You may often hear that a cancer prevention diet is a plant-based diet. But focusing on plant-based foods as the only characteristic of healthy eating habits can be a distraction. So what does it mean?
Let’s look at the details of the evidence on healthy eating habits to reduce cancer risk — and what it means for practical strategies you can use….
Latest Recommendations for Reducing Cancer Risk
The latest recommendations for diet and physical activity to reduce cancer risk from the American Cancer Society (ACS) were published in June 2020. Although they are organized differently than the recommendations of the American Institute for Cancer Research (AICR), the messages are consistent.
- Eating habits for lower cancer risk: Make plant foods the stars of your plate. Emphasize a variety of vegetables, fiber-rich pulses (dried beans and peas), fruits and whole grains. Limit or avoid red and processed meats, sugar-sweetened drinks, and highly-processed foods.
- When you consider cutting down on certain foods or drinks, does it trigger a panicky feeling of, “Don’t take them away!”? Try focusing instead on making room for the wide range of whole plant foods that each provide unique protectors. You may find that it’s easier than you think for the less-healthful choices to turn from frequent staples of your diet to enjoyable “sometimes” foods.
Questions about Food Choices for a Plant-Based Diet
Does it Need to be Vegan (Plants-Only)?
Recommendations for reducing cancer risk encourage a plant-based diet. Some people may choose an eating pattern that includes only plants. Traditionally, this is called a vegan diet, though some people use the term “plant-based diet” to mean plants-only eating. But a plant-based diet doesn’t have to be only plants.
The key to a plant-based diet is that it is mainly plant foods. That’s why some people prefer the term “plant-forward diet”. Vegetarian diets – which don’t include meat – can include choices such as milk and cheese, eggs, or fish and seafood. And plant-focused eating can even can include meat and poultry – just not in mega-portions. In all these options for a plant-based diet, the “stars” of the plate are a variety of vegetables, fruits, whole grains, and legumes (like dried beans).
Studies that show lower cancer risk among people who eat vegetarian diets are generally comparing them to people who eat “Western diets” – eating patterns that are heavy on red and processed meat, refined grains and added sugars. Overall, studies show plants-only diets may be slightly more protective against some cancers than other plant-focused eating patterns. But the far more consistent finding is the lower risk with all eating habits that focus on whole plant foods as the largest part of the plate.
Can Fish Fit in a Plant-Based Diet?
As long as meals focus around vegetables, fruits, whole grains and legumes (like dried beans, chickpeas, lentils and soy foods), fish can also be part of a plant-forward eating pattern. In fact, the AICR Third Expert Report notes limited evidence linking fish consumption with lower risk of liver and colorectal cancers. And a major study of U.S. vegetarians found particularly low risk of colorectal cancer among pesco-vegetarians (people eating a vegetarian diet that includes fish).
This evidence isn’t strong enough to warrant a recommendation to make fish part of a cancer-protective diet. For example, it’s not clear how much of any reduction in cancer risk stems from the fish and seafood itself, and how much of any protection seen reflects eating less red and processed meat. However, recommendations do advise that including seafood at least once or twice a week can add heart-health protection, especially when at least some is high in omega-3 fats. So as you consider strategies for how you will cut down on excess red meat intake, including fish more often can be a healthy and delicious option.
What about Dairy Products and Cancer Risk?
Despite what you may see in headlines, there’s no clear association of dairy products with increased or decreased risk of all cancers combined. Since the evidence is not clear-cut, neither the ACS nor AICR reports include a recommendation about dairy consumption.
Here’s the current evidence:
- Colorectal cancer: Evidence is strong that dairy products, and increased calcium consumption, reduce risk.
- Prostate cancer: Limited evidence suggests potential for increased risk of prostate cancer with diets high in dairy products or calcium. But a closer look at data from many studies combined shows prostate cancer risk only beginning to rise with consumption above 1000 mg/day of calcium from foods (not including supplements). At that level, eating habits could include two servings/day of dairy products (other foods will supply some calcium, too). More research is clearly needed. For now, the strongest message is for adult men to avoid excessive amounts of dairy, not to avoid it completely.
- Ovarian cancer: Careful examination of overall research for the AICR report found evidence too limited to draw any conclusion. That’s after analyzing consumption of individual dairy products, total dairy products, calcium and lactose.
What about breast cancer and dairy? You may have seen concerns about effects on women’s hormones – but this is based largely on theoretical conjecture rather than observed effects. Or perhaps you saw headlines about a study that found a link between high dairy consumption and breast cancer risk. Unfortunately, most articles about the study did not clarify that this compared women at the extreme ends of dairy consumption (top 10% and bottom 10%) in a very specific population that is not representative of Western populations as a whole.
Evidence is too limited to support any conclusion about dairy products and breast cancer. Here’s what analysis of overall research in the AICR report found:
- Dairy: Contrary to headlines people sometimes see, evidence graded “Limited Suggestive” links dairy intake with decreased risk of pre-menopausal breast cancer. A trend that’s not statistically significant links dairy consumption with lower risk of post-menopausal breast cancer, too.
- Calcium: Limited evidence shows high-calcium diets associated with lower risk of both pre- and post-menopausal breast cancer. (And in the context of most populations in these studies, calcium consumption tends to be a marker of dairy product consumption.
- This certainly does not establish dairy as protective. But it contradicts assertions based on individual studies suggesting that dairy is a breast cancer risk. Lacto-ovo vegetarian diets – plant-forward eating patterns that include dairy products and/or eggs – are linked in research overall with lower risk of heart disease and cancer.
There may be reasons why people choose to eliminate dairy from their diet, but doing so for cancer prevention would not be supported by overall current evidence.
Does Soy Protect Against Cancer or Increase Cancer Risk?
Among the controversies I’m most often asked about, soyfoods rate high on the list.
Are isoflavone compounds in soy like estrogen? Isoflavones have a similar chemical structure to human estrogen. But earlier studies in which they promoted growth of estrogen receptor-positive (ER+) breast cancer in mice relate to much higher blood levels than humans would have consuming soyfoods. In fact, studies now suggest that isoflavones tend to bind to particular estrogen receptors more likely to have tumor suppressor effects.
Randomized controlled clinical trials don’t provide consistent support for effects of soy protein or isoflavones on markers of breast cancer risk such as hormone levels, markers of breast cell growth, or breast density. And likewise, such studies show no effect on prostate-specific antigen (PSA) levels or hormones related to risk of prostate cancer.
Human population studies don’t link soy consumption with increased risk of any cancer. And limited evidence links soy with either no effect or decreased risk of prostate cancer. Observational studies also link moderate soy consumption (one to two servings a day) with lower breast cancer risk in Asia, where soy foods are commonly consumed throughout life. However, broader research now suggests that protective effects of soy against breast cancer may come mainly from soy consumption during adolescence.
After a diagnosis of breast or prostate cancer, studies show no harmful effects, and potential for soy foods to play a beneficial role as part of a diet supporting overall health. Limited evidence shows potential for greater overall survival after breast cancer, and perhaps decreased recurrence, among women (including those who had ER+ cancer) who include moderate amounts of soy. Among men followed 6 weeks to 2 years after diagnosis of prostate cancer, controlled clinical trials with soy protein or isoflavone supplements have shown either no effect or a decrease in progression of prostate cancer.
Does the form of soy matter? You can find soy that’s minimally processed (like steamed edamame), in traditional soyfoods that are moderately processed (like tofu, tempeh and soymilk), or as isolated components used as ingredients (such as soy protein isolate in cereal and bars, and soy fiber added to bread). Soy protein isolate powder and textured soy protein don’t contain more isoflavones, and may contain markedly less, than an equal portion of plain roasted soybeans. On the other hand, these isolated components provide don’t provide the full range of nutrients found in whole soyfoods.
Soyfoods can be a good option – though not a must-have — to provide protein as you limit red meat and shift to more plant foods.
Practical Strategies for a Plant-Based Diet and Cancer Prevention
Looking at current recommendations for a cancer prevention diet in the context of overall research, you can see that there are lots of different ways that eating habits fit together to reduce cancer risk and fit with individual needs and food preferences. Let’s pull together a few bottom line strategies:
1) Increase plants
- Flip the basic proportions of foods on your plate. Prepare vegetables with flavorings that suit your palate – making them so delicious that you’re happy to eat a portion at least the size of your fist at each meal. Include whole grains or pulses (like dried beans and lentils) – or both – in most meals.
- Tweak meat-focused dishes to replace all or some of the meat with plant foods. Swap beans, lentils, tofu, or edamame for meat in a stir-fry, chili, soup or stew. Although they don’t replace meat as a source of protein, adding mushrooms or eggplant can add nice texture in a dish with less meat. When you tweak the ingredients in a dish like this, experiment to see if boosting the garlic, onions, herbs or spices helps create the flavor profile you want.
2) Choose nutrient-rich plant foods
- Relatively unprocessed plant foods provide dietary fiber that helps protect against colorectal cancer. And whole grains, vegetables, fruits, beans and nuts contain nutrients and phytocompounds that in laboratory studies show potential to change expression of genes (like tumor suppressor genes) and influence cell signaling pathways, reduce inflammation, and prompt self-destruction of abnormal cells.
- Don’t get distracted by “health halos” on plant-based foods that are highly processed and contain a lot of fat and added sugar. For example, gluten-free crackers or cereal are sometimes made of highly refined grains lacking the fiber and phytocompounds of a whole grain. Cookies and plant-based milks can be made with plants-only ingredients, but still be high in sugar and calories. Plant-based or not, a food that’s high in added fat and sugar can make it harder to maintain a healthy weight, which plays a strong role in reducing risk of at least 12 forms of cancer.
3) Aim for variety.
- No single food has the full range of nutrients and phytocompounds that research suggests can each contribute to cancer prevention and overall health. Rather than searching for the “best” cancer prevention food, aim to include a wide variety of healthy choices over the course of each week.
- You might think of vegetables and fruits in categories, such as cruciferous vegetables (like broccoli, Brussels sprouts, cabbage, cauliflower), green leafy vegetables, deep orange vegetables, citrus fruit, berries, stone fruits (like peaches, apricots, cherries), “pome fruits” (apples and pears). See how many different choices you can include each week.
- Variety doesn’t only add a great range of nutrients, variety helps to keep healthy eating habits interesting. For example, at one time the only pulses I was familiar with were kidney beans (and only in chili or three-bean salad!) and garbanzo beans (in that three-bean salad or hummus). Of course the idea of including them several times a week would have been boring! As you add in lentils, black beans, tofu, edamame, split peas, cannellini beans (the big, soft white beans used in some Italian dishes) and others, this gets a lot more fun.
4) Be flexible.
- When you’re creating a meal for people who differ in eating preferences, turn to dishes that let everyone build their own personal dish. For example, a taco, burrito or grain-and-veggie bowl “bar” lets each person add the vegetables they like best. Provide add-on’s like cheese, yogurt, fish, poultry or meat for people to choose or not as they prefer.
- Accommodate differing preferences by using fish, poultry or meat as an optional add-on. For example, instead of cooking pasta dishes with meat in them, make them all-plant or plant-and-dairy, depending on everyone’s preferences. Offer meat as something some may add to the sauce, and have the sauce without meat for others.
- If you’re afraid plant-based meals will seem dull, think again! Traditional dishes from Italy, Greece, China, India, Morocco and other flavorful cuisines around the world include many beloved plant-only and plant-forward dishes. A quick Internet search might provide ideas for a fun variation on one of your usual go-to dishes.
Bottom Line on Plant-Based Diets and Cancer Prevention
Recommendations based on today’s best evidence are consistent in calling for eating habits that are focused on whole plant foods. Within that framework, each individual and family can create a plant-based diet that work for them. For some, that will be plants-only eating. Others will want to include modest amounts of seafood, dairy products, poultry, red meat, or some combination of these. Aim for variety, both for the range of nutrients and plant compounds, and to make sure that these healthy eating habits are so enjoyable you will be ready to continue this pattern long-term.
New to whole grains beyond a narrow range of bread and breakfast cereals? The Whole Grains Council provides the simple how-to of cooking time and water volume for cooking a wide range of different whole grains. Have fun exploring new choices, whether that means bulgur and quinoa, or millet, sorghum, and more. And if you need fresh ideas for how to use whole grains in different dishes, you’ll find recipes galore here.
Beans are another food that many of us feel confident about using in only a few particular dishes. For some fresh ideas, check these recipes using reduced-sodium Bush’s beans. (Beans in regular sauce can high in sodium. But you can swap reduced-sodium or plain unflavored beans that you drain and rinse in recipes that call for beans in sauce – just add your own garlic, onion, herbs, spices, vinegar or lemon to provide the extra flavor.)
What about lentils? Maybe you’ve been experimenting with using kidney, black, garbanzo and other beans in different ways, but lentils are a less-familiar option for you? Check out the recipe collections from Lentils.org.
And if you want to include seafood within plant-forward meals, but don’t feel confident about cooking fish, check out this guide to cooking seafood from the Seafood Nutrition Partnership. And then look through these simple recipes from Dish on Fish. Frozen seafood can be a super-convenient and more budget-friendly option. Timing doesn’t need to be an obstacle! Did you know you can cook it right from frozen? Check these tips (with videos!) from Wild Alaska Seafood.
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Segovia-Siapco G, Sabaté J. Health and sustainability outcomes of vegetarian dietary patterns: a revisit of the EPIC-Oxford and the Adventist Health Study-2 cohorts. Eur J Clin Nutr. 2019;72:60–70. https://doi.org/10.1038/s41430-018-0310-z
van Die MD, Bone KM, Williams SC, Pirotta MV. Soy and soy isoflavones in prostate cancer: a systematic review and meta-analysis of randomized controlled trials. BJU Int. 2014 May;113(5b):E119-30 doi: 10.1111/bju.12435.
Zhang FF, Haslam DE, Terry MB, et al. Dietary isoflavone intake and all‐cause mortality in breast cancer survivors: The Breast Cancer Family Registry. Cancer. 2017;123:2070-2079. doi:10.1002/cncr.30615
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Yogurt: Ivan Dzyuba – Copyright 123rf.com – 61699456_s
Tofu: Brent Hofacker – Copyright 123rf.com – 90368927_s
Plant food variety: Marilyn Barbone – Copyright 123rf.com – 97054592_m
Plant food flexibility: Dmitrii Shironosov – Copyright 123rf.com – 58987421_m