Abstract: Myopia is absent in undisturbed hunter-gatherers but ubiquitous in modern populations. The link between dietary phytochemicals and eye health is well established, although transition away from a wild diet has reduced phytochemical variety. We hypothesized that when larger quantities and greater variety of wild, seasonal phytochemicals are consumed in a food system, there will be a reduced prevalence of degenerative-based eye disease as measured by visual acuity. We compared food systems and visual acuity across isolated Amazonian Kawymeno Waorani hunter-gatherers and neighboring Kichwa subsistence agrarians, using dietary surveys, dietary pattern observation, and Snellen Illiterate E visual acuity examinations. Hunter-gatherers consumed more food species (130 vs. 63) and more wild plants (80 vs. 4) including 76 wild fruits, thereby obtaining larger variety and quantity of phytochemicals than agrarians. Visual acuity was inversely related to age only in agrarians (r = −.846, P < .001). As hypothesized, when stratified by age (<40 and ≥ 40 years), Mann-Whitney U tests revealed that hunter-gatherers maintained high visual acuity throughout life, whereas agrarian visual acuity declined (P values < .001); visual acuity of younger participants was high across the board, however, did not differ between groups (P > .05). This unusual absence of juvenile-onset vision problems may be related to local, organic, whole food diets of subsistence food systems isolated from modern food production. Our results suggest that intake of a wider variety of plant foods supplying necessary phytochemicals for eye health may help maintain visual acuity and prevent degenerative eye conditions as humans age.
Alex’s Notes: Myopia, or “nearsightedness,” is the most common form of visual impairment in the world. Although adolescent myopia is viewed as benign and easily correctable (think glasses), adult-onset myopia has actually been linked to more severe pathologies such as glaucoma, retinal detachment, macular degeneration, cataract, and blindness. Similar to many other diseases, there is reason to believe that oxidative damage of the eye and retina reduces visual acuity.
Interestingly, myopia is largely nonexistent in hunter-gatherer tribes, but becomes rapidly evident in those foragers who transition to a more Western diet and lifestyle. And the environment has to play a central role, as populations from the same genetic background living in different global areas have major differences in the prevalence of myopia. For instance, nearly 23% of Latino immigrants born in the United States reported having myopia compared to 14% born elsewhere.
The interplay with diet also becomes evident when we consider that humans foraged for wild food for more than 99% of our existence. There can be no doubt that the substantial shift to a Western diet has provoked greater occurrence of myopia and other chronic diseases, one reason being that phytochemicals are incredibly beneficial to eye health. Thus, the current study investigated the food system and visual acuity in an isolated hunter-gather tribe in Amazonian Ecuador and compared them with a neighboring remote agriculture community.
In 1979, the National Institutes of Health sponsored a medical study of isolated Amazonian Waorani foragers who had recently come into peaceful contact with the outside world.
These were the subjects of the current study. Previous work with the tribe showed that only a few percent suffered from any chronic diseases associated with the aging process, thus making the Kawymeno Waorani a promising group to investigate the underlying reasons for better eye health in foragers. They are a band of 121 individuals believed to descend from a pre–stone age culture that has not experienced agriculture, and their language shares no words with other languages.
The neighboring isolated Yumbo Kichwa was the comparison group. This indigenous communal subsistence agrarian community of 312 individuals lived in the same geographical rainforest region but avoided the Kawymeno because of a violent reputation of the latter. They rely on their gardens, domesticated animals, and sporadic minimal access to Western foods.
The researchers participated in procuring, preparing, and consuming food with both indigenous groups during four stays of between 3-4 months to experience the food system firsthand in all seasons. They took pictures of all consumed foods (animal and plant) for cataloging, and excluded foods for use in the current study if they were not consumed more than once per week. Since standard dietary intake measurement tools would have been impractical, the researchers stuck to frequent daily observations to record diet, lifestyle, and health characteristics of both populations. However, surveys on dietary patterns and health, including frequency of food consumption, were administered using focus groups, and data from individual and family medical and dietary histories were collected. Finally, the Illiterate E chart version of the Snellen eye acuity test was used to measure vision in both groups.
Out of 193 combined food species cataloged across both food systems, only 8 foods were common to both the Kawymeno foragers and Kichwa agrarians.
In other words, essentially two distinct food systems existed in the same environment. As expected, the Kawymeno foraged all of their food (130 species) in the rainforest while the Kichwa cultivated all virtually all of their food (63 species). A comparison of the food systems is presented in the table below, and an impressive 55 additional fruits consumed by the Kawymeno were not included as they were consumed on the spot rather than being gathered for the tribe.
|# of food species||% of food system||# of food species||% of food system|
|Total food system species||130||100||63||100|
|Wild native food species||122||93.8||20||31.7|
|Cultivated plant species||0||0||33||52.4|
|Semicultivated plant species||8||6.2||0||0|
|Domesticated food species||0||0||4||6.3|
|Total (all types) fruit species in diet||80||62.5||28||43.1|
It is needless to say that the Kawymeno had far more food diversity than did the Kichwa. Notably, about one-third of the Kawymeno foods were animals, all of which were wild native species. In fact, whole bodies of monkeys and/or peccary were eaten daily year-round by the entire tribe, considered a staple food, and even 6-month old infants were consuming their bone marrow. In both groups, low-alcohol beverages fermented with saliva are the staple drink. While the Kawymeno rotate through four different fruits and the roots of the cassava plant as the base for the drink, the Kichwa relied on the cassava roots year-round.
Fortunately, birthdates were provided for all Kichwa and Kawymeno participants (thank you Ecuadorian Ministry of Education data)
This allowed for stratification of the visual acuity results by age. Although there were no differences in vision between the groups in persons younger than 40 years, visual acuity declined with age in the Kichwa group only. Moreover, this could not be owed to near-visual work such as reading since neither group read or had access to TV, computers, etc. The Kawymeno tribesmen maintained 20/20 vision from youth to age 70+. It is unfortunate that the researchers did not also collect data on other eye diseases, but they do note that cataracts and growths were observed in some elderly Kichwa but were completely absent in the Kawymeno regardless of age.
|Right eye||Left eye||Right eye||Left eye|
|Younger: <40 y||83||82||83||84|
|Older: 40+ y||82||82||48||46|
20/20 = 85, 20/25 = 80, 20/30 = 76, 20/40 = 70, 20/50 = 65,
20/60 = 61, 20/70 = 58, 20/80 = 55, 20/100 = 50, 20/200 = 35
This is in stark contrast to the current study where both indigenous communities had absolutely zero cases of ocular disease in those aged under 40-years.Intensive near visual work related to regular schoolwork is often suggested as a cause of declining visual acuity and diagnosis of myopia in adolescents, which may very well hold some truth. Although, other studies have found that myopia is rare in children living in very isolated environments who engaged in prolonged near visual activities in school.
Interestingly, another cause of myopia has been suggested to be a lack of sunlight.Reduced exposure to bright natural light decreases the release of retinal dopamine, a known eye protectant. Then again, both groups in the current study spent their lifetimes outdoors and relied entirely on sunlight and firelight to see, yet only the Kichwa elders had visual decline.
Thus, the current study’s researchers,
“Propose that dietary transition does explain the difference in visual acuity observed between the Kawymeno Waorani and the Teresita Kichwa because potentially confounding lifestyle characteristics were similar for both groups… differences in diet are not due to either group’s consumption of refined starches or other modern processed foods. Both groups consumed a high-fiber diet of locally procured and organic animal and whole plant foods, and had virtually no access to modern foods throughout their life course, a dietary ideal rarely attained in populations enmeshed in the modern food system.”
It’s the phytochemicals
The protective effects are vast, and even randomized controlled trials have found improved visual acuity in persons suffering from myopia with the consumption of a phytochemical-rich bilberry extract. Our shift from a foraging-based food system to that of cultivation has greatly reduced the overall variety of food consumed in the human diet.Although the Kichwa use rainforest soil to plant gardens, they rarely eat wild rainforest plants as the foragers do, and appear to be largely locked out of the phytochemical cycle of the rainforest.
There are in fact 195,000 fruits in existence, and our consumption is limited to less than a few hundred worldwide. Add on top of that the lack of fruit and vegetable consumption by most persons and the overconsumption of the monotonous cereal grain staple-crops and it is no wonder every chronic disease to date has an oxidative stress component.