Zombie Metabolism: Nutritional Requirements

Introduction

I'm sure that when it comes to zombie metabolism, the first question has got to be 'Does the zombie diet meet its basic nutritional requirements?'.

Before the government fell, we were bombarded with nutritional advice, five-a-day, less cholesterol, more omega-3 oils, and now... let's just say, trans-fats are not my number one concern! And as for government advice? I'm pretty sure (no-one else believes me) that it was the Shadow Secretary of State I saw the other day, face-first in a dead dog... I'd recognise that comb-over anywhere.

But zombies don't follow government advice, mostly, they just follow us! (Ha! Sorry about the zombie humour, but if you don't laugh, you cry, etc. Though as long as you keep the noise down, either is good...)

Living on a diet of mostly meat and entrails, is it possible that they may begin to suffer from malnutrition, and eventually die.. properly? We hope so, but the news isn't good, human tissue may supply them with a surprising amount of their basic requirements. 

I used my Stryer for kindling a long time ago, so I will just have to go on memory. I'll start with the most obvious:

Protein

We all know that meat is an excellent source of protein. Human beings are capable of making a lot of amino acids themselves anyway. Many of these can be made from the intermediates of the citric acid cycle (we'll talk about that more if I'm still alive and not undead, later), glutamate being the most obvious. There are a number of amino acids that can be synthesized from other amino acids as well,
such as tyrosine from phenylalanine, which are also not essential to get in the diet, assuming that you can eat the precursor.

What about the essential amino acids? Those that we have no ability to make at all? Well, since the zombies are eating us, it stands to reason they will have access to all the amino acids that a human being needs, since they are in fact, eating human beings.

Fatty acids

This is a lesser known fact, but there are some fatty acids, absolutely essential for human health, that we can't make. But bad news, since many of these are used in the phospholipids of cell membranes, the zombies are again most likely getting what they need.

Having said that, it is not sufficient to simply get enough of these fatty acids. For optimum health, they must be consumed in the correct relative amounts. Back in the day when people used to worry more about what they ate, than about what ate them, most of us needed to eat more omega-3 fatty acids. A diet too high in omega-6 fatty acids may have increased the risk of cardiovascular disease, and perhaps even depression. Brain tissue is highly enriched in omega-3 fatty acids, but despite the well-known stereotype of the brain-loving zombie, they actually tend to stick mainly to the middle, where bones don't get in the way. 

Our meat, on the other hand, is probably relatively high in omega-6, but zombie hearts don't beat anyway, although they do look pretty depressed...

Carbohydrates

Diets were relatively high in carbohydrates back in the good ol' days, and the thought of worrying about the potential of carbs for weight gain makes me all nostalgic... Carbohydrates are not, however, an 'essential' part of the diet for human beings, because we can actually make glucose via the process of gluconeogenesis. But is this relevant to zombies? Only the liver (and the kidneys, at a much lower level) are capable of synthesizing glucose and exporting it. On the other hand, some tissues may carry out gluconeogenesis, without exporting the glucose, due to their lack of the enzyme glucose-6-phosphatase. Glycolysis is an important pathway, used by pretty nearly every living organism in the world, and I think it is likely to be equally important in the living dead organisms, especially considering their lack of circulation. I don't want to go into too much detail here, but this does merit further analysis.

In any case, both muscle and liver store glycogen, which may constitute a sufficient source of glucose for your average zombie, while their high protein diet may provide sources for gluconeogenesis.

Minerals

I wasn't going to mention iron, as zombies clearly get plenty of it! But then it occurred to me, it might not be clear why they need it - are there anaemic zombies? Well, next time you go out, while you are hacking your way through the hordes of the undead to loot your local Asda, just pay attention to the way that zombies don't appear to have any blood - plenty of slime and sticky black stuff, but no blood. You'll see, zombies don't so much bleed, as ooze. So perhaps they don't need iron as much as we do. But there are many enzymes that require iron atoms for their function, aconitase (citric acid cycle) for example, and the complexes of the electron transport chain often contain iron-sulfur clusters. This goes for many of the other minerals, such as zinc. They are often found in enzyme active sites, altering the ionisation states of amino acid residues or substrates. 

So minerals are undoubtedly essential for zombies, as even zombie enzymes will need minerals for their activity. Unfortunately, since they are eating us, they probably get enough in their diet.

There is one exception to this general rule - calcium. Great sources of calcium include things like dairy products, and broccoli. Not high up on the zombie food preference list. In us, the best source of calcium would probably be our bones, which zombies don't eat. The effects of calcium deficiency on zombies are quite obvious, and to our benefit. Their bones are extremely brittle and breakable, which is why it is so much easier to smash in the skull of a zombie, than that of another human attempting to take-over your territory.

Vitamins

There are lots of different vitamins, with lots of different recommended sources, but in general, we can say that we are probably a good source of all the vitamins that zombies need. Although there are two vitamins in particular that deserve a mention:

Vitamin C: Ask the average person about the best sources of vitamin C, and they will start talking about fruits and vegetables. So this might lead the average person to conclude that zombies will come to suffer from scurvy, and then to hope that their teeth will drop out, and they will be unable to chew on us (we've all thought about it at one time or another, haven't we?). But I'm afraid that these are idle hopes. The reason why meat is not usually considered to be a viable source of vitamin C, is due to the effects of cooking.

When fruits or vegetables are cooked, the vitamin C content decreases, roughly in proportion to the duration of cooking. (Please note that the bioavailability of other vitamins may increase, due to the breakdown of cell walls - this is why, when scavenging for food, fruit and vegetables should be prepared in a variety of ways, if the sound of cooking doesn't attract nearby zombies.) Since meat is normally cooked quite thoroughly, the vitamin C is all but destroyed. Zombies don't cook, which means that we do constitute a source of vitamin C. Sorry.

Vitamin D: Vitamin D is quite hard to obtain from foods, but is actually made in our skin on exposure to sunlight. Zombies don't go in for sunblock, and can be seen wandering around even in the middle of the day, when sunlight is at its most intense. However, if they are mostly covered in clothing, or if they have lost most of their skin, they may be suffering from a vitamin D deficiency, which could contribute to the weakness of their bones. Now I haven't actually seen any zombies with rickets, but come to think of it, zombies stuck in the London Underground are easier to smash than most...

Conclusion

So there we have it. With a few exceptions, it seems likely that the zombie diet does supply their basic nutritional requirements. To those who look at their hanging flesh and emaciated figures, the festering sores and the balding scalps, and say to themselves, 'they look pretty malnourished to me', we should remember that the zombie diet doesn't need to maintain optimum health and vitality, it just needs to keep them shuffling along. Remember, the zombie plague is a disease, not a lifestyle.