What do animals eat? (And how does this relate to an optimal human diet?)

(Geoffrey) #41

That’s a question I just don’t know for sure but I would surmise that it’s just a natural instinct that the mother has that tells her it’s time for them to start fending for themselves. Just like when the next rut is beginning the doe will fun off the young ones so she can breed again.

We actually do…well most humans do but I don’t. Humans eat leaves all of the time. Lettuce, grape leaves, poke salad, spinach, chard, dandelion, kale, goji leaves, celery leaves, beet leaves, mustard greens, collard greens, turnip greens, Perilla leaves and most herbs used are all leaves.
Grow a garden out in the country some time and you’ll see just how many animals eat the vegetables from that garden.

(KM) #42

Well yes, that’s basically the answer right there. Animals reproduce continually, they don’t produce two or three offspring and live with them for 18 to 30 years. If mammals were able to continue suckling their adult young, they’d wind up with 10 or 15 sucking them dry.


Hi Shinita, I’ve just been thinking more about milk and your input is very interesting indeed. It seems very probable to me that the reason mothers stop their young suckling is due to the need to have babies and raise more young for the survival of the species. This would be prevented by adult animals suckling as they would out compete the young animals for the milk.

This then leads me to wonder if another point you made is related to this? Is humans becoming lactose intolerant as they get older a way to ensure that there is no competition for the mothers milk from adults?

This was a bit of a light bulb on moment for me and Im not sure I would have come up with it myself. Thank you!


Many animals eat poop and dirt… Even some mammals. Yep, if the animal can get nutrients from it, it may be food.

I still am sure we can’t figure out what is good for humans looking at animal diets. As they are quite different from us in this regard. I mentioned that even some great apes need a diet we couldn’t do much with… And as @ffskier wrote and I think most of us very much aware, animals need survival in their own, very often not so great circumstances, it’s about survival. We can be way choosier, lucky us.

Isn’t seeds staple food for wild mice? IDK about birds, some are quite serious seed eaters. While zillion small birds eat animals (mostly insects) and seeds alike… Some birds eat fruits and some birds eat meat, some almost exclusive bones :smiley: But searching among the different species, maybe we could find birds eating mostly nuts and seeds… (Oh yes later I saw you wrote the same.) Sigh. I may watch documentaries all my life, I still don’t know enough of these things. I know what some animals eat but ratios and extra food in need…?

I still think many animals eat leaves and vegs isn’t a scientific term so I mostly translate it to leafy stuff. BUT if an animal eats leafy greens, they probably eat tree and bush leaves and grass and that is more numerous so it isn’t realistic to expect an animal to eat mostly vegs. It just makes no sense where grass and tree/bush leaves are everywhere. And all the other leaves that we don’t consider vegs.
It still wouldn’t say living mostly on vegs isn’t right, just that it’s not realistic in Nature where one usually should be opportunistic to some extent even as a herbivore. Living mostly on vegs is wrong for humans but we can’t see it looking at animals, just looking at our nutritional needs and the nutrients in vegs.

I wrote why, it seems wildly obvious to me. It doesn’t worth to provide for an offspring who already can get their own food. Evolution wants more offsprings (or in some cases, helping the existing ones like the grandkids but not the adults who are fine on their own already) and sometimes the mom needs some break too… There is the polar bear mom, giving rich milk to her cubs while starving for a long time… When they can eat something else, she can’t feed them anymore, she would die of hunger, she already lost the fat she could. I have huge respect for polar bear moms.

Bears are carnivores evolutionally. Some are herbivores, interestingly, poor things… :smiley: They have difficulties with the wrong food but they can survive and even slowly reproduce on it… Life does odd things sometimes.
We can get nutrients from both plants and animal food. Okay, that doesn’t make us omnivores as non-obligate carnivores and herbivores have this too (though I do wonder about cats, the obligate carnivores. they often eat plants - not as medicine, that’s different - , IDK about digesting it though)… But we too much depend on both and too effectively digest them both to be considered anything but omnivores IMO. We don’t need fermentation or cooking to get energy and enjoyment from plants.

Oh sure, if a diet needs supplementing, it’s not optimal in my opinion either. I just don’t see it right when people say vegans surely do it wrong due to the supplements when they eat a ton of supplements on their omnivore diet. It’s not what you did, I merely got reminded of that. And I personally always aimed to have a diet where my zero supplement behaviour doesn’t cause problems.
But a diet with some minimal supplements still may be healthy for some. Not everyone, there is no such diet. We have somewhat different needs. I can’t even do an optimal vegetarian diet (I can do an okayish one health wise I suppose) as my body wants a too low plant carb intake for it. Keto is easy but too carby with plants, for me (even if I eat meat). It’s very clear I don’t feel optimal with much plant carbs. But another person may live their best life there.

It depends on the species and the place where they live. Deserts, deep sea, mountaintops, they may be problematic. I saw documentaries about eagles suffering because there was no prey animal nearby (IDK why they lived there but they surely had some reason…). And of course, sometimes even the territory is too small because of humans…

Yes but very many still dies of starvation. Food scarcity is a serious thing in cold winters for very many animals. Main thing some survive and can make a lot of babies to help with the numbers. From the viewpoint of evolution. Evolution is a cruel one.

Not surprising to me. But it reminded me of chickadees. They are very opportunistic in winter. A big frozen animal is totally food for them. But why wouldn’t it be? It’s meat and it’s winter! IDK what other birds too, actually, apart from eating berries. Winter has more (both amounts and calorie wise) berries here than summer… But there are seeds too. We just feed the little birds to watch them, it’s not like they really need the support - but they still like it.

No, it’s still herbivore with omnivore-ish flavors :slight_smile: They still mostly eat grass :slight_smile: They just… supplement their diet. I don’t know why. Maybe it’s not even because of the nutrients, some ruminants are just that violent towards small animals coming close? No idea, really.


Thanks for your interesting reply.

With regard to the vegetables, your answer is exactly what I’m looking for. No animals eat our human created vegetables in the wild as they don’t exist, so should we eat them? How much of the aniamls diets do our hybrid vegetables constitute? Is it just a small part? Does it do them any harm healthwise?

There are wild versions of our fruits and vegetables as that’s where they came from originally. Do any animals eat these? From my research it seems that it’s pretty rare. As you say insects love them, but is that a warning for us not to eat them or or signal that they must be good for us to consume?

As to where i’m going with this train of thought, I’m trying to see if we can learn anything about what may or may not learn about what might constitute an optimal human diet by looking at what animals eat. So for example, horses eat grass but they have special stomachs and bacteria that we don’t have so therefore humans shouldn’t eat grass. That’s pretty obvious, but it gets more complicated when we get to nuts, seeds, dairy, honey, fungi and surprisingly vegetables. These are common and supposedly healthy human foods. How many animals eat these foods? It seems to me that the answer is surprisingly few. So are humans also one of these specially adapted animals or are these foods actually unhealthy for us and making us sick. I’m thinking lactose, lectins, oxalates and the such. Or does our ability to cook (fire) and ferment food (storage) make these foods edible for us? In that case should we be avoiding eating them raw? These are the kind of questions Im trying to answer and I think by looking at how many and what type of animals eat these foods, we might be able to get more of idea of which foods may or may not be healthy for us.


I think you and Shinta are on the right path with this answer.
As I put in my answer to Shinita:
"It seems very probable to me that the reason mothers stop their young suckling is due to the need to have babies and raise more young for the survival of the species. This would be prevented by adult animals suckling as they would out compete the young animals for the milk.

This then leads me to wonder if another point you made is related to this? Is humans becoming lactose intolerant as they get older a way to ensure that there is no competition for the mothers milk from adults?

This was a bit of a light bulb on moment for me and Im not sure I would have come up with it myself. Thank you!"

(Geoffrey) #47

Well nature does have a remedy for that. As long as the mother is still lactating she she cannot become fertile again. That’s why when a new male comes on the scene they will often kill all of the young so that the mothers will come into season again. This happens in the feline families, I don’t know about other species.


Hi Geoffray,

Thanks for your enlightened answer. A couple of replies from others have led me to this thesis regarding milk:

It seems very probable to me that the reason mothers stop their young suckling is due to the need to have babies and raise more young for the survival of the species. This would be prevented by adult animals suckling as they would out compete the young animals for the milk.

This then leads me to wonder if another point related to this. Is humans becoming lactose intolerant as they get older a way to ensure that there is no competition for the mothers milk from adults?

With regard to the vegetables, no animals eat our human created vegetables in the wild as they don’t exist, they just get them from farms and gardens. How much of the animal’s diets do our hybrid vegetables constitute? Is it just a small part? Does it do them any harm health-wise?

There are wild versions of our fruits and vegetables as that’s where they came from originally. Do any animals eat these? From my research it seems that it’s pretty rare.

The leaves question is very interesting. The reason I specifically stated tree leaves is because I’m not really sure where to place the green leafy vegetables in my categories! I didn’t want to complicate the thought experiment too much so I left them out. What category do you think they should be in: 2 - Grasses (and related plants) ie food that herbivore grazers would eat naturally, 3 - Leaves, shoots, trees ie food that giraffes, elephants and deer would eat, 4 - vegetables?

I’m tending to think green leafy veg would in their original forms be found in meadow type environments and therefore might be included in category 2. But they are now probably mutated from their original form that they should be in category 4 with vegetables. What do you think?


Ah very good point Geoffrey, I didnt know that. Ill add it into my thesis. Thanks.

(Geoffrey) #50

Interesting question. From my understanding it’s due to the evolution of man dependent upon the availability of milk to our ancestors. Milk was a common food to middle Europeans so they developed a tolerance whereas the rest of the world they didn’t. My heritage is German and Scandinavian, I am not lactose intolerant.

Good question as well. I believe it’s a small part just simply because there just aren’t that many home gardens growing near their natural habitats. But when there is the produce is like a candy store to them. One stop shopping for them.
In the wild they eat any and all fruit they can reach. It’s natures way of propagating the fruit species. With natural growing vegetables I believe they would only eat the greens or tops of them as most natural/wild growing vegetables are root vegetables (to the best of my knowledge) so the tops will be readily available.
Wildlife around commercial farm have a constant battle fending off the animals or as the farmers call them pests. In many cases the farmers are allowed to ignore the general hunting seasons and kill as needed to protect their crops.
Since there have been animals eating from the farms for as long as man has been cultivating the soil animals have been feeding on them so I doubt if there has been any harm from them doing so.

(Bacon is a many-splendoured thing) #51

Interestingly, a female rat will come into heat the evening after giving birth, and then will not have another oestrus until the pups are weaned. I once read an evolutionary explanation of this, but what I can remember of it no longer makes sense. But in the case of rats, I know that a strange buck on the scene may well kill the newborn litter and mount the doe, whereas the father will not. If these are pet rats, you don’t want the doe to become pregnant again right away, because pregnancy (and lactation) are a great drain on the mother, and two pregnancies back to back can be too much.

Mama rats can often sense birth defects in their pups, and while it seems grotesque to us, a mother will often kill and eat the defective pups, to recover the protein and nourish the remainder of the litter. Moreover, despite what I put in the previous paragraph, bucks are very tender and nurturing with their own litters, and they take especially good care of their sons when they start to grow old enough to teach. But this nurturing is not limited to the father, and sometimes other males in the colony will step in and help raise the pups. (This is especially true of neutered bucks in a mischief of pet rats.)

The size of rat litters is determined by the food supply. In the wild, a doe will generally give birth to only six or eight rats. Domesticated pet does, being better fed can have litters of up to around 18 pups. This is a challenge, because she only has eight teats.


A very interesting answer Paul, thanks for that.
Im just wondering if you are feeling OK though as you didnt mention bacon in your answer? Sorry, just a little joke to pay you back for your one earlier!

(Bacon is a many-splendoured thing) #53

Lactose intolerance does not develop until after weaning. It would be counter-productive in a nursing child. Human children can nurse well into their second or third year, and the mother can eventually become pregnant again while the child is still nursing. I believe it has something to do with the frequency of suckling, because the mother will almost invariably not become pregnant again until after the baby starts eating solid food.

Lactose intolerance develops some time between weaning and adulthood in all mammalian species.

It is the human default, too, but there are two specific mutations in human beings that allow the production of lactase in adulthood: one among the Maasai in Africa, the other among Northern Europeans. So if your ancestry is from either of those two populations, you are likely to be able to tolerate lactose in adulthood. But children from those lineages still get weaned at the appropriate time (usually later than is now customary in modern Western societies), and they don’t seem to compete for mother’s milk as adults. I’m of Northern European descent and love milk, but I can’t say I ever had the urge to nurse from my mother past, say, the age of six or so. (Of course, my focus was on men, not women, from age four or earlier.)

Sensitivity to milk proteins is an entirely different issue from making lactase or not, and many people who can tolerate lactose are nevertheless sensitive to milk proteins and therefore cannot have dairy, regardless.

:bacon::bacon::bacon::bacon::bacon::bacon::bacon::bacon::bacon: :rofl::rofl:


Hi Geoffrey,

Thanks once again for your insightful comments.

I was pretty convinced by your milk explanation but then I thought that as far as I know some sort of cow, goat or sheep exist in most places in the world. If that is so then milk would have been available to humans in those places. Maybe it’s to do with climate, but the Massai drink a lot of milk so temperature seems not to be a factor. There’s more to this I think. I hope we get a good answer.

I like your candy store and vegetables analogy for animals. It seems to be similar to humans and how pizzas, ice cream and soft drinks attract them away from their normal food. Both humans and animals are lured away from their normal food by the easy available, fattening calories. I wonder if the harms to health for the animals are similar to the harms for humans. Bears go diabetic shortly before hibernation as they fatten up, but this then goes away as they use up their fat during hibernation. I would think the limited quantity of vegetables and the fact they are only available for a restricted time that the effects on the animals health would be minimal. I wonder if rabbits kept as pets would give us the answer - is there such a thing as pet rabbits getting fat from eating too many carrots etc?

One point I’m unsure about though is with the assertion that “In the wild they eat any and all fruit they can reach. It’s nature’s way of propagating the fruit species. ” You have a lot more experience than me in this area but I’m wondering if this is limited to certain animals who are especially adapted for this rather than being widespread in the animal kingdom. It seems from the passage I quoted below fruit eating may require a specialised gut. My question is therefore, since we are descended from monkeys, who eat fruit, have we retained this specialsed gut, or have we lost it? Tree leaves form a large part of a monkeys diet and we have lost that ability. What about the fruit?

This is what I found on wikipedia (yes I know it may not be 100% trustworthy but it is the best summary I could find).

Frugivore adaptations for fruit consumption

Many seed-dispersing animals have specialized digestive systems to process fruits, which leave seeds intact. Some bird species have shorter intestines to rapidly pass seeds from fruits, while some frugivorous bat species have longer intestines. Some seed-dispersing frugivores have short gut-retention times, and others can alter intestinal enzyme composition when eating different types of fruits.[2]

Plant mechanisms to delay or deter frugivory

Since plants invest considerable energy into fruit production, many have evolved to encourage mutualist frugivores to consume their fruit for seed dispersal. Some have also evolved mechanisms to decrease consumption of fruits when unripe and from non-seed-dispersing predators. Predators and parasites of fruit include seed predators, insects, and microbial frugivores.[8]

Plants have developed both chemical and physical adaptations:

Physical deterrents:[9]

Cryptic coloration (e.g. green fruits blend in with the plant leaves)

Unpalatable textures (e.g. thick skins made of anti-nutritive substances)

Resins and saps (e.g. prevent animals from swallowing)

Repellent substances, hard outer coats, spines, thorns

Chemical deterrents:

Chemical deterrents in plants are called secondary metabolites. Secondary metabolites are compounds produced by the plant that are not essential for the primary processes, such as growth and reproduction. Toxins might have evolved to prevent consumption by animals that disperse seeds into unsuitable habitats, to prevent too many fruits from being eaten per feeding bout by preventing too many seeds being deposited in one site, or to prevent digestion of the seeds in the gut of the animal.[10] Secondary chemical defences are divided into three categories: nitrogen-based, carbon-based terpenes, and carbon-based phenolics.

Examples of secondary chemical defenses in fruit:

Capsaicin is a carbon-based phenolic compound only found in plant genus Capsicum (chili and bell peppers). Capsaicin is responsible for the pungent, hot "flavor" of peppers and inhibits growth of microbes and invertebrates.[8]

Cyanogenic glycosides are nitrogen-based compounds and are found in 130 plant families, but not necessarily in the fruit of all the plants. It is specifically found in the red berries of the genus Ilex (holly, an evergreen woody plant). It can inhibit electron transport, cellular respiration, induce vomiting, diarrhea, and mild narcosis in animals.[10]

Emodin is a carbon-based phenolic compound in plants like rhubarb. Emodin can be cathartic or act as a laxative in humans, kills dipteran larvae, inhibits growth of bacteria and fungi, and deters consumption by birds and mice.[8]

Starch is a polysaccharide that is slowly converted to fructose as the fruit ripens.


Hi Paul,

Glad to see the bacon’s made a comeback.

That was a really insightful answer, especially the part about ALL mammals becoming lactose intolerant as they grow up. I really didn’t know that. Very interesting and makes sense.

I’m starting to think diary might be the most difficult category to get a conclusive answer to as to whether it can be part of an optimal human diet. I think that we may have to look on dairy consumption as a specialised adaptation for certain humans (Masai, Northern Europeans etc), perhaps similar to how Pandas have adapted to eat only bamboo leaves whilst polar bears eat only meat.

(Edith) #56

You may enjoy looking up podcasts and other information by Bill Schindler, PhD. He is an experimental archaeologist and anthropologist who specializes in the evolution of food production.

According to him, until the past 100 years or so, our development of food processes involved making the food more nutritious: fire, soaking, fermentation, nixtamalization, etc. It is these processes that have allowed humans to become consummate omnivores that can live in pretty much any environment we choose.

Once the industrial revolution kicked in, food advances have been more for improving shelf life, increasing production at the expense of nutrition, creating addiction, etc.


Wow Edith thank you for the recommendation. That’s exactly one of the things Ive been wondering about. It will be great to listen to someone who really knows what theyre talking about when it comes to this subject. Thanks so much.


Carrots are way too sugary for rabbits, the candy analogue is spot on there. They shouldn’t eat much of it just like a kid shouldn’t half-live on candy, no matter if there is undereating involved or not. I would except rabbits getting sick, not just fat. But I am no expert for sure! Just a curious one liking animals and reading and watching things about them.
If the rabbit eats a lot of green leaves, that’s probably good for him? Not all vegs are alike. But maybe rabbits still need mostly grass? But if a proper leaf eater eats leafy vegs, that should be the right food. The attraction surely comes from 1. it being good food 2. easy access, tender stuff… If it’s too sweet compared to the normal food of the animal, that can cause problems. Humans made some super sweet vegs…

We clearly can digest fruit… A ton of sugar still isn’t good for us, though. But how we humans eat fruit and the sugar content of the fruit we eat is usually very little to do with natural resources…

Of course it can be. I would lose the will to live without dairy :smiley: It is not merely optimal but the only not miserable way of existence for me! But it really can help with nutrition and I don’t see any problems for people who can digest them well. And overdoing it is bad but it’s true for everything including water.
And I am pretty sure I digest milk WAY better than pandas digest their suboptimal poor leaves… I pity them. (They are still cute, of course. And they still are extant so they did it well enough.)


Since there has been some discussion around the definition of vegetables Ive been doing some thinking and some research. From the comments it seems what people define as vegetables varies and is pretty much an invented food category rather than anything scientific.

However, with this thought experiment, what I am eventually trying to get at is, can we learn anything about an optimal human diet via examining what animals eat? Therefore for the purposes of this discussion I am going to use the supermarket definition of vegetables ie if you can find it in the vegetable section of your supermarket, then for the purposes of this discussion it counts as a vegetable. Just for clarification this would includes things such as root vegetables (carrots, beets, potatoes), those from vines (tomatoes, green beans, pumpkins), leafy greens (lettuce, spinach, cabbage), legumes (beans, chickpeas, lentils) etc etc etc

As a special note regarding leafy green vegetables I was considering putting them in category 2 - Grasses (and related plants) ie food that herbivore grazers would eat naturally. However upon researching the matter further it seems leafy greens such as lettuce, spinach and cabbage have only been in our diet for a few hundred to 2000 years and have been so hybridised that they no longer bear any resemblance to what can be found in the wild!


Thanks for your comments Shinita, very interesting and thought provoking as always. I agree with most of your points this time. However I’m not sure about the fruit statement. I know that if people eat too much fruit they get diarrhoea - it happened to me once with pears and affected me for 5 days or so! I not sure I would call that optimal, edible maybe, but not optimal.

And as for Pandas and their leaves being suboptimal, I’m not sure that is the case. Since they are extremely specialised to eat only bamboo leaves I would tend to say the opposite and say this is actually their optimal food. However this is only my thoughts and I have no evidence to back this up. Maybe someone else knows better than us?