Chapter 98
Why There Is No Japanese Word for Hot Flash
As I note at see.nf/menopausal, both oxidative stress and inflammation have been linked to menopausal symptoms, but correlation does not necessarily mean causation. That calls for intervention studies with control groups, especially since studies on hot flashes showed such a large placebo effect (at least 35 percent relief) that it was even suggested that women be secretly treated with sugar pills.
The largest intervention study on the relationship between diet and menopausal symptoms was conducted as part of the Women’s Health Initiative. Instead of prescribing hormones, the researchers advised the randomized participants to eat a low-fat diet. The women barely followed the guidelines and did not really eat low fat, but they did reduce their meat intake a bit and ate at least one more serving of fruits or vegetables per day. The result? They were significantly more likely to have no more hot flashes or night sweats. They also lost more weight, but the benefit for vasomotor menopausal symptoms appeared to go beyond weight loss alone.
In a study on plant-based eating, two randomized groups received vegetarian diets, and one additionally ate walnuts, almonds, and flaxseed oil every day. They did better than those who additionally received extra-virgin olive oil. After 16 weeks, the meatless diet rich in plant omega-3 fatty acids lowered hot flashes significantly more than eating in the olive oil group. In fact, as little as two teaspoons of ground flaxseed per day can significantly reduce menopausal symptoms. In a head-to-head comparison between flaxseed and hormone therapy (typically bioidentical estrogen plus a form of progesterone), the flaxseed reduced menopausal symptoms to a similar extent as the hormone pills. This could, however, be attributable more to the phytoestrogens in flaxseed than to the omega-3 fatty acids.
Why There Is No Japanese Word for Hot Flash
Hot flashes are the menopausal symptom that most often sends women to the doctor. They afflict 80 to 85 percent of American and European menopausal women and, like night sweats, last on average more than seven years. Yet, as I lay out at see.nf/hotflash, these symptoms do not occur in everyone, nor are they inevitable. In Japan, for example, apparently only 15 percent of women are affected. In fact, Japanese does not even have a word for hot flash.
That is all the more remarkable because Japanese is said to be “infinitely more sensitive” than English in describing physical states and distinguishes all sorts of somatic sensations with extreme nuance. There are at least 20 words to describe the state of the stomach and intestines, but hot flashes seem to be so unusual there that researchers had to get creative to describe them in Japanese surveys. They hypothesized that it might have to do with soy.
I provide an overview of the intervention studies on soy foods and isoflavone supplements at see.nf/isoflavones. Dozens of such clinical trials have been conducted, and indeed, the equivalent of about two servings of soy foods per day reduced the frequency of hot flashes by about 20 percent and their severity by about 25 percent more than placebo. Estrogen hormone therapy achieved a net reduction of about 30 to 40 percent. Soy isoflavones also lessen other menopausal symptoms, including vaginal dryness, loss of bone density, depression, memory decline, and cognitive function overall.
Bottom line, wrote a knowledgeable consensus panel, soy can be used as a first-line treatment for menopausal hot flashes and night sweats. Soy nuts work well here as a whole-food source. The Harvard Medical School Center of Excellence in Women’s Health funded a randomized crossover study on the effects of a half cup of unsalted soy nuts per day (split into three or four servings over the course of the day). After two weeks, the subjects had 50 percent fewer hot flashes. The downside of soy nuts, however, is that roasting forms AGEs (see the chapter Glycation), so it would be better to incorporate canned soybeans into meals.
What would a combination of a plant-based diet with soybeans do? Two randomized controlled trials found that a reduced-fat plant-based diet with a half cup of cooked soybeans daily can reduce the number of severe hot flashes within twelve weeks by 84 to 88 percent. Overall, most study participants in the plant-based group no longer had moderate to severe hot flashes, while 95 percent of the control group still suffered from them.
Soy and Breast Cancer
Contrary to misinformation circulating on the internet, the best available evidence consistently shows that soy consumption helps prevent breast cancer. Every 5 grams of soy protein you consume per day—less than a cup of soy milk—reduces the risk of dying from breast cancer by 12 percent. This could explain why women living, for example, in Connecticut are ten times more likely to develop breast cancer than women in Japan. At see.nf/soybreast you will find a discussion of the mechanism and the reason for the controversy.
It is estimated that in the United States, one in eight women will develop invasive breast cancer over the course of her lifetime. Switching from cow’s milk to soy milk would presumably reduce breast cancer risk by a third, but that may say more about the breast-cancer-promoting effects of cow’s milk than about soy’s breast-cancer-preventive effects. Premenopausal or postmenopausal women who drink a cup of cow’s milk daily likely have about a 50 percent higher breast cancer risk than women who average less than a cup every two months. Researchers suspect this is due to the estrogen content of milk (especially since about 75 percent of dairy cows are pregnant) or to IGF-1, which is present in milk in both free and protein-bound form.
Is the anti-estrogenic effect of soy foods on the breast sufficient to actually influence disease course? The first human study on soy food intake and breast cancer survival was published in 2009 in the Journal of the American Medical Association and found that “among women with breast cancer, soy food consumption was significantly associated with reduced risk of death and recurrence [of breast cancer].” This study was followed by another and then another, and they produced similar results. This led many cancer experts developing dietary guidelines for cancer survivors to conclude: Soy foods are beneficial. Since then, two more studies have been published, so that five out of five studies, totaling more than 10 000 breast cancer patients, have now reached similar conclusions.
In summary, the findings show that soy consumption after a breast cancer diagnosis was associated with both reduced mortality and lower cancer recurrence—that is, a longer life span and a lower likelihood that the cancer comes back. This higher survival rate held true for women with estrogen receptor–negative as well as estrogen receptor–positive tumors and for younger as well as older women. In one study, for example, 90 percent of the breast cancer patients who ate the most soy phytoestrogens after diagnosis were still alive five years later, whereas half of those who had eaten little or no soy had died. So bring on the edamame.
Can We Hope for Hops?
Flaxseed also contains phytoestrogens (so-called lignans), which are believed to prevent breast cancer and increase the survival chances of those affected. Intervention studies with pre- and post-biopsies showed positive effects in breast cancer patients randomized to receive muffins with flaxseed compared with the placebo group. A higher lignan intake can lower breast cancer mortality by 33 to 70 percent.
Like soy, flaxseed has been shown to improve LDL cholesterol, arterial function, and blood pressure. Flaxseed also lowers other cardiovascular risk factors such as C-reactive protein and Lp(a) and can improve regulation of blood sugar and weight. Unfortunately, it does not relieve menopausal symptoms as effectively as soy. Meta-analyses of red clover or black cohosh, other phytoestrogen sources, also produced disappointing results.