Q&A: Lectins; Omega-3s; Carrots
Q. What are lectins, and should we avoid beans, seeds and grains since they contain lectins?
A. George S. Ellmore, PhD, an associate professor in the department of biology at Tufts University, responds: “A lawyer might answer this question with, ‘It depends.’ Lectins are proteins from plants used to store nitrogen and provide instant defense against animals trying to eat the plant since they can cause digestive upset, particularly when eaten raw. Lectins are found in roots, stems, leaves and seeds of many plants. The part of these plants that humans commonly eat is the seed (from a botanical standpoint). Lectins have been detected in the seeds of about 500 species of plants, including legumes (beans), nuts, oilseeds (such as sunflower seeds) and grains, such as wheat, rice, barley and rye.
“Once eaten by an animal, lectins bind to the sugar portions of the animal’s intestinal wall where they interfere with digestion and nutrient uptake. That is why lectins are sometimes called ‘antinutrients.’ However, after edible seeds are prepared by methods using heat [especially moist heat], they contain very little lectin. Yet, they provide concentrated packets of protein, fat, carbohydrate and fiber, all of which are nutritionally beneficial.
“For example, raw soybeans contain 10 to 20 grams (g) of lectin per kilogram (kg) of soybeans, but when heat-processed to make soybean meal or soymilk, lectins drop to 2 to 4 g per kg. Surprisingly, at that low level, lectins improve the health of the gut microbiota [bacteria and other microbes] in ways that may ease food allergies and prime the human immune system.
“While raw seeds use lectins to resist pests, cooked beans and grains have supported the diets of some of the longest-lived humans on the planet. Therefore, we should celebrate these heat-treated foods in our diet.”
Q. I know omega-3 fats from oily fish like sardines and mackerel are superior to omega-3 supplements. Will the canned versions of these fish provide the same benefits as fresh-caught?
A. Alice H. Lichtenstein, DSc, director of Tufts’ HNRCA Cardiovascular Nutrition Laboratory, notes: “There is no reason to assume omega-3 fats from oily fish like sardines and mackerel are superior to omega-3 supplements. A fatty acid is a fatty acid, regardless of the source. The main difference between fish and supplements is fish provides high-quality protein and other nutrients, which are lacking in supplements. Also, fish is a good alternative to protein foods high in saturated fat, such as meat.” So, eating fish provides multiple benefits at the same time.
“Canned fish products such as sardines and mackerel are good sources of omega-3 fat,” adds Lydia Fernandes, a dietetic intern at Frances Stern Nutrition Center at Tufts Medical Center. Direct comparisons between canned and fresh fish are challenging because some of the difference in omega-3 content comes from variations in the fish, such as the exact species, what they eat, where they’re harvested and when, rather than canning per se. Regardless, an oily fish, including canned, is a much better source of omega-3 fat than a white fish like tilapia.
“It is important to keep in mind, however, that canned seafood is often higher in sodium than fresh (depending on how it’s prepared),” Fernandes says. This can vary based on what the seafood is canned in and whether salt is added, though. For example, sardines canned in tomato sauce may be higher in sodium than sardines canned in oil. Compare Nutrition Facts labels to find the best options.
Q. I’ve been buying bags of carrots that have multiple colors—yellow and purple, as well as orange. Is the nutritional value, particularly beta- carotene, of non-orange carrots less?
A. Elizabeth J. Johnson, PhD, a scientist in Tufts’ HNRCA Antioxidants Research Laboratory, says: “With the exception of white carrots, all are good sources of carotenoids and other beneficial phytonutrients. Color is the best indicator of this. Orange carrots contain the highest level of total carotenoids, especially beta-carotene, which can be converted to vitamin A. Yellow and purple carrots contain good amounts of the carotenoid lutein, intakes of which have been associated with eye and brain health. Purple carrots contain higher amounts of phenolics, especially anthocyanins, which may be protective against cancer and heart disease. Each carrot type will have varied health effects because of these colored compounds. A healthy dietary pattern contains a variety of fruits and vegetables, which carrots of multiple colors can be a part of.”
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