The flexibility of human metabolism is an evolutionary adaptation, one that conferred longevity to individuals to withstand food shortages and thereby helped ensure the species' continued existence. In a relatively stable environment, survival of the individual depended on a combination of luck and beneficial genetic traits, but survival of a people relied on the traits alone. Only a catastrophic event could throw a species into instant turmoil. Natural disaster, a new, lethal disease or a more global phenomenon like an ice age might upend the order of daily existence. In those moments, a random genetic advantage, rather than a long-tested one, determined an individual's and even a species' fate. These monumental events were, in the past, always acts of nature. Never before have people been able to drastically change the environment enough to create our own cataclysm that directly challenges our built-in survival mechanisms. The unimaginable changes in food production and supply in recent decades has done exactly that. The world of feast and famine, deluge and drought no longer exists in the first world. Now, as if by a miracle of fate, we all live in a perpetual world of plenty. But our current good fortune is no stroke of luck at all; it's simply an advancement of civilization.
Since the start of the industrial revolution, human capacity and ingenuity have tackled one impossible dream after another: electricity, transportation, even space travel. One less celebrated triumph is in the agriculture and food industry. The impossible challenge was to feed an ever-increasing number of people. The explosion of the human population--recently surpassing seven billion and with no indication of slowing down--especially in the growing urban centers necessitated a grand revision of food production and distribution, at least in the prosperous first world countries. Agribusiness, large food conglomerates and national supermarket chains made feeding the growing population possible, and then some. America produces almost twice the needed per capita amount of food, measured in calories, the country needs. The application of efficient farming techniques, food manufacturing--largely from creative uses of corn--and innovation in food transport is a marvel of the past half-century. These industries, currently vilified for their complete disregard of the public health effects of their products, began with a more progressive motive, to supply affordable food to the masses, and have succeeded beyond anyone's wildest dreams. What is now commonplace in a supermarket--Chilean grapes, choice of any baked good and canned food that could feed a small army--was as unlikely as the fantasy world of 1984 only a few generations ago. Although the national debate over obesity has taken center stage, that's not a reason to ignore another achievement of industrialization.
Depressingly, the people enduring regular starvation--from sub-Saharan Africa to North Korea to those suffering from anorexia nervosa--have evolution on their side, not those who live in the land of plenty. The body has built-in mechanisms to survive long stretches with little food. Much as the electrical conduction system of the heart, the neural "wires" that produce each heartbeat, has several backup systems when the front line breaks down, digestion, metabolism and energy production can run on emergency as well. The eternally well-fed, if not overstuffed, have no such internal regulatory system to rely on. That's how a man-made life-changing event--limitless food supply--has overtaken our adaptive ability to cope. The premise that humans can override our instinctive reaction to food has proven largely to be false, as the sharp increase in childhood obesity and eating disorders can attest. Our internal food and weight regulatory system is thoroughly confused by the interminable excess food intake and availability. The physical effects in just a few decades, to both young and old, act like our own self-inflicted catastrophic event. A system that once ensured human survival now threatens our health and well-being. The easiest way to understand how the system has gone awry is through the adaptive, and maladaptive, ways our body reacts insulin.
Insulin is a hormone that regulates the transfer of energy from the blood supply to the rest of the human body. Food first needs to be digested in the stomach and then absorbed from the stomach and small intestines into the blood supply. After that, it's up to the endocrine system, primarily insulin, to distribute the energy to different parts of the body, to short-term storage--an easily accessible carbohydrate called glycogen--or to long-term storage, fat. In the normal ebb and flow of feast and famine, this regulatory system worked beautifully. The body monitored both energy needs and food intake, and the endocrine system released insulin to maximize the health and longevity of the body through lean and plentiful periods. Weight and metabolism, variables modulated by the endocrine system to maintain health, shifted accordingly. Most importantly, they are not end points but flexible components that fluctuate with the body's needs, not at one's will.
With the advent of limitless food supply, the well-honed system has gone awry, and the rise of childhood diabetes is a case in point. A generation ago, childhood diabetes, caused only by the inability to produce insulin, was to be differentiated from adult-onset diabetes, caused by insulin resistance-- slowed or limited reaction to the release of insulin--an effect of age, or more often weight gain. The public health problem of overweight children has made this nomenclature obsolete. Diabetes is now separated into type I, no insulin production, and type II, insulin resistance, and the unfathomable diagnosis of type II diabetes in children, with the same treatment and long term medical outcomes as in adults, including amputation and kidney failure, is now run of the mill.
What has condemned so many children to the early fate of an adult, debilitating disease is the world of plenty. Left to fend for themselves among the fast food chains, ever-present snacks and vending machines at school, children take in much more food than their bodies need. A child's metabolism no longer faces times of famine or drought, so, exposed to the inability of human metabolism to compensate for persistent, increased food intake, the inevitable cycle of weight gain and overeating continues. As in older adults, obesity, in those susceptible, triggers the onset of type II diabetes. Metabolism could rise, fullness could be triggered more quickly, hunger could wane, but the endocrine system doesn't work that way, for coping with a land of plenty never happened before. Nothing stops the overweight, diabetic child from continuing to eat. No such evolutionary adaptation exists.
The rise of eating disorders--as a general phenomenon, rather than the suffering of one individual--is a different but equally maladaptive response to a world of plenty. Although the ideal female form has, in previous times, been very thin, never before has the entirety of a population encountered this desired body shape and the world of plenty simultaneously. The push-pull of willful food restriction and limitless supply of any food imaginable has tested the human food regulatory mechanism and exposed its weaknesses. The response to starvation, namely slowed metabolism followed by obsessive hunger, is a powerful evolutionary adaptation and almost always wins. The end result, for the majority of dieters and people with eating disorders, is periods of overeating or binging. Repeated attempts to starve only strengthens these internal responses. Surprisingly, years of restricting food intake, even when interrupted by bouts of overrating, affects the body similarly to the overweight who have type II diabetes: their bodies become resistant to insulin. In this case, the body refuses to increase metabolism after years of starvation and instead puts extra food intake into deep storage. Metabolism, and therefore insulin effectiveness, rises only after an extended period of regular food intake. Becoming immune to insulin and storing extra food as fat seems to be the only default reaction to eating patterns outside the norm. In today's world of plenty, it is highly ineffective.