This news release reports on a study showing an association between eating plant protein and lower risk of early menopause. Researchers evaluated data from the Nurses’ Health Study II, a large-scale effort to identify risk factors of disease in women. The study appeared in the Journal of American Epidemiology. A sub-headline allows that the effect is “modest” but the news release headline implies a cause-and-effect relationship that can’t be proven with one study based on observing a sample group of people, particularly when the group is self-reporting and subject to errors in recall.
Early menopause, also known as premature ovarian insufficiency, is a cause of infertility and has other negative health repercussions. While autoimmune diseases and genetics are sometimes to blame, most cases have no known trigger. In this study, the authors hypothesize that either some diets cause a build-up of arterial plaque that may reduce blood supply to the ovaries, or that soy-based diets protect ovarian function and slow the rate of follicle depletion. While this study suggests a potential dietary link, according to the authors, it remains to be seen whether the findings “can directly translate to premenopausal women.” In other words, it’s too soon to suggest young women eat more plant foods solely to protect their reproductive health, although there are other good reasons to add nuts and legumes to your diet.
Replacing animal products with plant foods wouldn’t significantly raise a person’s food budget and might actually save money.
The news release does the minimum in conveying the size of the link between diet and early menopause risk, saying women who consumed about 6.5 percent of their daily calories as vegetable protein had a 16 percent lower risk compared with women whose vegetable protein intake was approximately 4 percent of calories.
It further states: “For a woman with a 2,000 calorie per day diet, the authors explain, this is equal to three to four servings of such foods as enriched pasta, breakfast cereal, tofu and nuts, or about 32.5 grams a day.”
The release could have provided better perspective by giving some absolute numbers. With a 10 percent overall risk, a 16 percent reduction would amount to one or two women in every hundred.
It also could have helped readers interpret this quote from researchers: “Though relatively few women in our study consumed very high levels of vegetable protein and our power for analyses of more extreme intake levels was limited, women consuming 9 or more percent of their calories from vegetable protein had a hazard ratio of 0.41 (95 percent confidence interval = 0.19-0.88)” compared to those eating less than 4 percent.
In more understandable terms, women consuming 9 percent or more of the calories from vegetable protein developed early menopause at slightly less than half the rate of those getting less than 4 percent of their calories from vegetable protein.
The news release doesn’t discuss harms such as allergic reactions or other adverse effects from eating certain plant foods such as soy, wheat, and nuts. However, a discussion of harms doesn’t seem to be warranted since the news release does not advocate consumption of a specific foods, but rather suggests that a moderate increase in a range of plant foods might offer a benefit.
The news release explains in detail how the study was conducted, including the fact that it captured data from 2,041 women who experienced early menopause. But it doesn’t mention limitations with using self-reported data on dietary intake and age of menopause. Nor does it spell out that this is a single observational study, which can’t establish a causal relationship. Its final sentence saying researchers “suggest that more prospective studies of their findings are warranted, including studies that compare soy-based and non-soy vegetable proteins” amounts to too little, too late.
It’s also worth noting that the study includes only nurses, a subset of the population who may not be representative of all US women in their dietary patterns, thus making it difficult to draw general conclusions. For example, if a woman is at risk for early menopause because of chemotherapy, would this study be relevant for her? That’s unclear.
The release mentions that adjustments were made for certain variables (“confounders”) but theoretically, there would be many variables to consider that weren’t studied or adjusted for.
The news release doesn’t disease monger. It does state that early menopause, defined as the cessation of ovarian function before age 45, affects about 10 percent of women and is associated with higher risk of cardiovascular disease, osteoporosis and early cognitive decline as well as cutting short fertility. The study itself cites prevalence figures ranging from 5 to 10 percent. The news release could have included that range instead of going with the higher estimate.
The news release states that the study was supported by a grant from NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development. The researchers reported no conflicts.
There don’t seem to be any common strategies to prevent early menopause, but the news release could have delved into alternative potential causes such as autoimmune disease, genetics and cancer treatment.
Availability isn’t an issue. Adding vegetable protein to your diet in the modest amounts involved in this study is a fairly easy thing to do. A completely vegetarian diet is more challenging, but that’s not what the study suggests.
The release states: “Few studies have evaluated how protein intake is associated with menopause timing, (researchers) add, and to their knowledge this is the first to look specifically at early menopause.” A researcher is also quoted saying, “A better understanding of how dietary vegetable protein intake is associated with ovarian aging may identify ways for women to modify their risk of early onset menopause and associated health conditions.”
We commend the use of the word “modest” in the sub-headline to describe the effect of vegetable protein on early menopause risk. But the news release makes missteps including the use of the word “significant,” which might confuse some readers into believing the study shows a significant impact on early menopause risk when in fact it appears to mean the data is statistically significant, or reliable.
Frequently, news reports about studies showing an association between food and health outcomes imply a causal relationship, which can’t be shown with a single study based on observations. This one does just that when it states in the headline and the lead that eating more vegetable protein “may protect against early menopause.” We wish news releases based on observational studies would be more upfront about limitations when describing the research. Adding a descriptor such as “these are useful findings that need further study” would help.
The following quote also may leave readers with the idea that they can control their reproductive future based on this study’s results
: “A better understanding of how dietary vegetable protein intake is associated with ovarian aging may identify ways for women to modify their risk of early onset menopause and associated health conditions.” Giving women better information so they can control of their health is a laudable goal, but this study doesn’t achieve that, and the news release should have made that more clear.
Further, the lead confuses matters by citing “foods such as whole grains, soy and tofu” when the foods that accounted for the greatest variation in vegetable protein intake in the study were pasta, dark bread, and cereal.