This news release from the California Walnut Commission describes a study showing that a healthy diet including walnuts is associated with lower risk of impaired physical function in older women. Researchers examined data from more than 50,000 participants in the Nurses’ Health Study, a large-scale, decades-long epidemiological project funded by the National Institutes of Health, that assessed risk factors for cancer and cardiovascular disease. They found an association between a diet that included certain fruits, lettuce and walnuts and reduced physical impairments.
The news release echoes a host of previous industry declarations that walnuts “may” provide a certain health benefit that in reality could probably be obtained from a range of foods. Laudably, this news release does offer some cautions about the findings. It describes study limitations and states that researchers “emphasized that overall diet quality, rather than individual foods, may have a greater impact on reducing risk of physical function impairments.”
Physical function — defined as the ability to perform certain tasks such as climbing stairs, walking several blocks, and dressing yourself — is a key driver of mobility and independent living in older adults and a strong predictor of mortality. However, the direct role of diet in preventing the decline of physical function hasn’t been well studied. Biological research has shown that greater adherence to a healthy diet is associated with better lipid and inflammatory profiles and lower cardiovascular disease risk, which are strongly related to physical function. This study’s large sample size, long-term follow-up, and wide range of data points seem to bolster evidence of a connection between a healthy diet and prolonged quality of life.
Walnuts are reasonably affordable, and most people have some idea of how much they cost.
The news release does not quantify the purported benefits of including walnuts in one’s diet. It says the study “suggests that consuming 1-2 servings of walnuts per week (1/4 cup per serving) was associated with reduced risk of developing impairments in physical function, which helps enable older women to maintain independence throughout the aging process.” What was the reduced risk? How did women who followed a healthy diet compare in their physical function to those who did not?
The release later tempered the message that walnuts — specifically — reduce the risk of physical impairment. It notes that the researchers “emphasized that overall diet quality, rather than individual foods, may have a greater impact on reducing risk of physical function impairments. Specifically, diet quality traits most associated with reduced rates of incident physical impairment were higher intake of fruits and vegetables; lower intake of sugar-sweetened beverages, trans fat, and sodium; and moderate alcohol intake.” It adds that among specific foods studies, “the strongest relations were found for increased intakes of oranges, orange juice, apples, pears, romaine or leaf lettuce, and walnuts.”
It also provides this insight from a researcher: “The simple message from this study is that eating an overall healthy diet, including certain foods, such as walnuts and other whole foods, may help women with the ability to do key everyday tasks as they age, like carrying groceries or dressing themselves.”
Nor does it state that walnuts were the only nuts examined in the study, so we don’t know if similar benefits might be found for women who consumed large quantities of almonds or pine nuts, for example.
As we stated in a recent review of a news release about walnuts and heart health, a brief mention of nut allergies and the high caloric content of nuts would be appropriate.
This news release cautions that the findings have limitations. Among them: the study included only women, so results may not apply to men; participants were not randomly assigned to eat walnuts or other foods but rather were just asked about their dietary choices; and subjects may have misreported their dietary intake since this information was collected by questionnaires every few years. Also, the news release mentions that because this was an observational study rather than a randomized trial, it’s possible that other lifestyle habits that are more common in adults who eat walnuts could contribute to the findings, even though researchers tried to control for such factors.
The news release does not exaggerate the problem of decline in physical function with age.
The news release discloses that the study was funded in part by the California Walnut Commission. However, it should also have mentioned that funding for the 30-year Nurses Health Study came from the National Institutes of Health and that one researcher involved in the study has received a grant from the International Nut and Dried Fruit Council to study nuts and cognitive function in aging.
The release notes that in addition to walnuts, the following dietary traits are associated with reduced rates of physical impairment: “higher intake of fruits and vegetables; lower intake of sugar-sweetened beverages, trans fat, and sodium; and moderate alcohol intake. Among food components, the strongest relations were found for increased intakes of oranges, orange juice, apples, pears, romaine or leaf lettuce, and walnuts.”
The news release states that walnuts are “unique among nuts in that they are primarily composed of polyunsaturated fat (13 grams per ounce), which includes alpha-linolenic acid (ALA), the plant-based omega-3 fatty acid. They are the only nut to contain a significant amount of ALA with 2.5 grams per one ounce serving.” It does not mention that there are other plant-based omega-3 sources such as flax seeds, chia seeds, soybeans, and leafy green vegetables.
Walnuts are known to be widely available.
The news release does not overstate the novelty of the study. It provides this quote from a researcher: “These results add to the large body of evidence that outline the many benefits of a healthy diet for women.”
The news release does not engage in sensational or unjustifiable language.