Beans, Lentils, and the Paleo Diet

As we continue to explore the foods our ancestors relied on during our evolutionary history, and what foods work best for us today, we come to legumes such as beans and lentils.  These are controversial foods within the Paleolithic diet community, while the broader nutrition community tends to view legumes as healthy.

Beans and lentils have a lot going for them.  They're one of the few foods that are simultaneously rich in protein and fiber, making them highly satiating and potentially good for the critters in our colon.  They're also relatively nutritious, delivering a hefty dose of vitamins and minerals.  The minerals are partially bound by the anti-nutrient phytic acid, but simply soaking and cooking beans and lentils typically degrades 30-70 percent of it, making the minerals more available for absorption (Food Phytates. Reddy and Sathe. 2002).  Omitting the soaking step greatly reduces the degradation of phytic acid (Food Phytates. Reddy and Sathe. 2002).

The only tangible downside to beans I can think of, from a nutritional standpoint, is that some people have a hard time with the large quantity of fermentable fiber they provide, particularly people who are sensitive to FODMAPs.  Thorough soaking prior to cooking can increase the digestibility of the "musical fruit" by activating the sprouting program and leaching out tannins and indigestible saccharides.  I soak all beans and lentils for 12-24 hours.

The canonical Paleolithic diet approach excludes legumes because they were supposedly not part of our ancestral dietary pattern.  I'm going to argue here that there is good evidence of widespread legume consumption by hunter-gatherers and archaic humans, and that beans and lentils are therefore an "ancestral" food that falls within the Paleo diet rubric.  Many species of edible legumes are common around the globe, including in Africa, and the high calorie and protein content of legume seeds would have made them prime targets for exploitation by ancestral humans after the development of cooking.  Below, I've compiled a few examples of legume consumption by hunter-gatherers and extinct archaic humans.  I didn't have to look very hard to find these, and there are probably many other examples available.  If you know of any, please share them in the comments.

To be clear, I would eat beans and lentils even if they weren't part of ancestral hunter-gatherer diets, because they're inexpensive, nutritious, I like the taste, and they were safely consumed by many traditional agricultural populations probably including my own ancestors.

Extensive "bean" consumption by the !Kung San of the Kalahari desert

The !Kung San are a hunter-gatherer group that has been extensively studied by Richard B. Lee and other anthropologists.  Dr. Lee published the book The !Kung San, which contains detailed information about the !Kung San diet gleaned over his three years of fieldwork.  The !Kung San relied heavily on a legume called the tsin bean, Bauhinia esculenta.  Here are two relevant quotes from The !Kung San:

The tsin bean is the second most important food of the !Kung in the Southern parts of the Dobe area and in Nyae Nyae [second to the mongongo fruit/nut- SG].

A typical day's backload of 5 kg of tsin beans without pods has an edible/waste ratio of 70:30 and provides 3500 g of edible beans.  Back in the camp, tsin beans are processed in several ways.  Unripe beans may be sun-dried before further processing.  A batch of 50 or so beans is roasted in the shell for a few minutes in the hot ashes and sand of the cooking fire.  Slight bursts of steam from the roasting beans indicate they are ready for eating.  Occasionally a bean explodes, but without much damage.  The beans are removed from the ashes, placed on an anvil stone, and opened with a single light tap of a rock or stick.  Each bean comes apart easily into halves.  Eaten whole, the beans have a rich, strong nutty flavor.  Alternatively, the shelled beans may be pounded in the mortar and then mixed with hot water and eaten as a soup or porridge.  The tsin bean is an excellent source of protein (31.6 percent), calories, potassium, phosphorous, thiamine, riboflavin, and nicotinic acid.

By dry weight, tsin beans are 31.6% protein, 36.1% fat, 23.2% carbohydrate, and 1.0% fiber.  They are therefore between a bean and a peanut in nutritional value.

Mesquite pod consumption by Southwest Native Americans

Mesquite is a leguminous tree that was a major wild food source for Southwest Native Americans.  However, these groups ate the starchy pods rather than the seeds, so the analogy to beans and lentils may not hold up very well.

Acacia seed consumption by Australian Aborigines

Australian aborigines extensively harvested and ate the seeds and gum of Acacia trees, another legume.  Here's a quote from the paper "Acacia in Australia: Ethnobotany and Potential Food Crop" (1):

Of the sixty or so species of Acacia in central Australia, Latz (1995) states that some 50% were, or still are, eaten by Aboriginal people and it is not only the seed which is consumed. Several species exude an edible sugary gum from wounds in the stem or branches which supplies a source of energy. Others are fed upon by insects which themselves secrete an edible substance while species such as A. kempeana are the host for various edible grubs often referred to by non-Aboriginal people as witchetty grubs.

Legume consumption by Neanderthals

Neanderthals (Homo neanderthalensis) were a hominin species closely related to modern humans.  They lived as hunter-gatherers in similar environments to some humans, and are thought to have eaten a diet rich in animal foods.  However, evidence is accumulating that their diets also featured a variety of plant foods, including wild legumes and grains.  Some of the most compelling evidence comes from the analysis of Neanderthal tooth plaque, which contains recognizable evidence of plant food consumption (2):

Our data show that Neanderthals in both environments included a spectrum of plant foods in their diets, including grass seeds (Triticeae cf. Hordeum), dates (Phoenix), legumes (Faboideae), plant underground storage organs, and other yet-unidentified plants, and that several of the consumed plants had been cooked. The identified plant foods from Shanidar match well with the soil phytoliths and macrobotanical remains found at other Neanderthal sites in the Near East, whereas those from Spy show use of USOs as predicted for European Neanderthals. Neanderthals’ consumption of these starchy plant foods does not contradict data from isotope analysis, because nitrogen isotopes record only the consumption of meat and protein-rich plant foods.

Did Neanderthals enjoy wild varieties of peas and fava beans?  It certainly appears that they did.

Humans are thought to have eaten a more diverse diet than Neanderthals in the Upper Paleolithic, and one that relied more on small game and plant resources than the Neanderthal diet (at least after the "broad-spectrum revolution").  It's hard to imagine that our human ancestors in Europe passed up these plant foods that Neanderthals relied on.

Conclusion

Beans and lentils appear to be Paleo.  Peanuts are probably Paleo too.  But I would eat them even if they weren't.

As usual, this post is not intended to undermine the Paleo diet concept, but rather to refine a framework that I find useful for thinking about diet and human health.