Never Try Anything New

This post consists of three observations that may or may not be related to one another.


The Paleo diet is built on the premise that all animal species, humans included, are rigidly dependent on the foods that have been in their diet for the greatest amount of time. The genome of each species is like a lock that only one key will open, and that key is the specific food or set of foods that the species has evolved to depend on. Any other foods are like non-fitting keys that not only lack the ability to open the lock but destroy the lock when one tries to jam them in anyway.

In other words, animals are not very adaptable dietetically.

It was on the basis of this belief that Loren Cordain asserted in his book The Paleo Diet that the “333 generations [that] have come and gone” since the dawn of the agricultural revolution have offered “scant evolutionary experience” for the human body to adapt to “new” foods such as cow’s milk, and therefore these foods must be killing us.


The quino checkerspot is a species of butterfly that is native to Mexico and California. Since time immemorial it has eaten only one food, the dwarf plantain. Unfortunately, global warming has created climatic conditions in its native habitat that are too warm and dry for the plant to survive in. In the 1990s, biologists began to warn that when the dwarf plantain went extinct, the butterfly that was completely dependent upon it would disappear with it.

But then a funny thing happened. The two surviving colonies of checkerspots spontaneously migrated from their natural, sea-level habitat to a new habit at higher elevation. When biologists discovered this relocation they also discovered that the checkerspot had chosen a completely new food source—a flowering plant that has little in common with the dwarf plantain. Far from ruining the health of the species, this sudden and total transformation of the species’ diet has caused its population numbers to rebound dramatically.


Last year, Lawrence David and colleagues at Duke University conducted an experiment that was designed to study the effects of radical changes in diet on the microbiome in human subjects. The term “microbiome” refers to the large and diverse populations of bacteria that live in the human gut, and without which we would be incapable of properly digesting food.

The Duke researchers recruited 10 healthy volunteers (six men and four women between the ages of 21 and 32) and placed them sequentially on two different diets for five consecutive days. One diet consisted entirely of plant foods (grains, legumes, fruits, and vegetables), while the other diet consisted entirely of animal foods (meat, cheese, and eggs). As you would expect, the nutritional compositions of the two diets were divergent in the extreme. For example, on the carnivorous diet, subjects got 70 percent of their daily calories from fat and consumed zero fiber, whereas on the herbivorous diet, subjects got only 22 percent of their calories from fat and fiber intake increased nearly threefold from baseline levels.

After just three days on each diet, significant changes were seen in the composition and functioning of the microbiome in all subjects. On the carnivorous diet, subjects exhibited a marked increase in the presence and activity of bacteria that thrive in a bile-rich environment, which makes sense, because the gut produces more bile when digesting animal foods. In contrast, on the herbivorous diet, the subjects exhibited a large increase in the presence and activity of bacteria that metabolize polysaccharides from plants.

The researchers even noted changes in gene expression within certain strains of bacteria in response to the disparate diets. So not only had the human subjects rapidly adapted to changes in diet through their gut flora, but the flora themselves had adapted epigenetically.

In three days.