apply this reasoning to obesity. Reducing Calories In works only if Calories Out remains stable. What we find instead is that a sudden reduction of Calories In causes a similar reduction in Calories Out, and no weight is lost as the body balances its energy budget. Some historic experiments in calorie reduction have shown exactly this.
CALORIC REDUCTION: EXTREME EXPERIMENTS, UNEXPECTED RESULTS
EXPERIMENTALLY, IT’S EASY to study caloric reduction. We take some people, give them less to eat, watch them lose weight and live happily ever after. Bam. Case closed. Call the Nobel committee: Eat Less, Move More is the cure for obesity, and caloric reduction truly is the best way to lose weight.
Luckily for us, such studies have already been done.
A detailed study of total energy expenditure under conditions of reduced caloric intake was done in 1919 at the Carnegie Institute of Washington.5 Volunteers consumed “semi-starvation” diets of 1400 to 2100 calories per day, an amount calculated to be approximately 30 percent lower than their usual intake. (Many current weight-loss diets target very similar levels of caloric intake.) The question was whether total energy expenditure (Calories Out) decreases in response to caloric reduction (Calories In). What happened?
The participants experienced a whopping 30 percent decrease in total energy expenditure, from an initial caloric expenditure of roughly 3000 calories to approximately 1950 calories. Even nearly 100 years ago, it was clear that Calories Out is highly dependent on Calories In. A 30 percent reduction in caloric intake resulted in a nearly identical 30 percent reduction in caloric expenditure. The energy budget is balanced. The First Law of Thermodynamics is not broken.
Several decades later, in 1944 and 1945, Dr. Ancel Keys performed the most complete experiment of starvation ever done—the Minnesota Starvation Experiment, the details of which were published in 1950 in a two-volume publication entitled The Biology of Human Starvation.6 In the aftermath of World War II, millions of people were on the verge of starvation. Yet the physiologic effects of starvation were virtually unknown, having never been scientifically studied. The Minnesota study was an attempt to understand both the caloric-reduction and recovery phases of starvation. Improved knowledge would help guide Europe’s recovery from the brink. Indeed, as a result of this study, a relief-worker’s field manual was written detailing psychological aspects of starvation.7
Thirty-six young, healthy, normal men were selected with an average height of five foot ten inches (1.78 meters) and an average weight of 153 pounds (69.3 kilograms). For the first three months, subjects received a standard diet of 3200 calories per day. Over the next six months of semi-starvation, only 1570 calories were given to them. However, caloric intake was continually adjusted to reach a target total weight loss of 24 percent (compared to baseline), averaging 2.5 pounds (1.1 kilograms) per week. Some men eventually received less than 1000 calories per day. The foods given were high in carbohydrates, similar to those available in war-torn Europe at the time—potatoes, turnips, bread and macaroni. Meat and dairy products were rarely given. In addition, they walked 22 miles per week as exercise. Following this caloric-reduction phase, their calories were gradually increased over three months of rehabilitation. Expected caloric expenditure was 3009 calories per day.8
Even Dr. Keys himself was shocked by the difficulty of the experiment. The men experienced profound physical and psychological changes. Among the most consistent findings was the constant feeling of cold experienced by the participants. As one explained, “I’m cold. In July I walk downtown on a sunny day with a shirt and sweater to keep me warm. At night my well fed room mate, who isn’t in the experiment, sleeps on top of his sheets but I crawl under two blankets.”9
Resting metabolic rate dropped by 40 percent. Interestingly, this phenomenon is very similar to that of the previous study, which showed a drop of 30 percent. Measurement of the subjects’ strength showed a 21 percent decrease. Heart rate slowed considerably, from an average of fifty-five beats per minute to only thirty-five. Heart stroke volume decreased by 20 percent. Body temperature dropped to an average of 95.8°F.10 Physical endurance dropped by half. Blood pressure dropped. Men became extremely tired and dizzy. They lost hair and their nails grew brittle.
Psychologically, there were equally devastating effects. The men experienced a complete lack of interest in everything except for food, which became an object of intense fascination to them. Some hoarded cookbooks and utensils. They were plagued with constant, unyielding hunger. Some were unable to concentrate, and several withdrew from their university studies. There were several cases of frankly neurotic behavior.
Let’s reflect on what was happening here. Prior to the study, the subjects ate and also burned approximately 3000 calories per day. Then, suddenly, their caloric intake was reduced to approximately 1500 per day. All body functions that require energy experienced an immediate, across-the-board 30 percent to 40 percent reduction, which wrought complete havoc. Consider the following:
•Calories are needed to heat the body. Fewer calories were available, so body heat was reduced. Result: constant feeling of cold.
•Calories are needed for the heart to pump blood. Fewer calories were available, so the pump slowed down. Result: heart rate and stroke volume decreases.
•Calories are needed to maintain blood pressure. Fewer calories were available, so the body turned the pressure down. Result: blood pressure decreased.
•Calories are needed for brain function, as the brain is very metabolically active. Fewer calories were available, so cognition was reduced. Result: lethargy and inability to concentrate.
•Calories are needed to move the body. Fewer calories were available, so movement was reduced. Result: weakness during physical activity.
•Calories are needed to replace hair and nails. Fewer calories were available, so hair and nails were not replaced. Result: brittle nails and hair loss.
The body reacts in this way—by reducing energy expenditure—because the body is smart and doesn’t want to die. What would happen if the body continued to expend 3000 calories daily while taking in only 1500? Soon fat stores would be burned, then protein stores would be burned, and then you would die. Nice. The smart course of action for the body is to immediately reduce caloric expenditure to 1500 calories per day to restore balance. Caloric expenditure may even be adjusted a little lower (say, to 1400 calories per day), to create a margin of safety. This is exactly what the body does.
In other words, the body shuts down. In order to preserve itself, it implements across-the-board reductions in energy output. The crucial point to remember is that doing so ensures survival of the individual in a time of extreme stress. Yeah, you might feel lousy, but you’ll live to tell the tale. Reducing output is the smart thing for the body to do. Burning energy it does not have would quickly lead to death. The energy budget must be balanced.
Calories In and Calories Out are highly dependent variables.
With reflection, it should immediately be obvious that caloric expenditure must decrease. If we reduce daily calorie intake by 500 calories, we assume that 1 pound (0.45 kilograms) of fat per week is lost. Does that mean that in 200 weeks, we would lose 200 pounds (91 kilograms) and weigh zero pounds? Of course not. The body must, at some point, reduce its caloric expenditure to meet the lower caloric intake. It just so happens that this adaptation occurs almost immediately and persists long term. The men in the Minnesota Starvation Experiment should have lost 78 pounds (35.3 kilograms), but the actual weight lost was only 37 pounds (16.8 kilograms)—less than half of what was expected. More and more severe caloric restriction was required to continue losing weight. Sound familiar?
What happened to their weight
