We have two house cats; one is fat and one is skinny. They were both born to feral moms about 4 years ago, one behind a pizza parlor and the other in a backyard. A non-profit trapped the moms as part of their TNR (Trap/Neuter/Return) program. The moms were spayed, treated and released. The offspring were also trapped or rounded up. We fostered the last one from each litter and eventually adopted both.
The backyard cat is a big, lanky, lean male. His pizza-parlor “sister” is smaller boned and very fat. They both eat the same food: supermarket “Fancy Feast” in 3oz (70kcal) cans, twice a day, plus Purina “complete” Cat Chow, ad libitum. The Fancy Feast is 11% protein, 2.0% fat, and 21.5% carbs (dry matter basis, calculated). The higher nutrition Cat Chow is 32% protein, 13% fat and 42% carbs (dry matter basis, calculated).
Both house cats seem to like both foods equally. They clean their dishes and put a big dent in the chow bowl daily. They also snack at an outdoor station where we feed our own small feral colony. That’s how we originally got involved with the local TNR non-profit. A litter of 4 adolescent ferals walked into our backyard about 14 years ago. They were way too old to socialize, so we fed and eventually trapped and TNR’d them all.
The food we give the ferals is the same Cat Chow (32% pro; 13% fat; 42% carbs), plus 2-13.5oz cans of Purina’s “Friskies.” The analysis of these 366kcal cans is again 11% protein, but 2.5% fat, and 27% carbs (dry matter basis). The ferals (and our house cats) also like these offerings equally, scarfing both down twice a day. Both the house cats and the ferals “know” each other and frequently eat side by side at the outdoor stations.
(As an aside, one of the ferals occasionally comes into the house, through a door left open in warm weather, and crosses to the kitchen to eat at the house cats’ station. But never, in the 14 years that we have faithfully fed them all, have any of the ferals ever allowed either of us to touch any of them, or even get close.)
All the ferals are lean. So why, given the way they are fed, is one of our house cats lean and the other fat? They both have access to all 3 types of food. Both have good appetites, and both have equal opportunities for exercise. Both run around the house and yard, frequently chasing each other or birds or butterflies. The big, lean male, is less active – more of a couch potato, but the fat female is completely undeterred by her girth.
If this were simply a comparison between two carnivores – our house cats – eating a high carbohydrate diet, one could hypothesize that the “pizza baby’s” genetic makeup was epigenetically “expressed” when she was exposed to the high-carb Fancy Feast and Friskies diet. Or, that the “pizza baby’s” mom already had those “expressed” genes (she survived by living behind the pizza parlor) and passed them on to her offspring who were thus born predisposed and are therefore likely to get fat on a high-carb diet. And our lean house cat – the “backyard baby” – was perhaps the product of a feral mom who hunted mice and voles and had a different set of genes or similar genes that had not been epigenetically expressed by what she ate. She therefore produced a large, well-shaped, lean male kitten. For further reading, see Dr. Cate Shanahan’s book, “Deep Nutrition.”
Restating the question: Why didn’t the young ferals who wandered into our backyard 14 years ago get fat on our nutritionally poor diet? Is it because they were offspring of a carnivorous mom who ate animal protein and fat and had not had her genes “expressed”? Is that why her offspring aren’t fat cats like our “pizza baby”?
We’ll never know. Our cats will never reproduce. But how about you and your offspring? We’re said to be omnivores, but I would say that humans, while not obligate carnivores, are perhaps facultative carnivores, a species that “does best on a carnivorous diet, but can survive-but-not-thrive on a non-carnivorous one.” This has been amply demonstrated, I think, by the effects that the high carbohydrate diet that we’ve been eating since the dawn of the Neolithic Age, made worse recently by the highly processed industrial foods we now eat.