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THE UNITED STATES OF FOOD REWARD

In the last chapter, I explained how most of us are driven to overeat by largely nonconscious brain processes that determine our food motivation, and that the brain is motivated by specific food properties like sugar, salt, and fat. Now, let’s take a closer look at how those properties have changed in the US diet over the years, and how those changes help explain our surging calorie intake.

The industrial era, which has covered roughly the last two hundred years in the United States, has been the shortest period of human history. During this time, technology increased the efficiency of agriculture so dramatically that few of us have to be farmers anymore. Without industrialized agriculture, I wouldn’t be writing this book, and you wouldn’t be reading it. But industrialization has gone far beyond simply increasing the efficiency of agriculture—it has profoundly transformed food processing, distribution, and preparation.

Of the 2.6 million years since our genus Homo emerged, we were hunter-gatherers for 99.5 percent of it, subsistence-level farmers for 0.5 percent of it, and industrialized for less than 0.008 percent of it. Our current food system is less than a century old—not nearly enough time for humans to genetically adapt to the radical changes that have occurred. Our ancient brains and bodies aren’t aligned with the modern world, and many researchers believe this evolutionary mismatch is why we suffer from such high rates of lifestyle-related disorders, such as coronary heart disease, diabetes, and obesity.

Unfortunately, we can’t go back in time to observe the diets and eating habits of our distant ancestors, and today we know only a few basic facts about what and how they ate. Yet current and historical nonindustrial cultures can provide us with a rich tapestry of clues about what life may have been like for our hunter-gatherer and subsistence farmer forebears. Let’s consider two examples and see what we can learn.

!Kung San

In the 1960s and 1970s, the anthropologist Richard Lee conducted a detailed study of a group of!Kung San hunter-gatherers in the Kalahari desert of Botswana, including descriptions of food collection, preparation, and eating practices. At the time, the!Kung San didn’t live so differently from how our ancestors did prior to the development of agriculture, with the exception of a few tools and foods obtained through trade. They relied on a wide variety of wild animal and plant resources for food, including large and small game, insects, nuts, fruit, starchy tubers, fungi, leafy greens, and honey. Although they recognized at least 105 plant species as edible, most of their plant food intake came from only 14 species. Approximately 40 percent of their calorie intake came from meat, with liver being particularly prized. But their primary source of food was the mongongo tree, which supplied about half of the!Kung San’s year-round calorie intake. The mongongo tree produces abundant quantities of a sugar-rich fruit containing a fat- and protein-rich nut. The fruit tastes similar to a date, and the flavor of the roasted nut has been described as “not unlike that of dry roasted cashews or almonds.”

With few exceptions, the!Kung San processed all foods in some way prior to eating them. They used cracking to breach the extremely hard shell of the mongongo nut after roasting. They pounded foods to increase the digestibility and palatability of tough or fibrous items, including starchy tubers, mongongo nuts, and tough meats. They sometimes pulverized foods as a means of combining flavors and textures to increase palatability. For example, the!Kung San would mash together roots and mongongo nuts, resulting in a cheesy substance. And as with all human cultures, fire was a key food-processing method for the!Kung San, who boiled and roasted pieces of meat. Prior to acquiring pots through trade, the only available cooking method was roasting, which Lee describes as follows: A root or a piece of meat is carefully buried in a mixture of hot sand and glowing embers at the edge of the fireplace. The appearance of steam rising from the mound of sand indicates that cooking is proceeding. When the food is done after 5 to 30 minutes, depending on size, it is removed and knocked sharply against a rock or log to dislodge adhering sand and coals; then it is scraped to remove charred parts. Inevitably, some sand and ash are eaten with roasted food.

Appetizing, isn’t it?

The!Kung San didn’t have many of the culinary tools we use to dress up food today: they rarely used such added flavorings as herbs and spices, they didn’t use salt, and they only occasionally had access to concentrated fat to add to their food. The!Kung San were rarely faced with serious calorie shortages; however, they were sometimes forced to rely on foods they weren’t particularly enthusiastic about when they exhausted their favorite foods in a particular location. They sometimes had access to highly palatable treats, including the Kalahari truffle and honey, but due to the limitations of living in a natural environment, they ate certain other foods daily “without much enthusiasm.” When maintaining this traditional lifestyle, they were extremely lean. In stark contrast to Western populations—which tend to be leanest in youth and grow wider with age—the!Kung San reached their maximum weight during peak reproductive years and declined thereafter.

Yanomamö

The Yanomamö are nonindustrial farmers who live in small permanent settlements that collectively straddle the border of Venezuela and Brazil in the Amazon basin. The anthropologist Napoleon Chagnon lived with and studied them extensively over a quarter-century period beginning in 1964. During this time, their primary foods were cultivated starches, including plantains, sweet potatoes, cassava, corn, and a variety of taro, with green and ripe plantain supplying the most calories. They also cultivated avocados, papayas, and hot peppers, but ate these in smaller quantities. They supplemented their starchy diet with a wide variety of wild animal foods, including large and small game, fish, insects, eggs, and honey. Their diet also included an assortment of wild plant foods, particularly fruit, nuts, starchy tubers, palm heart, and mushrooms.

The Yanomamö diet, as with most nonindustrial cultures, was very practical. Chagnon described their attitude toward food preparation as follows: “In general, the Yanomamö prefer foods that require little processing—a kind of ‘take it from the vine and throw it on the fire’ attitude that applies to vegetable and animal food alike.” They used four food preparation methods—roasting, boiling, smoking, and grating—but they didn’t use added flavors, fats, or salt, and they did little beyond cooking to increase the palatability of their foods. Because of their low salt intake, the Yanomamö were included in the INTERSALT study, an international study of salt intake and blood pressure, which determined that Yanomamö blood pressure remains remarkably low throughout life. There’s no way to know how much of this is due to their low salt intake as opposed to other factors, such as their high level of physical activity. However, lifelong low blood pressure is typical in nonindustrial cultures. The Yanomamö were relatively lean, and neither Chagnon nor other researchers reported any obesity among them, despite the fact that they tended to have adequate food supplies.

WHAT DO NONINDUSTRIAL DIETS HAVE IN COMMON?

As I hope our brief tour of the eating habits of two nonindustrial cultures has illustrated, the diets of our distant ancestors were probably radically different from ours today. The diets of nonindustrial cultures vary widely, yet they share important commonalities that fundamentally differentiate them from the diets of people living in modern affluent nations. If we can identify these commonalities, we may be able to understand what the diets of our ancestors were like, and in turn, what our bodies and brains are adapted to. Here are three prominent characteristics these diets have in common: First, they include a limited variety of foods. For example, although the!Kung San recognized at least 105 plants as edible, only 14 formed the bulk of their plant food intake, and only a subset of these 14 plant foods was available at any given season and location. Throughout the year, half of their calorie intake came from a single food, the mongongo fruit/nut. Over the course of the entire year, the!Kung San diet was quite varied; yet over the course of a day, it may have focused on only a few foods. Because of the seasonal availability of key resources, the same is true of most other nonindustrial cultures.

Second, they have a limited ability to concentrate the reinforcing properties of food. With only the most basic processing methods at their disposal, nonindustrial cultures—and presumably our distant ancestors—are forced by necessity to eat food in a less calorie-dense, less refined, less rewarding state. Most don’t have the ability to add refined starch, sugar, salt, or concentrated fat to their meals. The glutamate they eat comes from cooking meat and bones rather than from crystalline MSG. Added flavors, such as herbs and spices, are limited. Although we can find isolated examples of traditional cultures that use concentrated fats, salt, multiple spices, sugars, or more refined starches, none boasts all the enhancements of the affluent industrial diet.

Third, they use few cooking methods. The cooking methods of nonindustrial cultures are extremely limited by modern standards, with most cultures only using two or three methods. Even in affluent Western cultures, cooking methods were limited by technology until relatively recently. Until the 1820s, most cooking in the United States took place in an open hearth, which is a time- and labor-intensive method that makes complex cooking techniques difficult. Cast-iron wood- or coal-fired stoves replaced open hearth cooking in the 1820s, and they remained the dominant cooking method until they were replaced by gas and electric stoves in the 1920s. Techniques as simple as sautéing and temperature-controlled baking were difficult or impossible to perform in the home prior to these advances in technology.

To the modern palate accustomed to constant entertainment, nonindustrial diets, and likely the diets of our distant ancestors, would seem repetitive, bland, and sometimes unpalatable. Fortunately for our palates but not for our adiposity, we live in different times.

FOOD REWARD IN THE UNITED STATES

If we’re to believe that food reward has played a role in overeating and our expanding waistlines, we must have evidence that the food properties that titillate our brains’ reward circuits, and/or the food cues that make us seek them, have increased over time. Unfortunately for the American waistline, this evidence isn’t hard to come by.

A hunter-gatherer walking through a modern grocery store would be bewildered by the dizzying array of food choices, particularly those of high calorie density and palatability (not to mention all those boxes adorned with strange cartoon characters). The Food Marketing Institute reports that in 2013, the average US grocery store contained a staggering 44,000 items, up from an already impressive 15,000 items in 1980. In sharp contrast to the dietary habits of nonindustrial cultures, which are limited by availability, affluent industrial cultures are steeped in a vast abundance of food choices, most of which are professionally crafted to maximize reward value. This variety means we experience less sensory-specific satiety, almost like a perpetual buffet.

The magnitude of the change in US food habits over time, as demonstrated by USDA food-tracking data, is difficult to overstate. One of the things the USDA keeps tabs on is the proportion of food spending we dedicate to food consumed in the home versus outside the home, and this provides us with a rough approximation of how much people are cooking at home versus going out to eat. In 1889, Americans spent 93 percent of their food expenditures on food to be eaten at home, and only 7 percent eating out. Today, we spend about half of our food expenditures on food to be eaten at home, and the other half eating out. Much of the recent increase has come from fast-food spending, which has increased ninefold since 1960. These figures actually underestimate the magnitude of the change in US food culture, because today many of the foods we eat at home are actually commercially prepared, such as pizza, soda, cookies, and breakfast cereal.

It’s clear that our food culture has changed profoundly in this country over the last century, a period over which we’ve outsourced the majority of our food preparation to professionals. This shift toward outsourced food preparation on an industrial scale has led to remarkable changes in the processing and composition of the food we eat.

So how exactly did we get hooked on processed food? Let’s return to what we previously discussed about food reward. We know that the brain recognizes calorie density, fat, carbohydrate, protein, sweet flavors, salty flavors, and meaty flavors as innately reinforcing and that those properties drive our motivations, preferences, and habits. Examining the trajectory of food processing over human history, it’s clear that we’ve gradually purified these reinforcing attributes to their most concentrated states to satisfy our own palates. In nonindustrial diets, fat, starch, sugar, salt, and free glutamate rarely exist in highly concentrated form. In modern industrial diets, they’re used in nearly pure form as ingredients—and married together in irresistible combinations. To illustrate this, let’s take a closer look at sugar, fat, and glutamate.

Sugar holds a special place in the brain’s reward centers, perhaps because in the time of our distant ancestors, sweetness signified fruit or honey—both safe and valuable sources of nutrition. These were the only two sources of sweetness for most of human history. But we gradually figured out how to extract pure sugar from beets and sugarcane, although initially it was so expensive that only the wealthy ate it regularly. As technology advanced, concentrated sugar became cheaper, easier to obtain, and easier to use. In the 1870s, granulated sugar became widely available in the United States, making it more convenient to add sugar to food. A glass-blowing machine patented in 1899 led to the mass production of bottles, reducing the cost of sweetened beverages. Then, in the 1920s, refrigerated vending machines were invented, making it easier than ever to grab a cold, refreshing soda. The 1970s brought one of the most significant technological advances in US diet history: high-fructose corn syrup. This is a sweetener produced from corn starch that has approximately the same sweetness as cane sugar. Thanks to government-subsidized corn, it’s so cheap that food manufacturers can use it to beef up the reward value of their foods at virtually no cost, tickling the brain circuits that make us reach for the cookies.

My research partner Jeremy Landen and I stitched together records from the USDA and the US Department of Commerce to form a complete picture of added sweetener intake in the United States from 1822 to 2005. These data don’t include the natural sugars that come from fruit and vegetables, but they do include honey, cane sugar, beet sugar, and high-fructose corn syrup. Looking at this graph, it’s clear that we eat far more added sugar today than we did in the early 1800s. In 1822, we consumed the amount of added sugar in one twelve-ounce can of cola every five days, whereas today we consume that amount every seven hours. Again, advances in food technology and the increasing influence of the food industry are behind this shift. The competitive nature of the food market dictates a race to the bottom in which manufacturers converge on the most rewarding concentration of added sugar in each food: not too little and not too much. This optimal concentration is called the sugar “bliss point,” and it’s the subject of much industry research, as detailed in the excellent books Salt Sugar Fat and The End of Overeating, by Michael Moss and David Kessler, respectively.

As discussed in the last chapter, added fats are another highly effective way to rev up the brain’s reward circuits. Isolated fats, such as soybean oil, canola oil, and butter, increase the calorie density and reward value of foods at little additional cost, which is why they’re used liberally in commercially prepared foods, including restaurant food. USDA data reveal that total fat intake has increased modestly in the United States over the course of the last century, but added fat intake has doubled. The types of fats we use in our cooking have also changed profoundly—animal fats, such as butter and lard, have largely been supplanted by refined seed oils (vegetable oils) such as soybean oil. Rather than getting our fat from whole foods like meat, dairy, and nuts, we now get it primarily from oils that are mechanically and chemically extracted from seeds. These liquid oils are cheap and convenient to add to foods that would otherwise contain little fat, creating such food reward masterpieces as french fries and Doritos. Added fat increases the calorie content of food and our drive to eat it, ultimately causing us to overeat.

Free glutamate, responsible for the meaty umami flavor, occurs naturally—in small amounts—in cooked meats and bone stock. Today, the food industry uses highly concentrated crystalline MSG to give food the savory, meaty flavor our brains crave. To get around the health concerns that surround MSG, companies have developed alternative sources of glutamate that slip under our radar, such as hydrolyzed yeast and soy protein extracts. The purpose of these substitutes is the same: satisfy the brain’s innate preference for glutamate that keeps people coming back to flavored tortilla chips, salad dressing, soups, and many other foods.

IDENTIFYING THE ENEMY: TOO MUCH SUGAR OR TOO MUCH FAT?

In popular media, there is a perennial debate over whether sugar or fat is responsible for the obesity epidemic. This has led some people to view obesity research as a team sport rather than a scientific discipline. Allow me to end the debate by stating what most researchers find quite obvious: It’s both. In particular, the combination of concentrated sugar and fat in the same food is a deadly one for our food reward system. It’s also a pairing that rarely occurs in nature, so it’s tempting to speculate that it’s more than our brains are equipped to handle constructively. Think ice cream, chocolate, cookies, and cake—foods we crave, and foods we don’t need to be hungry to eat. What would they be without sugar, and what would they be without fat?

Although MSG has a bad reputation among health-conscious consumers, humans have always sought glutamate, and throughout history we’ve found ways to get it. The first source of glutamate, perhaps hundreds of thousands of years old, was simply cooked meat. Once we invented cooking vessels, we began boiling bones to make a meaty, glutamate-containing broth—something we’ve probably done since before recorded history. The next step was to develop fish sauce, which is very high in glutamate as a result of the decomposition of naturally occurring fish proteins. Primarily associated with traditional Asian cuisine today, the ancient Romans used a similar sauce called garum more than two thousand years ago. Soy sauce, another concentrated source of glutamate, has been popular in parts of Asia since the same era. The isolation of pure glutamate by Tokyo Imperial University researcher Kikunae Ikeda in 1908 and the subsequent commercial production of MSG were the culmination of a long historical process that gave us access to increasingly concentrated forms of glutamate. As with other reinforcing food properties, technology allowed us to distill the umami flavor down to its primary active ingredient, yielding a powerful tool for increasing the reward value of food.

But the march of progress hasn’t stopped there. Modern food chemists have created or isolated a vast number of seductive flavors that compel us to buy food. Although these usually appear on an ingredient label as the cryptic phrase “artificial flavors” or “natural flavors,” such terms often conceal a carefully engineered suite of dozens of ingredients.

Habit-forming drugs, which are reinforcing due to their direct actions on the brain’s dopamine system, are also more prevalent in modern affluent foods. Caffeine and alcohol are inherently reinforcing, meaning that they drive conditioned food and beverage preferences that can contribute to overeating. Alcoholic beverages are rich in calories—ranging from 90 to 180 Calories per serving. To put that into context, two beers per day can be the difference in calorie intake between a lean person and an overweight person. Most American adults drink alcohol regularly, and we virtually never drink it to satisfy a need for calories. We drink it because we like it, whether we’re hungry or not. Caffeine itself doesn’t contain calories, but it’s often associated with calorie-rich cream and sugar—and as with alcohol, we don’t take in these extra calories because we’re hungry for them. And theobromine, the mild habit-forming drug in chocolate, also drives us to eat excess calories.

Finally, cooking techniques have proliferated since the time of our distant ancestors, increasing the tools available to maximize food reward. Whereas most nonindustrial cultures have two or three simple cooking methods at their disposal, chefs today can bake, roast, broil, sauté, sear, deep-fry, poach, steam, boil, sous vide, pressure-cook, slow-cook, flambé, smoke, or grill—and pair these techniques with a wide variety of ingredients, including added fats like butter, sweeteners like sugar, and flavorings like salt.

It’s no accident that our modern food landscape looks this way: The innate preferences of the human brain have dictated it via consumer demand. The food industry competes fiercely for your “stomach share” by pushing your food reward buttons, trying to turn you into a repeat customer. It does this largely by appealing to the things your brain intuitively wants. Highly reinforcing food, and the use of food cues in advertising that trigger us to purchase it, are the inevitable outcome of a competitive economy in which companies jockey for our food spending.

Modern food technology gives us an exquisite degree of control over the rewarding properties of food, and it offers us tremendous food variety. As food technology has advanced, affluent diets have gradually evolved to mirror the innate food preferences of the human brain. While these preferences kept us alive and well in an ancestral environment, they cause us to overeat in an environment that satisfies them to an unprecedented degree.

SUPERNORMAL SEDUCTION

Technology has allowed us to create foods that are far more seductive than those that occur in a natural environment, and this leads to an equally unnatural response from the brain. The idea that our hardwired inclinations can be overstimulated by unnaturally powerful cues goes back to the 1930s. During a study of the nesting behaviors of the ringed plover, Koehler and Zagarus noted that the birds prefer to sit on artificial eggs that are an exaggerated version of natural eggs. A typical ringed plover egg is light brown with dark brown spots. When Koehler and Zagarus offered the birds artificial eggs that had a white background and larger, darker spots, they readily abandoned their own eggs in favor of the decoy. Similar experiments with oystercatchers and herring gulls showed that they prefer larger eggs, to the point where they will leave their own eggs in favor of absurdly large artificial eggs that exceed the size of their own bodies.

Essentially, birds have an innate preference for specific egg characteristics. Ringed plovers are wired to prefer a roundish egg with contrasting spots, such that a roundish egg with larger spots and more contrast elicits a stronger preference. Oystercatchers and herring gulls are wired to prefer large eggs, possibly because larger eggs tend to be healthier, and their preference for larger eggs extends well beyond the natural range. The Dutch biologist Nikolaas Tinbergen coined the term supernormal stimulus to describe the phenomenon whereby, as he put it, “it is sometimes possible to offer stimulus situations that are even more effective than the natural situation.” Whatever a species’ innate preferences are, they can often be overstimulated by presenting a cue that’s more powerful than what the species has evolved to expect—and this can sometimes lead to highly destructive behavior. It seems likely that certain human innovations, such as pornography, gambling, video games, and junk foods, are supernormal stimuli for the human brain.

In nature, supernormal stimuli are sometimes used as tools for exploitation. For example, the common cuckoo is a parasitic bird that exploits the innate preferences of its host species, one of which is the reed warbler. The egg of a cuckoo looks almost identical to a reed warbler egg, except it’s larger. Once hatched, the larger cuckoo chick ejects all reed warbler eggs and chicks from the nest. It begs for food using a song that closely resembles the sound of a whole brood of reed warbler chicks, tapping into its host’s hardwired feeding response to the sound of multiple hungry chicks. The large size and bright color of the chick’s mouth as it begs may also stimulate the parent’s desire to feed it more than a normal chick. By the time the cuckoo is ready to fledge, it’s quite a bit larger than its adoptive parent, which it has profoundly exploited for its own gain.

Likewise, our own innate food preferences are commercially exploited by concentrating and combining the properties we find most rewarding, resulting in foods that are more seductive than what our ancestors would have encountered. Creating an obesity epidemic wasn’t the objective; it was just an unfortunate side effect of the race to make money.

COLLATERAL DAMAGE

The tremendous influence of food reward on our eating habits becomes obvious when we take a close look at the American diet. The 2010 USDA Dietary Guidelines for Americans reported that the following six foods are the top calorie sources for US adults, in descending order of the number of calories that each contributes to our diet:

1- Grain-based desserts

2- Yeast breads

3- Chicken and chicken mixed dishes

4- Soda/energy/sports drinks

5- Alcoholic beverages

6- Pizza

Topping the list are “grain-based desserts,” a category that includes cake, doughnuts, and cookies. Next is bread, which is often viewed as an innocuous food but is usually made of refined white flour and is surprisingly calorie dense. Bread also happens to be the single largest source of salt in the US diet. Then comes “chicken and chicken mixed dishes,” which may owe its prominent position on the list to our fondness for fried chicken and chicken nuggets. Fourth on the list is soda/energy/sports drinks, or as I like to call it, sugar water. Fifth is alcoholic beverages, and sixth is pizza. Where are the fruit? Beans? Nuts? Most of the foods on this list are calorie-dense combinations of refined sugar, refined starch, concentrated fat, salt, and habit-forming drugs (caffeine and alcohol).

Because of how our brains are wired, we don’t form celery habits. We form cookie habits and pizza habits. These are the foods that make us want to eat more of them, eventually establishing deeply ingrained eating patterns that are hard to change. We don’t eat these foods for their health benefits—we eat them because they reinforce our behavior.

Here are the top six sources of calories for children and adolescents:

1- Grain-based desserts

2- Pizza

3- Soda/energy/sports drinks

4- Yeast breads

5- Chicken and chicken mixed dishes

6- Pasta and pasta dishes

This list is similar, but perhaps even more heavily weighted toward highly rewarding foods at the top. These are the foods our children are eating. In light of this, is it so surprising or mysterious that many of them have obesity?

Yet the reach of the food industry doesn’t stop in the dining room: It also extends into our living rooms, roadways, and offices.

MANUFACTURING CRAVINGS

As we discussed, once you’ve eaten a rewarding food a few times, cues associated with that food can trigger your motivation to seek it. For example, when we smell french fries, see images of them, or enter a place where we previously ate them, we crave french fries. The brain is saying, “This is a situation in which you can get a valuable food,” and it stimulates your motivation accordingly. Food advertising taps into this fundamental principle, exposing us to food cues that trigger our desire to purchase and eat food—and it’s highly effective.

The food industry pours a staggering amount of money into food advertising each year. In 2012, the ten largest food and beverage manufacturers alone spent $6.9 billion on food advertising, and fast-food restaurants spent more than $4 billion on top of that. To put that into perspective, the total amount of funding dedicated to obesity research by the National Institutes of Health, the primary funding agency for biomedical research in the United States, was less than $1 billion in 2012. The amount of money and effort put into convincing us to eat far outweighs that put into preventing overeating and its consequences.

The food industry spends this money because it gets results. People who view food advertisements tend to prefer, purchase, and request the advertised products. The average US adult views 20 food advertisements per day on television alone—adding up to more than 7,000 food cue exposures per year. Children are particularly susceptible to food advertisements due to their naturally high impulsivity and inability to understand persuasive intent. Children in the US view more than 12 food advertisements per day on television, totaling more than 4,300 per year. And food ads don’t compel us to buy brussels sprouts! Unprocessed, low-calorie foods like vegetables are neither very profitable to sell nor particularly compelling to consumers. Food cues are most effective when they predict highly rewarding foods rich in fat, sugar, starch, salt, and other reinforcing properties, and these are the foods that appear most often in advertisements. From the perspective of food reward, it’s difficult to imagine a more fattening food environment than the modern United States, and the rest of the affluent world isn’t far behind. We’re surrounded by a staggering variety of foods that are designed to appeal irresistibly to our innate food preferences, and we’re continually bombarded by cues that remind us of these foods. Home cooks and the food industry both play a role in this; however, the food industry is particularly effective at it, and the commercialization of food preparation has paralleled our increasing tendency to overeat and gain weight. Our expanding waistlines are an unintended but predictable consequence of the march of progress in a competitive economy.

Yet food reward isn’t the only thing that drives us to overeat. It goes hand in hand with convenience—another factor that titillates the brain circuits that determine our food intake, and one that we’ll explore further in the next chapter.