5. Craving or seeking. This is described as an intense drive to self-administer drugs. In food addiction research, craving is illustrated by the motivation to seek food. Drug craving and seeking have been experimentally described as a form of learning, where dopamine signaling facilitates the consolidation of memory; past experiences are used to inform future decisions. Rats “press the lever” for drugs because they have learned that it is rewarding. We press the credit card button for Frappuccinos.™
6. Interference with life. This is defined by important work, social, or other life activities being compromised. Obesity can significantly hamper an individual’s quality of life. Mobility is markedly more difficult. Airlines may refuse you passage if you don’t fit into the seat. Employers may refuse to hire you based on your weight. Diabetes can lead to limb amputation, requiring use of a wheelchair. During the thirty days of Spurlock’s Super Size Me adventure, he gained 24.5 pounds, experienced mood swings, sexual dysfunction, and fat accumulation in his liver. While his experience of eating every meal at McDonald’s may be deemed extreme, these physical and physiological effects occurred within only a thirty-day period.
7. Use despite negative consequences. This is defined as continued use despite knowledge that use will make the problems worse. The health consequences associated with obesity are numerous (see chapter 19). Despite knowing and experiencing these health problems, the eating pattern continues unabated.
What Makes Fast Food Addictive?
In humans, food addiction is often compared to established criteria for substance dependence.7 One problem with this approach is that it shifts focus away from the potentially addictive properties of the food and onto the individual “afflicted” with the addiction. We prefer to focus on the addictive potential of the food itself by placing it in the scope of other identified substances of abuse. Alcohol is the most analogous substance to fast food for several reasons, including its biochemistry (see chapters 11 and 22).
Fast food is high in calories, sugar, fat, salt, and caffeine. It is highly processed, energy dense, and specifically designed to be highly palatable. The majority of the fiber and a portion of the vitamins and minerals present in the original food have been extracted in processing (see chapter 14). Sugar, salt, and other additives are used to boost flavor. The end product is packaged and sold conveniently to deliver the contents. Which of these components could be addictive? Or are they addictive all together?
A market share analysis of McDonald’s, the largest hamburger chain in the world, shows that its Big Mac and French fries are the top two most popular menu items. Extra value meals constitute 70 percent of purchases at McDonald’s, Wendy’s, and Burger King. The most popular combination at McDonald’s is a Big Mac, medium French fries, and medium regular soda, providing 1,130 calories for $5.99.8
But we’re talking about addiction here. So let’s make it a large. Consider a food label for a typical fast food meal, consisting of a Big Mac, large French fries, and large Coke (32 ounces) (figure 5.1). No percentage daily value (%DV) is listed for sugar because there is currently no recommended daily intake for sugar (see chapter 16). Keep in mind that 50 percent of the American population is consuming this or a similar meal at least once per week.
Fig. 5.1. Supersize Me? A McDonald’s Meal and Its Nutritional Value. A Big Mac, large fries, and a large soda provide 1,360 calories (two thirds of a standard day’s allotment) and 1,380 milligrams sodium (almost an entire day’s allotment). While the fat content is 38 percent of calories (which is not bad), the sugar content is 95 grams, or 19 teaspoons, or 390 calories, which is more than double what the American Heart Association recommends for one day.
Salt
This sample meal contains 1,380 milligrams of sodium (salt). The 2005 Dietary Guidelines for Americans provided a “tolerable upper intake level” of 2,300 milligrams of sodium per day, which is why the %DV of the sample meal is 54 percent. Processed foods of many sorts contribute more than 3,400 milligrams of sodium per day to the average American diet. Salt is one method by which the food industry can preserve foods and increase their shelf life. So salt and calories almost always go together. (Think potato chips.) But is it addictive? Data to support addiction to salt are currently confined to animal models. Studies in rats show dopamine signaling in response to salt, and administration of opioids encourages bingeing on salt. However, in humans, salt intake has traditionally been conceived as a learned preference rather than an addiction. The preference for salty foods is likely learned early in life. Four- to six-month-old infants establish a salt preference based on the sodium content of breast milk, water used to mix formula, and the rest of their diet. But clearly people can modulate their salt intake. For example, patients who crave salt due to diseases of the adrenal gland can reduce their salt intake when given the appropriate medicine. Also, people’s taste for salt can be retrained; hypertensive adults can be retrained to a lower-salt diet within twelve weeks.9 So, based on the criteria for an addictive substance, salt doesn’t make the cut.
Fat
The high fat content of fast food is vital to its rewarding properties. This sample fast food meal contains 89 percent of the daily fat intake for an individual on a 2,000-calorie diet. In feeding studies, excess calories from fat are more efficiently stored than excess calories from carbohydrates (90–95 percent versus 75–85 percent). Therefore, fat intake has always traditionally been assumed to be the major determinant of weight gain. Animals will binge on pure fat when given intermittent access to it. They binge regardless of the type of fat ingested, which suggests that it is that fat content and not the type of fat present in fast food that encourages overeating (see chapter 10). However, rat models do not demonstrate other features of addiction to fat, such as tolerance or withdrawal. Keep in mind, however, that so-called “high-fat foods” are almost always also high in starch (e.g., pizza) or sugar (e.g., cookies). In fact, adding sugar significantly enhances preference for high-fat foods among normal-weight people.10 Thus, the combination of high fat along with high sugar is likely to be more addictive than high fat alone.
Caffeine
Soda is an integral part of the fast food meal. If you consumed a large soda with your McDonald’s value meal, the caffeine content would be approximately 58 milligrams. Soft drink manufacturers identify caffeine as a flavoring agent in their beverages, but only 8 percent of frequent soda drinkers can detect the difference in a blind taste test of caffeine-containing and caffeine-free cola.11 Thus, the most likely function of the caffeine in soda is to increase the salience (the quality that makes it “stand out”) of an already highly rewarding (sugared) beverage. Dependence on caffeine is well established, meeting all the DSM-IV-TR criteria for both physiologic and psychological dependence. In fact, up to 30 percent of people who consume caffeine may meet the criteria for dependence. Headache (attributed to increased cerebral blood flow velocity), fatigue, and impaired task performance have all been shown during caffeine withdrawal. In addition, reinforcement of intermittent caffeine consumption leads to tolerance.
While