The Effects of Soy Protein on Post-Thoracotomy Pain

Preclinical studies indicate that soy-containing diets suppress the development of pain
behaviors and hyperalgesia seen following nerve injury and recent data indicate a similar
protective effect of a diet high in soy protein in inflammatory and bone cancer pain models.
These studies further indicate that soy exposure is only protective when administered in
the period immediately preceding injury. Very few studies have directly studied the effects
of soy-containing diets on pain sensitivity in humans, but one recent randomized clinical
trial suggests that dietary soy supplementation may reduce pain due to osteoarthritis. The
proposed study will examine whether a soy protein supplement reduces the pain commonly
experienced following thoracotomy for lung surgery. This is a useful clinical model for
studying the effects of soy protein supplementation on pain because the pain associated with
surgery is quite severe and is one of the greatest concerns patients have about undergoing
surgery. The growing recognition that greater acute pain leads to persistent pain following
tissue healing underscores the importance of identifying viable strategies, including both
non-pharmacological as well as pharmacological, for reducing the acute pain associated with
surgery. Using a 2 group (soy protein supplementation vs. matched milk placebo
supplementation) design, patients undergoing elective major open thoracotomy for
segmentectomy, lobectomy, or bilobectomy will be randomly assigned to one of these two
treatment groups. Patients will begin taking the soy/placebo supplement 2-3 days prior to
thoracotomy and continue daily consumption of the supplement for an additional period
following surgery. The feasibility/pilot study will examine the effects of soy
supplementation on outcome measures during three post-operative time periods: 1) the
immediate post-operative period; 2) during 2-12 weeks following surgery; and 3) during 14-24
weeks following surgery. Pain is the primary outcome domain of interest in this pilot study
and measures will include pain severity ratings and pain medication use. Function and
quality of life are the secondary outcome domains of interest and measures will include
pain-related interference with daily activities, sleep, and health-related quality of life.
Outcome measures will be collected bi-weekly throughout the study. The study aims to
determine the feasibility and acceptability of soy supplementation in the period surrounding
thoracotomy, determine level of adherence to soy supplementation over the 6-month period of
follow-up, and estimate the effect size of soy supplementation relative to placebo in
reducing significant pain following thoracotomy. The proposed study will provide the
necessary groundwork to move towards such a larger randomized trial to evaluate the
pain-reducing effects of soy protein supplementation following thoracotomy.

Inclusion criteria: 1) undergoing major elective thoracotomy through a classic incision,
including segmentectomy, lobectomy, or wedge resection, 2) for women, a negative mammogram
within the past year; 3) for women using oral contraceptives or hormone replacement
therapy, the agreement to hold steady dosing of these medications for the duration of the
study; and 4) ability to comprehend the consent information and to complete all study
assessments.

Exclusion criteria: 1) age less than 18 years, 2) current alcohol or substance
abuse/dependence; 3) delirium, dementia, or cognitive impairment (MMSE < 24; (23)); 4)
use of analgesics (other than aspirin or non-steroidal anti-inflammatories) for a
condition other than the reason for surgery; 5) milk or soy allergy; 6) lactose
intolerance; 7) pre-operative chest pain; 8) women with a history of breast cancer; or 9)
[use of an antibiotic within 3 months prior to surgery.