Fat — Humanity’s Evolutionary “Backup Fuel Tank”

Peter Lee

Fat is the body’s reserve energy—our biological equivalent of a car’s backup fuel tank.

Throughout hundreds of thousands of years of human evolution, food was never guaranteed. Most of human history was lived in cycles of feast and famine. Out of that harsh environment, the human body developed a remarkable ability: when food was plentiful, it stored excess energy as fat; when food ran out, that fat became the fuel that kept us alive. In extreme starvation, the fat in an adult’s body can sustain basic energy needs for about five days. In an age of scarcity and low productivity, this mechanism was nothing short of a survival miracle.

But in the modern world, the story has changed.

Today, food is abundant, and nutrition is rarely lacking. What once ensured survival has now become a hidden danger. Excess fat often leads to diseases such as diabetes. I still remember my childhood, when being overweight was considered a mark of prosperity and status. Back then, few children were fat—those who were seemed “fortunate.” One of my classmates was notably chubby, as was his entire family. His father, a senior official in a petrochemical company, was later diagnosed with diabetes. In those days, people called it a “rich man’s disease.” Among tens of thousands of employees, he was the only one with such an illness. It was clear even then: diabetes was a disease of abundance, closely tied to overnutrition and excessive fat.

Too much fat can also cause high blood pressure.

In a time when everyone eats well and regularly, the body no longer needs to store so much energy. It’s like installing a huge spare gas tank on a car that only drives short distances and can refuel anywhere—completely unnecessary, even harmful. Fat tissue requires a constant blood supply, and the more fat the body carries, the harder the heart must work to pump blood through it. This added strain increases blood pressure and, over time, damages the heart, brain, and kidneys.

Excess fat also contributes to fatty liver and high cholesterol.

Normally, fat is stored under the skin and around the abdomen. But when fat storage exceeds healthy limits, it begins to infiltrate organs and the bloodstream, forming fatty liver and elevating lipid levels. Worse still, the number of fat cells in the body is finite. Once they are full, additional glucose from food can no longer be stored in fat, liver, or muscle. Blood sugar remains high, and persistent elevation may eventually lead to diabetes.

In short, the human ability to store fat is the result of long evolutionary adaptation—a life-saving mechanism for our ancestors. Yet in the modern world, that very advantage can turn against us. With stable access to food and nutrition, humans no longer need to carry excess fat. Instead, maintaining a leaner body has become a new form of health insurance.

Less fat, more lightness—and a longer, healthier life.