Adding soy protein to your diet may NOT stop biochemical progression

According to data from a small, randomized, clinical trial published in the Journal of the American Medical Association, daily use of a supplement containing soy protein isolate for 2 years after radical prostatectomy did not reduce risk for biochemical progression of prostate cancer in high-risk patients.

Bosland et al. conducted their randomized, double-blind clinical trial between July 1997 and May 2010 at seven US cancer centers. The trial was designed to compare whether consumption of a beverage powder containing 20 mg soy protein isolate supplement for 2 years reduces the rate of biochemical recurrence of prostate cancer after radical prostatectomy or delays such recurrence as compared to a similar placebo containing calcium caseinate as a placebo instead of the soy protein.

Patients had to be diagnosed with clinically localized (T1c or T2) prostate cancer and had to meet any one (or more) of the following criteria indicative of high-risk disease (see the trial design summary on

  • A preoperative PSA level of > 20.0 ng/ml
  • Seminal vesicle invasion on post-surgical pathology
  • Extracapsular extension on post-surgical pathology (excluding the bladder neck)
  • Positive surgical margins (excluding apical margins)
  • Micrometastases in any pelvic lymph nodes removed at surgery
  • A pathological Gleason score of ≥ 8

The patients were asked to start using the supplement (or the placebo) within 4 months of their surgery. They continued to take the supplement (or the placebo) for the next 2 years. PSA values were measured every 2 months for the first year and every 3 months thereafter.

In this study, biochemical recurrence of prostate cancer was defined as development of a PSA level of ≥ 0.07 ng/ml within the first 2 years following randomization. Time to such recurrence was also carefully monitored. Although patients are normally advised that no further therapy is needed after first-line surgery until they have a PSA higher than 0.2 ng/ml, this PSA level would seem to be a highly appropriate indicator of signifciant biochemical recurrence among men with high-risk forms of prostate cancer as defined above.

Here are the study results:

  • The study enrolled a total of 177 patients.
    • 87 men were randomized to receive the soy protein supplement.
    • 90 men were randomized to receive the placebo.
  • The trial was stopped early, at an interim analysis, because of the lack of any treatment effect.
  • Adherence to the treatment regimens was > 90 percent.
  • At the time of that interim analysis
    • 81 patients in the soy protein supplement arm were evaluable (i.e., had received treatment for the full 2 years)
    • 78 patients in the placebo arm were evaluable.
    • 22/81 patients (27.2 percent) in the soy protein supplement arm showed biochemical recurrence.
    • 23/78 patients (29.5 percent) in the placebo arm showed biochemical recurrence.
    • The hazard ratio (HR) was 0.96 (with a log-rank P = 0.89, implying no statistical significance).
  • No apparent adverse effects of either the supplement or the placebo were reported.

What is also worthy of note is that, in this randomized study of high-risk patients, 114/159 evaluable men (71.7 percent) showed no sign of biochemical recurrence at the extremely low bar of a PSA of 0.07 ng/ml within 2 years of their surgery.

The results of this study are also presented in a Reuters report available on line. In that report, Dr. Bosland is quoted as stating that:

When we did the analysis and there was an absolute absence of the effect, I was a little surprised. But in a way, it was good because the outcome was clear.

Separately, Dr. Eric Klein of the Cleveland Clinic is quoted as saying, “This adds to the evidence that nutrition supplements really aren’t beneficial” in men who have already received surgical treatment for their prostate cancer.

However, Drs. Klein and Bosland both noted that there are some data suggesting that men who start to eat soy early in life may be less likely to develop prostate cancer in the first place.

8 Responses

  1. I’m baffled by the aim of this study. Did anyone say that adding soy protein to one’s diet would stop biochemical progression?


    I have been consuming soy deliberately and taking a supplement for years, starting in early 2000, hopefully to help me cope with prostate cancer. I was on a minimal soy diet prior to diagnosis in late 1999 as I believed I was allergic to soy. Shortly after diagnosis, having learned about its possible benefit for reducing the hot flashes associated with androgen deprivation therapy, I “challenged” myself with soy and found I was not allergic.

    I would have stopped the supplementation during the vacation period of intermittent ADT, but about that time Dr. Maha Hussain’s study was published. Based on that, recognizing that it was a small study and suggestive rather than conclusive, I’ve been taking soy ever since.

    I found the Hussain results impressive, with stabilization of PSA in 83% of the hormone-sensitive group and in 35% of the hormone-refractory group. The dose in that study was 200 mg per day, and my recollection is that the study mentioned a reason for believing that less than that dose was not effective, but I do not recall the details and may be mistaken. However, it is possible that the dose in the Bosland study reviewed above, with a dose of just 20 mg per day, was below a threshold for efficacy. It is also possible that soy is best suited for lower-risk patients; indeed there is some evidence for that in the Hussain study, as the hormone-sensitive group did much better than the hormone refractory group.

    I was only able to access the abstract of the Bosland study, and I’m curious whether the Hussain research was cited. I’m curious why the dose issue was not addressed in the abstract.

    Soy consumption is one of those lifestyle nutritional tactics that can be personally assessed by each of us patients: if we take the dose and it has a desired effect, that’s fair evidence that it is working for us personally. While soy, in concert with the other lifestyle tactics I have employed for years for my high-risk case has never been sufficient to stabilize or decrease my PSA for my challenging, very high-risk case, I still think I have probably benefited in terms of slowing down the disease or preventing/minimizing metastasis. Of course, I have no way of knowing that is so with high confidence.

  3. Dear Richard:

    Lots of people have been arguing that adding soy to one’s diet could prevent the progression of prostate cancer … for years!

  4. Dear Jim:

    I was fascinated by your statement that “Soy consumption is one of those lifestyle nutritional tactics that can be personally assessed by each of us patients: if we take the dose and it has a desired effect, that’s fair evidence that it is working for us personally.”

    I have no idea how you can possibly justify that statement. All that you actually know when a “desired effect” like this occurs is that it may, perhaps, be associated with the intervention that you think you have implemented. Human organisms are far too complex to be able to know that intervention X definitively accomplished consequence Y in a single-patient study like this, however much it may feel as though that may be the case.

    Please note that I am not telling you that it definitely has not achieved the desired effect … only that (as you then note later), you can’t be sure that it has. Single-patient studies can definitely generate hypotheses … but actual proof that the hypothesis is correct is a whole different matter.


    Hi Sitemaster,

    I’m responding to your post of July 10, 2013 at 5:07 pm, which related to my post of 4:11 pm. On reading your response, I realized that my assumption of being able to assess a personal impact from a personal intervention, such as soy consumption, may have been overly optimistic, but there is some basis and here it is. I’m convinced this often works.

    For those of us with rather regular PSA monitoring, if we are cruising along without new treatment or changes in our lifestyle patterns except for one item, and we see an uncharacteristic change in our PSA levels after that one item has changed, especially a change in the result pattern that is maintained, that is at least fair evidence that that change has made a difference, as I see it.

    That would be similar to what happens after medical intervention. I’ve seen changes in my own PSA levels that appear to be due to an intervention (or ceasing an intervention) in finasteride use, Avodart use, thalidomide use, probably Celebrex at 2 X 200 mg daily, and of course after ADT itself with the LHRH agonist and antiandrogen drugs. I think I’m seeing a more favorable pattern due to radiation in this fourth triple ADT cycle compared to three previous cycles, where trends have been quite consistent. The small Phase II 2006 study of pomegranate juice by Pantuck and colleagues relied on such PSA analysis in observing an impressive extension of PSA doubling time.

    Of course even an observed change is not proof of causality, but it may be the best evidence we have as patients to choose what works and what does not work for us. I fully concur that we cannot be sure something is working just because of a change in the pattern of PSA results. We might even be experiencing a placebo effect.


    Hi Richard (and Sitemaster),

    As Sitemaster said, lots of people have been advocating soy, and you can find the related published medical research by going to and searching for “soy AND prostate cancer”, narrowing the search as you please. By clicking on the list of authors in any hit of interest, you’ll get a copy of the abstract, if there is one, as well as a link to a free copy of the complete paper, if a free copy is accessible.

    A research team from the University of Michigan and Wayne State University has been very active in studying soy and prostate cancer, and here is a link to one of their recent papers (by Ahmad et al.).

    I’m citing this source because of the unusually favorable assessment mentioned in the abstract:

    “Isoflavones have been investigated in detail for their role in the prevention and therapy of prostate cancer. This is primarily because of the overwhelming data connecting high dietary isoflavone intake with reduced risk of developing prostate cancer.”

    Frankly, while I’m a fan of soy consumption for us prostate cancer patients, I was surprised to see the word “overwhelming” used to characterize the data indicating that soy reduces the risk of developing prostate cancer. If they are right, that would move soy to the “wow” level for nutritional tactics. Any thoughts?

  7. Dear Jim:

    I’m not suggesting that you (or anyone else) shouldn’t act on what seems to work for you. My point is only that just because it seems to work for you doesn’t have any definable implications beyond that. Lots of patients make the misguided assumption that just because something “seemed to work” for them, it is going to work for other people too. This is the territory of snake oil salesmen!

  8. Yup … We now use words like “hero”, “unique”, “overwhelming”, etc., with little credible correlation to the actual definitions of these words. This tendency has finally invaded the scientific literature … to all our loss!

    The use of the word “overwhelming” in this context is ridiculous and inappropriate. If isoflavones were “overwhelmingly” effective in modifying our risk for prostate cancer, it would be pretty obvious by now.

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