External Forces Trump Inner Balance

You may be thinking if your body is so good at defending your set point, how did your set point become too high? Ultimately, your behavior—how you respond to the environment—trumps your physiology, or your body’s inner workings. Eating is complex behavior that is affected by many different factors, including genetics. How food tastes, how hungry we feel, and even how we respond to social cues around food (for example, whether we eat more at a party or while alone) are all affected by our genes. And these genetic differences affect how we respond to our environment. Over the past few decades, changes in our society have altered our environment dramatically. Oversized portions of high-calorie (and often inexpensive) foods are readily available, day and night. And modern conveniences—everything from electric toothbrushes to leaf blowers to cars—mean we don’t have as many opportunities to exercise. These and other factors, which are detailed in the next chapter, are the driving forces behind our rising set points.

On a fundamental level, we eat to survive. Leptin and other hormones regulate this unconscious drive. But we also have a conscious desire to eat, which is clearly affected by the smell, taste, and appearance of foods. Your emotional state also comes into play. Some people eat more (or less) when they’re upset, angry, or depressed (For more on breaking these patterns, see Chapter 9). We also eat out of habit, simply because it’s time for lunch (or a snack or dinner) or because people around us are eating. As in most cultures, Americans often plan their work and social schedules around eating rituals.

Source: George L. Blackburn, M.D., Ph.D., "Break Through Your Set Point: How to Finally Lose the Weight You Want and Keep It Off," 2008

The Vermont Prison Overfeeding Study

Whereas the Keys study explored the body’s response to a minimal number of calories, another intriguing study looked at the opposite end of the spectrum: calorie overload. In 1964, researchers at the Vermont College of Medicine asked volunteers to gain 15% to 25% of their body weight in less than three months.

The impetus for this study was to better understand exactly what happens to the body during weight gain. For instance, do fat cells increase in number or simply grow larger? At first, the scientists sought volunteers from a usually reliable source of guinea pigs: graduate and medical students at the college. But the study design, which required the volunteers to eat four large meals a day at the nutrition lab, proved far too time-consuming for busy students. So the researchers turned to a more captive crowd: inmates at the Vermont State Prison. They hired a cook to prepare the meals and served the food on china plates instead of tin. The prisoner’s ample diets included standard American fare: cereal, eggs, and toast for breakfast, sandwiches for lunch, and dinners of meat, potatoes, and vegetables. The fourth meal, which the men ate just before bedtime, was similar to breakfast.

The volunteers started out at normal weights, which ranged from about 135 to 185 pounds. During the ten-week-long study, the men managed to gain between 15% and 25% of their body weight, which amounted to an average of nearly 36 pounds. To do so, they had to eat 8,000 to 10,000 calories a day—more than three times the normal number of calories they would have needed to maintain their weight. The weight changes were largely due to gains in body fat. By taking small samples of fat from the men’s bellies, thighs, and arms before and after the overfeeding, the researchers demonstrated that this excess fat didn’t create new fat cells but rather expanded the existing ones.

This study and similar ones on the prisoners revealed other interesting phenomena related to body weight and the set point. Researchers found that the prisoner’s metabolic rates went into overdrive after the overfeeding period. These changes provide further evidence of the body’s drive to restore balance and return to its set point. When the experiment ended and the men went back to eating regular amounts of food, they lost weight quite quickly—not just because they were eating less but because their metabolic rates were still racing. Note that the prisoners did not remain at the new, higher weights for very long, so they did not reset their set points to new, higher levels. That contrasts with people who have been overweight for long periods of time.

The rapid weight loss these prisoners experienced is the mirror image of what happens when overweight people try to lose weight. If your set point is too high and you try to lose weight quickly, your body will fight to defend that weight and slow down your metabolism. But if your set point is within a normal range, your metabolism will speed up when you gain weight quickly.

In recent years, many studies have reaffirmed the observations from these historic reports. One pivotal 1995 study, by Jules Hirsch and colleagues at the Rockefeller University in New York City, used sophisticated techniques to carefully measure the metabolic rates of forty-one obese and nonobese volunteers who followed strict diets that caused them to either lose or gain 10% of their body weight. The researchers found that when people gained 10% of their usual weight, their bodies focused less on conserving energy and more on wasting it. But when people lost more than 10% of their usual weight, the opposite occurred: their bodies fought to save energy rather than expend it. This explains why it’s so difficult to lose more than 10% of your weight at a time.

So no matter where you start (overweight, thin, or somewhere in between) and no matter how you manipulate your diet (eating too much or too little), your metabolic rate will automatically adjust in an effort to keep you at the same set point.

Source: George L. Blackburn, M.D., Ph.D., "Break Through Your Set Point: How to Finally Lose the Weight You Want and Keep It Off," 2008

The Minnesota Starvation Study

Just a few years before the Framingham study began, a very different type of experiment was already underway in Minnesota, led by Ancel Keys. Dr. Keys is known for his pioneering work on the link between saturated fat and heart disease and for the development of K-rations, the balanced, portable meals given to soldiers during World War II. But his study involving a group of thirty-six conscientious objectors who volunteered to starve for the sake of science ranks as his most intriguing yet controversial work. Today, ethical regulations would never allow this type of study to take place.

The purpose of the study was to understand the physical and mental effects of starvation, anticipating the need to learn the best ways to re-feed people who had experienced extreme starvation (namely, civilians throughout Europe after World War II). The men endured six months of semistarvation, eating a diet similar to that in war-torn Europe—lots of potatoes and turnips and very little meat or dairy products. During the study, the men had to continue exercising, walking at least 22 miles a week, or about 3 miles a day. They were rationed about 1,600 calories per day—approximately three quarters of what these healthy young men needed to stay at their previously normal weight levels.

The men lost an average of about 25% of their body weight over six months, which caused them to resemble the concentration camp survivors they were hoping to help. They became sluggish, uncoordinated, depressed, and irritable. Keys documented the study in a two-volume tome, The Biology of Human Starvation, which includes this description penned by one volunteer:

I’m hungry. I’m always hungry—not the hunger that comes when you miss lunch but a continual cry from the body for food. At times I can almost forget about it but there is nothing that can hold my interest for long.

These feelings may be familiar to veteran dieters who’ve tried very low-calorie diets. Even among people who are overweight or obese (unlike these normal-weight volunteers), the very same mechanisms kick in during the self-imposed starvation of a diet. Faced with the physical and emotional strain, the body fights back to stay alive. Keys calculated that the men’s metabolic rates had decreased by about 40% by the end of the starvation period. One volunteer said it was as if his "body flame [was] burning as low as possible to conserve precious fuel and still maintain [the] life process."

After six months of starvation, the men entered a rehabilitation phase, during which they gradually received increasing amounts of food over a three-month period. Perhaps not surprisingly, the men’s response to this relative abundance provoked some unusual behaviors. Some ate until they vomited and then asked for more. Others ate until they weren’t physically capable of eating another bite of food, yet they still claimed they were hungry. Again, these behaviors may sound familiar to people who’ve tried so-called crash diets designed for rapid weight loss.

The take-home lesson is that it’s extremely challenging to try to lose a lot of weight over a short time period. Your body will rebel against these efforts, helping you regain the weight you’ve lost and possibly triggering strange (and potentially unhealthy) eating behaviors.

Source: George L. Blackburn, M.D., Ph.D., "Break Through Your Set Point: How to Finally Lose the Weight You Want and Keep It Off," 2008

The Framingham Heart Study

One line of evidence comes from people involved in the Framingham Heart Study, which dates back to the 1940s. Back then, very little was known about why people had heart attacks. This landmark study, which continues to this day, sought to answer that question. In 1948, researchers recruited more than fifty-two hundred men and women between the ages of 30 and 62 who were living in the Boston suburb of Framingham, Massachusetts. They recorded their height, weight, family health history, and gave them a physical exam every other year.

Over the years, scientists began collecting more data from the participants, such as measuring their blood pressure and cholesterol levels, and asking them about their eating, exercise, and smoking habits. In 1971, the Offspring Study, which includes the children (and their spouses) of the original group, was launched. And researchers began recruiting the third generation in 2002. Among the most important discoveries from the study was that cigarette smoking and obesity increase the risk of heart disease, and physical activity could lower that risk.

Researchers also found that over about a thirty-year period, the average participant gained about 20 pounds. This typical, slow gain is healthy and normal. The number of calories these participants ate balanced the number of calories they burned within a tiny percent during those years. If you figure that the average person eats about one million calories per year and you calculate the energy cost of those 20 pounds (that is, how many extra calories would a person have to eat each day, on average), it comes out to about 10 additional calories per day. That’s less than The amount of calories in a single jelly bean! The body’s internal control system is very is precise.

Source: George L. Blackburn, M.D., Ph.D., "Break Through Your Set Point: How to Finally Lose the Weight You Want and Keep It Off," 2008

Obesity as a Metabolic Disease

The reason weight-loss medications can’t provide any real results is that we have a complex, overlapping system of checks and balances that help "defend" our body-weight set point. Many different genes contribute to your body weight, and thus it’s impossible to manipulate it by focusing on just one hormone (or other substance). Others will jump in to compensate. The brief explanation of leptin and the other major players in this defensive strategy barely skims the surface of this intricate system. The take-home message is that these factors are beyond your conscious control. Our broader understanding of these factors has dramatically changed the framework of how we view the problem of weight gain and obesity. Instead of thinking of obesity as the consequence of a lack of restraint or willpower, it’s now increasingly recognized as a disease that results from a breakdown in the body’s normal system of checks and balances.

Source: George L. Blackburn, M.D., Ph.D., "Break Through Your Set Point: How to Finally Lose the Weight You Want and Keep It Off," 2008

WATCHING THE SET POINT AT WORK

Now that we know how the set point works, let’s step back and take a look at some of the other evidence in support of the set point theory. These observations include both short- and long-term studies and anecdotes from people in a variety of different settings.

The Framingham Heart Study

The Minnesota Starvation Study

The Vermont Prison Overfeeding Study

Movie Stars

External Forces Trump Inner Balance

Source: George L. Blackburn, M.D., Ph.D., "Break Through Your Set Point: How to Finally Lose the Weight You Want and Keep It Off," 2008

The Sensing Stomach

The stomach communicates with the brain through the ANS, and the nerve of interest to our story is the vagus nerve (see illustration). In Latin, vagus means "wandering," an accurate description of how this vitally important nerve travels from the brain to the stomach. When filled with food or liquid, the stomach’s stretch receptors send a message via the vagus nerve to the brain that says, "I’m full!" Have you ever noticed that eating a large, heavy meal can cause you to perspire? That’s the vagus nerve working overtime. As discussed, the autonomic nervous system prepares the body for fight or flight by raising your heart rate, increasing your blood pressure, and causing you to sweat. So by eating too much, you’ve made your body ready for fight or flight, even though you’re just sitting at a table eating dinner!

Not surprisingly, most weight-loss aids (in addition to surgeries) focus on fooling the body’s natural tendency to hold on to weight, mostly by manipulating levels of brain chemicals. Back in the 1950s and 1960s, dieters took amphetamines, which speed up metabolism by boosting the activity of the sympathetic nervous system. But they’re also addictive and have many unpleasant side effects, including paranoia and heart problems.

(For more information on weight-loss medications, see the Appendix).

Source: George L. Blackburn, M.D., Ph.D., "Break Through Your Set Point: How to Finally Lose the Weight You Want and Keep It Off," 2008