Appetite is important. It is your body’s built-in mechanism for food intake regulation. Its job is to drive you to eat enough to meet your body’s energy and micronutrient needs, and no more. The appetite mechanism works very well under normal circumstances. Obviously, it never would have survived millions of years of evolutionary testing if it did not work to the benefit of our health. But our modern lifestyle does not constitute “normal circumstances” in relation to the environment in which most of our evolution took place. Consequently, our appetite cannot be entirely relied upon to ensure that we don’t overeat.
In recent years scientists have learned a lot about how the appetite mechanism works. Let’s take a look at five factors that are now known to influence appetite and how you can manipulate them to make your appetite more reliable.
Food In The Stomach
Most people know intuitively that feelings of fullness are generated from the stomach. When you eat, your stomach distends, or stretches. The distension of your stomach activates the appetite control switch in the hypothalamus of the brain, which tells you to stop eating and diminishes hunger until it is time to eat again. This is how your appetite switch is turned off. When food enters your stomach it stimulates the release of a protein called cholecystokinin, or CCK. When CCK is released, the first thing it does is to close down the valve from the stomach into the GI tract. This slows the movement of food from the stomach. The longer food stays in your stomach, the more full you feel. Because of its effects, CCK is sometimes referred to as the “feel-full” protein.
The unique properties of CCK were discovered almost 40 years ago when researchers at Cornell and Columbia universities demonstrated that injecting CCK into humans reduced appetite up to 20%.
The appetite control switch was designed to work best with the natural foods that humans ate exclusively thousands of years ago. Many of the processed foods we eat today are far more calorically dense than those natural foods, meaning they contain more calories in less space. Unfortunately, these processed foods enable us to eat more calories than our bodies need before the appetite control switch gets activated. It is not unusual for an individual to eat a fast food meal of 1,000 calories in less than 10 minutes. But it takes more than 10 minutes for food to stimulate enough CCK to make you stop eating. Thus, when you eat high-calorie processed foods, you can easily overeat before CCK–your body’s natural gastric pacemaker–begins to work and you feel full.
Your appetite mechanism will work better if you base your diet in foods with lower energy density: namely, fruits, vegetables, lean meats and whole grains.
Blood Glucose Level
Due to the recent popularity of low-carb and glycemic index diets, the average person believes that declining blood glucose levels are the primary cause of hunger. There is actually little evidence of a causal relationship between declining blood glucose levels and hunger. However, there is solid evidence of a correlation between declining blood glucose levels and hunger. That is, people do tend to become hungry at the same time their blood glucose level is decreasing. Whether hunger results directly from the sensing of declining blood glucose levels by “glycostat” neurons in the brain or through some intermediary factor remains to be discovered. Interestingly, the feeling of fullness that occurs immediately after eating precedes the rise in blood glucose that follows carbohydrate absorption.
Research has shown that low-carb and low GI diets do not reduce hunger compared to other weight-loss diets. It seems pointless to try to regulate your appetite by eating for blood glucose control.
Leptin is an appetite-regulating hormone that is produced by fat cells. It acts on the hypothalamus, the brain’s hunger center, to turn off the hunger switch. The more fat your fat cells contain, the more leptin they produce and the more your appetite shrinks.
At least that’s how it works under normal circumstances. However, there appears to be a second factor that affects leptin production, and that’s habitual eating patterns. If you consistently overeat, your fat cells will reduce their leptin output to accommodate your preferred eating patterns by allowing your appetite to remain large despite the fact that you’re getting fatter.
Fortunately, this effect is reversible. If you restrain your eating for a week or so your leptin production will return to normal. However, as you lose body fat, your leptin production will decrease and your appetite will again increase. It’s a Catch-22! Your best way out is to exercise plenty, so you can eat as much as your appetite demands without getting fat.
Over the past 30 years, the number of calories in the average American’s diet has increased significantly. This increase is widely believed to have been driven by increases in portion sizes in restaurant menu items and packaged foods that resulted from substantial decreases in the cost of producing food and competition among food businesses. The combination of this influence and that of the constant deluge of commercial advertising for food has essentially inflated our appetites—or created a breach between our physical and social appetites for food. Researchers such as consumer psychologist Brian Wansink of Cornell University have shown that the amount of food we consume is strongly influenced by the accessibility of food, how much food is put in front of us, and social pressure to eat more, including the pressure of commercial advertising. A perfect example of the latter influence is Taco Bell’s invention of “fourth meal,” a late night meal of fast food that the television viewer is encouraged to ad to his or her daily eating routine.
To reduce the effects of food overabundance on your eating, experts generally recommend that individuals train themselves to pay better attention to the physical signs of appetite, hunger and fullness. The goal is to eat only when physically hungry and, when eating, to eat only until comfortably satisfied, never stuffed. As you get a better sense of how much food you really need to satisfy your physical appetite, you can also train yourself to purchase, prepare, serve and order smaller portions that meet this standard without exceeding it.
Evolution gave us bodies that are able to store energy reserves for times of scarcity in the form of excess body fat. These reserves accumulate automatically when we increase our eating without increasing our activity level, or decrease our activity level without decreasing our eating, or simultaneously increase our eating and decrease our activity level. We modern humans are much less active than our ancestors were. Evolutionary biologists estimate that our Paleolithic ancestors each burned 1,000 calories per day more than we do through activity. But our appetites are the same, which means that the modern lifestyle tends to make us fat. In such an environment you can’t trust your appetite, because your body “thinks” you’re trying to store excess body fat by moving so little.
Everything changes when you start exercising, however. As you burn 500 or more extra calories each day through training, your appetite automatically adjusts to help your body run better—specifically, it increases enough to replenish the critical fuel stores (mainly muscle and liver glycogen) that you deplete each day but not enough to prevent the shedding of excess body fat, which of course slows you down. Research has shown that when they increase their training load (hence the number of calories they burn each day), athletes on “ad libitum” diets (meaning they eat according to their appetite, not by counting calories) automatically increase their calorie consumption and lose body fat. Thus, the best way to consistently eat the right amount is to continue eating according to your appetite and increase your training in pursuit of performance.