By Krista Kleczewski, Claire Karlsson, and Edyth Dwyer
Evidence is growing about the many ways in which eating nuts, seeds, and legumes can improve your health. Eating walnuts or legumes like peanuts, beans, or lentils have been linked to healthier hearts and a lower risk of diabetes, but now studies show they may also cut your risk of getting cancer! Here’s what we know and don’t know.
In addition to erroneously thinking that peanuts are nuts, many people think almonds, cashews, and pecans as nuts, but they are actually types of seeds. The difference is based on the plant they grow on, where peanuts grow underground below the plant roots, nuts and seeds grow inside or outside the plant’s fruit. Although this article uses the term “nuts,” the studies we describe include many combinations of nuts, seeds, and legumes. It’s also important to note that each study has different methods, and they need to be interpreted differently. Some studies looked at fewer than 100 people and closely tracked their diet and health, while others were meta-analyses that collected results from many studies of thousands of people and summarized their findings.
What are some health benefits of nuts?
In 2015, a Dutch study of 120,000 men and women between the ages of 55-69 found that those who ate about half a handful of nuts or peanuts each day were less likely to die from respiratory disease, neurodegenerative diseases, diabetes, cardiovascular diseases, or cancer than those who consumed no nuts or seeds. The same benefit was not seen for peanut butter, however, which suggests that the salt, vegetable oils, and trans fatty acids in peanut butter may counterbalance the benefits of the peanuts. A serving of nuts is about the size of 30 almonds, and a study found that eating several servings a week had health benefits. A 5-year study conducted in Spain of 7,000 men and women aged 55 to 80 years old found that eating at least three servings of nuts per week reduced the risk of cardiovascular and cancer death. Another study similarly found eating nuts – especially walnuts — reduces the risk of developing cancers, diabetes and heart disease when eaten as a part of the Mediterranean Diet, which also emphasizes fruits, vegetables, whole grains, and legumes. Walnuts were highlighted by the study as reducing inflammation associated with certain cancers and other conditions like diabetes and heart disease. More evidence is needed, however, to determine the specific impact of walnuts on cancer risk.
Eating large amounts of peanuts, walnuts, or almonds can reduce the risk of developing breast cancer, according to a 2015 study of 97 breast cancer patients. The researchers compared the lifetime consumption of peanuts, walnuts and almonds among breast cancer patients with the consumption of those without breast cancer, finding that women who ate large quantities were half to one-third as likely to develop breast cancer. No difference was found between people who ate a small amount of nuts, legumes and seeds and those who ate none at all, suggesting that a person needs to consume a substantial amount of these over their lifetime to reduce their chances of developing breast cancer.
Another study looked at the risk of breast cancer for people who ate nuts and peanuts compared to people who did not. Some types of breast cancers respond to the body’s natural hormone estrogen, growing faster when exposed to estrogen. These are called Estrogen Receptor (ER) positive cancers. ER negative cancers are not influenced by exposure to estrogen. In a study of over 4,000 women in the Netherlands, those who ate 10 grams (a large handful) of nuts per day had a 45% lower risk of developing ER negative breast cancer when compared to those who ate no nuts, but it did not significantly affect ER positive breast cancer.[5,6] Since ER negative breast cancer occurs in only a third of the 12% of women who are diagnosed with breast cancer, the risk to the average person decreased overall by about half of 1% when their diet included that many nuts.
Girls who regularly eat nuts in their diet may be less likely to develop breast cancer as adults. A 2020 study of more than 9,000 girls between the ages of 9-15, and found that girls who regularly ate peanut butter or any kind of nuts were 36% less likely than girls who did not to have developed benign breast conditions when followed up with 10 years later. Although not dangerous, benign breast conditions (such as breast cysts or hyperplasia) increase a woman’s chances of eventually getting breast cancer. 
Can eating nuts, legumes and seeds reduce colorectal cancer risk?
To find out whether snacking on foods with peanuts lowers your chances of getting colorectal cancer (also called colon cancer), researchers studied more than 23,000 adults in Taiwan, ages 30 and older. The researchers reported in 2006 that women who ate meals with peanut products at least twice each week were less likely to develop colorectal cancer. More research is needed to see if this benefit is actually from the peanuts.
A 2021 meta-analysis collected results from over 40 studies, and it examined whether eating more nuts would have an impact on colon cancer risk. Researchers found that eating 5 grams of nuts per day could decrease the risk of colon cancer by 25%. Since the lifetime risk of colon cancer is about 4%, a 25% reduction would mean a decrease from 4% to 3% of the overall risk of colon cancer for people regularly eating nuts. Five grams is about 5-6 almonds, and this study found that the benefits of eating nuts started for people averaging just 2 grams per day and continued to decrease for people eating up to 9 grams per day. After that, the effects leveled off, so eating more than 9 grams was not more beneficial than eating 9 grams. A meta-analysis combines results from many studies, so the 2-9 grams per day were average amounts, whether the person eats them all in one day or spread out over the course of a week.
In one of the largest studies of diet and cancer, which was conducted in 10 European countries, researchers discovered that eating nuts and seeds reduced women’s chances of developing colon cancer, but did not lower the risk for men. Women who ate a modest daily amount of nuts and seeds (about 16 peanuts or a small handful of nuts or seeds) every day were less likely to develop colon cancer, and women who ate the largest quantities of these foods were the least likely to develop colon cancer. Again, more research is needed to understand these findings.
Researchers have also investigated whether a diet containing nuts and peanuts can improve patient chances of survival for those who have already been diagnosed with colon cancer. In a study of over 800 patients with advanced (stage III) colon cancer, patients who ate more nuts were more likely to survive after treatment, without being re-diagnosed with colon cancer. This study measured a serving of nuts to be one ounce, or about 15 cashews. When compared to those who ate no nuts, those who ate 2 or more servings of nuts per week had 46% lower risk of re-diagnosis of their cancer, as well as a 53% lower risk of dying from the cancer. This study has several important limitations to keep in mind. Not only was it a relatively small study, but it only examined Stage III colon cancer patients, comparing cancer patients who ate nuts to those who did not eat nuts. This means that the results cannot be generalized to the average American’s risk of colon cancer.
Eating nuts also seems to lower the risk of developing diabetes, which may then lower the risk of developing pancreatic cancer. In addition, a large study of women found that frequently eating nuts was associated with less chance of developing pancreatic cancer,13 one of the most deadly cancers.
A 2021 meta-analysis that examined results from over 30 studies, found that the chances of developing pancreatic cancer risk decreased for those who ate more nuts. The average lifetime risk of developing pancreatic cancer is about 1.5%. Because the results show a 6% lower risk for those eating nuts, this means the overall risk of pancreatic cancer may lower from 1.5% to 1.4% for people who regularly eat nuts.
A 2010 study examined the possible link between ovarian cancer and foods high in phytoestrogens and/or fiber, including nuts, beans, and soy. They found that these foods seemed to help prevent “borderline ovarian cancer”—slow-growing tumors that are less dangerous and more likely to affect younger women. However, these foods did not seem to protect against the more aggressive types of ovarian cancer.
What makes nuts good for your health?
There is still some debate about why nuts might be so beneficial. Omega-3 fatty acids are found in peanuts, walnuts, and some seeds, and researchers think their health benefits may help to prevent cancer. The omega-3 acids can help protect cell structures and walls, and since they are anti-inflammatory; that might reduce the risk of cancer for people who regularly eat peanuts, walnuts, and seeds. 
Some research has shown that walnuts can also improve your gut biome, meaning it helps you grow healthy bacteria in your gut. To test this, an experiment was done on 18 people, where some were assigned to eat walnuts and others ate no nuts. Blood and fecal samples were tested, and researchers were able to see changes in the bacteria, and lower levels of “secondary bile” which suggests the nuts decreased inflammation in their intestines. This experiment studied a very small group of people, so more research is needed to understand why these nuts, seeds, and legumes improve the risk of cancer over a lifetime.
The Bottom Line
There is growing evidence that nuts, legumes, and seeds reduce the risk for several types of cancer, as well as having other health benefits. Researchers are still investigating whether the health benefits of nuts are because people who eat nuts have a healthier overall diet, but tree nuts seem to have some health benefits on their own. Peanuts and peanut butter may also have benefits, but the higher levels of fat and sodium could explain why these legume products show fewer health benefits. Peanuts, walnuts, almonds, and other nuts are high in calories, so don’t overdo it. It seems safe to assume that adding these foods to your diet, in small quantities several times a week, is a good idea, especially if you use them to replace less healthy snacks.
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