What do we know about diet’s impact on prostate cancer?
Dr. Mucci: Epidemiology studies of diet, lifestyle, and prostate cancer have really evolved a lot over time because of PSA screening and our understanding of the disease’s biologic heterogeneity. With PSA screening, we are both diagnosing more men with prostate cancer and diagnosing more men with a more slow-growing form of prostate cancer.
What we’ve learned is that the relationship between the majority of dietary and lifestyle factors seems to be more associated with the risk of aggressive prostate cancer. We’re starting to see that certain factors are associated with either worse or better survival. It has taken us a while as a field to realize that the relationship of risk factors varies for aggressive versus nonaggressive cancer.
It has also taken us a while to understand the role that PSA screening has played in our studies.
The other consideration with prostate cancer is that it could be many years, if not decades, after diagnosis before a man experiences metastatic disease. Thus, we need long-term follow-up studies to understand the impact of lifestyle factors.
In terms of diet, I don’t think there is yet strong evidence for any particular lifestyle factor to say it is causal. There are some probable factors and some new factors we’re starting to think about.
There is good data on the role of an antioxidant known as lycopene. Lycopene is commonly found in high levels in cooked tomato products such as tomato sauce, but also in things like salsa. What is interesting about lycopene is that it accumulates at high levels in the prostate. A number of epidemiology studies have shown lycopene to be associated with a much lower risk of aggressive prostate cancer. There was a small, randomized study in which men were given capsules of cooked tomato products. The study showed lycopene could make changes in the prostate tumor tissue. So there is probable evidence for cooked tomato products and lycopene in prostate cancer prevention.
We are also starting to see evidence emerge around regular consumption of coffee, either decaffeinated or caffeinated. Coffee is one of the strongest antioxidants available, even stronger than berries. Coffee is interesting for a number of cancers. It seems to be associated with a lower risk of liver cancer, potentially colorectal cancer, and diabetes. In randomized studies, we also see that coffee helps regulate insulin levels after a meal. Insulin may be very important for advanced prostate cancer.
Again, I wouldn’t say this evidence is convincing yet, but we’re starting to see many studies suggesting the benefit of regular coffee consumption.
There is also emerging evidence about fish consumption. In particular, fatty fish like tuna or salmon are associated with a lower risk of aggressive prostate cancer.
On the other side, there is now data suggesting high calcium intake at the levels you’d get more from many supplements may be associated with an increased risk of a more aggressive form of prostate cancer.
Finally, the association between obesity and aggressive prostate cancer is strong. Any dietary factors, or dietary patterns, that contribute to obesity may be associated with more aggressive prostate cancer and with worse outcomes for patients.
Join us to read the remainder of Dr. Mucci’s comments on diet and prostate cancer.
Carbohydrates + Prostate Cancer
Dr. Snuffy Myers talks further about CT scans and cancer risk.
Dr. Stephen Freedland is a urologist at Cedars-Sinai in Los Angeles, California, and the Director of the Center for Integrated Research in Cancer and Lifestyle, Co-Director of the Cancer Genetics and Prevention Program and Associate Director for Faculty Development at the Samuel Oschin Comprehensive Cancer Institute.
Dr. Freedland treats the whole patient and not just a man’s prostate cancer.
What do you tell your patients about prostate cancer and diet?
Dr. Freedland: Given the link between obesity and prostate cancer, I focus on getting my patients to lose weight. The easiest way to lose weight is to cut out all the extra sugar in your diet: cookies, cake, candy, all of that. A meta-analysis published in the Journal of the American Medical Association of all the popular diets found that the best diet for weight loss was a low-carb diet. That was the best diet. They’re all decent, but low carb is the best.
Is that true primarily for American patients or for everyone?
Dr. Freedland: I think it’s true for everyone. A recent study published in the Lancet followed over 135,000 people in 18 different countries on over five continents. They found that the more carbs you eat, the more likely you are to die earlier. Eat fewer carbs, live longer. Fewer carbs and more fat make you live longer.
This is a landmark study that supports what an increasingly loud minority of us has been saying. Fat is not the problem. Carbs are the problem.
I focus my patients on their carb intake. Let’s focus on the carbohydrates in the diet and see which of those we can get rid of. If you’re having whole-grain oatmeal for breakfast, maybe that can stay. But most people are having pancakes with butter and syrup. We can get rid of that.
While you’re giving up the sugars, cakes, and candies, we focus on what we can put in their place: fruits and vegetables.
Yes, fruits have sugar, but it’s a natural source. As long as patients aren’t juicing, natural fruits contain a lot of fiber that will slow the absorption of sugar in the intestine. Nuts, beans, and those types of things are also good replacements.
I worry that because we’ve been advocating that people cut out fat and tell them to eat lots of fruits and vegetables, people are going to go to the store, buy fat-free ice cream and say, “I had a salad with my dinner so I can eat all the ice cream I want now. I’m being healthy!”
Remember the old food pyramid from the 1980s? Carbs were at the bottom of the pyramid, the largest food group.
Dr. Freedland: Right. Lots of bread. Our entire way of thinking has been very carb-centric. Let’s eat carbs and avoid fat. And the result has been that the obesity rates have almost tripled in the United States in the last 30 years.
What do you say to people who argue that you should have carbs in balance with fat and protein?
Dr. Freedland: Your body doesn’t need carbs. There are animals and people raised without eating a single carb. You can’t survive without eating fat. You can’t survive without eating protein. You can survive without eating carbs.
What protein sources do you recommend?
Dr. Freedland: People get in this mindset that red meat is bad and fish is good. Fish (we think) is good because it contains fish oil, an omega-3 fatty acid. But I found an article that looked at tilapia. It turns out that tilapia doesn’t have much fish oil. If you want fish oil, you know what are better sources than tilapia? Doughnuts and bacon.
Dr. Freedland: Doughnuts and bacon have more fish oil than tilapia per gram.
I guess not all fish are created equal.
Dr. Freedland: Correct. And not all meat is created equal. A nice grass-fed steak probably has as much omega-3 fatty acid as many kinds of fish. The worst protein for prostate cancer is charred meat. Those black lines you get on your steak in charring form heterocyclic amines that can cause cancer. This is true mostly for meat because that’s what you tend to char, but it’s also true for chicken and potentially fish.