 In this series, I'll look at the factors that lead to both overeating and satiety. What food components make us feel full? Why does more variety lead to eating more quantity? And what lifestyle approaches can we implement to increase the good food choices and reduce the bad ones? Keep watching to find out. Anyone can lose weight eating less food. Anyone can be starved thin. Starvation diets are rarely sustainable, though, since hunger pangs drive us to eat. We feel unsatisfied on low-calorie diets, unsatiated. We do have some level of voluntary control, but our deep-seated instinctual drives may win out in the end. For example, you can consciously hold your breath. Try it right now. How long can you go before your body's self-preservation mechanisms take over and overwhelm your deliberate intent not to breathe? Your body has your best interest at heart and is too smart to allow you to suffocate yourself or starve yourself for that matter. If our body was really that smart, though, how could it let us become obese? Why doesn't our body realize when we're way too fat and allow us the leeway to slim down? Maybe our body is actually very aware and actively trying to help, but we're somehow undermining those efforts. How could we test this theory to see if that's true? So many variables go into choosing what we eat and how much. There are psychological, social, cultural, and aesthetic factors. To strip all that away and stick just to the physiological, Columbia University researchers designed a series of famous experiments using a food dispensing device. The term food is used very loosely here. Their feeding machine was a tube hooked up to a pump that delivered a mouthful of bland liquid formula every time you pushed a button. Research subjects were instructed to eat as much or as little as they wanted at any time. In this way, eating was reduced to just a rudimentary hunger drive without the usual trappings of sociability, meal ceremony, and the pleasures of the palate. How much would people be driven to eat? Put a normal weight person in this scenario and something remarkable happens. Day after day, week after week, with nothing more than their hunger to guide them, they eat exactly as much as they need, perfectly maintaining their weight. They needed about 3,000 calories a day, and that's just how much they unknowingly gave themselves. Their body just intuitively seemed to know how many times to press that button. Put an obese person in that same scenario and something even more remarkable happens. Driven by hunger alone, with the enjoyment of eating stripped away, they wildly undershoot, giving themselves a mere 275 calories a day total. They could eat as much as they wanted, but they just weren't hungry. It's as if their body knew how massively overweight they were, so it dialed down their natural hunger drive to almost nothing. One subject started out at 400 pounds and steadily lost weight. After 252 days sipping the bland liquid, he lost 200 pounds. This groundbreaking discovery was initially interpreted to mean that obesity is not caused by some sort of metabolic disturbance driving people to overeat. In fact, the study suggested quite the opposite. Instead, overeating appeared to be a function of the meaning people attached to food beyond its use as fuel, whether as a source of pleasure or perhaps relief from boredom or stress. In this way, obesity seemed more psychological than physical. Subsequent experiments with the feeding machine, though, flipped such conceptions on their head once again. If you take the lean study subjects and covertly double the calorie concentration of the formula, they unconsciously cut their consumption in half to continue to perfectly maintain their weight. Their body somehow detected the change in calorie load and sent signals to the brain to press the button half as often to compensate. Amazing! Do the same with obese persons, though, and nothing changes. They continue to drastically under eat just as much as before. Their body seems incapable of detecting or reacting to the changing calorie load, suggesting a physiological inability to regulate intake. Might the brains of obese persons somehow be insensitive to internal satiety signals? We don't know if it's cause or effect. Maybe that's why they're obese in the first place, or maybe the body knows how obese it is and is shutting down the hunger drive regardless of the calorie concentration. Indeed, the obese subjects continue to steadily lose weight eating out of the machine regardless of the calorie concentration of the food being dispensed. It would be interesting to see if they regain the ability to respond to changing calorie intake once they reach their ideal weight, regardless. What can we apply from these remarkable studies to facilitate weight loss out in the real world? We'll explore just that question next.