This study will find out if a meal replacement of this type is satisfying and tolerable for men with prostate cancer. Participants will receive meal replacements of TalityTM as their expected sole source of nutrition for 4 weeks. The purpose of the study is to test whether TalityTM Synthetic Meal Replacements are suitable to be used in larger studies of patients with prostate or other types of cancer.

Primary Objective: Determine the appeal/tolerability/palatability of a diet consisting solely of TalityTM synthetic meal replacement in participants with prostate cancer Secondary Objective: Evaluate the effect of TalityTM on safety parameters including laboratory tests, nutritional status and adverse effects

Inclusion Criteria:

• Biopsy-proven prostate cancer with stable or rising PSA levels, defined as three consecutive PSA levels, each value greater than 1 week apart, with fluctuation between the three values no more than 10% downward. The third PSA needs to be within 30 days prior to enrollment and >= 0.1.
• Patients may previously have been on any regimen of chemotherapy completed at least one month prior. Patients may be on any stable form of anti-androgen therapy.
• Males >= age 18.
• All patients must have a life expectancy of > 6 months.
• Patients must have an ECOG Performance Status of <= 1
• Patients must have no clinically significant abnormalities of organ or bone marrow function
• Patients must have the ability to understand and the willingness to sign a written informed consent document, and the willingness/ability to comply with the protocol activities.

Exclusion Criteria:

• Chemotherapy within one month prior to enrollment or plans to receive chemotherapy within one month after enrollment. Patients who are expected to require new or modified anti-androgen therapy during the course of the study are also excluded.
• Patients may not be receiving any other Investigational Agents during the course of the study.
• Patients who experience frequent symptoms of a gastrointestinal nature (e.g., diarrhea, abdominal bloating, constipation or pain) are excluded.
• Known CNS metastases.
• Patients who, in the opinion of the Principal Investigator, have a clinically significant co-morbid disease that is likely to affect the ability of the patient to complete the trial, interfere with their ability with measurement of self-reported outcomes or result in adverse events unrelated to TalityTM are excluded.
• Patients with a history of food allergy are excluded.
• Concomitant medications necessary to treat baseline disorders are allowed (e.g., hypertension, diabetes, and hyperlipidemia).
• Patients requiring concomitant medications that, in the opinion of the Principal Investigator, have an unacceptable risk of adverse effects due to their nature (e.g., anti-coagulant therapy, immuno-modulatory agents for autoimmune disease) must be excluded.
• Pregnant or nursing patients will not be enrolled since prostate cancer is limited to males.
• HIV-positive patients with active infections, HIV related cancer or poorly controlled viral loads must be excluded. HIV-positive patients who are stable on anti-viral therapy may be enrolled.