Don't Feed the Ghosts in Your Metabolic Machine

We had indications quite early in the pandemic that diet quality was, if anything, trending down. 

On the one hand, this is entirely understandable. If ever there was a need for whatever comfort so-called “comfort foods” can provide, this was the year.

On the other hand, this was a singularly unfortunate trend at the worst conceivable time. 

Risk factors for dire COVID outcomes are, apart from age, overwhelmingly dominated by cardiometabolic indicators: blood pressure, blood sugar, blood lipids, body mass index. These, in turn, are overwhelmingly responsive to the overall quality of diet. Degradation in diet quality, always a chronic liability and slow-motion menace, is- during the pandemic- a threat in fast forward. The notorious pandemic weight gain blithely dubbed “the COVID 19” acutely elevates the risk for adverse outcomes, from hospitalization to death. We can ill afford to be glib with lives literally at stake.

These acute concerns reanimate a vintage question related to appetite: do our cravings guide us reliably to what the body needs? 

I trust everyone recognizes that the Homo sapiens body is not subject to acute potato chip deficiency- so clearly, not every specific expression of dietary want is indicative of dietary need. But at a more general level- cravings for sweet, or salty, or savory; for the unctuous mouthfeel of cream, or for meat to sink teeth into- are often thought to hint at metabolic need. After all, the body is endowed with intrinsic wisdom predicated on its evolutionary craftsmanship. Accordingly, shouldn’t it be sending valid signals?

The answer to that question is both yes, and no, depending entirely on context. The best way I know to explain this involves a visit- figurative will do- to the great plains of the American West where the deer, and for our purposes more importantly, the antelope- play. 

Pronghorn antelope are a staple of the open grasslands of the American West- even today, when there are less grasslands and fewer antelope than once upon a time. Still, drive across Colorado, Wyoming, Arizona, and other parts of a range that once extended from Canada to Mexico, and you can’t miss them.

The pronghorn are lovely animals, but for our purposes here, just one thing about them is germane: they are simply too fast. The fastest land mammal in North America, the pronghorn can run at speeds approximating 60mph.

That speed need not be extraordinary; after all, gazelles in Africa can run that fast, if not even just a bit faster. But the gazelles have an excellent excuse for their speed, namely: cheetahs. That’s how natural selection works. Predator and prey are opposing beneficiaries in an arms race that evolution pushes relentlessly toward equilibrium. When chance mutations favor a bit more speed in the prey, only the fastest predators live to pass on their genes- and a new equilibrium comes to prevail. Cheetahs sometimes prosper at the expense of gazelles, and that is all the explanation we need for the gazelle’s speed.

But what of the pronghorn in North America? What predator stalks them at speeds exceeding 60 mph?

Today, absolutely none. The pronghorn are fleeing from ghosts.

Studies of this matter going back nearly 30 years suggest that super-swift predators stalked the open spaces of North America up to about 10,000 years ago. There were cheetahs here, too, back then- and a variety of long-legged hyena, along with an array of other threats fleet of foot and long of fang. The pronghorns were racing, routinely, for their lives.

Those predators are, alas, all extinct now- a dubious consequence of our own population of this continent. Wherever we go, mass extinction of megafauna- and in particular any predators that unnerve us- inexorably follows. Disadvantageous though this is for the web of life, the pronghorn may be described as beneficiaries. We dispatched the threat that any hunter might run them down.

But the pronghorn haven’t dialed down their speed in response. They can still run 60 mph, even though not a thing can now hope to catch them. That is at odds with the parsimony of nature, which tends to waste no energy. Why run 60mph if 40mph is more than enough to see you to safety?

Because the brilliant engineering prowess of natural selection is blind. When pronghorn genes for great speed offered an advantage, they were passed along to become the normal endowment of pronghorn newborns. When the advantage disappeared, there was no mechanism to reverse course. Until or unless being slower offers pronghorn a survival advantage, there is no way to undo the legacy of long-extinct predators.

Which bring us back to ourselves, our cravings, and the COVID 19. 

Our cravings are adaptive in context, like the speed of the pronghorn. A diet of actual foods derived from natural sources is highly frugal in its delivery of salt, sugar, fat, and meat. All of these take effort; none of these is apt to be over-consumed amidst the challenges of Paleolithic subsistence. Our cravings are adaptations related to survival, but not survival today. They likely tell of what our bodies need, but only when our bodies have the orientation of native context. In a modern context where salt, sugar, fat, and meat are all accessible in constant excess, and where junk has taken over as a veritable food group all its own- such impulses are all noise, no signal. 

Our options extend beyond resisting Stone Age longings that mislead us into modern temptation. The nature, intensity, and frequency of cravings is much influenced by the prevailing dietary pattern. Eat less salt, and lesser amounts are craved; ditto for sugar, added fats, and meat. Familiarity is one of the most reliable determinants of dietary preference, and we can all, step by step, “familiarize” ourselves with ever more wholesome, ever less processed food. I have long referred to this process as taste bud rehab, and it reliably alters taste preference, and reliably attenuates those pesky, obsolete cravings. We can all talk our taste buds out of loving the junk they once mistook for food, and into loving the food we choose to be with. We can all progress toward loving food that loves us back.

The pronghorn are stuck with their excessive speed, fleeing from ghosts. We, too, have ghosts- in our metabolic machinery- but understanding can set us free of their haunting influence. We are not obligated to feed them.