Categories
Book Summaries health

Evolutionary Medicine (The Story of the Human Body)

The emerging and important new field of evolutionary medicine proposes that we have created an environment that is not well matched for our bodies.

While farming led to more food and modern sanitation and medicine led to less infant mortality and increased longevity, there have been many cultural changes that have changed the interactions between our genes and environments in detrimental ways. These diseases are mismatch diseases, defined as diseases that result from our Paleolithic bodies being poorly adapted to modern behaviors.

We don’t hear of scurvy today because it is easily preventable, even among people who don’t eat fresh fruit, by adding vitamin C to processed foods. Scurvy is a mismatch disease of the past. Consider cavities, which are the work of bacteria that stick to teeth in a thin film of plaque. Most of your mouth bacteria are harmless, but some species create problems when they feed off sugars, releasing acids that dissolve the underlying tooth, creating a pit.

If you don’t treat it, a cavity can expand worm its way deep into the tooth, causing tremendous pain and serious infection. Humans have little defense against these cavity causing microbes, other than saliva, perhaps because we did not evolve to eat so much starch and sugar.

Apes don’t have a lot of cavities, and hunter-gatherers only rarely did. Ever since farming, most of the world has been dependent on cereals and grains for most of their calories, making a cavity-preventing diet almost impossible. Cavities are the price we pay for cheap calories.

Cursed is the ground for your sake; in toil you shall eat of it all the days of your life. Both thorns and thistles it shall bring forth for you, and you shall eat the herb of the field. In the sweat of your face you shall eat bread till you return to the ground, for out of it you were taken; for dust you are, and to dust you shall return. (Genesis 3:17–19, King James Bible)

It is hard to read God’s verdict without seeing it as an allegory for the first cause of the mismatch: the end of the hunter-gatherer lifestyle. Since then, which began six hundred generations ago, humans have had to toil miserably as farmers, and grow their daily bread rather than pluck luscious fruits for the taking. According to Jared Diamond, farming was the worst mistake in history.

Despite having more food and more children than hunter-gatherers, farmers work harder and eat a lower-quality diet (less diverse foods) and more often face starvation, because of floods, drought, and other disasters. They also live in more populous places, where infectious disease is more common, as well as social stress.  

They are more susceptible to diseases such as scurvy (from insufficient vitamin C), pellagra (from insufficient vitamin B, beriberi (from insufficient vitamin B1) , goiter (from insufficient iodine), and anemia (from insufficient iron).

Pandemics

The great influenza epidemic of 1918 at the end of World War I killed between forty and fifty million people, three times more than the number of civilians and soldiers who died in the war itself.

The pandemic was especially lethal among healthy young adults because they had naïve immune systems with less antibodies to influenza, making them more susceptible to pneumonia (the actual cause of death).

There are more than one hundred infectious mismatch diseases that were caused by the origin of agriculture. Fortunately, in the last few generations modern medicine
and public health have made great progress in preventing and combating many of these diseases. For the first time in millennia, people in the developed world rarely worry about epidemics. But this complacency could be misguided.

Despite the many new technologies that help us avert, track, and treat infectious diseases, human population are denser than ever, keeping us vulnerable to new infectious epidemics.

Sleep

There are many reasons why we sleep differently than we used to. One is that the Industrial Revolution transformed time, by giving us bright lights, digital entertainment, and other ways to stimulate us beyond our normal bedtime hour. For the first time in history, most people can stay up late, making sleep deprivation worse. And people today suffer from insomnia because of more stress (a mix of physical and psychological factors), such as too much alcohol, bad diet, no exercise, anxiety, depression, and various worries.

It is possible that the unusual, stimulus-free environments makes sleeping more difficult. When you sleep, your body goes through several stages of light sleep, and you become less aware of outside stimuli as you enter a deep stage sleep where you are unaware of the external world. This has been an adaptation to avoid falling asleep with lions around.

Insomnia may occur because of too much isolation. We don’t hear evolutionary normal sounds such as the hearth crackling and hyenas barking from a distance, reassuring subconscious parts of the brain that everything is fine.

Regardless of the cause, we sleep less well than we used to. At least 10 percent of the population in developed countries regularly experience insomnia. Lack of sleep rarely kills you, but too much sleep deprivation will prevent your brain from working properly and eats away at your health. Your body produces more stress hormones like cortisol instead of a growth hormone that promotes cell repair. Sleep-deprived people also crave more sugary foods.

Sugar

Glucose is the essential sugar that makes up starch. Table sugar (sucrose) and milk sugar (lactose) are both made up of 50 percent glucose. You need enough glucose in your blood to prevent cells from dying (especially in your brain), but too much glucose is toxic to body tissues. Your brain and pancreas stabilize blood glucose levels by regulating levels of the hormone insulin. Insulin is produced by the pancreas and sent into the bloodstream when blood sugar levels go up. Insulin’s main function is to keep glucose level from getting too high. The most important thing to know is that when glucose levels rise after a meal, your body’s immediate goal is to get those levels down quickly, causing the excess glucose that you cannot use quickly to be stored as fat.

Fructose is another kind of sugar, and like sucrose and lactose, can be found in cake. Fructose is also present in fruit and honey, as well as table sugar. But unlike glucose, which can be burned by cells throughout your body, fructose is almost completely metabolized by the liver. Yet the liver can only burn so much fructose at once, so it converts excess fructose into fat, which either is stored in the liver or released into the bloodstream. Both paths cause problems.

Stress

A little stress is good, but chronic stress is a problem as it elevates cortisol levels for a long time. Too much cortisol is bad for many reasons, including promoting obesity. Cortisol causes you to release glucose and to crave calorie-rich food (why stress makes you crave comfort food). Both responses elevate insulin levels, which promote fat storage, particularly in visceral fat, which is four times more sensitive to cortisol than subcutaneous fat.

It’s worse than that, constantly high levels of insulin affect the brain by cutting off its response to leptin, a hormone which fat cells secrete to signal satiety. The stressed brain thinks you are starving, while at the same time activating other reflexes to make you less active. As long as the environmental causes of stress remain (job, poverty, commuting), you keep secreting too much cortisol, which leads to too much insulin, which makes you hungrier and less active.

Another vicious cycle is sleep deprivation, which is caused by high stress, hence high cortisol levels, which then increase cortisol levels. Insufficient sleep elevates ghrelin levels, another hormone. This “hunger hormone” is produced by your body to and stimulates appetite. People who sleep less have higher ghrelin levels and more likely to be overweight.

Apparently, we are not adapted to cope with relentless stress and sleep deprivation. We were also never adapted to be physically inactive. But exercise does not make you lose weight, but helps you keep the weight off. Physical activity increases the respone of muscle cells but not fat cells to insulin, causing fat uptake in your muscles rather than your belly. Physical activity also increases the number of mitochondria that burn fat and sugar. These and other changes in metabolism explain why active people can eat so much without getting fat.

Diabetes

Diabetes is a group of diseases, all characterized by the inability to create enough insulin. Type 1 diabetes, usually in children, occurs when the immune system kills the cells in the pancreas that make insulin.

The most common form is Type 2 diabetes. It is an example of a formerly rare mismatch disease associated with metabolic syndrome and is now one of the fastest growing diseases in the world.

Generally good diet advice is to stay away from unnatural trans fats, they are poison. Unsaturated fats were found in hunter-gatherers, including plenty of Omega 3.

"Silence is the best expression of scorn" - G.B. Shaw

This site uses Akismet to reduce spam. Learn how your comment data is processed.