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Saturday is a relative slow day in my household, so it felt somewhat of a rebuke to read on the BBC that the Tsimané people have an ideal lifestyle, walking some 17,000 steps a day, as compared to the lethargic wealthy West, who aim for 10,000 daily steps but rarely take them.
Those of you who are too sunk in lassitude to read the news item will probably certainly not strain yourselves to click on the link to the Lancet article on which the item is based.
Let me save you time and effort by summarizing the main points:
The Tsiname people do not have clogged arteries.
17% of their diet is game including wild pig, tapir and capybara (the world’s largest rodent). 7% is freshwater fish including piranha and catfish. Most of the rest comes from family farms growing rice, maize, manioc root (like sweet potato) and plantains (similar to banana), topped up with foraged fruit and nuts
72% of calories come from carbohydrates compared with 52% in the US. 14% from fat compared with 34% in the US, Tsimane also consume much less saturated fat. Both Americans and Tsimane have 14% of calories from protein, but Tsimane have more lean meat.
Since it is the BBC, there must be a show of editorial balance, and this was achieved in a glancing fashion:
One idea is that intestinal worms – which dampen immune reactions – could be more common and this may help protect the heart.
Note that this is presented as just an idea, not an established fact.
Since it is a BBC story, every noble story has a moral at the end.
Prof Gurven said: “We need a more holistic approach to physical exercise rather than just at the weekend. Bicycle to work, take the stairs, write your story on a treadmill desk.”
Dr Thomas said: “To maintain health we need to be exercising much more than we do. The modern world is keeping us alive, but urbanisation and the specialisation of the labour force could be new risk factors [for an unhealthy heart]. They also live in small communities, life is very social and they maintain a positive outlook.”
Dr Gavin Sandercock, reader in clinical physiology (cardiology) at the University of Essex, said: “This is an excellent study with unique findings. The Tsimane get 72% of their energy from carbohydrates. The fact that they have the best indicators of cardiovascular health ever reported is the exact opposite to many recent suggestions that carbohydrates are unhealthy.”
Prof Naveed Sattar, from the University of Glasgow, said: “This is a beautiful real life study which reaffirms all we understand about preventing heart disease. Simply put, eating a healthy diet very low in saturated fat and full of unprocessed products, not smoking and being active life long, is associated with the lowest risk of having furring up of blood vessels.”
By this stage you may be reconsidering your plans for this Saturday, cancelling your lunch engagements and setting off on a long run, with some game hunting on the side. However, I am steeped in Anglo-Saxon skepticism, so I thought this uplifting tale was worth a few minutes of research.
My first thought was that clogged arteries are only one risk factor, and that one should take a more rounded view of the health of this tribe before coming to any conclusions. My next question was whether they had done any genetic research, since this was an obvious confounder, or better, a gateway into understanding the genetics of cardiac disorders. A third question, although not fully formulated, was “Worms, what sort of worms?”
A glance at https://en.wikipedia.org/wiki/Tsiman%C3%A9 gleans the following:
The average Tsimané woman has nine children in her lifetime. A study of 983 Tsimané women found that 70% were infected with the parasitic roundworm Ascaris lumbricoides, which is believed to have increased their fertility rate by suppressing their immune system, leading to two additional children over the course of a lifetime.
The parasite effect on fertility is one for Greg Cochran, who notes that parasite can sometimes alter host behaviour to their apparent advantage: https://westhunt.wordpress.com/2016/02/10/cat-ladies/
There is some epigenetic work on this tribe, but of more importance in my view is that there are some genetic differences, probably indicating that variants are under selection in response to a high infection environment.
Apologies for making you do all this energetic clicking, which can be exhausting, but here is a more detailed account of the tribe by one of the authors:
The key point, as I see it, is that the BBC is implying that you have much to learn from the Tsiname, without telling you a relevant fact:
Average life expectancy at birth was 43 years between 1950-89 and increased to about 50 during the period 1990-2002. Half the population is under 15 years of age.
Cannot write more because I have to drive to the supermarket.