There were a group of medical professionals (from Europe and America) that studied a variety of native populations from around the world - who noticed that they were virtually free from chronic diseases that were plaguing the west.

Multifaceted

Explanation:

There are a number of reasons that a native population might not be affected by diseases that plague the West here is an outline:

Diet: The Western diet is has been notorious for being over processed and full of refined foods and too much sugar. Although, in recent years the healthy lifestyle movement has been taking off. Native populations also follow their own diet and most of the time it is free from additives and other harmful substances that make cause diseases.Lifestyle: Most Westerners live a sedentary lifestyle while other native populations are engaged in physical activity through out their life as a part of their daily living. Physical activity is key for a healthy body and healthy heart.Social Practises and cultural traditions: Social practises in the west almost always revolve the presence of food and lots of it. Over eating and having large amounts of food is not unheard of in these events and this is unlike many places in the world where food is consumed based on need and availability. Isolation: Isolated populations are just not aware of the other types of food and social practices that are common in the West. This lack of information is sometimes what saves these populations from also engaging in consumption of a harmful lifestyleGenetics/Medical practices: This is a key factor in diseases and the passage of traits to offspring. Often times in the West the medicinal practices are enough to preserve life and allowed passage of disease traits to offspring, in some native populations these genes are filtered out of the gene pool and disease resistant traits are passes along.

In conclusion, it is difficult to pinpoint a single factor that can influence disease prevalence in a specific population as the causes are numerous.