Such knowledge has important implications for future prebiotic research and could help establish formulations for valuable recommendations for consumers, said Jeff Leach from the Paleobiotics Lab, a New Mexico-based independent research group investigating the implications of dietary and nutritional evolution and its bearing on modern health.
"Future prebiotic research may be well-served with a better understanding of the nutritional landscape on which humans evolved," he told attendees at the Harvard Medical School Conference Center.
While the term 'prebiotic' is relatively new, being coined by Professor Glenn Gibson from the University of Reading and Professor Marcel Roberfroid from the Catholic University of Louvain in 1995 (Journal of Nutrition, Vol. 125, pp. 1401-1412), the consumption of inulin, the most extensively studied of the indigestible prebiotic carbohydrates, dates back tens of thousands of years.
As Leach eloquently explained: "As our early ancestor moved from the rainforest to the parched savanna-woodlands of subtropical Africa, subsurface tubers, rhizomes, corms, and perennial bulbs, many rich in prebiotics, would have been a ready and important source of energy." (Biosciences Microflora, 2005, Vol. 25, pp. 1-8).
The traditional view of our prehistoric (non-literate) hunter-gathering ancestors is of eating meat and cultivating vegetables and crops, like maize, but take a closer look at the facts and a different view is revealed, said Leach.
"Squint at the archaeological record and you'll see inulin farmers." he said.
Such a view comes about because inulin (beta (2,1) linear fructans) is the major polysaccharide in many subsurface tubers and bulbs like onions and agave. The latter is the most abundant plant in the White Mountains in Arizona and more famous from the tequila industry.
"Digestion-inhibiting compounds and plant toxins present in many below-ground food sources would have limited their role as staples in early diet of Homo until technological adaptations, such as fire, were introduced," explained Leach in the journal Biosciences Microflora, an article co-authored with Glenn Gibson and Jan Van Loo from Belgium's Orafti.
Leach's interest in prebiotics started with his study of the large earth ovens that our ancestors used to cook these subsurface tubers over the course of several days. Such ovens have been found the world-over, with some dating back hundreds of thousands of years.
By cooking the agave and other inulin-rich plants in earth ovens, where temperatures were less than 100 degrees Celsius, the loss of inulin from the cooking process was minimal, being less than 10 per cent.
The archaeological record also shows that the pits used for these earth ovens got bigger and bigger, with some in the American Southwest reportedly capable of producing between two and four thousand pounds (900-1800 kg) of edible agave.
Studies have shown that inulin-rich plants dominated the dietary intake of our ancestors in these regions, with about 60 per cent of the calorific intake coming from such sources. This would equate to a total dietary fibre intake of between 250 and 400 grams every day, with between 50 and 100 grams of inulin every day, said Leach.
"These were big-time inulin eaters." he said.
Modern recommendations for inulin and oligofructose intake are between five and eight grams per day.
The Lower Pecos Region in the American Southwest is said to have ideal surface conditions and slow rates of soil erosion, as well as deep caves, giving Leach and his fellow archaeologists ideal conditions for the conservation of not only the stone ovens, but also for human coprolites (faeces). Indeed, the faecal samples are so well preserved, Leach said that some "look as good as the day they were laid down."
Over 16 years more than 20,000 faecal samples have been recovered from 11 caves, he said, with some between five and eight thousand years old. Testing the so-called 'paleofaeces' is the focus of a collaboration with Glenn Gibson to see if they are packed full of the Bifidobacteria that are boosted in the intestine by consumption of prebiotics.
Professor Gibson told NutraIngredients.com that a PhD student at the University of Reading was starting to assess these samples, but that a couple of checks must first be made - are the faeces human, and are they uncontaminated?
The next stages in this ongoing research could be to go back to the skeletal record to check for signs of disease, particularly osteoporosis. Significant research has reported that the prebiotics inulin and oligofructose increase calcium absorption, leading to higher bone mineral density, bone content, and lower risk of the disease.
Taken together, the research has important implications for modern nutrition, food science and medicine, suggested Leach.
"Human nutritional studies, must consider our evolutionary-based and thus genetically determined optimal diet when considering optimal diets for consumers."
But while the health benefits of prebiotics in the modern diet are the focus of more and more research, Leach said he was the only archaeologist specifically looking into the topic of prebiotics in the ancient diet. "I'm certainly the only archaeologist that can spell 'fructo-oligosaccharides'," he said.