Men are not mice — No link between fats eaten and risks for prostate cancer
Guys who are looking forward to enjoying a great barbecue this Memorial weekend may be interested in the results of what’s probably the world’s largest study looking to see if there is any link at all between dietary fat and risks for prostate cancer. If no link can be found at all, then, of course, it would rule out fat as a cause. So what did it find?
Good news, unlike the continual doom and gloom in the media. Every time we turn on the television or open a newspaper, it seems there’s another scary claim about the evils of fat. As each scare turns out to fall flat, those facts rarely seem to make headlining news. Major studies have demonstrated that being fat isn’t linked to prostate cancer, nor does losing weight lower risks. The news is just as reassuring about the fat they eat.
You probably guessed that, just by knowing this study hadn’t made the news. Even its authors appeared to have expected different results. They opened by writing that, while biologically plausible mechanisms have been proposed for why fat might increase risk for prostate cancer, recent observational studies on people haven’t been able to demonstrate any credible association, including two large prospective studies. These findings have been downplayed and not widely reported, they said, with some proposing that the groups of people were too homogenous and their dietary fat intakes didn’t vary enough, or that different dietary assessment techniques have been used.
So, for this study, they set out to investigate the links between dietary fats from various animal products and risks for prostate cancer among men with a variety of dietary patterns and by grades and stages of their disease. They used the data from the prospective cancer study of 142,520 men from 19 clinical centers across 8 European countries (Denmark, Germany, Greece, Italy, the Netherlands, Spain, Sweden, and the United Kingdom). The men (average age 52) recruited for the European Prospective Investigation into Cancer and Nutrition study had been healthy and cancer free at the time of enrollment. The researchers used nearly all of the original cohort, only excluding those for whom there had been no dietary data completed or the reports exhibited dubious outlier extremes.
The men’s diet information was assessed in several ways and, while self-reported, the researchers took extreme care to design their dietary questionnaires to accurately measure the men’s fat intakes, using food-frequency questionnaires and diet histories, portion sizes and fat contents measured in foods in each country. To further validate the dietary intakes, they randomly selected a sample of 13,031 men among all EPIC centers, who completed carefully standardized 24-hour diet recall surveys. The men’s body mass index didn’t differ significantly by their fat intakes, although the men eating the most fats were slightly more likely to be married and significantly more likely to be smokers.
Cancers were identified through cancer registries available in 6 countries and they used a combination of self-reported and medical records and billing codes to confirm the other cases. For their further analyses, they also obtained the TNM stages and Gleason grades for most of the cancers through each medical center. The men were followed for an average of 8.7 years, during which time there were 2,727 cases of prostate cancer found.
The results were just published in the current issue of the American Journal of Clinical Nutrition. They found:
There were no statistically significant associations between intakes of total fat, the subtypes of fat, of the P:S ratio [polyunsaturated to saturated] and risk of prostate cancer. Compared with the lowest quintile [intake] of total fat intake, men categorized in the highest quintile had [a hazard ratio] for prostate cancer [that was lower] of 0.96 [95% CI: 0.84, 1.09]. Individuals categorized in the third quintile of total fat intake had a 15% lower risk of prostate cancer in comparison with individuals categorized in the lowest quintile... each 10% increase in energy [calories] from fat was associated with a 5% lower risk of prostate cancer, but this result was not statistically significant..
They found no tenable correlation between dietary fat and prostate cancer. This held after adjusting for weight, height, smoking, education, marital status and calorie intakes. All of the risks hugged null (ratios of 1/1 = 1). In fact, if you want to split hairs, higher total fats, saturated fats, monounsaturated fats, polyunsaturated fats and P:S ratios were all associated with (1-5%) lower overall risks for prostate cancer, although not significant. [Click on image to enlarge.]
They did a separate analysis based on sources of dietary fat and also found no statistical correlation between fats from red and processed meats, dairy products or fish and shellfish and the risks for prostate cancer. Interestingly, they also found no benefit among those with the highest intakes of what are popularly considered healthy fats, as in fish.
They did another analysis, excluding the first 4 years of follow-up to eliminate any possibility that the men had preexisting diseases, but it didn’t change their findings at all. Neither did their results change when they included or excluded the men’s calorie intakes.
Body of human evidence
To evaluate their findings with the body of evidence, they examined the most recent research, 7 studies with a total of 9,247 cases of prostate cancer. Those had also found no tenable link between dietary fat (total, saturated, polyunsaturated or monounsaturated) and prostate cancer risk. All of the risks hugged either side of null (RR=1). As they emphasized:
Thus, the totality of the evidence indicates that a higher intake of dietary fat is not a risk factor for prostate cancer.
All of the untenable associations found in their computer analysis, they noted, were likely due to chance. There is no biologically plausible mechanism to support a role for a high intake of fat in reducing the degree of cell differentiation association with high-grade [higher-severity] prostate cancer, they said.
These are similar to the findings of the Second Expert Report issued by the World Cancer Research Fund and American Institute for Cancer Research, examined here last year. Examining 2,471 international cancer-related dietary studies, it found no credible link between meats or processed meats, dairy products, vitamins, produce, alcohol, sugars, sodas and 17 different cancers, including prostate cancer.
The EPIC researchers concluded:
In conclusion, the results from this large prospective study showed that a high intake of dietary fat was not associated with an increased risk of prostate cancer. These findings add further evidence that the intake of dietary fat is not an important predictor of prostate cancer risk.
Men trump mice
The fear of fat appears so ingrained into our consciousnesses, that this study received no media attention the week it came out, while the media reported a study that had been published more than a month earlier... looking at prostate cancer in specially-bred transgenic mice. This study, by researchers at the University of California, Los Angeles, published in Cancer Research**, opened by writing: “Epidemiological studies suggest that environmental factors associated with Western lifestyle may promote the development of clinical prostate cancer,” specifically implicating dietary fat. So, this study sought to identify a mechanism for how lowering dietary fat in calorie-controlled diets could slow the development of prostate cancer.
The mice they used had been bred to develop neoplasia as early as 2-4 weeks and invasive adenocarcinomas between 6-9 months due to an overexpression of c-Myc in their mouse prostates. In other words, they’ve been bred so that anything and everything will give them cancer. At three weeks of age, 33 were given high-fat feeds of 42% fat from corn oil and 28 were put on a 12% corn oil feeds. They were killed at 7 months of age and 12 of the mice getting the low corn oil feed had invasive cancers compared to 23 of the high fat fed mice. Eleven mice. From this, the only diet-related conclusion that can be made is that transgenic mice don’t appear to do as well given high corn oil feeds.
Anything more is speculation and, in fact the discussion is filled with words such as possibly, suggest, may, could and believed. The authors were actually exploring various mechanisms and markers — Akt-mTOR pathway, androgen levels, IGFBP-1 levels — in cancer cell growth and such research is important for perhaps leading to a treatment for prostate cancer. But not in making dietary prescriptions on humans.
While most anything will give special research mice cancer, countless such scares suggested in animal studies haven’t played out when humans are examined. We’re ‘bred’ with resiliencies to a variety of exposures. So, while virtually everything gives mice cancer and in toxic enough doses can be harmful to us — even things essential to our survival like water, salt, sugars and fats — that doesn’t mean the ranges we eat cause us any harm at all. And, as the medical researchers across 8 countries [with no conflicts of interest declared] concluded this month, the totality of the evidence on humans shows that higher intakes of dietary fat is not a risk factor for prostate cancer.
Human studies trump mice every time.
For the sake of our sanity, with the sensationalized scares and whiplash that the media tries to give us — with dietary claims that contradict each other all in the same week — keep one simple fact in mind. Over the past fifty years, while we’re eating all of this supposedly “bad” food and Western diet, health and life expectancies in the U.S. have “dramatically improved,” according to former Health and Human Services Secretary Tommy Thompson. Cancer rates and deaths from cancer have continued to fall every year since the early 1990s, including nine of the top ten cancers commonly associated with “poor diets and sedentary behaviors.” Despite the negative media portrayals, cancers are primarily diseases of aging. And, as the HHS’s latest report on the health of the nation revealed, we’re healthier than ever and living longer, too.
Now, go out and enjoy your Memorial weekend barbecue!
© 2008 Sandy Szwarc
** This study notes: “The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.”