The 'Appeal to Nature' Fallacy

“It’s natural! It must be good for you, right? All those synthetic chemicals are so unnatural and bad for you, but this is natural so it’s good.” I know you’ve heard that before. You know what, that might even be you. (If it is, stop it. Here’s why).

People like to make contrasts between the man-made world and the natural world. People also incorrectly assign good or bad traits, such as healthiness, to objects based on this classification. Here’s a little example.

Snake venom. Hey, it’s natural, it’s fine! Deadly Nightshade. A natural flower, can’t hurt me. Cancer. Who can argue that’s not a natural process? Tobacco, hemlock, poisonous mushrooms, the list goes on. The point is, just because something is naturally occurring, doesn’t mean it is beneficial to health or even safe. The flip side is also true: Synthetic things do not have to be bad for you.

The reality is that the toxicity of a substance is on a sliding scale, completely independent of the source, whether naturally occurring or man-made. For example, a sugar molecule is a sugar molecule, regardless of how it became a sugar molecule. It has a specific formula and structure and will be processed in the body in exactly the same way if you got it from a banana or synthesised it in a chemistry lab. Similarly, whether you feed someone cyanide from a lab, or cyanide from almonds, they’ll die. (Don’t do this). This is an incredibly important point that many people do not understand. Their “super-healthy all natural green tea extract” can just as easily be synthesised in a lab, and you know what, it will be exactly the same molecule and have the exact same effects in the human body.

This leads into my next point: All things are made of atoms, stuck together in various combinations to make molecules. This might seem like an obvious statement at first, but there are a lot of hidden implications here. The effect of any substance in the body is solely dependent on the shape of the molecule and the atoms that make it up. All natural things, all man-made things, they are all ultimately made up of exactly the same building blocks.

Just in different proportions.

 Furthermore, the human body is essentially a blob of enzymes. An enzyme is a folded protein molecule with a certain shape. Molecules interact with the human body by fitting into the shapes in the enzyme molecule. This is interaction in the body at its most fundamental level: the shapes of molecules fitting into shapes in enzymes. These enzymes have no way of discriminating between the molecules that interact with them; as long as they are the correct shape, an interaction occurs. This is common to every single living organism on earth.

Cue abusive comments from overzealous biologists

One area in which this is easily demonstrated is in the pharmaceutical industry. They aim to synthesise molecules with just the right shape to mimic molecules that are already present in the body, in order to interact with particular enzymes, in order to get the desired effect. We understand in extreme detail how the vast majority of drug-enzyme interactions work, right down to the molecular level and the actual shapes of the objects involved. This is why painkillers, antibacterials, antidepressants, statins, stimulants, anti-cancer drugs, anti-seizure drugs, and every other drug ever developed for humans and animals works – because they mimic naturally occurring molecules. And the simple fact that all of these are undeniably active, useful substances with quantifiable and predictable responses demonstrates that the human body, and indeed biology in general, cannot discriminate between ‘natural’ and ‘man-made’ molecules.

Note the similarity in structure - this causes the amphetamine molecule to target receptors designed for dopamine in the brain, and cause change in mood, euphoria, focus and increased heart rate.

This principle extends to completely inert and inactive molecules in the human body – if a molecule doesn’t fit into any enzymes, and doesn’t react with anything in the body, it will pass out of the body unchanged with no effects on the body. These inactive molecules can be man-made or natural. A natural example is dietary fibre in your food. Made up of glucose molecules (a type of simple sugar), the molecules are woven together in a way that your digestive enzymes cannot attack, and so they pass through the digestive tract untouched. A man-made example is blood-replacement fluid made of perfluorocarbons, which are completely synthetic molecules made of carbon and fluorine. These never occur in nature, but are so inactive in the body that it is perfectly safe to pump them by the litre into your veins. Blood substitutes are widely used throughout the medical industry to address blood bank shortage issues, avoid disease transmission and replace large volumes of blood lost in an accident.

Breathing fluids such as LiquiVent have a high capacity to dissolve gases such as oxygen, and so are used in situations where lung function is compromised, especially in neonatal care.

So next time you hear someone say that they prefer ‘natural’ things, with the sole justification that if it’s natural it must be healthy, feed them a pufferfish.