Reference
Richman EL, Stampfer MJ, Paciorek A, Broering JM, Carroll PR, Chan JM. Intakes of meat, fish, poultry, and eggs and risk of prostate cancer progression. Am J Clin Nutr. 2010;91(3):712-721.
Design
A prospective trial in which consumption of processed and unprocessed red meat, fish, poultry, and eggs was tracked and examined to see whether specific dietary habits affect the risk of prostate cancer recurrence or progression.
Participants
1,294 men diagnosed with prostate cancer who were participants in the Cancer of the Prostate Strategic Urologic Research Endeavor; participants were without recurrence or progression as of 2004–2005 and were followed for an average of 2 years.
Main Outcome Measures
127 events were observed during the 2,610 person-years of follow up. Events were defined as prostate cancer death, metastases, elevated prostate-specific antigen, or secondary treatment.
Key Findings
Men previously diagnosed with prostate cancer who consumed the greatest amounts of eggs or poultry with skin were at double the risk of an adverse event compared to men consuming lesser amounts. For eggs, comparing the highest and lowest quartiles of consumption, or an average of 5.5 eggs per week against 0.4 eggs, the hazard ratio was 2.02 [95% CI: 1.10, 3.72; P for trend = 0.05]. Comparing highest and lowest quartiles of poultry consumption yielded a nonsignificant hazard ratio of 1.55. A comparison between the upper and lower tertiles of those eating poultry with skin yielded a statistically significant hazard ratio of 2.26. (95% CI: 1.36, 3.76; P for trend = 0.003). An interaction was observed between poultry and prognostic risk at time of diagnosis. Men with high prognostic risk and a high poultry intake had a 4fold increased risk of recurrence or progression compared with men with low/intermediate prognostic risk and a low poultry intake (P for interaction = 0.003). Dietary fat consumption did not have an effect. Eating processed or unprocessed red meat, fish, or skinless poultry after prostate cancer diagnosis was not associated with prostate cancer recurrence or progression; consumption of eggs and poultry with skin appeared to increase risk of recurrence.
Practice Implications
These data suggest that men who have been diagnosed with prostate cancer should be warned against consuming eggs or poultry with skin on. Concerns over red meat consumption were not supported.
An estimated 192,280 cases of prostate cancer were diagnosed in 2009. Of these cases, more than 90% were still localized or regional disease for which 5-year survival is almost 100%. In the remaining 10%, distant metastases had already occurred and of these nearly 20,000 men, only 32% are predicted to survive 5 years.1,2
There is already a degree of understanding as to what dietary elements increase risk of getting prostate cancer. It has been suggested that consuming a diet “low in fat, high in vegetables and fruits, and avoiding high energy intake, excessive meat, excessive dairy products and calcium intake, is possibly effective in preventing [prostate cancer].3
The same factors that initiate prostate cancer do not necessarily promote recurrence or progression. This study is one of several attempting to identify modifiable factors that affect progression of prostate cancer.
A 2006 study by Chan et al reported that men consuming larger quantities of fish or tomato sauce after diagnosis had lower risks of recurrence: “Men in the highest versus lowest quartile of post-diagnostic fish consumption had a multivariate hazard ratio (HR) of progression of 0.73 (95% CI: 0.52–1.02); the comparable HR for tomato sauce was 0.56 (95% CI: 0.38–0.82).4
Richman et al, the authors of this current study, hypothesized that consumption of unprocessed meat and red meat, because of their high saturated fat content, would increase risk of progression. They assumed that poultry and eggs, because they contained lower levels of saturated fat and because they contained more omega-3 fats, would protect against progression.
The data do not support either assumption. Instead poultry with skin and eggs had significant effects, while red meat did not. This is significant as men with prostate cancer in an attempt to follow a healthier diet often decrease red meat and increase poultry consumption. This may be a mistake.
A 2004 review by Dagnelie et al found no association between eggs or poultry and risk of being diagnosed with prostate cancer.5 In a 2007 paper, Giovannucci et al suggested that different factors may promote prostate cancer progression after diagnosis than those that originally initiated the cancer. In addition, they suggest that still other factors may increase the risk of the cancer’s being more aggressive.6 The same paper reported that increased levels of alpha-linolenic acid in the diet were associated with higher risks of prostate progression, a troubling piece of information for adherents of the Budwig diet.
The Richman paper is not the first to associate poultry with prostate cancer. A 2001 paper by Michaud et al reported an association between poultry skin and metastatic prostate cancer risk.7 The American Institute of Cancer Research suggested a possible association between total poultry and prostate cancer in their 2007 report.8
The authors of this current study had thought that levels of saturated fats in food would be the primary predictor of risk. Their results did not support this idea. They have proposed two possible explanations for their results. First, cooked poultry skin contains large amounts of heterocyclic amines and these chemicals promote prostate cancer growth. Second, eggs contain large amounts of choline, which also may promote prostate cancer growth.
Other researchers have already suggested a link between heterocyclic amines and prostate cancer, proposing this as an explanation for their observed association between higher meat intake and prostate cancer.9
Cooked poultry contains more heterocyclic amines than any other type of meat—so much so that Bogen and Keating proposed in 2001 that African American men were at higher risk of prostate cancer because of their higher chicken consumption.
“[Heterocyclic amine]… intakes were estimated to be greatest for African American males, who were estimated to consume approximately 2- and approximately 3-fold more [heterocyclic amines] than white males. … This difference … may at least partly explain why prostate cancer (PC) kills approximately 2-fold more African American than white men.10
The high choline of eggs may explain their association with prostate cancer progression;egg consumption raises serum choline levels.
Eggs’ high choline may explain their association with prostate cancer progression. Egg consumption raises serum choline levels. A Swedish paper from 2009, by Johansson et al, tells us that high plasma choline is associated with greater risk of prostate cancer.11 Prostate cancer cells contain more choline than healthy prostate cells.12 In fact, radio-labeled choline is used for PET scan imaging of prostate tumors.13
This study certainly has its limitations, and many may still be leery of accepting these findings. Eggs or poultry may simply be markers for other factors or behaviors that affected risk. Because the participants were only followed for 2 years, the number of events was small. But if these findings are correct, what are the implications for our patients?
Obviously, men diagnosed with prostate cancer may be disgruntled when you tell them they should avoid consuming large amounts of eggs or poultry with skin. Many men have been doing the opposite, avoiding red meat and eating more eggs and poultry as their primary sources of protein.
If heterocyclic amine levels do play a significant role in prostate cancer progression, a greater effort should be made to lower exposure. More focus should be placed on cooking techniques to lower production of these chemicals. Emphasis can also be put on dietary components that inactivate heterocyclic amines, reducing exposure.
Some practitioners may find this to be a shift in emphasis; supplements for treating prostate cancer are often targeted at increasing cancer cell apoptosis. This research suggests greater emphasis should be made on removing chemicals that trigger, promote, or enable prostate cancer growth, in particular heterocyclic amines and choline.
For more research involving integrative oncology, click here.
