About two or three years ago a very large, what they call, meta analysis was done involving all peer reviewed published studies on soy and breast cancer. The question that was being asked: do phytoestrogens (which have been shown to have some of the same abilities regarding stimulating cell growth as our natural estrogens) in soy increase or decrease the risk of developing breast cancer. Meta analysis are done by looking at the results of all studies and then doing a statistical analysis on those. Results gotten from this type of number crunching are pretty solid.
This analysis of soy showed: ready for this? That soy did not create an increased risk. AND that it was not protective either. In other words, after hundreds of studies, the jury is still out on whether if you have a hormone sensitive cancer (especially breast cancer) soy should be decreased or even eliminated from your diet.
But here's my two cents about soy and in particular tofu.
One half cup of tofu contains about 94 calories and 10 grams of protein. Many vegans and vegetarians, especially those newbies and non cooking folks, tend to relay on tofu as their main protein sources. From seventeen to the the age of about 25, I was one of them.
There are a couple of significant events that made me question the qualities of, specifically, tofu in diets.
Years ago when I was new to my practice, I saw a child that had a rash that looked very similar to a diaper rash. I prescribed time and trusted natural remedies and advised hygiene practices that I was sure would clear it up. The mother brought the baby back again, and again and again (was I really cut out to doctor?). Back then I did not ask as much about food and diet as I do now. But at some point I did inquire about dietary habits and intake. The parents were vegetarian, and the mother was breast feeding. She ate tofu once to twice a day. I consulted with a naturopath that had been out for several years longer than I had, and they confirmed that yes tofu and soy products can tend to be allergenic and it can show up in children looking like diaper rash. We removed the tofu from the mother's diet and the rash cleared up. After all that time, I remember feeling as if it were a miracle. I kept this as a clinical pearl that I used to inquire when I saw other children, particularly being raised as vegetarians or vegans, but did not go further with regards to looking into the nutritional and allergenic qualities of soy products.
The second significant event was when I was the lead naturopath at a public women's clinic. The clinic to this day is located in a very progressive community tending towards the use natural medicine, and holistic living including vegetarianism. I was seeing a number of women who were eating a soy product one to three times a day. They were complaining of fatigue, hunger, some with anemia, some complaining of weight gain. This was another point in time where I paid attention to diet and advised using more of a variety of plant based protein than tofu. When they took my suggestions, they often began to feel better, and many dropped weight as well.
What I have learned about soy products is the following. Tofu contain products called phytates that block the absorption of calcium, magnesium, iron and zinc. These are minerals that tend to become deficient during chemotherapy treatments too. Calcium is involved in bone strength (among many other things), magnesium is important in red blood cells production, metabolism and liver function, and iron is essential in red blood cell production and function; zinc is essential in immune function.
Soy also contain products that block the digestive enzyme trypsin. Trypsin is involved in protein digestion. This can result in gas or bloating, or even in developing some constipation, diarrhea and some gut dysbiosis.
Soy is also what they call a goitrogen if eaten in high amounts. A goitrogen is a constituent that causes your thyroid gland from functioning properly. So my patients at the women's clinic may have been gaining weight because their thyroid function slowed down as a result of eating so much tofu.
Finally, tofu does contain a good amount and variety of phytoestrogens. Children being raised on a vegan or vegetarian diet supplemented mainly by soy products can develop problems related to the estrogens found in this food.
Fermented soy products such as tempeh and miso do not seem to have the same problems as the processed tofu does.
So what is my recommendation regarding eating tofu and soy products for breast cancer patients who have a hormone sensitive cancer? There are lots of plant based types of proteins other than soy to choose from. Using a variety is the key. You want to use types of foods that are non allergenic, do not have a high inflammatory index, and that allow you to absorb as much of the mineral and other nutrients as possible. Though we don't know if soy contributes to estrogen load, we should be focused on using a variety of foods. Even using a variety of non dairy milks in your morning coffee other than soy milk is good.
And one last note. Many of my patients have decided not to include any kind of soy in their diets. However, many foods contain things such as soy lecithin, and small amounts of soy like in tamari and soy sauce. In those cases, the amount of soy and thus phytoestrogens you are ingesting is very, very small and insignificant. Studies focus on the big stuff like what you would consume at a tofu based meal.