training program who took a supplement containing protein (part of which was soy protein) immediately following exercise saw significant gains in muscle growth and lean body mass.
Athletic Performance and Exercise Recovery 33 to 40 grams daily In one preliminary study, elderly men participating in a 12-week strength training program took a liquid supplement containing 10 grams of protein (part of which was soy protein), 7 grams of carbohydrate, and 3 grams of fat either immediately following exercise or two hours later.¹¹ Men taking the supplement immediately following exercise experienced significantly greater gains in muscle growth and lean body mass than those supplementing two hours later, but strength gains were no different between the two groups. A controlled study of female gymnasts found that adding 0.45 grams of soy protein (0.45 grams per pound of body weight per day) to a diet that was adequate in protein during a four-month training program did not improve lean body mass compared with a placebo.¹² No research has compared different sources of protein to see whether one source, such as soy protein, has a better or more consistent effect on exercise recovery or the results of strength training.

Used for	Amount	Why
Obesity	Refer to label instructions	Soy appears to have several effects on the body that might help with weight loss.
Obesity 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.¹⁵ 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.¹⁶ However, controlled studies comparing soy protein with other protein sources in weight-loss diets have not found any advantage of soy.¹⁷ ^{, 18} ^{, 19} When soy protein is used for other health benefits, typical daily intake is 20 grams per day or more. Learn More

Used for	Amount	Why
Premenstrual Syndrome	Refer to label instructions	Supplementing with soy protein may help relieve premenstrual swelling and cramping.
Premenstrual Syndrome In a double-blind trial, supplementing with soy protein (providing 68 mg of isoflavones per day) for two menstrual cycles was significantly more effective than a placebo at relieving premenstrual swelling and cramping.²⁰ The placebo used in this study was cow's milk protein. Some doctors believe that cow's milk, because of its estrogen content, can worsen premenstrual symptoms. If that is the case, then the beneficial effect of soy protein may have been overestimated in this study. Learn More

Also indexed as:

soy protein

About this treatment

Interactions with Supplements, Foods, & Other Compounds

Soy contains a compound called phytic acid, which can interfere with mineral absorption.

Interactions with Medicines

Certain medicines interact with this supplement.

	Some medicines may increase the need for this supplement.
	Some medicines interact with this supplement, so they should not be taken together.
	Some interactions between this supplement and certain medicines require more explanation. Click the link to see details.

Note: The following list only includes the generic or class name of a medicine. To find a specific brand name, use the Medicines Index.

	Dessicated Thyroid
	Levothyroxine
	Liothyronine
	Liotrix
	Ipratropium Bromide
	Theophylline
	Warfarin

Side Effects

Last Review: 05-11-2011

Learn more about Aisle7, the company.

The information presented in Aisle7 is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications. Information expires June 2011.

© 1995-2011 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated. This information does not replace the advice of a doctor. Healthwise, Incorporated disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

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