Chapter 7: Rooting out the causes of disease

By Dagmar
In Interesting stuff
Nov 25th, 2015


Why diabetes is so common among desert dwellers


Gary, the author of this book has put more focus into the Central America and surrounded areas than any other part of the world. Here we are back in Mexico, examining the physiological traits of indigenous people, which are not necessarily genetically related, but they face the same health problem: adult onset of diabetes (type 2). The Navajo people and Seri of Mexico were the two populations on which the author focused the most.

There was a significant shift in the causes of death among these people over a half century. In the past, most of these people died accidentally, such as a bite of a snake. Today, they are being eradicated by a chronic metabolic disease that is largely induced by the Western diet and lifestyle.

“… pay protracted attention to diet change and its role in disease.”

I have picked these few words in relation to the cause-effect of the type 2 diabetes which has achieved pandemic parameters worldwide. Gary says:

Seri are the last culture in Mexico to have retained hunting, fishing and foraging tradition instead of adopting agriculture…

Gary’s wife Laurie screened Sari people for the type 2 diabetes in an office while Gary interviewed ‘the elders of each family about their genaological histories’. He wanted to see how the mixed ancestry (100% Sari or otherwise) could influence their susceptibility to this debilitating disease. There were some people who had common ancestors with Pima and Papago tribes, which have had the highest incidence of the disease in the world (at the time of writing the book).

However, not only the genes contribute to the aetiology of diseases. I remember reading quite an apt analogy: the genes are the bullets but the lifestyle is pulling the trigger. As Gary continues in the chapter, you can read that the Seri people (and other indigenous tribes) used to live on “seafood, wild game and desert plants like cactus fruit and mesquite pods”. Since that has changed remarkably and people adopted more westernized diet, they started to suffer from various metabolic diseases. This was particularly the case for Alfredo, an old man Gary spoke to. His great-grandmother was of Papago-Pima origin. Those who had better access to the convenience stores and fast-food restaurants suffered the diabetes and premature death at higher rates than those in whose lifestyle there was less dramatic transition to the westernized diet, including drinking alcohol. Interestingly, the body weight correlated less with this trend: Seri people, despite being somewhat heavier, had a lower incidence of the disease than others of Papago-Pima origin. Gary concluded that rather than amount of food it was the quality or composition of food that contributed to the increased prevalence of disease: the kind of fats and carbohydrates consumed on regular basis.

Have you heard of the ‘Pima paradox’?

Despite all the effort, money and research from the government and the scientific community, those westernized Pima people were not able to lose weight while their relatives living the traditional way of life have had no health issues, despite eating about the same amount of calories. There it appears that not only the westernized Pima consumed high amount of fat and sugars, they also did not consume foods that contain protective compounds which help their traditional counterparts avoid obesity, metabolic syndrome and diabetes. This is a dual effect of the westernized lifestyle. Add the low physical activity among modern Pima people and it does not require much to understand what is going on.

Protective effect of native foods

Gary writes about how since 1980s he has been collecting a list of traditionally prepared desert foods for nutritional analysis by the scientists in the University of Arizona. They also analyzed the glycaemic index and examined how particular foods stressed pancreas for producing insulin. Unsurprisingly, they found out that the traditional foods and meals based on desert legumes, cacti and acorns were very slowly digested and absorbed, keeping blood sugar concentrations low and preventing spikes in insulin release. The scientists named these foods ‘slow-release foods’, in contrast to the fast foods such as cakes, ice cream and similar highly processed foods containing simple sugars. To be more precise, the slow-release foods were rich in complex carbohydrates, soluble fibre and tannins (the tannins are also present in tea), having two to four times lower glycaemic index than processed western foods.

Interestingly enough, it was not only the North America natives whose diet was typical with this. Similar composition of the diet was found among Aborigins of Australia, who also suffer metabolic disorders after adopting westernized diet and lifestyle.

Gary’s colleague and friend, Jennie Brand-Miller, once came up with a question that what if there is ‘something that helps a number of desert plants in adaptation to arid conditions helping controlling blood sugar and insulin levels in humans that consume them?’

After that Gary unwound a thread of thoughts about how complex this drought-defence system of plants was and how it would be difficult to find whether there were specific compounds typical for these desert plants across continents, aka a ‘convergent evolution’. It well might be that different compounds in different plants have the same effect on people and even that people might have adapted to these compounds, so once they are not present in their diet, they are highly susceptible to metabolic disorders such as diabetes. What is more, not only nutritional factors could be behind this effect, but also the anti-nutritional factors, preventing or slowing down absorption of certain dietary compounds or nutrients. The scientists proposed a theory that perhaps the extracellular mucilage found in cacti and other similarly drought-adapted plants (that gooey globs of soluble fibre which helped the plant to be more efficient in preserving its limited water stores) might be one of the disease protective factors. It was found that when ingested, the mucilage and pectins slow down the digestion and absorption of sugars in our intestines.

opuntia fruit

Opuntia fruit.

Prickly pear, or opuntia, a cacti fruit, is one of such foods that have been present in the diet of desert people in North America. When conducting research, this very fruit was found to slow down the absorption of consumed sugar and cholesterol into the blood of examined natives which were at a high risk of diabetes. As the scientists found out, at least of 22 species of cacti used by native Seri people had such properties and were present almost all year round. These jelly forming substances not only made the simple sugars less available to the intestine epithelium, therefore delaying its absorption; it was also found that they reduced the gastric motility, hence the stomach emptying was delayed which brought a higher satiety and helped to prolong the time between meals. This is quite in contrast to the current habit of constant munching on snacks between main meals in the Western society.


North American natives explained. What about the Australian Aborigines?

Gary made it clear: prickly pear was not present in Australian deserts. He looked for similar plants which would also contain slow-water-release mucilage that would function as slow-release food in the intestines of Aborigines. What he found was that the cacti were not the only plants having this effect on the American natives’ absorption. There were dozens of other plants with these properties which have evolved on both continents.

But that was not all. According to the genetic survey, there were found genetic differences, so called micro-polymorphism, between the hunter-gatherers and those who had a history of agriculture. Seri people were the hunter-gatherers and their genetic make up was different from the agricultural natives of North America. They were simply better fitted into their desert coastal homeland. It was assumed that these traits were a result of the interactions between the environment and genes.

Then, another question was asked:

“… do long-time hunter-gatherers with such polymorphism respond to certain desert and marine foods differently than other people do?”

The scientists tested the Australian Caucasian and Aboriginal volunteers with two types of potatoes: a fast-release domesticated white potato as we know it and a bush potato (Ipomoea costata) which was well known to Aborigines. These bush potatoes were known for a slow-release carbohydrates content. It was found that both groups produced lower insulin response to the bush potato in comparison to the white potato, but the Aborigines had a response lower by third when compared to the Caucasians. This was interpreted as the Aborigines were better adapted to their bush potato and therefore protected from the risk of diabetes when eating it than the Caucasians were. In comparison to the Seri people, of which the history goes back some 10,000 years, the Aborigines date their history back 40 000 years, which is a significantly longer period of time, allowing for better genetic adaptation.  This was an excellent example of the thrifty gene’ theory.

Gary continues with the explanation for this observation as an adaptive response to the uncertainty of food among the hunter-gatherers so their bodies were better adapted to the famine. However, if you have expected that the hunter-gatherers experienced more famine due to insecurity in food supply than the agricultural societies which stored the surplus and used it over the winter months in the European region, you would be surprised that there is little evidence to support this scenario. According to the research, the frequency in famines increased less than 10 000 years ago due to the dependency of the agricultural societies on the yields. If those failed, people struggled to feed themselves because they were less equipped for alternative resources, unlike their hunter-gatherer counterparts. Remember the Great Famine in Ireland?

Another factor in such famine outbreaks, which was not discussed in the book however, was the increased number of people in the agricultural society in contrast to the small tribes of hunter gatherers. It is easier to feed a small group of people from natural resources than the whole city when the staple crop fails.

It is obvious that while both different societies maintained their way of life on which they evolved over millennia (the agricultural societies formed very gradually allowing for adaptation and the survival of the fitter), they remained healthy and free from the metabolic syndrome. However, when a sudden change appeared, as when the hunter-gatherer society adopted a western agricultural diet within a few years or a couple of decades, the negative effect kicked in. As Gary summarized:

Significant adaptation through evolutionary processes to new diets rarely occurs over the course of two to three generations.

Although Gary outlined four major circumstances that contributed to the negative impact of this shift among the affected societies, I have amended them a bit (and added a fifth point), since some of them looked more like repeating the same factor over two paragraphs or merging two distinct factors into one paragraph.

  1. Loss of the protective secondary plant compounds from wild plants when switching to the domesticated high GI crops bred for higher yield and energy content at the expense of protective plant compounds.
  2. Shift in breeding animals for human consumption: raising a livestock on the starchy food rather than letting it grazing on fields changes the nutritional profile of its meat and its quality.
  3. Industrial revolution in Europe since the 17th century and its impact on milling practices, reducing content of fibre in flour and producing very fine flour which raises blood glucose and insulin much faster and higher than coarser flour (such as bulgur wheat).
  4. Inclusion of food additives, such as trans-fats and fast releasing sugars into the processed food. The three times higher raised levels of blood glucose and insulin were mentioned after the consumption of fast food meal than it was ‘experienced during preagricultural periods in our evolution’.
  5. Increased convenience of food, portion sizes and palatability of processed food together with the increased sedentary lifestyle resulted in the society being less fit than ever.
Mixed diet among indigenous populations

If you have thought that hunter gatherers only ate wild animals and plants, you would be wrong. The domestication of crops and animals has  a long history. Gary summarized that even in the past the humans like Pima and Papago in Arizona deserts consumed about 60% of food from domesticated resources during wet season, while in dry season they relied on wild resources adapted to draught. Hence, there was a mix of wild and cultivated crops forming a diet in various cultures across the globe. This was applicable to people in developing countries which also maintained a mixed diet of farmed and wild resources until recent times, when the Westernized lifestyle entered their lives, too. And that was the change that brought a widespread pandemic of obesity and related metabolic disorders like diabetes and cardiovascular diseases in populations that have never seen these before.

Quality vs. quantity of macronutrients in research

Gary also mentioned that once the diseased people return to their ancestors’ diet, there can be seen a ‘rapid recovery’. This was demonstrated in 1993 in a study performed on 22 Pima Indians who were exposed to their traditional diet and also to the modern fast-food diet. The food quantity was not the cause of changed metabolism, because they consumed the same amount of calories in both diets, with the same content of carbohydrates and fats. It was rather the quality of nutrients that was the culprit.

In another smaller study, indigenous people of Central America, who suffered diabetes and were taking medication for it, have seen a massive improvement within 10 days so that they had to seek medical advice on lowering the dose of medication. They ate all-you-can-eat slow-release food, which is even more encouraging, since the limitation of the calories was not behind the effect. Again, it was the quality, not quantity, of the diet that caused the positive changes.

This effect was also reproduced within a month among diabetic Australian Aborigines who were made to adopt dietary habits and lifestyle changes (activity) of their ancestors and who saw remarkable improvement.  In more detail, their diet contained about 54% protein, 26% fat and remaining 20% were from the slow-release carbohydrates. Such shift led to decreased blood glucose levels and improved insulin sensitivity. Some critics objected that these changes could be due to the weight loss. The reply was that this diet based on high protein and low carbohydrate did not worsen, but improved health of diabetic Aborigines. That, however, does not mean that it is an optimal diet for everybody.

Finally, Gary experienced himself the positive effect of wild plant foods on his stamina together with 20 other Native Americans when making a pilgrimage of 220 miles in 12 days back in 1999. He concluded the chapter with saying, that:

Yes, genes matter, but diverse diets and exercise patterns matter just as much. 




Chapter 1: Discerning the histories encoded in our bodies

Chapter 2: Searching for the ancestral diet

Chapter 3: Finding a bean for your genes and a buffer against malaria

Chapter 4: The shaping and shipping away of Mediterranean cuisines

Chapter 5: Discovering why some (don’t) like it hot

Chapter 6: Should we change places, diets or genes?

Chapter 7: Rooting out the causes of disease

About "" Has 48 Posts

Graduated at London Metropolitan University: BSc (Hons) Human Nutrition in 2014. Working as a research assistant at the MRC, The University of Cambridge.

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