So, the End of Overeating next addresses the big question — why is homeostasis under assault? And there are multiple levels to that answer.
First, it’s critical to understand the scientific concept of palatability. In our common usage, it just means that food tastes good or is pleasant. In scientific usage, it refers to the capacity of a food to stimulate the appetite, thus prompting us to eat more. And the most palatable foods, in that sense, are usually foods that contain sugar, fat, and salt. Why? In large part, that seems to be because those are relatively uncommon in natural food, yet are pretty important to our survival.
However, it’s not simply the case that we can keep piling on sugar or lard and make something palatable. We will quickly begin to interpret that sensory input in negative ways as cloying or greasy or too salty rendering the food unpalatable. No, it’s the particular combination of sugar, fat, and/or salt that makes a food highly palatable. And both human and animal research indicates that the right combination of sugar, fat, and salt creates foods that many of us will eat in excessive amounts.
Dr. Kessler provides many examples throughout his book of the ways different foods are processed and cooked to make them highly palatable. By way of illustration, I’ll quote just one such example here. It’s the Bloomin’ Onion, something I used to enjoy at Outback before I was diagnosed with celiac disease.
“Bloomin’ Onions — the trademark Outback Steakhouse dish — are very popular, and they too provide plenty of surface area to absorb fat. Fried in batter and topped with sauce, their flavor comes from salt on sugar on fat.”
Our constant access to foods high in sugar, fat, and salt is pushing up our bodies’ settling point, the homeostatic point which your body believes is your proper weight. And once the settling point has been adjusted upwards, it’s very difficult to reset it to a lower weight. That’s one reason our weight as a population is increasing even as our obsession with diets also increases. In a way, that’s somewhat ironic.
Sugar, fat, and salt are also clearly reinforcing. In animal studies, scientists focus on two questions to determine if a substance is reinforcing.
Are they (the animals) willing to work to obtain it?
So they respond to other stimuli they’ve learned to associate with the substance?
In this section of the book, Dr. Kessler outlines many scientific studies illustrating the ways that sugar, fat, and salt — especially in combination — are reinforcing. He also details studies that show that three additional features exert a powerful influence on our desire for more.
First, quantity. Give a rat two pellets of food rather than one, give a person two scoops of ice cream rather than one, and they’ll eat more. Portion size matters.
Second is the concentration of rewarding ingredients. Adding more sugar or fat to a given portion boosts its desirability (although only up to a point; in excess, either one can lessen its appeal).
Finally, variety plays an important role.
Dr. Kessler then spends a number of chapters exploring the different ways these stimuli impact and condition our brains. He makes the studies extremely accessible to the lay reader; I learned a lot as I read this part of the book. One of the interesting things I discovered was that we become conditioned by stimuli suggesting that a rewarding food is nearby. Our brains release dopamine when we encounter such cues in order to encourage us to seek out and obtain the food. We are rewarded more for the hunt in some cases than for the actual experience of the food itself. When you think about the way things work in nature, that makes sense, of course. But it works against us in an environment full of highly palatable and highly available foods.
Emotions also help make foods memorable. If you think about meals you remember in your past, most of the time it’s not so much the food itself that makes it memorable. It’s the setting, the people, and the events associated with the meal that fixes it in our memory. And all of that leads to an emotional attachment through association. A particular food spurs a memory of emotion and we begin to link the emotion with the food. The food industry tries to tap into that sort of association in much of its advertising.
Ultimately, our brains can be rewired and a particular eating behavior habituated. I was struck while reading this section of the book how much that habituation resembles what the Christian Fathers have called a ruling passion. It’s a process where trigger leads to action without the deliberate activation of our will. We do something without thinking about it and sometimes even without awareness. Obviously, some of us are more likely to reach that point with highly palatable food than others, but as a population we are clearly susceptible.