From Caveman to Caving in: Understanding Why We Eat

By Caterina Florissi and Dr. Francine Kaufman

How do our brains and bodies motivate us to eat? What makes us eat past the point of hunger? And how we can develop healthier eating habits?

Thousands of years ago, some of our ancestors, as hunters and gatherers, roamed vast savannas searching for food. Traveling long distances, men scavenged for meat, speared fish, and hunted down animals. Women foraged for nuts, seeds, fruits, and vegetables. Their work was demanding, tiring, and relentless. It was also necessary for survival.

To keep them going on their essential search, our ancestors evolved not one, but two, systems to motivate them to eat. One encouraged them to eat when they needed energy. The other led them to see food as a gratifying and fulfilling reward.

Fast-forward to the present day, and the hardwiring that drives us to eat remains the same. Yet, our food environment has changed substantially. Developing a deeper understanding of our drives, the advantages they once served, and the challenges they now pose can help guide us on a path to a healthier lifestyle.

Two drives to eat

Traditionally, researchers have identified two drives that motivate us to eat: one ensures we consume enough calories to survive (known as “homeostatic”); the other encourages us to eat for pleasure (known as “hedonic”).

Homeostatic drive (from ‘homeo-’ and ‘-stasis,’ meaning staying the same)

Our homeostatic drive works to maintain our body’s energy reserves. To do so, careful bodily systems diligently manage our intake, storage, and use of nutrients.

Short-term monitoring takes place at the level of a meal or snack. As food moves down the digestive tract, receptors in the stomach and intestines detect expansion. Additional receptors also recognize the presence of proteins, carbs, and fats. This information is relayed to the brain, which determines whether we should feel hungry or full.

Longer-term, tissues and organs release chemical signals – natural hormones - based on the state of their energy stores. When reserves are running low, for instance, fat tissues reduce release of the hormone leptin (which signals fullness) while the stomach increases release of the hormone ghrelin (which signals hunger). Together, falling levels of leptin and rising levels of ghrelin act on the brain to stimulate appetite and eating behaviors. Similarly, dips and peaks in levels of insulin (which also signals fullness) can increase or decrease hunger, respectively.

Hedonic drive (from ‘hedonism,’ meaning pleasure)

In contrast, our hedonic drive is motivated by pleasure and reward. To ensure we kept looking for sources of energy, our ancestors evolved to crave foods high in fat and sugar. Today, our brains remain engineered to both like and want these foods.

Liking refers to the emotional state of enjoying food. When we eat meals or snacks, we appreciate different scents, flavors, and textures. Sweet and high-fat foods, in particular, bring us intense feelings of pleasure. They’re even believed to trigger the release of natural opioids, molecules whose effects include pain management and euphoria.

Separately, wanting refers to the motivation or need to eat more of something. This need can persist, even if we do not enjoy the taste or already feel full from what we’ve consumed. The difference between liking and wanting can be understood in terms of a drug addiction – a person may dislike, but still intensely crave a drug. The same brain pathways that regulate drug addiction are also involved in the consumption of food. As expected, foods that combine both fat and sugar have been found to be especially addictive.

The two systems underlying our homeostatic and hedonic drives do interact with one another. Notably, our hedonic system can override homeostatic signals of fullness, leading us to continue eating. At some point, however, we become full enough to turn away even the tastiest of treats.

From caveman to caving in

While our homeostatic and hedonic drives served us well in our early days, they have not aged well in our current environment. Rather, our modern landscape is saturated with processed, high-carb and sweetened foods. These foods have made it difficult for our homeostatic system to detect when the body has sufficient energy stores and have kicked our hedonic system into overdrive.

On the homeostatic front, the same signals our ancestors relied on fall short when processing today’s foods. Their inadequacy can be understood through the changing nutrient profiles of our meals. Living in hunter-gatherer societies, our ancestors routinely consumed foods rich in protein, fiber, and complex carbs. These nutrients took time to digest, giving the body more time to send the brain signals of feeling full. Today, the food industry produces nutrient-poor products that are quickly digested and leave us less satisfied.

In our current environment, the abundance of products that are high in carbs and added sugars also poses another problem. More often than not, packaged foods and beverages are prepared with excess amounts of both sugar and fat. These properties exploit our hedonic system, dangerously increasing their addictive properties and leading us to overeat.

Tips for healthier eating

So, what can we do to lead healthier lives?

1) Practice mindful eating – With time and the right diet, we can learn to recognize, follow, and trust our homeostatic signals of feeling full. Before reaching for food, take a moment to notice whether you’re physically hungry, or whether you may be responding to another feeling instead (e.g., stress or boredom). Eat at meal times and, if desired, have a healthy snack to avoid grazing throughout the day.

2) Choose filling foods – When preparing meals, look for foods high in protein and fiber. These nutrients will help you feel and stay full, lowering the hedonic temptation to keep eating. Eggs, fish, avocados, and leafy greens are a few great options.

3) Avoid sugary and processed products – While cheap, tasty, and convenient, processed and high-carb foods are readily liked and wanted. They also lead to rapid increases in glucose, which cause insulin levels to rise and fall more quickly than usual. As your glucose and insulin levels drop, your body will feel hungrier sooner. Instead, opt for ‘real’ foods, such as fresh meat, vegetables, fruits, nuts, or seeds, that do not have the same addictive properties. Cooking at home can make for great opportunities to incorporate more ‘real ingredients’ in your meals. Check out Catherine Newman’s recipes for inspiration.

4) Skip the juice and soda – When in doubt, stick with the drink of our ancestors: water. Other beverages tend to contain large amounts of sugar. These not only trick the homeostatic system into feeling hungrier, but also activate the hedonic urge to continue drinking for pleasure.

As they were in our ancestors, our homeostatic and hedonic systems remain fixed within us. By keeping these tips in mind, we can aim to channel our ancestral drives into eating habits that help us stay healthy today.