Rebuild from Depression in Motherhood Amanda Rose, Ph.D., forthcoming 2007 Chapter 14: Grains and Legumes Excerpt on phytic acid Phytic acid and mineral loss In the research for this book I am struck by the solid research about phytic acid and yet the American public s relative lack of knowledge about its effects. I certainly never heard about them in my vegetarian days, yet they have profound implications for the vegetarian diet. Some nutritionists estimate that vegetarians whose primary source of protein comes from grains and legumes absorb only about 15% of the minerals in those foods. Based on the research I present here, that is a fair estimate, though absorption from soy-based foods is even lower. If you are a vegetarian, you can very quickly double the minerals you are absorbing by using the techniques I describe. Phytates Matter Whole grains and fresh legumes are problematic, unfortunately, because of their natural level of phytic acid, which inhibits the absorption of key minerals that we are trying to increase in our diets: zinc and magnesium specifically. Phytic acid binds to minerals in your digestive tract and escorts them out through your bowels. There will be no cell-building or body-building with these minerals, even though the label on the grain or legume suggests you are eating mineral-rich food. Research has shown that phytates inhibit the absorption of significant levels of minerals in the phytate-laden food. Researchers have conducted experiments on mineral absorption that show clearly that phytates matter. In a 2004 study in the Journal of Nutrition, Egli, et al. report results from their study of
the effects of dietary phytates on zinc absorption. They controlled the phytate content of meals for their subjects by providing a phytic-acid free bread at some meals and bread with phytates added back at other meals (with levels similar to whole grain bread). They analyzed the feces of the subjects for mineral content and found that the feces were higher in zinc after they ate the bread with phytic acid. That is, less zinc was being absorbed into their bodies through their intestinal tract when they ate the bread with natural levels of phytic acid. In a study with the same design in The American Journal of Clinical Nutrition in 2004, Bohn et al. come to similar conclusions regarding magnesium absorption. In the table below I list the findings from these two studies. In the magnesium study they examine breads with different levels of phytates. The higher the phytic acid content, the lower the absorption of magnesium. Compared to the bread without phytic acid, in which participants absorbed about 32% of the available magnesium, participants absorbed only about 13% of the magnesium in the higher-phytate bread and about 24% of the magnesium in the lower-phytate bread. Participants absorbed 23% of the zinc in the bread with phytic acid compared to 35% in the bread without in the zinc study. These results make clear two points. First, we absorb relatively little of the minerals in our food even when there are no phytates present. Keep this in mind as you read food labels. All of the nutrients on the label will not make it into the cells of your body. Second, even in lower-phytate products, we can absorb about 50% more minerals if we could reduce the phytate content to zero. In higher-phytate foods such as soybeans and whole wheat, we might more than double our absorption of minerals if we can reduce the phytate levels to zero.
Table 14.2: Magnesium and zinc absorption in breads with phytic acid w/ phytates % absorbed w/o phytates % absorbed Magnesium a (high phytate) Magnesium a brown bread 13% 33% 24% 32% Zinc b 23% 35% a Egli et al. 2004; b Bohn et al. 2004 Where are the phytates? Some parts of the grain have a higher phytate content than others. And as perhaps a cosmic joke on the health conscious who want to keep grains in their life, the whole grain form has a higher content of phytic acid as a rule than does the refined white form. In the table below that lists breakfast cereals, note that the phytate content varies as a function of the amount of whole wheat in the cereal whole wheat cereals have a higher phytate content. So, for processed grains, you need not worry much about these techniques I discuss in this section. Of the tiny bit of mineral value left after the processing, most of that quantity is available to be digested.
Table 14.3: Phytates in wheat cereals Mg phytate/ 100 grams Frosted Flakes 58 Post Toasties 80 Super Sugar Crisps 274 Raisin Bran 659 Special K 666 Shredded Wheat 1,481 All Bran 3,168 Source: Harland and Oberleas 1987 Legumes vary in phytate content as well. Note Table 14.4 below. The stand-out among legumes for high phytate content is soybeans, though peanuts and peanut butter are strong competitors. The level of phytic acid in soybeans exceeds the levels I cite in Table 14.2 above the study of magnesium absorption with different bread types. You will likely absorb about 10-15% of the minerals in your soy product if it is not prepared properly to reduce the phytic acid content. In a half cup of tofu in which you think you are getting approximately 75 milligrams of magnesium, your body may absorb 8-10 milligrams. The recommended daily allowance for magnesium is 350 milligrams, for some perspective, and that 350 milligrams may be very low for someone who is deficient.
Table 14.4: Phytate Content of Legumes Chickpeas Split peas Blackeyed peas Peanut butter Soy-based TVP beef Soy flour Soybeans, dry a Oberleas and Harland 1981 b Harland and Oberleas 1987 c Harland and Oberleas 1977 Mg phytate/ 100 grams 208 a 664 b 815 b 1,252 a 1,265 c 1,398 c 2,322 c Breaking down phytic acid: phytates bad, phytase good Since phytic acid inhibits our mineral absorption, the degree to which we can break it down will increase the availability of minerals in our foods. Grains and legumes not only have phytic acid, but also an enzyme called phytase which, when activated, will break down the phytic acid in our grains or legumes. Several grains have high levels of phytase and there are very effective strategies to break down the phytic acid using fermentation techniques. For some grains and for legumes, the strategies are more time-consuming and are still not highly effective. I will discuss the easy grains first. Two general methods are effective for many grains: 1) Bread and baked goods should be sourdough. Traditional methods of sourdough preparation effectively break down phytic acid (Leenhardt et al. 2004, Lopez et al. 2001). In
our home, all baking projects have turned into sourdough projects, including cakes and sweet breads. If the bread is one that rises, the rise time allows the phytase to break down the phytic acid. If the baked good is not one that rises, we make the batter in advance (minus the baking soda) and allow it to ferment for about six hours before adding the baking soda and baking. I have included some of our favorite recipes in the Appendix. 2) Soak whole grains for porridge and entrées in an acidic solution. For breakfast cereals or grains in salads such as tabouli, soak them for two to twelve hours under the following optimal conditions for best results: Soak in water, about equal parts water to grains (enough to cover them well). The water temperature should be between 45 and 55 C (113-131 F), just above body temperature. Add an acidic ingredient to water to achieve a ph level of 4.5 to 5.5. For best results use whey, yogurt, or kefir (approximately 2 tablespoons per cup of grain). Otherwise add about 2 tablespoons of lemon juice per cup of grain. Cover with a clean dishcloth to keep the bugs out. Soak in a warm spot for two to twelve hours (see below for grain differences). Use the ground grain rather than the whole grain kernel. In Mellanby s work in 1950, he found that phytic acid levels in ground wheat were reduced to zero in just one hour (ph of 4.5 and temperature of 45 C), whereas whole wheat kernels still maintained about 40% of their phytic acid levels after 12 hours of soaking.
Not all grains are equal The fermenting/soaking method is only as effective as the original level of phytase in the grain or legume. Some of the grains and legumes that are part of many of our diets have low phytase levels. You can soak them and soak them and they will still have a high phytate content. In a 1950 study, Mellanby reported an experiment reducing the phytic acid content of various grains which I present in the figure below. Note that with rye and wheat it takes only two hours to reduce the phytate content under optimum conditions. With oats and corn, soaking for 12 hours is insufficient the phytic acid levels are still about 75% of their original levels. Other problematic grains include millet and sorghum. Legumes face a similar problem. Figure 14.1 Phytic Acid Remaining in Grains After 12 hour soak, ph = 4.5, 45 degrees C Wheat 100 75 50 25 0 0 1 2 4 6 Hours 12 % remaining Oats 100 75 50 25 0 0 1 2 4 6 Hours 12 % remaining Rye 100 75 50 25 0 0 1 2 4 6 Hours 12 % remaining Corn 100 75 50 25 0 0 1 2 4 6 Hours 12 % remaining Source: Mellanby 1950
MAKE ONE CHANGE WITH BREAKFAST Replace your breakfast cereal with whole grain, ground porridge. Soak that porridge overnight according to the process described in this section. You will benefit twice: (1) by replacing a processed cereal with a whole grain alternative and (2) by reducing the phytate content of that cereal grain. It s fast: Because of the soaking, your breakfast cereal will cook in 1-2 minutes, making it a fast and easy breakfast solution. Add fat: Use real butter from grass-fed cattle, preferably raw butter. Let the cereal cool down a bit before adding the raw butter or you will cook the butter, too. The fat will help your body absorb the minerals in the cereal and will add Omega 3 fatty acids to your meal. And when you re feeling ambitious: Buy the whole grain kernel and grind your cereal grains fresh just before soaking. Legumes Beans used to be a cheap and easy solution to cooking problems in this household. Beans are becoming increasingly complex. They are high in phytic acid; we established that fact in Table 14.4 above. Beans are also fairly low in phytase, however soaking methods do reduce the phytic acid content in most beans. But typically some phytic acid remains. In a 1986 study, researchers found that soaking beans for 18 hours and then cooking them reduced the phytic acid content by between 60% and 75%. Of the beans they studied, 42% of the
phytic acid remained in kidney beans, about 40% remained in pinto beans, and about 25% remained in great northern beans (Khokhar and Chauhan 1986). Best results for bean preparation come by soaking and then discarding the soaking water. Results might be optimal if the soaking water includes whey, yogurt, kefir, or lemon juice to increase the acidity of the water. Though it is important to note that you are not likely to reduce the phytic acid content to zero and you will lose some minerals in the soaking water you discard. Soy and its unavailable minerals In this house, soy products used to be a staple. We valued them for their low cost and high protein and mineral content. One of those 12 ounce tubs of tofu has 100 milligrams or so of magnesium. That s 25% of the recommended daily intake of magnesium. It s too bad that only about 10 milligrams are absorbed into your body. To make matters worse, there is some discussion in the nutrition literature that the phytic acid in soy may make soy protein less useable for our bodies (Reddy et al. 1989, 57-69). A study of phytic acid in soybeans documents in detail the phytic acid level at different stages of preparation. I provide many of those stages in the figure below. Keep in mind that the activities I list in the figure are successive: the researchers boil the beans, pour off the water, soak them again, dehull them, steam them, drain them, and cool them. The phytic acid levels change very little with all of this effort. It is only when they ferment the beans in the form of tempeh that the phytate levels reduce to about 45% of the levels of the soaked soybean. Fried tempeh is an improvement still, but if the tempeh is stored for two weeks at 5ºC and then fried, the researchers reached the optimal (but not perfect) reduction of the phytic acid. A 2003 study also found that the phytic acid level decreased by only 31% by fermenting soybeans (Egounlety and Aworth 2003).
Keep these results in mind as you shop for soymilk and tofu. Soybeans in soymilk are soaked, strained, and cooked. Tofu has an additional step a coagulant is added. Both of these products retain nearly 100% of the phytates according to the results of the research I present. Eat tempeh for a soy fix, but eat it sparingly if you do not prepare it yourself and do not know that traditional preparation methods were used. Figure 14.2 <Figure not yet public> Cooking strategies for low-phytase foods There is a clear cooking strategy for legumes, oats, corn, and millet to maximize their mineral content: prepare them with a food that is higher in phytase. In a 2003 study, phytic acid researchers used combinations of cereals and legumes to reduce phytic acid levels (Eglit et al.). They reduced phytic acid levels virtually to zero in an hour and a half or less for the following mixtures: 90% whole grain corn plus 10% whole grain wheat 90% whole grain corn plus 10% whole grain rye 30% polished rice, 60% whole grain chickpea, 10% whole grain buckwheat 70% low-extraction wheat, 20% dehulled toasted soybean, 10% whole grain wheat Thus, the best legume preparation method will be some sort of legume-grain combination where the grain is wheat, rye, or barley. A key for oats in the morning is to mix them with other cereal grains high in phytase. The ground, mixed-grain cereals common in health food stores provide a good solution. Or simply add some rye flakes to your oats before you soak them.
Germination of grains and legumes Germinating grains and legumes to make sprouts is a popular food strategy and is fairly effective at reducing the phytic acid content in the grain or legume. To germinate grains and legumes, you soak them first overnight, strain the water, rinse the food, and place it in a sprouting environment. In the first phase of soaking, some mineral content is lost in the soaking water, but the process of germination then increases the mineral content to make up for part of what was lost. In addition to reducing the phytate content of grains and legumes, you can add folate and other vitamins to your food as well through germination. Researchers have found that the vitamin C content of foods increase with germination (Ahmad and Pathak 2000). But the depression-busting nutrient, folate, increases as well. In a study of a grain, ragi, used in India, researchers studied the folate content of the ragi every twelve hours for nearly four days. After the first day of germination, the folate content of the grain increased markedly from 16 mg/100 grams after twenty four hours to 110 mg/100 grams after 92 hours.
Figure 14.3 Folate and Germination folate in ragi as a function of germination time 120 100 80 60 40 Folate content of ragi 0 24 48 72 92 Germination time in hours Source: Babu 1976 20 Phytates can be therapeutic The bad news about phytates is that they inhibit mineral absorption. The good news about phytates is that they inhibit mineral absorption. Sometimes it s all about perspective. Here s the key question: What s more important for you now, increasing your body levels of magnesium and zinc or decreasing your levels of iron? For younger women reading this book, low iron is more likely a problem than high iron. For women who are postmenopausal, high iron may be a problem. Excess iron is implicated in disease as well and phytates in your diet is an effective way to reduce your body s iron levels. Depending on your own circumstances and stage in the life cycle, your needs are going to be different. Pick and choose the food preparation suggestions in this chapter accordingly. Visit our website: www.rebuild-from-depression.com