Howdy freedivers, and welcome to this week’s update from our number one furry fanatic, Dr Otter!

An oft-neglected but essential part of Freediving performance is a good solid diet and today we’ll be looking at some important aspects of nutrition. Specifically, we’ll examine the role of iron in the diet, and look at some ways to ensure you’re getting the right amount.

No Cyril, not that kind of Iron…

What Makes a Good Diet for Freediving?

Avid fans of this blog-spot will probably already be familiar with Dr Otter’s approach to the Alkaline Diet which is far and away the most-quoted (and probably the most useful) approach to freediving nutrition. For a full rundown on the physiology behind it, you might want to check out the original article here, but in summary, although there are some issues with the idea of “alkalinising the blood” the alkaline diet is unambiguously good for freediving because:

It promotes a high intake of fruit and vegetables It decreases the amount of processed food and additives you’ll consume which reduces the “acid load” that the kidneys have to deal with. It more broadly helps us to focus on nutrition as an important part of performance It may help the body to deal more effectively with , but this needs more research.

One thing that an Alkaline diet won’t necessarily do for you, however, is help you get enough iron which, as we’ll see below, might end up being a bit of a problem…

Why is Iron Important for Freediving?

Again, this is a question that Dr Otter has tackled before, as part of our extended series on static breath-hold. You can find the relevant article here. In short, though, Iron is an essential component of Haemoglobin which, as most of you will already know, is the protein in Red Blood Cells which carries oxygen, and Myoglobin, which does the same thing but in muscles.

At the atomic scale, haemoglobin looks something like this:

You can see the haem - that is, iron containing - groups in green. There are four of them. Simply put, the more haemoglobin you have in your blood, the more oxygen you can carry, and you can’t make haemoglobin at all without iron. If you’re(that is, you’ve got too little haemoglobin in your blood) you’ll definitely struggle to hold your breath as long as the next guy. And the leading cause of anaemia? You guessed it - iron deficiency - it’s as simple as that.

Will Eating More Iron Increase the Amount of Haemoglobin in my Blood?

This, unfortunately, is a much more difficult question. Here’s a diagram that shows how iron is absorbed utilised in the body:

As you can see, iron is absorbed from the gut and the majority of it is indeed contained in haemoglobin. You’ll also notice, though, that a lot of other cells, including those in the bone marrow, take up iron. This means that taking in more iron doesn’t necessarily mean you’ll get more haemoglobin. You could end up with more of other cell types - or indeed free iron in the blood instead.

Another important thing to notice is that losses of iron from the body are minimal - the body really doesn’t have an effective way of getting rid of iron and this means that, if you’re not careful, you can actually end up poisoning yourself by taking too much iron in your diet. If this happens gradually over time, it’s usually called haemochromatosis and can actually be fatal. Here you will find a great article about iron supplement.

Thankfully, overloading yourself with iron is actually pretty hard to do for the simple reason that you tend to absorb only “what you need” from your gut. “What you need”, though, is really the tricky thing to pin down here.

As a freediver, you’ll obviously want the highest concentration of haemoglobin you can get, but the systems that control erythropoiesis (red blood cell production) in the body have other things to consider: The higher the concentration of haemoglobin in the blood, the more viscous (that is, sticky) it becomes and the more likely you are to have a stroke or a heart attack as a result.

Hard-out erythropoiesis is usually only triggered by things like altitude training or prolonged hypoxia and, unless you’re really training specifically in those areas, you’ll probably find that regardless of how much iron you eat (assuming you’re getting a basic minimum), the level of haemoglobin in your blood doesn’t change a huge amount. Normal levels are between 14 and 17.5 g/dl for Men and 12.3-15.3 g/dl for Women and you’ll be doing well to budge them from that range by diet alone.

What Can I do to Make Sure I’m Getting Enough Iron?

Notwithstanding everything in the previous section, it’s important to make sure that your daily intake of iron is high enough that it’s not a limiting factor in the amount of erythropoiesis your body can support. Estimates of the actual amount you require vary wildly (in a short search today I found everything from 1-33mg a day recommended) but for most adults, the consensus seems to be about 8mg a day, or around 14-18mg if you’re a pre-menopausal woman. Children, of course, need less than this and if you’re in an altitude or prolonged hypoxia training cycle, it’s probably a good idea to have more.

Iron is actually pretty poorly absorbed in the diet (that's why you need to take in more than the 1-2mg you're losing each day), and is barely absorbed at all in its oxidised form (Iron III). Traditionally we think of red meat when we think of foods that are rich in iron, because this is where a lot of readily available (reduced) Iron II (also called haem iron) can be found. For Freedivers, though, red meat is a bit of a disaster, having a high acid load, lots of saturated fat, and being pretty difficult to digest.

But don’t panic. The status of beef and lamb as the best source of dietary iron is probably a myth put about by the meat industry. In fact, it actually contains a rather measly 3.8g/100g. There are plenty of foods that have a much higher iron content than steak which won’t make you feel like Austin Powers’ nemesis “Fat Bastard” on Christmas Day. Here are some of them:

Spirulina (28.5mg/100g) - Just don’t try eating 100g of it…

Cashew Nuts (6.05mg/100g)

Pumpkin Seeds (8.07mg/100g)

Dark Chocolate (17.4mg/100g)

Cooked Spinnach (3.57mg/100g)

Tofu (up to 9.73mg/100g) - depends on preparation methods

The one objection that meat lovers might make to this list (which, by the way, is as long as your arm) is that a lot of Iron from plant based sources is in the oxidized (Iron III) form which is poorly absorbed. This is, in fact, true, but there’s an easy solution: Vitamin C. This is found in foods like citrus fruit, green leafy vegetables, broccoli, kiwifruit, bell peppers etc etc. and helps to reduce the Iron III to Iron II (“haem iron”)which is much more easily absorbed. Unlike Iron, vitamin C is excreted easily from the body and so it’s really very hard to overdose. Knock yourself out.

What About Iron Supplements?

As long as you’re taking something less than 14mg of haem iron a day from your supplement, you’re likely not doing yourself any harm, but the bottom line here is that, unless you’re actually iron deficient, you’re probably wasting your money. A healthy diet which contains adequate amounts of green leafy vegetables, nuts, seeds and pulses, as well as lots of Vitamin C will almost certainly supply all the iron you need.

In addition it’s worth noting that pretty much the only way you can kill yourself or cause significant iron toxicity (unless you’re cooking every day in an iron pot) is by overusing supplements. It’s actually pretty easy to kill yourself (or especially a child) by overdosing on iron. As little as 3g (10 prescription tablets) is enough to kill a 2 year old. I can think of better ways to go…

Got a burning Physiology or Medical Question? Get on the cyberspace blower to Dr Otter direct at info@freedive-earth.com. See you next time!