We have an uncanny ability to pick out the subtle distinctions in calorie density of foods, but only within the natural range.

The traditional medical view on obesity, as summed up nearly a century ago: “All obese persons are, alike in one fundamental respect,—they literally overeat.” While this may be true in a technical sense, it is in reference to overeating calories, not food. Our primitive urge to overindulge is selective. People don’t tend to lust for lettuce. We have a natural inborn preference for sweet, starchy, or fatty foods because that’s where the calories are concentrated.

Think about hunting and gathering efficiency. We used to have to work hard for our food. Prehistorically, it didn’t make sense to spend all day collecting types of food that on average don’t provide at least a day’s worth of calories. You would have been better off staying back at the cave. So, we evolved to crave foods with the biggest caloric bang for their buck.

If you were able to steadily forage a pound of food an hour and it had 250 calories per pound, it might take you ten hours just to break even on your calories for the day. But if you were gathering something with 500 calories a pound, you could be done in five hours and spend the next five working on your cave paintings. So, the greater the energy density—that is, the more calories per pound—the more efficient the foraging. We developed an acute ability to discriminate foods based on calorie density and to instinctively desire the densest.

If you study the fruit and vegetable preferences of four-year-old children, what they like correlates with calorie density. As you can see in the graph below and at 1:52 in my video Friday Favorites: Cut the Calorie-Rich-And-Processed Foods, they prefer bananas over berries and carrots over cucumbers. Isn’t that just a preference for sweetness? No, they also prefer potatoes over peaches and green beans over melon, just like monkeys prefer avocados over bananas. We appear to have an inborn drive to maximize calories per mouthful. 

All the foods the researchers tested in the study with four-year-old kids naturally had less than 500 calories per pound. (Bananas topped the chart at about 400.) Something funny happens when you start going above that: We lose our ability to differentiate. Over the natural range of calorie densities, we have an uncanny aptitude to pick out the subtle distinctions. However, once you start heading towards bacon, cheese, and chocolate territory, which can reach thousands of calories per pound, our perceptions become relatively numb to the differences. It’s no wonder since these foods were unknown to our prehistoric brains. It’s like the dodo bird failing to evolve a fear response because they had no natural predators—and we all know how that turned out—or sea turtle hatchlings crawling in the wrong direction towards artificial light rather than the moon. It is aberrant behavior explained by an “evolutionary mismatch.”

The food industry exploits our innate biological vulnerabilities by stripping crops down into almost pure calories—straight sugar, oil (which is pretty much pure fat), and white flour (which is mostly refined starch). It also removes the fiber, because that effectively has zero calories. Run brown rice through a mill to make white rice, and you lose about two-thirds of the fiber. Turn whole-wheat flour into white flour, and lose 75 percent. Or you can run crops through animals (to make meat, dairy, and eggs) and remove 100 percent of the fiber. What you’re left with is CRAP—an acronym used by one of my favorite dieticians, Jeff Novick, for Calorie-Rich And Processed food.

Calories are condensed in the same way plants are turned into addictive drugs like opiates and cocaine: “distillation, crystallization, concentration, and extraction.” They even appear to activate the same reward pathways in the brain. Put people with “food addiction” in an MRI scanner and show them a picture of a chocolate milkshake, and the areas that light up in their brains (as you can see below and at 4:15 in my video) are the same as when cocaine addicts are shown a video of crack smoking. (See those images below and at 4:18 in my video.) 

“Food addiction” is a misnomer. People don’t suffer out-of-control eating behaviors to food in general. We don’t tend to compulsively crave carrots. Milkshakes are packed with sugar and fat, two of the signals to our brain of calorie density. When people are asked to rate different foods in terms of cravings and loss of control, most incriminated was a load of CRAP—highly processed foods like donuts, along with cheese and meat. Those least related to problematic eating behaviors? Fruits and vegetables. Calorie density may be the reason people don’t get up in the middle of the night and binge on broccoli.

Animals don’t tend to get fat when they are eating the foods they were designed to eat. There is a confirmed report of free-living primates becoming obese, but that was a troop of baboons who stumbled across the garbage dump at a tourist lodge. The garbage-feeding animals weighed 50 percent more than their wild-feeding counterparts. Sadly, we can suffer the same mismatched fate and become obese by eating garbage, too. For millions of years, before we learned how to hunt, our biology evolved largely on “leaves, roots, fruits, and nuts.” Maybe it would help if we went back to our roots and cut out the CRAP. 

A key insight I want to emphasize here is the concept of animal products as the ultimate processed food. Basically, all nutrition grows from the ground: seeds, sunlight, and soil. That’s where all our vitamins come from, all our minerals, all the protein, all the essential amino acids. The only reason there are essential amino acids in a steak is because the cow ate them all from plants. Those amino acids are essential—no animals can make them, including us. We have to eat plants to get them. But we can cut out the middlemoo and get nutrition directly from the Earth, and, in doing so, get all the phytonutrients and fiber that are lost when plants are processed through animals. Even ultraprocessed junk foods may have a tiny bit of fiber remaining, but all is lost when plants are ultra-ultraprocessed through animals.

Having said that, there was also a big jump in what one would traditionally think of as processed foods, and that’s the video we turn to next: The Role of Processed Foods in the Obesity Epidemic.

We’re making our way through a series on the cause of the obesity epidemic. So far, we’ve looked at exercise (The Role of Diet vs. Exercise in the Obesity Epidemic) and genes (The Role of Genes in the Obesity Epidemic and The Thrifty Gene Theory: Survival of the Fattest), but, really, it’s the food.

If you’re familiar with my work, you know that I recommend eating a variety of whole plant foods, as close as possible to the way nature intended. I capture this in my Daily Dozen, which you can download for free here or get the free app (iTunes and Android). On the app, you’ll see that there’s also an option for those looking to lose weight: my 21 Tweaks. But before you go checking them off, be sure to read about the science behind the checklist in my book How Not to Diet. Get it for free at your local public library. If you choose to buy a copy, note that all proceeds from all of my books go to charity.