Legumes

Terminology and Description

In the Fabaceae or Leguminosae family, legumes comprise roughly 650 genera and 18,000 species, several feeding humanity for millennia.¹ Their classification, popular and scientific, creates confusion. The public and American olericulturists Vincent Rubatzky and Mas Yamaguchi make vegetables an overbroad category by including legumes.² This book disagrees, considering them here and vegetables in Chapter 15. Chapter 12 notes that some agronomists call legumes that feed humans “grain legumes.”³ This expression emphasizes that people eat the seeds rather than other plant parts, useful information given that livestock eat legumes like alfalfa (.Medicago sativa) and clover (Trifolium species), which this book omits, in their entirety. Yet the adjective “grain” risks conflating legumes and cereal grains, which Chapter 12 treats.

Also prevalent is the tendency to designate seed legumes “pulses,” though the American Pulse Association, Pulse Canada, and USA Dry Pea and Lentil Council define only dried legume seeds as such.⁴ These organizations exclude fresh seeds, peanuts (Arachis hypogaea), and soybeans (Glycine max). This parsing is pointless because all are legumes with similar, though nonidentical, nutrients. For example, peanuts and soybeans have more fat and calories than beans (Phaseolus vulgaris, P. lunatus, P. acutifolius, and P. coccineus) and peas (Pisum sativum).

American historian Ken Albala (b. 1964) grouped all seed legumes under the term “bean,” language that aligns with chickpeas’ designation as garbanzo beans.⁵ But such terminology blurs the ancient tendency to separate peas and beans. For example, in the second century BCE, Roman statesman and agriculturist Cato the Elder (234-149 BCE) differentiated broad beans (Vida faba), also known as fava or faba beans, from chickpeas (Cicer arietinum).⁶ Between the first century BCE and the fourth century CE, Roman scholar Marcus Terentius Varro (116-27 BCE), Roman soldier and agriculturist Lucius Junius Moderatus Columella (4-70 CE), Roman naturalist Pliny the Elder (23-79), and Roman agricultural writer Rutilius Taurus Aemilianus Palladius were not content to designate all edible legumes as beans, distinguishing among peas, lentils (Lens culinaris), chickpeas, lupines (Lupinus species), and broad beans.

The difference between pea and bean, if one must be specified, is partly linguistic because people have long used the term “pea” to mean the garden pea—or the pea, chickpea, and cowpea (Vigna unguiculata)—whereas the name “bean” is broadly applied to many legumes. Another difference concerns preparation. Peas may be eaten uncooked, but beans should be soaked in water and boiled to make them palatable. Although the seed is the unit of consumption, people eat seeds and pods as green beans or snap peas.

Egyptians and Romans observed that legumes improved soil fertility without understanding why. In 1886, German chemists Hermann Hellriegel (1831-1895) and Hermann Wilfarth (1853— 1904) supplied the answer by describing nitrogen fixation.⁷ Rhizobium bacteria and legumes interact symbiotically. The bacteria infect legume root filaments, known as hairs, forming nodules. Nodules shelter these bacteria, which convert the soil’s nitrogen gas (N₂) into ammonium cations (NH/). Plants, and in turn herbivores and omnivores, depend on this transformation because roots cannot absorb nitrogen gas but can take up ions as nourishment. Ammonium benefits not only legumes. Unabsorbed surplus remains available for next year’s crops.

No chapter can discuss all legumes that sustain humankind. Our efforts focus on four genera— Phaseolus, Arachis, Glycine, and Pisum—that have nourished people since prehistory. Being 20-40 percent protein by weight, legumes fed the poor with little access to meat, fish, poultry, eggs, or dairy.⁸ Beans nourished North and South America, spreading throughout the Old World after

1500 CE. Peas helped fuel the Neolithic Revolution in southwestern Asia, dispersing worldwide during prehistory and history. Peanuts contribute to American, African, and Asian diets. A Chinese domesticate, soybeans feed the w'orld’s peoples and livestock. Many items have soybean oil or protein as an additive.

Calories, Nutrients, and Health

Nutrient Density

“Of all the foods, legumes most adequately meet the recommended dietary guidelines for healthy eating,” w'rote New' Zealand nutritionist Bernard Venn.⁹ “They are high in carbohydrates and dietary fiber, mostly low in fat, and supply adequate protein w'hile being a good source of minerals and vitamins, although lacking in vitamin B,₂.” Chapter 13 amasses evidence that potatoes (Solatium tuberosum) rather than legumes are most nutritious, though his opinion is germane to our investigation here.

Peanuts’ Nutrients

Of this chapter’s legumes, raw' peanuts have the most calories at 567 per 100 grams.¹⁰ Most come from the 49.24 grams of fat per 100 grams of dry-roasted peanuts. At 9.4 calories per gram of fat (see Chapter 2), peanuts’ 49.24 grams of fat in 100 grams total supply 462.86 of 567 calories as lipids. Of total fat per 100 grams, 6.9 grams are saturated. The rest are monounsaturated and polyunsaturated in roughly a 5:3 ratio. The 104.14 calories not from fat are carbohydrates; 8.5 grams per 100 grams of raw peanuts are fiber, cannot be digested (see Chapter 2), and supply few calories. Table 8.1 lists calories and nutrients in peanuts, peas, soybeans, and green beans.¹¹

This book does not demonize calories. The issues are whether calories exceed, balance, or trail requirements and whether foods have empty energy, as w'ith processed junk, or many nutrients. Table 8.1 shows that peanuts occupy the second category, with 100 grams having 25.8 grams of protein, 96.5 percent of the U.S. Food and Drug Administration’s (FDA) daily value (DV) for manganese, 57 percent for copper, 42 percent for magnesium, 25.4 percent for iron, 21.8 percent for zinc, 20.1 percent for potassium, 60.4 percent for vitamin B, (niacin or nicotinic acid), 60 percent for vitamin B₉ (folate, folic acid, or pteroylmonoglutamic acid), 55.5 percent for vitamin E, and 42.6 percent for vitamin B, (thiamine or thiamin).¹²

Referencing Chapter 4’s Table 4.1 and Chapter 5’s Table 5.3, peanuts have more protein at 25.8 grams per 100 grams total than wild salmon (Oncorhynchus species) at 19.84 grams, wild catfish at 16.38 grams, farm catfish at 15.23 grams, and bison (Bison bonasus and B. bison) at 20.23 per 100 grams total but less than beef, pork, mutton, goat, and venison at 36.1, 27.8, 33.43, 27.1, and 36.08 grams, respectively.¹³ By mass, peanuts have more vitamin E than salmon, trout (species in genera Oncorhynchus, Salmo, and Salvelinus), avocados (Persea americana), red peppers (Capsicum annuum), Brazil nuts (Bertholletia excelsa), turnip greens (Brassica rapa ssp. rapa), and mangos (Mangifera indica), and more manganese than sunflower seeds (Helianthus annuus), cashews (Anacardium occidentale), almonds (Amygdalus communis), potatoes, onions (Allium сера), bananas (Musa x paradisiaca), and carrots (Daucus carota ssp. sativus).¹⁴

Phaseolus Beans’ Calories and Fat

Peanuts are just one of several nourishing legumes. Readers concerned about fat intake may appreciate that Phaseolus beans have little. Table 8.2 shows that 100 grams (half a cup) of red kidney, pink, great northern, and cranberry beans have 0.4 grams of fat.¹⁵ The same quantity of black beans has 0.5 grams of fat and of navy and pinto beans 0.6 grams. This dearth translates into few' calories, with a range between 104 for 100 grams of great northern and 127 for an equal amount of navy beans.

TABLE 8.1

Nutrients in Legumes 100g

TABLE 8.2

Calories and fat in Phaseolus vulgaris 100g

Soybeans’ Nutrients

The next section discusses peas, though soybeans’ aliment is considered here. Their preparation—to which a U.S. Department of Agriculture (USDA) handbook devoted twenty-three pages—affects calories and nutrients.¹⁶ Rather than treat all, this section examines roasted soybeans, tofu, soy sauce, and tempeh given their antiquity, popularity, and nutriment. Additionally, tofu deserves attention because it is eaten “everywhere” in China, the world’s most populous country.¹⁷

Roasted soybeans may be the oldest preparation and appear to have sustained China’s poor during famines since at least the first century CE. Tradition credited Chinese nobleman and alchemist Liu An (179-122 BCE) with inventing tofu or soybean curd, though scholars doubt this claim.¹⁸ American anthropologist Christine M. Du Bois (b. 1962) suspected that tofu arose serendipitously when someone seasoned soybean porridge or gruel with sea salt, whose magnesium chloride (MgCl₂) solidified soy proteins.¹⁹ This process resembles cheesemaking, which Chapter 7 described. American anthropologist Sidney Wilfred Mintz (1922-2015) characterized soy sauce as “the most widespread fermented legume product on earth.”²⁰ Being a microbial process, fermentation required bacteria, fungi, mold, or their combination. Preferences dictated addition of ingredients like grain and brine. Wheat (Triticum monococcum, T. dicoccon, T. aestivum, and T. durum) was popular because it complemented soybeans as a northern Chinese crop. After fermentation, compression of the mixture yielded the liquid known as soy sauce. Indonesians may have invented tempeh or tempe around 1000 CE, though no text mentioned it before the eighteenth century.²¹ The mold Rhizopus oligosporus ferments soaked, cooked beans into tempeh, a savory cake with meaty texture and flavor.

Table 8.3 tabulates calories and nutrients in 100 grams of roasted soybeans, tofu, soy sauce, and tempeh. Tempeh’s 14 percent of DV for vitamin B,₂ (cobalamin) is noteworthy because few plant foods supply it.

Legumes’ Non-Nutrients

Despite legumes’ nutriment, they may have been comparatively late additions to diets. American botanist Lawrence Kaplan (1926-2018) asserted that hunter-gatherers first targeted tubers, roots, leaves, insects, and game.²² Only later did they turn to seeds like legumes and grains. Many legumes would have been unappealing raw given toxins and chemicals—such as phytic acid discussed elsewhere—that retard nutrient absorption. Peas, however, are free from this hazard. Fire’s control and use for cooking (see Chapter 3) destroyed many of these substances, permitting legumes’ consumption. Once in the food supply, they grew' to dominate diets such that humans use more Fabaceae species than those in any other family.²³ For example, people worldwide eat more soybeans, discussed later, than any other plant, doubtless because countless foods contain soy protein or oil.²⁴ American journalist and food writer Michael Kevin Pollan (b. 1955) estimated that tw'o-thirds of processed items have one or both.²⁵

Legumes as Inexpensive Protein

Since domestication, legumes have given commoners inexpensive protein.²⁶ Their value since antiquity (c. 3000 BCE-c. 500 CE) is difficult to overstate for people who ate them at nearly every meal.²⁷ The previous section noted that they may be up to 40 percent protein by mass, but the body cannot absorb it as well as animal protein. Legume protein is better assimilated when combined with whole grains, meat, fish, poultry, eggs, or dairy. Beans, however, are seldom consumed with animal products because of separate trajectories. As early as 1930, the U.S. Census Bureau documented an inverse correlation between bean consumption and income.²⁸ The poor eat beans whereas the affluent eat meat and kindred foods. This reality affirms Chapter 4’s remark that meat has long signaled privilege.

TABLE 8.3

Nutrients in Soy Foods lOOg

Legumes and Mortality

Returning to Venn’s judgment, a 2004 paper documented an 8 percent decline in mortality among Japanese, Swede, Greek, and European-Australian septuagenarians for every 20 grams (0.7 ounces) of legumes eaten daily.²⁹ No other food matched this improvement, though fish and shellfish and a high ratio of unsaturated to saturated fat also lessened mortality. Among legumes, the authors cited Phaseolus beans, peas, chickpeas, lentils, and soybeans as whole beans, tofu, natto, and miso. Like tempeh and soy sauce already mentioned, natto and miso are fermented.