June’s Men’s Health Month- Vegetable Fats May Lower Prostate Cancer Risk

Approximately 2.5 million men in the United States are living with prostate cancer. While we have some knowledge of what kind of diet may increase or decrease risk of getting prostate cancer, we know little about what effect food choices will have on these men once they do have cancer. Erin Richman, first at Harvard and now at the University of San Francisco has over the last few years given us a few hints. She first came to our attention with her 2010 study that suggested that high intake of eggs or chicken skin was associated with a greater risk of progression. Then more recently her 2012 paper suggested that dietary choline, which is supplied in large quantity by eggs, was linked with higher risk. She is now the lead author in a new study that’s suggests that dietary fats may effect significantly prostate cancer progression and overall mortality. Her data suggest that moderate changes, particularly reduction of animal fat and carbohydrate and replacement with vegetable fat, might have a lower risk of death from prostate cancer and also from other causes.

The new study was published June 10, 2013, and compared men who were diagnosed with non-metastatic prostate cancer against their dietary intake of fat seeking an association with the eventual lethality of the disease.

The participants in this study were part of “The Health Professionals Follow-up Study” cohort that was initiated in 1986 among 51,529 male health professionals aged 40 to 75 years. Prostate-specific antigen (PSA) screening practices were added in 1994. Dietary data were collected via food frequency questionnaires at baseline and every four years thereafter. To be included in this study, men had to be free of cancer at baseline and have a diagnosis of non-metastatic prostate cancer between 1986 and 2010. This narrowed the larger cohort down to the 4,577 men followed in this current study.

Food frequency questionnaires were completed at baseline and every four years of the study. The men reported their usual intake of approximately 130 foods and beverages during the prior year. They reported fried food consumption, types of cooking oil, and visible fat on meat consumed. Consumption of fat was calculated including saturated fats, polyunsaturated fats, mono-saturated fats, trans fat and whether fats were animal or vegetable derived.

The primary outcome tracked was lethal prostate cancer, defined as a distant metastases or death due to prostate cancer, and all-cause mortality. Death was attributed to prostate cancer only if cancer metastases were present and no more plausible cause of death was mentioned in medical records or death certificate.

During the 8.4-year course of this study, 1064 of the participants died, 315 of them from lethal prostate cancer. The difference that consumption of varying types of dietary fats made on the outcome measures is summarized below:

Crude rates per 1000 person-years for lethal prostate cancer:

(Type of fat: highest vs. lowest quintile of intake)

Saturated 7.6 vs. 7.3

Monounsaturated 6.4 vs. 7.2

Polyunsaturated: 5.8 vs. 8.2

Trans-fat: 8.7 vs. 6.1

Animal fat 8.3 vs. 5.7

Vegetable fat 4.7 vs. 8.7

All-Cause mortality rates per 1000 person-years for lethal prostate cancer:

(Type of fat: highest vs. lowest quintile of fat intake)

Saturated 28.4 vs. 21.4

Monounsaturated 20.0 vs. 23.7

Polyunsaturated: 17.1 vs. 29.4

Trans-fat: 32.4 vs. 17.1

Animal fat 32.0 vs. 17.2

Vegetable fat 15.4 vs. 32.7

Replacing 10% of energy intake from carbohydrates with energy from vegetable fat was associated with a 29% lower risk of lethal prostate cancer and 26% lower all-cause mortality.

No other fats were associated with lethal prostate cancer. Saturated and trans fats after diagnosis (replacing 5% and 1% of energy from carbohydrate, respectively) were associated with higher all-cause mortality.

This sounds pretty straightforward. All those men with prostate cancer should focus on eating fewer carbohydrates and animal fats and increase the vegetable fats in their diet.

The impact specific foods that are top sources of vegetable fat were analyzed. The authors report several were “suggestively associated” with lower risk, that is, while the data did not reach statistical significance, it was pretty close. These almost associations are worth mention not as if they are fact (they were not significant), but for our contemplation as they hint at a problem with this study. Eating an additional single serving of salad dressing per day (1 Tbsp) after diagnosis was “suggestively associated” with a 29% lower risk of lethal prostate cancer and a 13% lower risk of death. A one-ounce increase in daily nut consumption was “suggestively associated” with an 18% lower risk of lethal prostate cancer and an 11% lower risk of death.

Does the salad dressing really deserve credit or was it simply a measure of salad and vegetable consumption? These findings may not be as simple as they sound. The beneficial effects associated with vegetable fat intake seen in these data may be from other components of the food sources of the vegetable fats or other foods paired with them. While the study authors attempted to adjust for all known dietary factors (calcium, vitamin E, lycopene, vitamin D, choline, phosphorous and zinc) they cannot rule out some confounding factor.

Seed oils and nuts provided most of the vegetable fats in this study population and we know that these foods have multiple effects including increasing plasma antioxidants, reduction of insulin, LDL cholesterol, and various inflammatory markers. As an example, the authors cite the research on flax seed and prostate cancer. Are the associations seen in this study the result of the oil consumed or some other phytonutrient components found in the food from which the oil was derived? As mentioned in the past, the fats in nuts will improve cardiovascular risk, but not to the degree seen in studies and so it is assumed that some of the benefit of eating nuts is that they provide a range of phytonutrients that are also protective.

We may not know the answers to these questions, yet these results are still worth paying heed to. Based on these results it is still prudent for men with prostate cancer to consume less animal fat and fewer carbohydrates, and to replace the “lost calories” with calories from vegetable fats. It appears that even moderate changes may have significant impact.

Source: AANP, Jacob Schor ND. References:

1. 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.

2. Richman EL, Kenfield SA, Stampfer MJ, Giovannucci EL, Zeisel SH, Willett WC, Chan JM. Choline intake and risk of lethal prostate cancer: incidence and survival. Am J Clin Nutr. 2012 Oct;96(4):855-63.

3. Richman EL, Kenfield SA, Chavarro JE, Stampfer MJ, Giovannucci EL, Willett WC, Chan JM. Fat Intake After Diagnosis and Risk of Lethal Prostate Cancer and All-Cause Mortality. JAMA Intern Med. 2013 Jun 10:1-8.