No one can argue with the cardiovascular benefits of diet and exercise, but what about prostate cancer (PCa)? There is plenty of evidence based on observational research that certain diets, such as the Mediterranean diet, appear to help keep prostate cancer in check. However, a skeptical scientist may argue that a certain amount of bias influences such studies, and that a different kind of research is needed.
Some types of research give stronger results
Common sense tells us that the larger the sample, and the more often the study is repeated with the same results, the higher the quality of the conclusions. Let’s say you notice (observe) that when you put your dog’s dish down in front of it, the dog salivates. You think, that’s interesting. You start watching the dog every time you set a bowlful of food down in front of it, and the same thing happens. You try it over and over, always with the same results. This is an observational study, and it gives you the basis for theorizing that dogs drool over food. However, you only tested one action with one dog, so you want to be more confident that you’re on the right track.
So, let’s say you invite five neighboring dog owners to bring their pets over at dinner time (along with their dog’s food and dish). When all the hungry dogs are assembled, each owner including you puts the bowl of food down in front of their dog and you record what happens. Sure enough, you see that all six dogs salivate. You do this every day for a week, with the same outcome every time. This study has a better design: your sample is larger and you repeated it for seven consecutive days. Your results are stronger, but how can you be sure that it’s the presence of food that makes their mouth water? You can’t rule out the possibility that the act of a human putting, say, a tennis ball down in front of the dog would also make the dog salivate. To explore that question, you would have to set up a much more ambitious trial to compare the effect of a bowl of food vs. a tennis ball. That would involve two groups of randomly assigned dogs, bowls of food, and tennis balls. Is it worth going to all that trouble? After all, the stakes for dogs are not very high.
Randomized, controlled studies increase credibility
However, when it comes to cancer, a greater investment of time and money is worth it. Let’s go back to the question of whether diet makes a positive difference with PCa. An Oct. 2017 article calls for better research to determine if lifestyle changes can control PCa.[i] The authors state that randomized, controlled trials (RCTs) are needed for best results. According to the National Institutes of Health, an RCT is “a study in which the participants are assigned by chance to separate groups; neither the researchers nor the participants can choose which group.”[ii]
The MEAL study
Fortunately, a national randomized trial is actually occurring to examine whether a high vegetable diet can prevent PCa from progressing in men who are on Active Surveillance. It is called the MEAL (Men’s Eating and Living) study. Four hundred seventy-eight patients from 91 centers were enrolled between 2011 and 2015. Participants were randomly assigned to either a dietary intervention or a control condition. Their baseline clinical and demographic factors were recorded. There were no significant differences between the groups (based on age, race/ethnicity, geographic region, time since PCa diagnosis, PSA, clinical stage, or Gleason score) so the two groups were considered matched.
No data from the MEAL study will be released until the two year follow-up is complete for all participants. This will soon occur, since patients were last enrolled during 2015. Then the statistics will be collected and analyzed.
Many researchers and doctors are eagerly awaiting the conclusion of this trial, since the randomized, controlled design ensures that the evidence will be stronger than that from observational studies. We can only hope that when the two groups are compared, those who practiced the dietary intervention will have lower rates of disease growth and progression. The news could be cause for excitement and hope. Stay tuned.
[i] Ballon-Landa E, Parsons JK. Nutrition, physical activity, and lifestyle factors in prostate cancer prevention. Curr Opin Urol. 2017 Oct 18. doi: 10.1097/MOU.0000000000000460. [Epub ahead of print]