How Diets and Dying Related to Demographics

When we seek to understand consequences of our actions and the hidden complexity that underlies them we can make better decisions. One set of decisions that everyone participates in throughout life is choice of diet. The impact of what we consume on a daily basis is often only felt many years later — and can be an accident of birth.

Life expectancy has increased in most of the world over the last century due to many factors, a big one being lower infant and child mortality. Accounting for that and other factors, as the percentage of a population that is “old” grows larger, some populations have a natural advantage in the way they age. 

Some of this advantage can be attributed to dietary traditions that were adopted before a significant percentage of the population was older (65+).Food safety, antibiotics, a decline in infectious diseases, and improved medical care all offer explanations as to why people live longer. Dramatic reductions in infant and child mortality also account for a large part of the increased average life expectancy of the last century. There are also sudden downward shocks from diseases throughout history. For example, the  lowered life expectancy in the US by 12 years in 1918 (a bigger impact than WWI). In countries including Botswana, Zimbabwe, and South Africa, where AIDS hit significant parts of the population, you see a sharp decline a few decades ago and then an almost as sharp an increase in life expectancy above previous rates as the disease began to be understood, treated, and prevented.

As a higher percentage of people live longer, we have started to notice more diseases that are caused by lifestyle, for example through dietary customs — customs that were at least partly due to a group’s local environment and traditions. The interesting thing to note is that in the past, say 100 years ago and earlier, many of these “modern” diseases did not impact as many people simply because a smaller fraction of the population lived long enough.

That is, there are some diseases, like AIDS, that can harm or kill at any age. Then there are other diseases which are in large part brought about by long-standing habits and which take years to present in their hosts, such as cardiovascular disease, some types of cancer, brain health, and type 2 diabetes.

This isn’t to say that people did not live long lives 100 years ago. This is the impression that you can get if you look only at life expectancy averages, which were so low 100 years ago (around 40 years of age) largely because of high infant and child mortality.

That, combined with a growing population that skewed on the younger side (more births and immigration), the fraction of the population that was older was quite small. Less than 5% of the US population was  in 1910. This figure was 13% by 2010. I’m calling that increase enough to notice the health effects present with age.That means that there are populations that are inherently disadvantaged because of the foods they have historically eaten and continue to eat to this day. The disadvantages are only noticed once enough of the population lives long enough for the dietary effects to be felt. (In this post I’m ignoring the impact of the food industry creating new foods, but will return to that issue in the future.) Similarly, there are other populations whose customary diets provide a natural health advantage. One such example is the Mediterranean diet.According to a recent study announced last week, adhering to a Mediterranean diet has been connected to larger brain volume in older adults (see the  for more detail).

“After adjusting for age, sex, intracranial volume, education, energy intake, smoking, physical activity, and body mass index, a higher diet quality score was tied larger total brain volume, gray matter volume, white matter volume, and hippocampal volume.” from 

The Mediterranean diet has also been shown to have a protective  effect  and  which tend to  affect older adults.

Whether you adhered to a Mediterranean diet throughout your life is largely an accident of birth, in terms of location, culture, and time. If you live in a place where foods in the Mediterranean diet are not commonly found, or if your culture prefers other foods, you may not experience the health benefits mentioned above — regardless of your intent to live a healthy life. And this difference was probably not noticeable when a small part of the overall population lived to old age.

The “,” conducted in the 1980s across , where local cuisine had been stable for generations, showed a connection between diet and type of cancer (if any) that afflicted the population. This was a massive research endeavor conducted in collaboration across the government of China, Cornell University, and Oxford, and which came to support plant-based diets for health. Again, the life expectancy of the Chinese populations studied had already increased due to other factors.  However, it was observed that people in certain regions of China were living longer and experienced less cancer than others, in large part due to their local dietary traditions established generations earlier.

And after the study, as China became richer and more global, and as more  began to be adopted (as Western foods became more sought after out of changing tastes and the presumed status of these foods), different diseases became prevalent, such as type 2 diabetes.Heart disease and cancer are among the top causes of death worldwide. Again, part of the reason is that other causes of death (infant mortality, so high in the past) are now so low. Heart disease and cancer are now the top two causes of death in both the US and China. We can see how an accident of culture and history led certain populations to benefit over others as a larger percentage of the population lived to older age.Our lives are packed with examples of unintended consequences like this one. Most have yet to be recognized or understood.

Previously published as on the .