It’s Fall! The leaves are turning rustic and vibrant colors, the Pumpkin Spiced Lattes are abundant, and we are all starting to look into plane tickets for the holidays (GASP! $600!?). As the cold weather approaches, we want to give you some warm, delicious recipes that will keep you cozy throughout the season. Not only will these recipes keep your temperature and your spirits high, but they will also provide you with an abundant amount of healthy nutrients to help you avoid catching that cold going around the office. In this Thai Sweet Potato Chowder recipe (sweet potatoes are in season in October), we’re going to focus on the cancer preventive agent genistein.

Overall healthy ingredient profile

All the ingredients in this recipe have various medicinal properties and all are associated with cancer prevention! Sweet potatoes, with their deep orange color, are a fine source of vitamin A and carotenoids (both protective against several kinds of cancer). They also have plentiful fiber, making them excellent for keeping the intestinal tract healthy. The skins of sweet potatoes are also good for you. Coconut milk stimulates metabolism and helps balance blood sugar levels by preventing insulin spikes. It also has  antifungal, antibacterial and antiviral properties, which can enhance immune function. Lemon grass has been used traditionally to treat a variety of conditions including inflammation, fungal infections, insomnia, and high blood pressure; it also has volatile oils containing citral and myrcene that are antioxidants of interest for cancer prevention. Capsaicin, which could be found in the Thai curry paste in this recipe, tones up your circulation and has antibacterial properties. Basil has also been found to combat cancer and heal neuropathy caused by surgery. Snow peas contain a variety of antioxidants that boost immunity and are anti-imflammatory. This soup also contains tofu, a source not only of low-fat protein, but of genistein, a promising but controversial anticancer compound, which is found in soybeans and soy products (though not in soy sauce).

Evidence for and against cancer prevention by genistein

Genistein is an isoflavone and anitoxidant that has anti-neoplastic activity in multiple tumor types and has been in various clinical trials for cancer. Many studies attribute genistein’s anticancer activity to apoptosis (spontaneous cell death) and autophagy (controlled digestion of damaged organelles within a cell), altering the cell cycle, inhibiting angiogenesis and metastasis. However (like most science!), other studies do not show anticancer activity with genistein. Genistein is also a phytoestrogen that targets estrogen and androgen-mediated signaling pathways in carcinogenesis pathways. The Mayo Clinic site gives soy a “C” grade for cancer by stating that the human research is limited and “dietary and lifestyle habits, culture, and genetics” must also be taken into consideration. Let’s look more closely at why it’s complex by considering the evidence for and against genistein in hormone-related cancers of the prostate and breast. 

Prostate cancer

Research is mixed for genistein’s ability to protect against prostrate cancer. Amazingly, soy intake in some studies has been shown to correlate with a 42-75% lower risk of  prostate cancer. Between 1988 and 1990, 14,000 Japanese men had elevated blood levels of three isoflavones (genistein, daidzein, and equol)  that appeared to protect them against prostate cancer. Genistein and daidzein can be found in soy products, but equol is a bacterial flora found in the intestines. Of all the compounds, genistein showed the most promising antiproliferative effects against prostate cells in humans, protective effects against metastasis, and blocking mechanisms against an enzyme that destroys anticancer vitamin D metabolites in cancer cells. Some clinical trials have hinted that soy foods may lower PSA levels and may benefit prostate cancer survivors and others have found no reduction of PSA levels in men with low-volume prostate cancer. Animal studies are described in this review

Breast cancer

Clinical trials of genistein with cancer-free women show no differences in hormone levels or breast density, a marker of increased breast cancer risk. Women who are able to metabolize isoflavones into equol may benefit from genistein consumption. The type or source of genistein, whether dietary or in a processed supplement form, may also influence study results according to a Phase 2 breast cancer prevention trial.  There are studies (including this one) that support the idea that soy isoflavone consumption from fermented soy products can reduce the risk of breast cancer.  Some sources say that it’s unfermented soy (soy milk, popular tofu products) that cause more harm than good. Fermented soy, on the other hand, is frequently praised as the type that provides all the benefits.

Soy is not recommended for women battling breast cancer, since soy may disrupt anti-estrogen treatment. However, it may be beneficial for breast cancer survivors, reducing recurrence risk. It was reported in August at the American Association for Cancer Research Annual Meeting 2015 that genistein’s ability to activate anti-tumor immune responses and reduce expression of immunosuppressive mechanisms may explain why lifetime genistein intake reduces risk of breast cancer recurrence. Recent epidemiologic studies with breast cancer survivors show that consuming moderate amounts of soy foods, comparable to what Asian women consume, does not increase a woman’s risk for poorer outcomes. Caucasian or postmenopausal Asian women who ate two to three servings a day of soy foods had the lowest risk of recurrence or death compared to women who ate less than a few servings a week. A meta analysis of studies of some 10,000 breast cancer patients found that consuming at least 10 milligrams of isoflavones daily was associated with a 25 percent decrease in breast cancer recurrence whether the women were from Asia or the U.S.

Sources of genistein

Legumes (beans, nuts, lentils…) contain genistein. Soybeans contain the most and chickpeas contain the least. Here is a comprehensive table of foods containing genistein and the amount they contain. A list of fermented soy bean products is here.

Safety suggestions

Soy is likely safe when used in the diet in adults, children, and infants; of course it should be avoided in allergic individuals. Soy may cause skin problems, asthma, bloating, constipation, fatigue, immune changes, increased heart rate, insomnia, and intestinal inflammation, among others. Soy may also increase the risk of bleeding, lower blood sugar levels, cause high blood pressure, and may interfere with the way the body processes certain drugs. Soy should be used cautiously in people who have health issues that might be affected by soy. For more details on soy safety, see a summary form the Mayo Clinic here.

The Harvard School of Public Health recommends staying away from supplements that contain concentrated soy protein or extracts, such as isoflavones, since their long-term effects are unknown. 

Of particular note regarding this post, soy should be used cautiously in people with hormone-sensitive cancers such as breast, ovarian, or uterine cancer, or hormone-sensitive conditions such as endometriosis. Soybeans are among plants producing compounds that mimic the activity of estrogens. 

If on weighing it up you decide not to include the tofu (and genistein) in this recipe, you can replace it with cauliflower, a less controversial cancer preventive. We assure you that either way this recipe is very delicious!

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