All food is toxic. Not meat. Not plants. Not eggs. Not red wine. Everything.
This is a far more appropriate starting point for a discussion of nutrition than any other. It might sound a little controversial, but it won't take me long to convince you.
Let's start by looking at a couple of good reasons why this is a more apt perspective to start from than most:
We eat to not die as a priority over any other health goal on average. The red herring here is the fact that most people will report dieting to 'look good'.
Dieting, however, is a concern of the affluent. People with no cash will just eat whatever they can. This is most obvious in the correlation between poverty and obesity today—the relative cost of highly processed and refined food high in sugar is far lower than more healthy alternatives. A century-odd ago, low-income earners were a little better off because healthy food was cheaper in relative terms.
The fact that food can make you look good shouldn't make you forget it's first and foremost a survival need, because you respond to that whether you pay attention or not.
It's the fundamental motivation for the popularity of many current diet trends. Paleo, keto, and the 'carnivore diet aren't just trendy because they're new, but because they are making historically sick people feel far, far better with an emphasis on celebrities fixing their autoimmune issues.
This is, at the core, because they are strict elimination diets that are eliminating toxins from these people's food intake.
Because all food is toxic, which seems pretty important by itself.
Animal products can be bad for you
I won't spend too long on this, because I would be surprised that people didn't know animal products can be problematic. Two problems in particular are most often cited:
- Any meat probably causes cancer, if only because of the effects of cooking them, and preserved meats (e.g. processed, cured) almost certainly do.
- Meat, eggs, and dairy can also mess with the balance of the particles that transport cholesterol around the body.
A quick note on that last point: all cholesterol is actually the same and frankly quite crucial for you to continue living. The 'good' and 'bad' cholesterol that people talk about are actually different kinds of transporters for cholesterol. One type of particle transports cholesterol out of the liver, and one transports excess cholesterol back to the liver. The particles that transport cholesterol out of the liver are the "bad cholesterol".
There are two main reasons these outgoing particles can be a problem. You don't want so many of these that the other kind of particles can't deal with the excess cholesterol. This can cause issues, but not the ones people get all excited about. More importantly, if these outgoing particles are too small, they can get trapped in other structures in the body. When they get trapped, they can mess with our cardiovascular system in quite complicated and still not fully understood ways. It's so poorly understood that the connection between animal products and these particles are still not really clear—just that they seem related, and not always in a good way.
That said, if you had none of these outgoing particles, you'd simply die because nothing would be delivering cholesterol. You want them, you just don't want a whole bunch of small ones. This, you'll see, is the same principle for everything this article is about. Everything is toxic if you don't get too much or not enough of it. Too much "good cholesterol"—the other kind of particle—is also a problem for example, it's just harder to get there.
So, those issues, plus many other more or less dubious links to various illnesses that may affect us to a greater or lesser extent, are a problem if we consume too much animal products. Not to mention all the crap we feed animals that ends up poisoning us too.
The problem with all of this, of course, is that none of the links are proven to be causal, nor are they particularly specific. So, plenty of scope to argue one way or the other. Plenty to wind ourselves in knots about given that "too much" isn't really something that can be objectively identified.
Plant products are also almost all super bad for you
We might conclude, therefore, that the safer option is to just go for a plant-based diet. Vegetables are healthy, right? Of course not. Read the heading.
The plants we eat constitute a tiny minority of the plants. The reason for that is twofold. Firstly, a la Jared Diamond's Guns, Germs, and Steel, there really aren't that many plants suitable for cultivation on a large scale. The other reason is because plants are actually pretty scary.
Just anecdotally, imagine eating some unknown berries off a neighbourhood tree, or some mushrooms growing in your local park. With any luck, the idea triggers all the alarm bells you had socialised into you when you were small enough to want to eat random streetside vegetation.
This is because the whole thing plants do is try their best to not die before seeding. The most common way to do that is to develop defences against the stuff that wants to eat you. These defences are often toxic. Here's a list of some of the plants that are poisonous to animals. You'll notice that many of them are extremely familiar. The second entry is asparagus. I'd bet you never knew the asparagus you eat is baby asparagus, because grown-up asparagus have berries that induce vomiting and abdominal pain. I'll also bet you had only the vaguest idea that the homely raw potato:
affects the nervous system, causing headaches, diarrhea and intense digestive disturbances, cramps, weakness and confusion, and in severe cases coma and death
Plants are not benevolent creatures. Almost all plants are really quite bad for you and take issue (in the loosest sense) with the fact that you're eating them. It's only that tiny proportion which we've carefully cultivated over tens, or hundreds, or thousands of years that are reliably safe enough for regular consumption. These, we buy at the store, and don't think too much about it.
This also may be something of a problem. It is fashionable now to highlight all the ways in which even these grocery-store vegetables might be problematic in a similar kind of way to the more familiar red meat bashing. For example, the largest category of toxic compounds in plants are known to damage the DNA of humans and other non-human animals by way of clastogenesis. There are hundreds of thousands of these compounds, though, so we don't really have a good idea of how common this particular issue is. This, despite the fact that these toxic compounds are so ubiquitous that there are more than forty different kinds in the humble cabbage.
These concerns, and similar concerns about other plant compounds, are the main thrust of popular books like The Plant Paradox or the Carnivore Code. They really should be just as concerning to us as the research on meat and illness insofar as we have evidence that too much of these things seem like they can be bad for us.1
My point here is all food is toxic, with particular reference to over-consumption. We don't really know how problematic these toxins are, for the most part, or what the mechanisms might be. What we do know is that we should expect food to make us sick. And, because nutrition is a complex dynamical system, these factors are going to affect different people in different ways. Some more than others. That's why some people go vegan and feel much better, and some people go carnivore and feel much better and no one can explain why. No one really knows!
The problematic parts of plants are also good for us
Interestingly, these same features of plants that are causing consternation in some of the newest trendy diet circles are also causing excitement in others.
Agriculture is really a capitalistic enterprise at heart. The accumulation of goods, initially a means of subsistence but eventually for profit. This means you have to grow some good shit. It's no use trying to grow teosinte because people want it's more modern incarnation, sweetcorn.
This is a shame, because teosinte is something like 30% protein and 2% sugar. Sweetcorn is about 4% protein and 10% sugar. It's less of a shame for farmers and our tastebuds though because teosinte is both tiny and difficult to harvest as well as not very pleasant to eat. We deliberately breed out the undesirable aspects of plants from a taste and convenience perspective and this has led to a substantial reduction in the quantity of nutrients available to us. Those toxic compounds we read about earlier are one such nutrient. Some of these (again, who knows how many or how impactfully) act as antioxidants which are often seen as beneficial compounds which help us resist inflammation. You might know some of these: the resveratrol in red wine or the lycopene in tomatoes for example.
The breeding of plants for taste, size, harvestability, and robustness to transport has slowly bred out nutrients we know are associated with health. This is the thrust of another circle of health enthusiasts arguments, such as that written about in books like Eating on the Wild Side.
We could go ahead and pick a side here—decide we want more of these nutrients, or that we're happy these toxins are being bred out. But that would be missing the point. Nutrition is a complex dynamical system and both perspectives are probably both right and wrong in a way so complex as to be almost uninterpretable.
Eat heaps of everything (except obvious junk)
We have a similar thing going on with meat. Meat is linked unspecifically to a number of issues, but also contains important nutrients like creatine, choline, carnatine, and carnosine, which all seem pretty important for physical and mental health.
The point of this all, so far, is to make clear that eating is a necessary hazard, and we don't really know how much is too much or how little is too little. It's all good for us and bad for us. Probably, on average, it's all more good for us than bad so long as we don't invest too much in a small selection of foods. The more diverse the kinds of food we're eating, the more nutrients we get and the less likely we are to get a build up of whatever toxins are bad for us.
This is all noted without even touching on the human microbiome, with an emphasis on our gut flora. The bacteria and organisms that live in your body also eat what you eat and an extremely unnerving amount of evidence is emerging that the health of this community has incredible implications for your health.
I'm most familiar with the effects of the gut microbiota on mental health, and it really does seem like some mood-disordered outcomes are predominantly the result of an unhealthy gut and inflammation more than anything else. But, if we have only the vaguest sense of what food is good for our bodies and why, we have an even more fragile grasp of food and the gut.
What does seem clear in the health enthusiast circles of this domain is that variety is pretty important. Whether it's the Diet Myth or the Mind-Gut Connection, we see the same arguments for more kinds of fats, proteins, and carbohydrates as we do in the other dieting circles.
Of course, eating everything isn't really possible for a number of people. Issues like irritable-bowel syndrome and various intolerances must come into play. This is, in fact, the origin of many of these new diet trends. By eliminating all/most meats, or all/most plants we eliminate a huge number of possible toxins and so it should come as no surprise that the proponents of these diets are often recovering sick people. That doesn't, however, stop them from advocating eating as much of whatever you can eat as possible.
With a caveat.
The one set of foods that appears to be just clearly bad for us are those which have been heavily processed and/or refined with emphasis on high sugar content. Obviously not all processed food is bad for you. Not, you know, milk or flour. Not cooked potatoes (which, remember, would be quite problematic indeed unprocessed) or cooked chicken (which again, would be a worry uncooked). But food that has been artificially altered substantially from its more basic form is, as a rule of thumb, not ideal. From preserved or cured meats to refined sugar to even things like orange juice, which though minimally processed, has been refined such that its sugar concentration is obscene. These kinds of foods are, everyone seems to agree, quite a problem.
So, assuming you have enough money to not fall into the junk food trap, the first rule of good nutrition is to eat all of the things. Getting more specific than that is basically a leap of faith.
As an interesting tangent, 'nutrient pollution' is not just a problem for us! In conservation circles nutrient pollution or eutrophication refers to events in which too many nutrients enter bodies of water. This excessive fertilisation throws off the balance of these ecosystems. In particular, it encourages algae to go wild and strangle all the other life. Similarly, fertiliser burn is what happens when you over-fertilise your plants. Too much and the plant might be left unable to photosynthesise properly. ↩