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How We Learned to Eat Enough, But Get Bored of Plenty

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Editor's Note:

Robb Wolf is a former research biochemist, health expert, and author of the New York Times bestselling The Paleo Solution. He has been a review editor for the Journal of Nutrition and Metabolism and Journal of Evolutionary Health; serves on the board of directors of Specialty Health medical clinic in Reno, Nevada, and is a consultant for the Naval Special Warfare Resiliency program. This post was excerpted from Wired to Eat © 2017 by Crown Publishing Group.

Every moving critter on the planet, from bacteria to people, unconsciously uses a process called optimum foraging strategy (OFS). OFS is a pattern of movement that tends to maximize the amount of calories and nutrition an individual obtains while minimizing the amount of energy expended to do so. If we think about this like a bank account, it makes perfect sense: you must have more money going into your account than out, or you will have problems. For certain predatory or omnivorous animals, this may mean staking out a choice spot to waylay prey, while grazing animals attempt to find the choicest fodder with the least amount of movement. It’s hard out there in the wild when you’re a critter both competing for food and avoiding becoming someone else’s snack! OFS plays into how our genes are wired to experience the world. Our genetics are expecting an environment in which procuring a meal requires a significant amount of energy, but we were pitched a curveball by the changes in not just our food supply but also our sleep and activity patterns. Nature does not exist in a supermarket. We now live in a state of plenty unimaginable a few hundred years ago. It is this mismatch that is at the heart of not just weight gain but also most of the health issues we face.

OFS has another facet that is important when we bring this story back to how and why we overeat in the first place—a concept called palate fatigue. Our palate is our sense of taste (which includes significant input from our sense of smell). In our not-so-distant past, palate fatigue played an important role in keeping us alive. When an organism encountered a new food, there was both opportunity and risk. This new food source might prove to be nutritious and calorically dense—a boon for the individual. But what if it contained poisons or toxins? Eating too much of this novel food could mean the end of the line.

Quite literally, palate fatigue means “getting tired of this taste.” Palate fatigue sets in for two reasons. The first reason involves minimizing our toxicant load. It may surprise you to know that all plants produce substances that are either poor tasting or outright toxic. This is the natural defense mechanism plants use to avoid being consumed wholesale by insects and animals. Caffeine and nicotine, found in many plants, are substances bitter to our taste and neurotoxic to many insects. Some critters developed an evolutionary strategy to deal with these toxins. Koala bears, for example, are able to eat a diet almost exclusively composed of eucalyptus leaves, which contain substances that are unappealing and toxic to most other animals. Even if a plant tastes good to us, we will become bored of the food at some point because there are still toxins in things as benign as apples, carrots, and blueberries if we overeat them.

The second reason for palate fatigue is somewhat the opposite of avoiding toxins and relates to optimizing nutrient intake in the form of vitamins, minerals, and other food-based nutrients such as polyphenolics (one of the likely health-promoting elements in chocolate and green tea). Human health seems to benefit from getting as much variety as possible, so long as a few guidelines are observed, which we will explore shortly.

The palate fatigue story and its related concept, satiety (a sense of fullness), becomes critically important when we look specifically at the foods we eat, because the macronutrients (protein, carbs, and fat) deliver different degrees of satiety. In broad brushstrokes, lean proteins such as a chicken breast or pork loin are highly satiating. This is likely due to the fact that humans cannot consume more than about 35 percent of their calories from protein before suffering from protein toxicity. We need other nutrients such as fat or carbohydrate to allow us to function properly. Thus, lean proteins send a very strong signal of “Okay, I’ve had enough.” Fiber-rich carbohydrates tend to be the next most satiating, as they effect changes to the stomach’s mechanoreceptors, which communicate to the brain that we are filling our stomach.

Most experts consider fat, on a calorie-by-calorie basis, the least satiating of the macronutrients, but there are some important nuances here. It is rare to find a natural food that is all or mostly fat. Most people would find it chal¬lenging to guzzle a glass of olive oil. Even butter, which has been a compo¬nent of traditional diets for ages, has experienced some degree of processing to separate the milk fat from the whole milk. Avocados and coconuts have high levels of fat, but also a decent amount of sugars and carbohydrates.

As we will see, some of these satiety studies look only at the short term (hours) when considering the satiety effects of various foods. This may be a bit misleading, as the effects of hormonal dysregulation and overeating play out over days, weeks, months, and years. Fat does not cause much stomach distension, but it is calorically dense and triggers the release of hormones that provide satiety over the longer haul.

So, although the academic research on the satiety of these macronutrients orders things out as protein > fiber-rich carbohydrate > fat, my clinical experience has shown some variation in this story. For some, a higher fat intake, particularly with adequate protein, causes a spontaneous reduction in caloric intake due to a profound sense of satiety. Folks who eat this way tend to experience fairly easy fat loss and dramatic improvements in health parameters such as blood sugar and inflammation. Keep in mind, however, that this might have nothing to do with the satiety of fat specifically and everything to do with removing junk carbs from the diet, which can hijack the neuroregulation of appetite and make us feel hungry.