“On the rocky slopes of Gibraltar, a troop of Barbary macaques lingers near a popular tourist overlook. An adult female pauses mid-stride, crouches beside a patch of rust-red earth poking through the concrete road, and begins pinching off small fragments with surprising precision before popping them into her mouth. She chews, swallows, and moves on. It looks bizarre. But according to a new study, the dirt may help her body cope with the chocolate bars, ice cream cones, and potato chips that visitors keep slipping her despite rules against it.”
They call it “junk food” for good reason, but what if it really was, quite literally, junk—like, of less nutritional value than dirt? Well, that’s exactly what new research on the famous monkeys of Gibraltar suggests. Sort of.
Thanks to the island’s tourists, some of the monkeys now consume a significant amount of ultraprocessed food—biscuits, chocolate, bread, crisps, cheap ice cream—and they’ve also taken to eating pawfuls of calcium-rich red earth, known locally as terra rossa.
The two things seem to be closely related. While other monkey populations have been known to consume dirt, none does it quite like the macaques of this strategically vital rocky little British colony, perched between Europe and Africa.
Over a period of about two years, researchers spent hundreds of hours observing 230 monkeys. During that time, they counted 46 separate incidents of what appeared to be deliberate dirt-eating.
By examining the sites where the monkeys foraged the dirt, the researchers were able to establish the creatures had not been digging up insects, seeds or eggs: They wanted to eat the dirt. The researchers also studied video footage of the dirt-eating and noted a distinctive pattern of harvesting and eating that looked totally different from the monkeys’ normal “ground-feeding postures.” The monkeys ate smaller pieces of dirt and even larger fragments measuring centimeters across.
The vast majority of the dirt-eating took place among groups living on the central and upper portions of the great rock, where the terra rossa—and the tourists—are most heavily concentrated.
Tourist numbers drove the behaviour. When more tourists were around, in the summer months, the monkeys ate more human food, and they also ate more dirt.
On a number of occasions, researchers saw monkeys eat dirt directly after consuming human food.
Monkeys in the area called Middle Hill, by contrast, logged no human contact during the study, and not a single case of dirt-eating was recorded. Interestingly, other researchers who had studied the monkeys of Middle Hill many years earlier, when the monkeys there did come into regular contact with tourists and military personnel, said they remembered incidents of dirt-eating.
The researchers have two theories to explain the monkeys’ behavior. The first is that the monkeys were eating the clay as a kind of buffer or detoxicant. Ultraprocessed food couldn’t be more different from the monkeys’ natural diet—herbs, leaves, seeds and a small amount of insects—and the researchers believe this could irritate their digestive systems and cause harmful changes to the composition of their gut flora. Particular kinds of clay are known to absorb harmful substances in the gut, alter stomach acidity and promote the growth of beneficial bacteria.
The second explanation—the explanation I favour—is that consumption of human foods is causing malnutrition in the monkeys, deficiencies in key minerals and nutrients, which they attempt to remedy by eating the clay.
This kind of behavior is known as pica, and it happens in humans too. Pica in humans can also take the form of eating dirt and clay, as well as things like paper and hair. Nutrient deficiencies, especially iron, zinc and calcium deficiencies, are usually the main triggers. Correcting deficiencies through diet or supplementation is often enough to cure pica.
We know from human studies that consumption of ultraprocessed food is closely linked with malnutrition. For example, a study of children in Brazil from last year showed that consumption of ultraprocessed food was associated with lower dietary bioavailable iron, 2.5 times higher odds of anemia (iron deficiency) and over twice the risk of being overweight.
This study illustrates a key concept in the science of ultraprocessed foods. It’s called the “double burden” of malnutrition: simultaneous “overnutrition” (excess calories leading to weight gain) and “undernutrition” (deficiencies in vitamins, minerals and other micronutrients). You can eat too much and yet too little.
Likewise, an Australian study from 2024 showed that more consumption of ultraprocessed foods was linked to reduced intakes of vitamins A, E, C and B12, folate, zinc, calcium, iron, magnesium, potassium and phosphorus.
If there were human data linking cases of pica to consumption of ultraprocessed food, that would provide an even more compelling link and, surely, prove the malnutrition hypothesis about our clay-eating monkeys. Sadly, evidence for pica leaves much to be desired. Hospitalizations in the US for the condition have risen briskly—there was a 93% increase between 1999 and 2009–but the behavior itself is often hidden and undiagnosed, and may just go away if the underlying deficiency goes away.
Even so, a parallel between monkeys and us can be made. Just like the macaques of Gibraltar, we should not be eating ultraprocessed food. It’s as maladaptive for us, raised as a species for over 200,000 years on minimally processed whole foods, especially nutrient-dense animal foods, as it is for monkeys that should be eating plants and creepy crawlies rather than hot dogs and ice-cream cones. The rise of ultraprocessed food and its displacement of the foods our ancestors thrived upon has brought with it an efflorescence of chronic disease without precedent in human history. For the monkeys of Gibraltar, the effects may be no worse than a newly acquired taste for clay, but for us, with an unlimited supply of factory-made food at our fingertips, the effects are obesity, diabetes, heart disease, strokes, autism, ADHD, Alzheimer’s, irritable bowel syndrome, Crohn’s disease, cancer—the works.
Support Alex Jones by picking up an all-new Alex Jones Live t-shirt, a Trench War Dagger, or the Alex Jones Signature Faraday Bag Bundle at TheAlexJonesStore.com.
