Eating foods rich in vegetable protein - such as tofu, enriched pasta, nuts, and breakfast cereal - is linked to a lower risk of early menopause, compared with consuming protein that comes mainly from animal sources.
So concludes a new study - led by the University of Massachusetts Amherst and Harvard T.H. Chan School of Public Health in Boston, MA - published in the American Journal of Epidemiology.
Menopause, defined as the time of a woman's last menstrual period, is a natural stage of life, much like puberty. For most women, it happens around the age of 51, although some may experience it a few years earlier or a few years later.
Bodily changes associated with the menopause can start a few years before the last period. These include reduction in the female hormone estrogen, which is produced in the ovaries.
Early menopause is defined as menopause that occurs before the age of 45. This can be spontaneous or induced, for instance as a result of chemotherapy or surgical removal of the ovaries.
Early menopause that occurs spontaneously or naturally is thought to affect around 1 in 20 women in the United States.
Higher risk of health problems
Early menopause in women has been linked to a higher risk of premature death and a number of health problems, including osteoporosis, cardiovascular diseases, and neurological disorders.
Women who undergo early menopause may also have reduced fertility that starts as much as 10 years beforehand.
The authors note that the causes of early menopause are poorly understood, and that in most cases, the diagnoses do not attribute them to genes or autoimmunity.
In their discussion of earlier related research, they explain that while previous studies have looked at protein intake and timing of menopause in women, to their knowledge, theirs is the first to examine it in relation to early menopause.
"Study participants in these evaluations were substantially older at baseline than in our study, precluding the ability to specifically evaluate risk for early menopause," they note.
Detailed food questionnaires
Thus, for their study, the team analyzed data from the Nurses' Health Study II to examine the link between diet and early menopause.
Their analysis covered 85,682 women who experienced natural early menopause from 1991 onwards. It did not include women who underwent early menopause that had been induced - for example, by hysterectomy or chemotherapy.
The detailed food questionnaires filled in by the participants allowed the researchers to look at food and beverage consumption over the period prior to onset of early menopause.
The detail included how often the women had consumed individual servings of 131 food, beverage, and supplement types. The reported frequency ranged from "never," to "once a month," to "six or more times per day."
Over the period covered by the study (1991 to 2011), the results showed that 2,041 women experienced early menopause.
Three to four vegetable protein servings
When they analyzed the data, the team found that higher vegetable protein consumption was linked to a lower risk of early menopause.
In contrast, they found no link between high animal protein intake and early menopause, one way or the other.
Specifically, the results showed that women with a 6.5 percent daily calorie intake taken up by vegetable protein had a 16 percent lower risk of early menopause, compared with women whose vegetable intake took up only 4 percent of their daily calories.
If one assumes that a woman's daily calorie intake comes to around 2,000 per day, then 6.5 percent in vegetable protein is the equivalent of three to four servings (or 32.5 grams) each day of foods such as nuts, tofu, breakfast cereal, and enriched pasta.
The link was the same when the team took into account other factors that have been linked to early menopause, including smoking status, body mass index (BMI), and age.
The researchers call for further studies to look in more detail at the link between vegetable protein and lower risk of early menopause. They suggest, for example, that it might be interesting to see whether soy-based and non-soy vegetable proteins have different effects. They conclude:
"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 of menopause and associated health conditions."