With their relatively high calorie count, adding nuts and seeds to your daily food intake can seem like a counterintuitive move – especially if you’re focused on losing excess weight. But the truth is, these tasty plant foods are nutritional superstars: They supply important phytochemicals that have antioxidant and anti-inflammatory properties that protect against cancer, promote cardiovascular health, increase insulin sensitivity and support a healthy gut microbiome.
Eating nuts and seeds regularly is consistently linked to longer life in observational studies. Possible explanations for this association include lowering glycemic load and promoting cardiovascular health.
Recently, researchers have been investigating connections between consumption of nuts and risk of cancer or death from cancer. Most recently, results from the Shanghai Breast Cancer Survival Study suggested that participants with higher than average nut consumption had a 52% lower risk of cancer recurrence, metastasis, or death from breast cancer.
Lowered risk of cancer
There is abundant research now on intake of nuts and cancer incidence. Three different research groups performed meta-analyses of the literature in 2020 and 2021, analyzing approximately 30-45 studies. All three concluded that higher nut consumption was associated with a lower risk of cancer, and all three found a dose-response association, meaning as nut intake increased, cancer risk decreased. Two of the three noted that only tree nuts (not peanuts or peanut butter) were associated with reduced risk of cancer. One analysis found that nuts were associated with reduced risk especially of cancers of the digestive tract.
Direct anti-cancer effects
Some phytochemicals in nuts, like those in greens, berries, and other plant foods, have direct anti-cancer effects. For example, laboratory studies on cancer cells have found that phytochemicals present in nuts, such as polyphenols and fatty acids, promoted cancer cell death and inhibited cell proliferation, metastasis, and angiogenesis.
The studies discussed here have focused on nuts, not seeds, but lignans in flax, chia, and sesame seeds have anti-estrogen properties and are linked to a lower risk of postmenopausal breast cancer.
Oxidative stress, inflammation, and insulin sensitivity
Oxidative stress and inflammation are driving factors in heart disease, cancer, and other chronic diseases. Phytochemicals in nuts and seeds also have antioxidant and anti-inflammatory actions, such as tocopherols and tocotrienols (vitamin E), omega-3 ALA, and polyphenols such as quercetin, resveratrol, anacardic acid, and ellagic acid.
Using nuts as a major calorie source reduces the overall glycemic load of the diet compared to common high-glycemic calorie sources such as rice, pasta, bread, and potatoes. Evidence from randomized controlled trials has suggested that eating nuts regularly improves insulin sensitivity in patients with type 2 diabetes.
Nuts have total and LDL cholesterol-lowering properties that have been supported by many randomized controlled trials. Although we usually think of cholesterol in relation to cardiovascular disease, cholesterol plays a role in cancer as well. Cancer cells use cholesterol to fuel their high level of proliferation, and cholesterol may also be an important player in cellular signals that promote the survival of cancer cells.
One of the three meta-analyses on nuts and cancer risk found that nuts were especially protective against digestive cancers. The researchers thought this could be because the fiber in nuts helps reduce intestinal transit time, which reduces the duration of the colon’s exposure to dietary carcinogens. It could also be because of beneficial effects of nuts on the microbiome. Randomized controlled trials on walnuts and almonds have found increases in the populations of beneficial gut bacteria.