The Tsimane people dwell in thatched huts in a remote corner of Bolivian jungle, and at dinner, the main meal sometimes consists of monkey - capuchins or howlers. Other days, a hog-nosed racoon, or with some luck and a gruelling all-day hunt, a man might take a peccary, a kind of wild pig. Some find piranha or catfish in local rivers. For side dishes, the Tsimane may gather wild fruits and nuts, or harvest small farm plots, where they grow rice, plantains and corn.
And according to a study published Friday in the Lancet, a peer-reviewed British medical journal, the Tsimane have the lowest rates of heart disease ever measured. Is their diet the secret?
In the United States and parts of Europe where heart disease is the leading cause of death, the news is expected to arouse widespread curiosity and a question: how do they do it?
The Tsimane ''have the lowest reported levels of coronary artery disease of any population recorded to date'', according to the paper written by a team of doctors and anthropologists.
The scientists estimated heart disease during examinations of 705 Tsimane, each of whom travelled about two days by boat and road to get to a clinic. There, they underwent sophisticated X-ray scans of their coronary arteries to determine the amount of calcium plaque, a measure of heart disease. On this basis, the Tsimane measured much healthier than any other people studied, including groups from the United States, Europe, Korea and Japan, according to researchers.
''If you think of the calcium plaque as a reasonable measure of arterial age, their arteries are 28 to 30 years younger than ours,'' said Randall Thompson, one of the authors and a cardiologist at St Luke's Mid America Heart Institute in Kansas City. ''Obviously the Tsimane are achieving something that we are not.''
Previous studies of remote groups have raised doubts about modern lifestyles. For example, a 1984 analysis found that members of the Luo tribe in Kenya who migrated to Nairobi had higher blood pressures than those who remained in the villages. Another, from the '60s, found that the Masai of East Africa had remarkably low levels of blood cholesterol, despite a diet dominated by meat and milk. The Inuit of Greenland also reportedly had low levels of blood cholesterol. And electrocardiograms of Kung Bushmen led researchers to say their study ''confirmed the impression ... that hypertension and ischaemic heart disease, two of the most important heart ailments in Western society, do not occur in the Bushman''.
The studies of the Tsimane began in 1999 when Michael Gurven, a University of California at Santa Barbara anthropologist, first visited, and a few years later, with colleagues, formed a project to study Tsimane lives and health. What distinguishes the Tsimane research is that rather than measure loose predictors of heart risk as the previous research had done, the scientists used computer-enhanced X-ray scans, known as CT, or computed tomography, to gauge how much plaque was clogging the arteries around the heart.
These calcium scores ''are the best predictors of heart disease,'' said Matthew Budoff, a UCLA cardiologist and expert in coronary calcium. ''It's a direct measure of atherosclerosis. It's literally measuring the disease in the artery.''
The prevalence of heart disease in the United States has inspired a galaxy of research efforts and by most accounts, the causes are manifold: smoking, diabetes, obesity, diet, stress and a lack of exercise are commonly blamed.
For example, a recent analysis of studies of 55,685 people published in the New England Journal of Medicine reported that among people genetically at a higher risk of heart disease, those who had a ''favourable lifestyle'' - that is, were not obese, did not smoke, exercised at least once a week and ate a sound diet - were about half as likely to experience heart disease.
The relative importance of each of those lifestyle factors is often a matter of fierce debate, however, and the differences over what constitutes a healthy diet is fraught with scientific disagreement and uncertainty. In recent decades, indeed, efforts to quantify a healthy level of dietary salt have metastasized into an epic feud.
''There's a consistency of data throughout the world that people who have low cholesterol, keep active, don't smoke, avoid obesity and maintain their blood pressure live a longer life,'' said Dennis Bier, a professor at Baylor College of Medicine and editor of the American Journal of Clinical Nutrition.
But he warned that figuring out how these factors contribute to health is difficult to know.