Why We Eat (Too Much)

Why is it so hard to lose weight and keep it off? The answer lies in understanding your body's ancient wisdom and metabolic systems, shaped by millions of years of evolution.

1. The First Spark of Life and Energy

Four billion years ago, single-celled bacteria overcame their energy limitations by forming a symbiotic relationship, a pivotal moment in life’s evolution. Early bacteria struggled to generate enough energy because they couldn’t process oxygen. A high-energy counterpart emerged, capable of utilizing oxygen to produce vast amounts of energy on an industrial scale. By engulfing these powerhouses—precursors of mitochondria—older bacteria expanded their energy capacities and thrived.

This symbiosis set the stage for complex life. Mitochondria, still present in all living organisms, are now essential for converting food into the energy required for survival. Without these microscopic engines, human life as we know it wouldn’t exist.

Examples

• Early anaerobic bacteria maxed out their energy potential until the aerobic variety appeared.
• Symbiosis between two types of bacteria led to mitochondria, existing in every cell today.
• These tiny units power plants, humans, and every other life form on Earth.

2. Bigger Brains at a Cost

Humans are energy-intensive machines, with our brains consuming 25 percent of our daily calories. What allowed our ancestors to afford such energy-expensive organs? Their solution was reallocating their energy budgets—mainly by developing shorter guts than other primates, conserving energy for their brains.

Shorter gastrointestinal tracts became a tradeoff for humans, but it was made possible by their mastery of cooking. Cooked foods are predigested, requiring less physical effort to chew and break down in the gut. This freed energy to expand neural capacity, distinguishing early humans from their primate relatives.

Examples

• Gorillas, while similar in size, carry longer digestive systems compared to humans, accounting for energy differences.
• Cooking food—like roots and tubers—unlocked nutrients efficiently without relying on robust teeth and stomachs.
• The energy diverted to brain growth explains why humans are distinctively intelligent compared to other mammals.

3. Cooking Transformed Our Evolution

The use of fire wasn’t just about staying warm; it fundamentally reshaped humans—both culturally and biologically. By cooking their food, early Homo erectus made it easier to chew and digest, conserving energy and unlocking nutrients. Meat consumption further supported this evolutionary tradeoff, allowing the brain to prioritize growth over other physical traits.

Fire wasn’t just about survival—it was the first human technology. By relying on cooked meals, prehumans reduced the energy and time required for digestion. Over millennia, this innovation gave humans a biological and cultural edge over other species.

Examples

• Archaeological evidence in South African caves revealed that Homo erectus cooked food one million years ago.
• Cooked meals significantly improved the digestion of starchy vegetables and tough meats.
• Fire use led to smaller jaws, weaker teeth, and larger, energy-demanding brains in humans.

4. Negative Feedback Keeps Our Bodies Running

Our bodies operate like finely tuned systems, correcting imbalances to sustain equilibrium. When hydration levels deviate, sensors like the kidneys send chemical signals to regulate water intake and expulsion. A similar negative feedback system stabilizes our energy storage, preventing dangerous weight gains or losses by adjusting metabolism.

Hydration and metabolism are survival mechanisms that align with our biological needs. These systems prioritize balance, keeping vital functions like temperature, energy storage, and brain activity under control. Yet, modern lifestyles sometimes push these natural processes beyond their intended limits.

Examples

• Without prompt feedback from the kidneys, dehydration could lead to death.
• Reduced food intake triggers sensors in the hypothalamus, slowing metabolism to conserve energy.
• Overhydration disrupts electrolytes, demonstrating how negative feedback adjusts urine levels to mitigate danger.

5. Overeating Speeds Up Metabolism

Surprisingly, overeating doesn’t lead directly to runaway weight gain. Experiments have shown that consuming excess calories causes the body to burn energy faster to maintain homeostasis. This dynamic highlights our body’s defense systems against obesity.

Rather than storing unlimited energy, the body reacts to overeating by increasing metabolic rates. While this makes energy surplus difficult to sustain, our bodies are arguably adept at resisting weight gain—but only within limits.

Examples

• Ethan Sims’ 1976 study showed prisoners’ metabolic rates rose when overfed by up to 10,000 calories daily.
• The Mayo Clinic confirmed that overeating consistently results in around a 10 percent increase in metabolism.
• Stored energy buffers, like fat reserves, are carefully controlled by leptin signals to prevent excess storage.

6. Starving Yourself Backfires

Calorie restriction isn’t the key to weight loss. Prolonged dieting slows metabolism, as the body responds to perceived famine by hoarding energy. This metabolic brake results in sluggish energy expenditure, making weight regain all but inevitable when normal diets resume.

The physiological trauma of semi-starvation studies revealed significant drops in metabolic activity, leading to muscle loss and severe energy conservation. Once food is abundant again, the body prioritizes fat storage to prepare for future deprivation. This adaptation explains why yo-yo dieting is both common and counterproductive.

Examples

• Ancel Keys’ 1944 experiment showed metabolism dropping by 50 percent in volunteers on semi-starvation diets.
• Subjects regained more weight than they originally lost due to altered metabolic responses.
• Even basic functions like body temperature and heart rate slowed under calorie restriction.

7. Fat Cells and Hormones Govern Weight

Our bodies rely on hormonal signals to regulate weight via fat storage and energy expenditure. Leptin, a hormone produced by fat cells, communicates with the brain to balance metabolism and hunger. These systems help our bodies manage energy efficiently.

When energy stores are abundant, leptin reduces appetite and increases metabolic rates. Conversely, when fat stores decline, leptin levels fall, triggering hunger and slowing metabolism. This intricate communication shows how fat cells are central to weight control.

Examples

• Researchers in 1994 showed leptin as the "sensor" for energy stored in fat cells.
• Elevated leptin levels prompt the hypothalamus to raise metabolism and suppress overeating.
• Declining leptin levels during calorie restriction boost hunger cues and slow energy use.

8. The Modern Food Landscape Wreaks Havoc

From vegetable oils high in omega-6 to excessive sugar, Western diets have overwhelmed our body’s finely tuned feedback systems. These changes, prompted by misguided dietary advice, disrupted natural hormonal signaling and led to widespread obesity.

Industrial vegetable oils dull the effectiveness of leptin, making it harder to regulate weight. Meanwhile, high-sugar diets wreak havoc on insulin production, causing spikes and dips in blood sugar levels that drive carb cravings.

Examples

• A 2016 study showed American diets consist of nearly 60 percent highly processed foods.
• Government recommendations in the 1980s demonized saturated fats, increasing omega-6 consumption.
• Excess sugar intake destabilizes blood sugar cycles, leading to hunger and poor impulse control.

9. Biology Clashes with Modernity

Our bodies evolved to prevent weight gain and balance energy use, but today’s food environment overrides those systems. Cheap, calorie-dense, sugar-loaded processed foods confuse the brain’s signals and disrupt metabolic processes once geared for survival.

Evolution designed us to value high-energy meals, but this instinct now clashes with the abundance of unhealthy food options. From sedentarism to marketing, modern life has undermined the very systems that once kept Homo sapiens healthy and strong.

Examples

• The human preference for sweet and fatty foods stems from survival instincts in scarcity.
• Ultra-processed snacks high in sugar and omega-6 block leptin’s ability to regulate hunger.
• Sedentary office lifestyles further reduce the body’s ability to burn excess energy.

Takeaways

1. Learn to decode food labels and avoid products high in sugar and omega-6 fats to help leptin function effectively and maintain long-term hormonal balance.
2. Stop obsessing over calorie restriction. Instead, focus on eating whole, nutrient-dense foods that naturally satisfy hunger and fuel your body.
3. Prioritize regular activity alongside healthy eating habits to enhance metabolic health without triggering conservation mechanisms.