Human Errors #4: Dietary Needs

We are told of the importance of a balanced diet – carbohydrates, proteins, vitamins etc. But have you noticed almost no other species seems to need this?! Not pets, not wild animals – they die if they starve, but they don’t get diseases because they didn’t get a balanced diet. So why is it only humans need a balanced diet, asks (and answers) Nathan Lent in Human Errors.

 

When it comes to micronutrients (vitamins, minerals, amino acids):

“Our bodies fail to make many of the things that other animals do.”

Our terminology adds to the confusion: we call some nutrients “essential”, which sounds like “critical”. Wrong. Every nutrient is critical. When we say “essential”, we mean the body can’t produce it, so it has to be ingested. Never heard of Vitamin K or Q? That’s because the human body produces them; so we don’t care about them.

 

From an evolutionary point, something weird happened to us humans: we have lost the ability to make certain nutrients. In case of Vitamin C, for example, it’s because one gene in the chain mutated (the GULO gene); and unfortunately, that was a critical piece in the sequence:

“It’s as if you removed the spark plug from a car.”

Given that vitamin C deficiency causes a horrible disease called scurvy, which is fatal, how come that mutation didn’t get eliminated? That’s because our ancestor happened to live in a region (tropical forests) where her diet was rich in vitamin C; thus, the loss in internal capability didn’t matter. Until we moved away from those regions and our diet changed…

 

In case of Vitamin D, the ingested form “is not fully active”, which means it has to first be processed by the kidney and liver. The precursor is also produced in the skin, but only if we get enough sunlight. But of course, we migrated to non-sunny climates, we wear clothes that limit exposure of the skin, and we live indoors. It gets worse. Without Vitamin D, we can’t absorb calcium needed to keep our bones strong. Thus, a Vitamin D deficiency sets off a chain of other problems. You might ask: if that’s true, how could our ancestors move away from sunny climates, and start wearing clothes? Wouldn’t evolutionary pressure have, er, killed that move? Aha, but we learnt agriculture, alongside which we domesticated hens and ate eggs. Animal meat and eggs became continuously available, compensating for the change in environment.

 

Some nutrients aren’t produced by other species either e.g. Vitamin B12 and iron. Plants get them from the soil, and then they flow up the food chain. But even then, it is easier to extract certain micronutrients from animal food than vegetables. Hence non-vegetarians fare better than vegetarians. Wait a minute – how do herbivores handle this problem? Aha, their guts often have microbes that can do the extraction for them. Whereas our intestines are much smaller than proportionally sized herbivores, so we can’t extract enough. This is a recurring theme – we humans are comparatively worse than other animals in our ability to extract nutrients.

 

As if all this wasn’t bad enough, problems get compounded by our cooking and preservation techniques, which remove many nutrients. Even worse, for many nutrients, our body’s ability to extract nutrients degrades with age. And of course, our life expectancy only keeps increasing, so you get the picture. To add to our woes, certain food molecules interfere with the absorption of other nutrients. So eating more food with the right nutrient isn’t enough, one has to eat them in the right combinations.

 

It’s almost a miracle we live so long, isn’t it?