Sugar
Although anecdotal reports abound supporting human “sugar addiction,” we are still not completely sure whether this is full-fledged dependence or merely habituation. Adding a soda to a fast food meal increases the sugar content tenfold. While Coca-Cola estimates that currently 42 percent of soft drinks sold nationwide are diet drinks (e.g., Coke Zero), when purchased at McDonald’s, 71 percent are the sugar-sweetened variety. In fact, in 2009 only seven items on the McDonald’s menu did not include sugar—French fries, hash browns, sausage, Chicken McNuggets (without dipping sauce), Diet Coke, black coffee, and iced tea (without sugar). While soda intake is independently related to obesity,13 fast food eaters clearly drink more soda. It is likely that the widespread phenomenon of “soda addiction” is driven by the inclusion of caffeine, a known addictive substance.
All criteria for sugar addiction have been demonstrated in rodent models.14 First, rats exposed to intermittent sugar access (following restriction) will binge. Second, these animals show signs of withdrawal (teeth chattering, tremors, shakes, and anxiety) when the sugar is withdrawn. Third, seeking and craving have been demonstrated where animals consume more sugar after a two-week imposed abstinence—just like Salvador and his soda. Elevated dopamine levels perpetuate the binge, and overconsumption increases with time, consistent with tolerance. Finally, cross-sensitization has been demonstrated in sugar-addicted rats who readily switch to alcohol or amphetamine use. So, based on the data, sugar is addictive, and soda is doubly so.
Deconstructing Darwin
There is some evidence that sugar may be addictive in humans. Experimental studies show that obese subjects will use sugar to treat psychological symptoms. Overweight women who were self-reported carbohydrate cravers reported greater relief from various mood disorders in response to a carbohydrate-containing beverage as compared to a protein drink. But perhaps the best evidence for an opiate-like effect of sugar is the product Sweet-Ease. This is a sugar solution into which hospitals dip pacifiers for newborn boys undergoing circumcision, to reduce the pain of the procedure.
Evolutionarily, sweetness was the signal to our ancestors that something was safe to eat because no sweet foods are acutely poisonous. (Even Jamaican vomiting sickness occurs only after consumption of unripe ackee fruit, which is not sweet.) So we gravitate to sweetness as a default. How many times do parents have to introduce a new food before a baby will accept it? About ten to thirteen times. But if that new food is sweet, how many times do you have to introduce it? Only once. And if a sucrose solution on a pacifier can provide enough analgesia for performing a circumcision, that’s an evolutionary winner, isn’t it?
Pleasure versus Happiness
You may have heard of the “gross national happiness index,” an indicator that measures quality of life or social progress in more psychological terms than does the economic indicator of gross domestic product (GDP). By all accounts, America is not very happy. Despite having the highest GDP, we score forty-fourth on the happiness index. Of course, our workaholic attitudes (Americans are afforded the least vacation time in the developed world) and the recent economic downturn all contribute to our unhappiness. But could our unhappiness be related to our food?15
By all estimations, obese people are not happy. The question is whether their unhappiness is a cause or a result of their obesity. At this point we can’t say for sure, and it is entirely possible that both are correct. Here’s how. Happiness is not just an aesthetic state. Happiness is also a biochemical state, mediated by the neurotransmitter serotonin. The “serotonin hypothesis” argues that deficiency of brain serotonin causes severe clinical depression, which is why selective serotonin reuptake inhibitors (SSRIs) which increase brain serotonin, such as Wellbutrin and Prozac, are used as treatment. Interestingly, these medications are also used for obesity. One way to increase serotonin synthesis in the brain is to eat lots of carbohydrates.16
You can see where this is going. If you’re serotonin-deficient, you’re going to want to boost your serotonin any way you can. Eating more carbohydrates, especially sugar, initially does double duty: it facilitates serotonin transport and it substitutes pleasure for happiness in the short term. But as the D2 receptor down-regulates, more sugar is needed for the same effect. The insulin resistance drives leptin resistance (see chapter 4), and the brain thinks it’s starved, driving a vicious cycle of consumption to generate a meager pleasure in the face of persistent unhappiness. And this vicious cycle can happen to anyone. Just substitute a little pleasure for a little unhappiness, and presto! Addiction in no time at all.
You, the Jury…
There is one obvious hole in this thesis, and I’m sure you’ve been chomping on it throughout this entire chapter. Can anyone become addicted to fast food? Everyone in America eats fast food, but not everyone is addicted. With narcotics, chronic use pretty much assures addiction—ask Rush Limbaugh about his OxyContin—but fast food doesn’t fit this paradigm. There are lots of habitual fast food consumers who can stop if they wished. Instead, is there a subset of people who are “addictable” and who have chosen food as their preferred substance of abuse? This might explain why people who stop smoking start eating.
Doctors are starting to come around to the concept of food addiction. Nora Volkow, the head of the National Institute on Drug Abuse (NIDA) is on record supporting the concept of food addiction.17 Yet not everyone is sold on the idea that obesity and addiction are related. For instance, in 2012 a British group challenged the obesity-addiction model,18 arguing that not all obese people demonstrate addiction, that not all obese people have reduced dopamine receptors on neuroimaging, and that rats are not humans (although, of course, some humans are rats). By that token, not everyone who drinks becomes an alcoholic, but we do know that some people become addicted.
So what’s your verdict? Is Salvador addicted to his sodas? Is fast food addictive? After treating obese children for the last fifteen years, I can categorically say that there are loads of people who can’t kick the habit. In fact, it’s more likely that children are unable to—perhaps because they were raised on the stuff or because their brains are more susceptible.19 There are several caveats to declaring fast food addictive. How often do you partake (consistently or intermittently)? With whom do you partake (with your family, or alone)? What do you order? How old are you? And, most important, do you have a soda (or sweet tea in the southeastern United States) with your meal? I’ve laid out the data that demonstrate that fat and salt increase the appeal of the fast food meal, but it’s the sugar and the caffeine that are the true hooks. We’ll come back to this time and again throughout the book, as this is where the action is.
Janie is thirteen years old. When she was five she developed a hypothalamic brain tumor, which was surgically removed. In the subsequent seven years, she gained 160 pounds (to a maximum weight of 242 pounds) and her oral glucose tolerance test showed massive insulin release, consistent with hypothalamic obesity. On an experimental