Soy Protein

Aka: Soy Protein, Phytoestrogen, Glycine Max, Soy Isoflavone

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II. Precaution

  1. Soy lacks the Amino Acids Cysteine and Methionine
  2. Combine with rice, corn or wheat
    1. To supply all Essential Amino Acids

III. Mechanism

  1. Weak Estrogen and anti-Estrogen effects
    1. Weaker than Estradiol by factor of 1/1000
  2. Phytoestrogen Sources
    1. Lignan in seeds and grains
    2. Isoflavone (genistein, daidzein) in legumes
      1. Soybeans
      2. Red Clover
  3. Inhibit tumor growth in culture

IV. Dietary sources

  1. Soy-rich foods (richest sources)
    1. Soy milk (1 cup): 3-10 grams Soy Protein (90-140 cals)
    2. Tofu (3 oz): 10 grams Soy Protein (90 cals)
    3. Tempeh (1 ounce): 5 grams Soy Protein (55 cals)
    4. Soy flour (1/2 cup): 20 grams Soy Protein (220 cals)
    5. Soy Protein (2 tbs): 25 grams Soy Protein (110 cals)
    6. Edamame (1 cup): 22 grams Soy Protein (250 cals)
  2. Licorice
  3. Red clover
  4. Thyme
  5. Tumeric
  6. Hops
  7. Verbena
  8. Alfalfa
  9. Beans

V. Benefits: Potential

  1. Associated with significant reduced Breast Cancer risk
    1. Initial Retrospective Studies (needs confirmation)
    2. However, avoid in those with Estrogen receptor positive Breast Cancer
  2. Decreased lipid levels (Soy Protein - not subcomponents)
    1. Decreases LDL Cholesterol (up to 13%)
    2. Decreases Serum Triglycerides (up to 10%)
    3. Reynolds (2006) Am J Cardiol 98(5): 633-40 [PubMed]
  3. May increase Bone Mineral Density
    1. Soy Protein decreases Fracture risk
      1. Zhang (2005) Arch Intern Med 165(16): 1890-5 [PubMed]
    2. Soy Isoflavone decreases postmenopausal spinal bone loss
      1. Ma (2008) Clin Nutr 27:57-64 [PubMed]

VI. Benefits: Variable

  1. Hot Flushes
    1. Effectiveness appears dependent on pharmacogenomic factors
      1. Equol is a soy metabolite with Estrogenic Activity
      2. Only 40% of North American women convert Soy Isoflavone (daidzein) to equol
        1. Conversion is most common in Asian and Hispanic women
        2. The majority who lack this conversion are unlikely to see benefit from soy
      3. References
        1. Clarkson (2011) Menopause 18(7):732-53 [PubMed]
    2. Some studies show benefit in Hot Flushes
      1. Faure (2002) Menopause 9:329-34 [PubMed]
      2. Han (2002) Obstet Gynecol 99:389-94 [PubMed]
      3. Howes (2006) Maturitas 55:203-11 [PubMed]
      4. Welty (2007) J Womens Health 16:361-9 [PubMed]
    3. Other studies suggest no benefit in Hot Flushes
      1. Nikander (2003) Obstet Gynecol 101:1213-20 [PubMed]
    4. Requires large, often intolerable doses (60 g/day)
      1. Albertazzi (1998) Obstet Gynecol 91:6-11 [PubMed]

VII. Adverse Effects

  1. Most common side effects
    1. Diarrhea
    2. Menstrual irregularities (Amenorrhea or prolonged periods)
  2. Thyroid suppression may occur
  3. Recent flawed study showed adverse neurologic effects
    1. Further well performed studies required
  4. Unknown longterm effects on Estrogen receptors
    1. Caution in Estrogen receptor positive Breast Cancer
    2. Does not appear to increase endometrial thickness at typical isoflavone doses (40-80 mg)
      1. Penotti (2003) Fertil Steril 79:1112-7 [PubMed]

VIII. Dosing: Sources of dietary Soy Protein and isoflavone

  1. Recommended doses for Hot Flashes in Menopause
    1. Soy Protein 25-60 g/day
    2. Isoflavone 60 mg/day
  2. Equivalent sources to meet 25-60 gram daily intake
    1. Soy Milk (4 glasses)
    2. Tofu 2 portions or one third brick
    3. Edamame 1/2 cup
    4. Soy Protein powder in shake (1 serving)

IX. References

  1. Albertazzi (1998) Obstet Gynecol 91:6-11 [PubMed]
  2. Ingram (1997) Lancet 350:990-4 [PubMed]
  3. Morelli (2002) Am Fam Physician 66(1):129-34 [PubMed]
  4. Potter (1998) Am J Clin Nutr 68(suppl):1375-9 [PubMed]

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