Trypsin inhibitors--Trypsin is an important protease in our digestive system. Proteases are enzymes that break down proteins, so trypsin is a crucial part of our ability to digest protein. In the wild, plants make protease inhibitors as a defense mechanism, deterring animals from eating them. There haven’t been many studies on trypsin inhibitors in Moringa, and those that have been done have been carried out only on very limited samples. Based on these studies, though, protease inhibitors seem to be found only in moderate amounts in M. oleifera leaves, and the ones that are there seem to be very heat-sensitive, so a quick cooking deactivates most of them (Vanderjagt et al. 2000). Some nutritious foods, such as soybeans, are notorious for their trypsin inhibitors (e.g. Guillamón et al. 2008). In fact, many legumes with very high protein contents are not eaten precisely because they have such high levels of trypsin inhibitors and other antinutritional factors. Unlike these species, Moringa oleifera isn’t known for its indigestibility. So, based on the available evidence and a long history of consumption by people, trypsin inhibitors don’t seem to be present in side-effect producing quantitites in M. oleifera.
Tannins- Tannins are the bitter substances that make tree bark brown. Tannins are polyphenols, large, complicated molecules made up of lots of phenol (benzenes-with-an-OH-group-stuck-to-them) rings. Tannins are or were used in tanning leather, hence the related names. Tannins interact with proteins, which is why they are used in tanning leather. Tannins often bind to proteins and make them come out of solution. When they are not in solution they can’t be digested. So, like protease inhibitors, they are defense compounds that are produced by plants to make themselves unpleasant to eat by inhibiting digestion. Makkar and Becker (1997) found tannins in concentrations of about 12 grams per kilogram. They declare these to be only “moderate” amounts and we will take their word for it. Again, though, this illustrates that the studies that have been conducted on moringa have been carried out on samples gathered only in a few geographical regions and therefore might not reflect the variability found across the species. Also, the results of chemical studies can vary tremendously depending on the exact extraction and sample preparation method used (Hagerman 1988). This also means that it is sometimes hard to compare between studies. For example, Albrecht and Muck (1991) measured tannin contents in a variety of legumes and found that tannin contents varied from 0 to 27 grams per kilogram. This would seem to bear out Makkar and Becker’s (1997) conclusion that the 12 grams per kilogram in Moringa oleifera leaves is indeed “moderate.” However, given that their methods differed slightly, it is hard to know just how Moringa oleifera tannin levels compare to those in other foods. In addition, because Makkar and Becker only used a single sample, it is hard to know how much variation there is in tannin concentrations across Moringa oleifera and the different products made from moringa that people consume. However, in contrast to things like grapes, persimmons, or raw nuts, which are notorious for their tannin content, moringa has not such reputation. Given that it has been a human food for millenia, it would seem likely that if high tannin concentrations were a problem, we would know about them. So, given the information available, the tannin concentrations are not stratospheric in moringa and seem low enough that they should not deter anyone from eating the plant. Moreover, in
Saponins--Sapon- is the Latin root for “soap” and these compounds have a soapy behavior (Osbourn 1996). If you can get flowers of the plant Ceanothus, wet them and rub them between your hands—a nice lather will result. This lather is due to the saponins. Other plants are famous for their saponin concentrations. Here in the American tropics, there is a plant so well known for its saponins that it is called Sapindus saponaria and is known by various common names like “jaboncillo” (little soapy one). Lots of plants are or have been used for their saponins, for bathing, for washing clothes, or for stupefying fish. To stupefy fish, the plants are crushed and thrown into a body of water. The fish, which are sensitive to saponins, stop swimming and may even die, making them easy to collect.
Saponins are disagreeable not just to fish. Fungi seem to be particularly susceptible and saponins might be an evolutionary response by plants to fungal attack (Osbourn 1996). But, like tannins, they are unpleasant tasting and potentially toxic. If you have ever eaten quinoa without washing it very well you will have eaten disagreeable, bitter tasting saponins. Soaps help disperse lipids (fats) and make them more soluble in water. Biological membranes are made up mostly of lipids. As a result some saponins seem to be able to kill cells by making the membranes open up, releasing the cell contents. So, again, they are an example of compounds that plants have come up with that deter other organisms from attacking them. Makkar and Becker (1996) showed that Moringa contained some saponins (see also Richter et al. 2003). They found saponin levels higher than those in soy (and no one avoids soy because of saponins), and report that the toxicity of the saponins in moringa seems to be very low. Like all aspects of moringa, it would be good to have more studies, but based on the available evidence there would seem to be no reason to avoid eating Moringa in a normal diet because of its saponin content (see also Makkar and Becker 1997 and Gidamis et al. 2003).
Lectins--Lectins are compounds known as glycoproteins that, when eaten by people, bind to the mucopolysaccharides that stick out of the membranes (made, remember, mostly of lipids) of the cells in the intestinal wall. The most famous lectin is ricin, the toxic compound that was used to assassinate Georgi Markov in 1978 and has been sent in letters to some US politicians. Other well-known lectins include phytohemagglutinin, the compound that makes kidney beans so toxic if they eaten raw or are not cooked at a high enough temperature to denature this protein. In the name “phytohemagglutanin,” the “hema-“ refers to blood, and “agglutanin” to agglutination. One of the effects of phytohemagglutanin is to cause red blood cells to stick together or agglutinate, which presumably inhibits oxygen transport and clogs capillaries. This is just one of the many ways that plants, being sessile organisms that can’t run away when confronted by a predator, defend themselves against attack (Peumans and Van Damme 1995). Makkar and Becker (1996) found no traces of lectins in their analysis, though the seed does, famously, have coagulating proteins. These are the proteins that are used in Moringa water purification, about with more later (see Sutherland et al. 1994, also Coelho et al. 2009 for other moringa lectin uses). So, even though moringa is so rich in proteins, lectins do not seem to be important components of the chemical repertoire of moringa leaves.
Calcium oxalate--If you read a little about moringa, you will see repeated a thousand times that moringa has “more vitamin C than oranges, more calcium than yogurt, etc…” More about this litany later, but for now let’s turn to calcium. My work (Olson and Carlquist 2001 for example) showed that there was plenty of calcium in all moringa parts—but in the form of calcium oxalate crystals. These crystals are another line of plant defense, this time against chewing or piercing insects. Blocky crystals get in the way of their mouthparts. For humans, calcium oxalate is worrisome because in the best case it isn’t available to the body and in the worst case can contribute to formation of kidney stones (Finkelstein and Goldfarb, 2006). For years it wasn’t clear how much of the “more calcium than yogurt” was actually nutritionally inaccessible calcium oxalate. See my post on calcium oxalate and Radek and Savage (2008), but the short answer is a classic moringa best-case scenario. Yes, some of the calcium in moringa is bound up in non-bioavailable oxalates. Most of these oxalates are simply excreted, meaning that they don’t contribute to kidney stones. And, in addition to calcium oxalate, there is still a huge amount of bio-available calcium. Thank you moringa!
Glucosinolates--Beyond its well-proven nutritional benefits, one of the main promising aspects of Moringa oleifera is its battery of antioxidant glucosinolates, or mustard oils. Glucosinolates are the stinky, spicy, sulfur-containing compounds that give radish its bite, cabbage its pungency, wasabi its heat, and papaya its sometimes slightly fetid smell. They are what seem to give moringa its potential promise in cancer chemoprevention (Guevara et al. 1999, Fahey et al. 2004, etc.), glucose regulation for diabetics (Kar et al. 2003, Ndong et al. 2007), and other exciting potential applications. We will learn more about glucosinolates in greater detail in a later post, but for now the question is regarding side effects.
Glucosinolates are potentially important in connection with side effects because some of them lead to the formation of goiters. Goiters are highly enlarged thyroid glands, hence the technical name of the condition, thyromegaly (thryo- denoting the thyroid and megaly from mega- or large). Some glucosinolates interfere with proper thyroid function and lead to thyromegaly. Therefore, a natural question is whether glucosinolates in Moringa oleifera have the potential to cause goiters (Abuye et al. 2003). Moringa is a member of Brassicales, the great order of mustard-oil producing plants. This means that it is a relative, though a bit distant, of the Mustard Family, Brassicaceae. Many Brassicaceae are well known for containing progoitrin, which, when eaten and then split apart in the initial stages of digestion, releases substances known as oxazolidonethiones, which do lead to goiter formation. However, progoitrin has never been identified in any Moringa species. Likewise, no Moringa species are known to have high levels of glucosinolates constructed around the double ring known as an indole group (Faizi et al. 1994, Guevara et al. 1999) Indole glucosinolates are also important goiter-causing compounds. As a result, there is no evidence that points decisively toward a risk of goiters from consuming moringa. However, it could be that some thiocyanates, the sulfur- plus cyan-group containing compounds common in moringa, just might be goitrogenic in very high concentrations (well beyond those found in a normal diet). This is just one of many potential research directions awaiting examination in moringa and to which the International Moringa Germplasm Collection is designed to contribute.
Abortifacient potential-- One aspect of moringa biology that really does need attention is its potential to provoke abortion. I have never heard of anyone losing their baby from eating moringa in a normal diet. However, it does seem to be a traditional abortifacient in India (Nath et al. 1992) and does seem to provoke uterine changes in rats that have had their ovaries removed and so otherwise lack female hormones (Shukla et al. 1989). In addition, there is a fair amount of research looking at the ability of moringa to cause abortions in rats. As with most research on moringa’s medical and nutritional potential, none of these articles are top-ranked journals with global circulations, and many have methods that are hard to interpret for example, Sethi et al. (1988) appear to have ground up moringa leaves, extracted the contents with alcohol and then dried this tincture down (see also Nath et al. 1992). They then adminstrated 175 milligrams of this paste per kilogram of rat body weight. For a 65 kilogram human, this would mean taking 11 grams of this hyper-concentrate. I am not at all clear regarding how many kilos of fresh moringa leaves would be needed to make 11 grams of this extract, but it must be quite a bit, way more than any sane human being would ingest in any meal. Still, people do odd things and I am sure that someone has or will eat such hugely equivalent amounts of moringa sooner or later. Centuries of use an as edible food have established moringa as a safe addition to anyone’s diet, apparently including pregnant women, but it is clear that more research would be helpful. Moringa’s potential abortifacient potential at very high doses illustrates an important point: don’t go overboard on anything. Include moringa as a tasty, nutririous, and maybe even cancer-preventive element of your diet. But eat it as you would any other nutritious, tasty, and cancer-preventive vegetable like tomatoes.
Some people (me included) complain of a heartburn feeling if they ingest dry moringa leaves, as in capsules or mixed into a shake without cooking. Well, it serves you right. Moringa is a food, not something to be taken in a capsule. Would you take broccoli dried and ground up and sit back and wait for its health benefits? A hamburger? Of course not. So do what God intended and cook up a nice dish with moringa in it, something tasty. If you can, use fresh leaves and cook them a couple of minutes (just don’t overcook them). They are delicious and will give you no unpleasant feeling in your tummy. If you can’t get ahold of fresh moringa leaves, by all means use dried ones. There are so many yummy pastas and sauces and rice dishes you can put the dried leaves, ground or whole, in, that there is no reason to choke down horrible tasting raw moringa leaf powder.
It makes as much sense to ask if “taking” moringa has side effects as it does to ask whether “taking” broccoli has side effects. You should eat moringa, not “take” it. The research that has been carried out to date, plus thousands of years of human consumption, place moringa firmly as a safe and welcome addition to the table, but if you are a moringa nut and eat massive quantities of just moringa, you might feel bad, from concentrating saponins, tannins, or any other compounds. Similar things would happen if you ate only spinach, for example. And remember, you might be one of those rare people who is allergic to a common food like broccoli, but this is not a dependable “side effect” of the food. This is a characteristic of your own unusual physiology. Any new food might provoke an allergic reaction, and you just might that rare person who is allergic to it (though there is some evidence to suggest that moringa actually helps counteract some allergic responses, see for example Mahajan and Mehta 2007, Agrawal and Mehta 2008, etc.).
Even though people have been eating moringa for thousands of years, all aspects of moringa need more study. Most of the studies that have been carried out have examined very small samples of moringa germplasm, i.e. samples from just their local area. No effort has been made to study samples from across the entire genus Moringa and including the full genetic diversity of the species. The studies that have been carried out are hard to compare with one another and their methods make their relevance to human nutrition difficult to interpret at times (for example, the massive abortifacient doses given to rats). Any studies in humans have involved very few subjects. Practically none of these studies are in prestigious international journals. Taking moringa science from a situation in which there is a great deal of promise but still many outstanding questions is exactly the aim of the International Moringa Germlasm Collection. Here we are uniting in one place multiple samples of all Moringa species, the first step in being able to resolve, once and for all, the outstanding questions regarding this useful plant. In the meantime, all evidence suggests that moringa can be a side-effect free and nutritious part of your diet.
Agrawal, B., and A. Mehta. 2008. Antiasthmatic activity of Moringa oleifera Lam: A clinical study. Indian J Pharmacol. 40: 28–31.
Albrecht, K. A., and R. E. Muck. 1991. Proteolysis in Ensiled Forage Legumes That Vary in Tannin Concentration. Crop Science 31: 464-469.
Coelho, J.S., N.D.L. Santos, Thiago H. Napoleão, F.S. Gomes, R.S. Ferreira, R.B. Zingali, L.C.B.B. Coelho, S.P. Leite, D.M.A.F. Navarro, and P.M.G. Paiva. 2009. Effect of Moringa oleifera lectin on development and mortality of Aedes aegypti larvae. Chemosphere 77: 934–938.
Fahey, J. W., A. T. Dinkova-Kostova, and P. Talalay. 2004. The “Prochaska” microtiter plate bioassay for inducers of NQO1. In Methods in Enzymology Vol. 382, Parte B, H. Sies y L. Packer (eds.). Elsevier Science, San Diego, California. p. 243-258.
Fahey, J. W., A. T. Zalcmann y P. Talalay. 2001. The chemical diversity and distribution of glucosinolates and isothiocyanates among plants. Phytochemistry 56: 5-51. [corrigendum: Phytochemistry 59: 237].
Finkelstein, V. A. y D. S. Goldfarb. 2006. Strategies for preventing calcium oxalate stones. Canadian Medical Association Journal 174: 1407–1409.
Gidamis, A. B., J. T. Panga, S. V. Sarwatt, B. E. Chove y N. B. Shayo. 2003. Nutrient and antinutrient contents in raw and cooked young leaves and immature pods of Moringa oleifera, Lam. Ecology of Food and Nutrition, 42: 399-411.
Guevara, A. P., C. Vargas, H. Sakurai, Y. Fujiwara, K. Hashimoto, T. Maoka, M. Kozuka, Y. Ito, H. Tokuda, and H. Nishino. 1999. An antitumor promoter from Moringa oleifera Lam. Mutation Research 440: 181-188.
Guillamón, E., M. M. Pedrosa, C. Burbano, C. Cuadrado, M. de C. Sánchez, and M. Muzquiz. 2008. The trypsin inhibitors present in seed of different grain legume species and cultivar. Food Chemistry 107: 68–74.
Hagerman, A. E. 1988. Extraction of tannin from fresh and preserved leaves. Journal of Chemical Ecology 14: 453-461.
Kar, A., B. K. Choudhary, and N. G. Bandyopahyay. 2003. Comparative evaluation of hypoglycaemic activity of some Indian medicinal plants in alloxan diabetic rats. Journal of Ethnopharmacology 84: 105-108.
Mahajan, S. G., and A. A. Mehta. 2007. Inhibitory Action of Ethanolic Extract of Seeds of Moringa oleifera Lam. On Systemic and Local Anaphylaxis. Journal of Immunotoxicology 4: 287-294.
Makkar, H. P. S. y K. Becker. 1996. Nutritional value and antinutritional components of whole and ethanol extracted Moringa oleifera leaves. Animal Feed Science and Technology 63: 211-228.
Makkar, H. P. S. y K. Becker. 1997. Nutrients and antiquality factors in different morphological parts of the Moringa oleifera tree. Journal of Agricultural Science 128: 311-322.
Nath, D., N. Sethi, R. K. Singh, and A. K. Jain. 1992. Commonly used Indian abortifacient plants with special reference to their teratologic effects in rats. Journal of Ethnopharmacology 36: 147-154.
Ndong, M., M. Uehara, S. Katsumata y K. Suzuki. 2007. Effects of oral administration of Moringa oleifera Lam on glucose tolerance in Goto-Kakizaki and Wistar rats. Journal of Clinical Biochemistry and Nutrition 40: 229-233.
Olson, M. E. and S. Carlquist. 2001. Stem and root anatomical correlations with life form diversity, ecology, and systematics in Moringa (Moringaceae). Botanical Journal of the Linnean Society 135: 315-348.
Osbourn, A. 1996. Saponins and plant defence — a soap story. Trends in Plant Science 1: 4–9.
Peumans, W. J., and E. J. M. Van Damme. 1995. Lectins as plant defense proteins. Plant Physiology 109: 347-352.
Radek, M., and G. P. Savage. 2008. Oxalates in some Indian green leafy vegetables. International Journal of Food Sciences and Nutrition 59: 246-260.
Richter, N., P. Siddhuraju, K. Becker. 2003. Evaluation of nutritional quality of moringa (Moringa oleifera Lam.) leaves as an alternative protein source for Nile tilapia (Oreochromis niloticus L.). Aquaculture 217: 599– 611.
Sethi, N., D. Nath, S. C. Shukla and R. Dyal. 1988. Abortifacient activity of a medicinal plant “Moringa oleifera” in rats. Ancient Science of Life 7: 172-174.
Shukla, S., R. Mathur, and O. Prakash. 1989. Histoarchitecture of the genital tract of ovariectomized rats treated with an aqueous extract of Moringa oleifera roots. Journal of Ethnopharmacology 25: 249-261.
Sutherland J. P., G.K. Folkard, M.A. Mtawali, and W.D. Grant. 1994. Moringa oleifera as a natural coagulant. Conference notes, 20th WEDC Conference Colombo, Sri Lanka, Affordable Water Supply and Sanitation.
Vanderjagt, D.J., C. Freiberger, H.-T.N. Vu, G. Mounkaila, R.S. Glew, and R. H. Glew. 2000. The trypsin inhibitor content of 61 wild edible plant foods of Niger. Plant Foods for Human Nutrition 55: 335–346.