Association of Plant-Based Diet Index with Quality of Life in Patients with Prostate Cancer - Stacy Loeb

July 3, 2023

Stacy Loeb shares her significant research on the impact of plant-based diets on prostate cancer risk. The conversation pivots around Dr. Loeb's study which builds on earlier findings that higher plant-based food consumption correlates with lower fatal prostate cancer risk. Her newer research explores the potential benefits of such diets on quality-of-life outcomes post-diagnosis, especially with issues such as erectile dysfunction and urinary control, prevalent after prostate cancer treatment. Utilizing data from a longstanding Harvard study involving over 3,000 male health professionals diagnosed with prostate cancer, her team found minor improvements in various functional outcomes among those consuming more plant-based foods. Dr. Loeb concludes with a simple recommendation for patients: "Eat more plants," as it carries no downside but potential upsides in risk reduction, weight loss, cardiovascular health, and environmental impact. She hopes future research can examine the possible mitigating effects of plant-based diets in patients with high genetic cancer risk.


Stacy Loeb, MD, Urologic Oncologist, NYU, Langone Health, New York, NY

Alicia Morgans, MD, MPH, Genitourinary Medical Oncologist, Medical Director of Survivorship Program at Dana-Farber Cancer Institute, Boston, Massachusetts

Read the Full Video Transcript

Alicia Morgans: Hi. I'm so excited to be here with Dr. Stacy Loeb, who's a professor of urology and population health at NYU and the Manhattan VA. Thank you so much for being here with me today.

Stacy Loeb: Thank you so much for having me.

Alicia Morgans: Wonderful. Stacy, you've done so much work for the urology community and really thinking about how we can do something actively, perhaps with our diets to make a difference in terms of prostate cancer risk. Can you tell us a little bit about the work that you presented at ASCO 2023 related to a plant-based diet?

Stacy Loeb: Yeah, for sure. The first study that we did that was published last year was looking at plant-based diets to reduce the risk of fatal prostate cancer. We found that basically the more plant-based foods you consumed, the lower the risk of fatal prostate cancer. So then I got together a group of people, including a lot of great collaborators, yourself included, to look at plant-based diets and quality of life outcomes in people who are already diagnosed with prostate cancer.

It's very interesting because there are some previous studies showing that people who follow plant-based diets, for example, have a lower risk of erectile dysfunction, and that is one of the main issues that occurs after prostate cancer treatment. So we wondered, could we see some of these same benefits, for example, less erectile dysfunction or better urinary control in people who follow a plant-based diet after their diagnosis of prostate cancer?

Essentially, what we found is that there were small improvements in really all of the different functional outcomes, which include sexual health, urinary health, bowel health, and hormonal or vitality status in the people who consume more plant-based foods. It was a small difference, but every bit counts for sure. And people are always asking, "What can I do to help?" And so this is something that's very easy that people can actually do that can make a small difference in their functional outcomes.

Alicia Morgans: Absolutely. Tell me, who were the patients that were included in your investigation for this work?

Stacy Loeb: Yes, that's a great question. This is all data from the health professionals' follow up study. This is a very longstanding prospective cohort study out of Harvard University. So these are all male health professionals. And the people in our study specifically were more than 3,000 of these health professionals who had been diagnosed with prostate cancer and who were followed over time. So they completed surveys after their diagnosis that were telling all about their sexual function, urinary control, bowel function, and hormonal and vitality. And so that was linked up with their dietary questionnaires to look at associations between the dietary patterns and the functional outcomes.

Alicia Morgans: Great. And so that's a huge cohort and a really nice, real world cohort, I think. And so I commend you and the team for engaging in that way. It's a really robust cohort. I wonder though, one thing that I would imagine was hard within this is that you're getting these dietary surveys and you're getting them over years and years and years, and you have to find a way to define your plant-based diet. So how did you do that on the dietary survey? What did you categorize as someone have a majority plant-based diet?

Stacy Loeb: Yeah, so that's a really good question. Interestingly, this database doesn't really include a lot of people who were on a strict plant-based diet. That is to say there were very few people in the dataset who were a vegetarian or a vegan. What we did is classified people really along a spectrum of just how much of the food that they consume is plant-based versus animal-based. So there are some easy ways to do this that have been published extensively called the Plant-Based Diet Index. Basically, you get plus points for the plant-based foods that you eat and minus points for the animal based foods. And so we were able to stratify people along this spectrum.

For instance, if you divide people into quintiles where the first quintile is the most heavily animal based with the least plant-based food, and then the fifth quintile is the most plant-based and least animal-based food. So I guess what's very nice about the study is that these are people on an omnivorous diet. So even people who weren't fully plant-based, just changing around the composition of their diet to include more plant-based foods was able to make some difference. Now, it's possible we would've found a larger impact if we followed people who were actually on fully plant-based diets, but unfortunately there just aren't many of those individuals in this particular data set.

Alicia Morgans: But such an important point because when individuals are sitting in clinic with me, at least they say, "What can I do?" And having changes that are a little bit more moderate rather than some extreme recommendation that you know, "You should be fully vegan, fully plant-based," is something that I think patients feel a little more empowered to participate in. Though of course, there are certainly patients who are very eager and excited to really embark on a plant-based or vegan diet, but it's nice that you don't have to be 100% to potentially get a benefit, at least in this data set.

Stacy Loeb: Yeah, absolutely. I mean, I think it's important that we meet our patients where they're at, and even small changes can incrementally make a difference. And if somebody feels overwhelmed with this, even just start with one day a week, meatless Monday, and then you can go up from there.

I tell patients it can be easier to add things before subtracting things from the diet so you don't feel like you're losing out on something. Just try a new dish, try a plant-based dish that's using chickpeas or lentils or tofu as the protein instead of beef or chicken and see how it goes. And then maybe just keep adding on from there. But I think people are surprised at how easy it is these days. There's apps like HappyCow to help people find plant-based food anywhere in the world. There are just so many programs online and great recipes. and the Physicians Committee for Responsible Medicine both have tons and tons of recipes that were created by physicians and nutritionists. So I think there's just so many more resources out there these days to help people who are trying to introduce more plant-based foods into their patterns.

Alicia Morgans: Wonderful. So if you had to summarize this particular work and give a recommendation to somebody sitting with you in clinic, what would that be?

Stacy Loeb: Eat more plants.

Alicia Morgans: A simple message.

Stacy Loeb: Pretty straightforward. Simple message. We found that it reduces the risk of lethal prostate cancer, and it seems like it can make a small benefit in terms of some of these important quality of life outcomes after treatment. Importantly, there's just really no downside. There's level one evidence that it reduces cardiovascular disease. It's also level one evidence that it leads to weight loss. There's a lot of things to be gained from this, not to mention it's better for the environment as we're all concerned about planetary health and climate change. So I guess I just don't really see any downside, only upside to giving this a try.

Alicia Morgans: Absolutely. Final question, where do you go from here? What are you going to investigate next?

Stacy Loeb: I think it'll be really interesting to look at people who are at high genetic risk. Specifically nowadays, more and more patients are getting genetic testing, for example. And especially in a screening context, if you find out that you're at high genetic risk, let's say you're a BRCA2 carrier and have a lot of anxiety about the future risk of developing cancer, I think it would be great to look more into lifestyle modifications such as the plant-based diet and that population to see if some of this increased risk could be mitigated.

Alicia Morgans: Wonderful. So something that our patients can do, they can act on now and as a simple message, eat more plants for all the reasons that you mentioned. Thank you so much for sharing your work and your expertise with me today.

Stacy Loeb: Thank you so much.