Aidan:

Hello and welcome to episode 253 of the Ideal Nutrition podcast. My name is Aidan Muir, and I’m here with my co-host, Torwen Eerkins. And we are going to be talking about how much certain nutrients affect iron absorption. We are doing this for a few reasons. One is I want to do something a little more practical. We have done plenty of iron deficiency type stuff. I just want to talk about some specific numbers.

And changes you could potentially make. Or changes that might not matter at all. One of the places I wanted to start is a kind of personal story. It is relevant for me as a dietitian. When I first became a dietitian, I had learnt that calcium’s absorption is inhibited by caffeine or coffee consumption. Technically, that is true. I was telling people that for a year. I remember working with certain people who wanted to increase their calcium intake.

Then they say they have milk in their coffee. And I remember sharing this fact with them. About how calcium is inhibited by caffeine. Then one day, I do not know how or where I learnt this, but I learnt the difference is so insignificant. And I started looking at research on this. We are talking about such a small difference. We are talking something along the lines of this. If you had a cup of coffee with 300 mg of calcium, about 6 mg is inhibited. I was like, damn, I have given people information that is technically true.

But it probably makes their life worse. Probably, yeah. It is just not a good thing to be doing. Then it made me start asking questions about a lot of other stuff. If somebody says this improves absorption, the next question is always, how much by? Is it meaningful? The same thing if this inhibits absorption. How much by? I think that is a very relevant discussion in the iron space. Deficiency is so prevalent. If there is advice around doing things to improve absorption or decrease it, I think it is worth knowing how much this matters.

Torwen:

Absolutely. And when we talk about nutrient bioavailability, we mean the portion of that nutrient that is absorbed and used through food. It is absorbed through the cells lining the intestine. So, iron has been reported as about 25 to 30% absorbed from organ meats. It is about 7 to 9% from vegetables. It is 4% from grains. Then, around 2% from dried legumes. Obviously, that is a huge array. It does make a big difference.

So, we are going to be going through what makes a difference in absorption. We are going to start with the positives. So, enhancers of iron absorption. I want to start with vitamin C, or ascorbic acid. That is the biggest enhancer, especially for non-heme iron absorption.

Before we run through this, maybe we should do a little background on the different types of iron. We have previously done an episode, like Aidan mentioned, on iron deficiency. That is episode 239, if you want to go and have a listen. In terms of nutrition strategies specifically, heme iron comes from animal sources. So, things like red meat, poultry and fish. It is absorbed more efficiently by your body.

Non-heme iron, on the other hand, is found in plant foods. Things like lentils, beans, spinach, fortified cereals and whole grains. And absorption is much more variable. It is influenced by what you eat. So, if we circle back again to enhancers of iron absorption, vitamin C, we are mainly looking at absorption of non-heme iron. The way that it works is it helps convert ferric, or Fe3+ iron.

It converts it to the more absorbable ferrous, or Fe2+ form. That means it is more soluble in the gut. Even adding something like 50 milligrams of vitamin C to a plant-based meal can actually double iron absorption. It can even increase it up to six times in that meal.

Aidan:

And that would also apply to certain vegetables as well. If you had a decent amount of vegetables, we can talk about anti-nutrients later. You could get to that 50 milligram kind of range through that as well. So that would be super relevant too.

The next one we will talk about is not an absorption one. But it is kind of an additive one, in a way. It is cooking in cast iron. This is something I had seen a lot of people talk about. But I was unsure how much it mattered until a few years ago. It can increase the iron content of food by around 15% on average.

With all of these numbers, I, or both of us, put a bunch of research into the show notes. We have combined the research that has specific numbers, and our own take. For example, if one study said 12% and another said 17%, I will use a number like 15%. The numbers will not line up 100% perfectly.

But it is using a bit of our own judgement as well. With the cast iron thing, it is around 15% on average. But there are some cases that are noticeably higher than that. For example, if something is cooked in a tomato-based sauce, the absorption has been measured to be noticeably higher than that as well.

Torwen:

The next one is in terms of supplements. Sometimes supplementing on an empty stomach can help. That is because it reduces competition between that iron supplement and inhibitors. We are about to talk about those in the next section.

Aidan:

On the effectiveness of that, what I found was this. It seemed to be about 40% better on an empty stomach. But there were catches mentioned that are pretty clear. For example, it does seem to increase the likelihood of gastrointestinal symptoms. So whether this should be done is on a case-by-case basis. In some cases, it would make sense. In others, it is probably worthwhile trying to address that. Often, that is one of the biggest reasons that stops people from supplementing.

Torwen:

Cool. Did you have any other positives that you wanted to chat about?

Aidan:

Another interesting one was animal sources alongside plant sources. Having animal sources alongside plant-based iron sources improves absorption by about 1.5 to 3%. Specifically, because we know there is more heme in animal-based sources, non-heme iron absorption increases, even though the meat contains heme iron. I do not think I have put it in here. But I was talking to Tyler about this the other day.

We massively simplify it by saying heme iron and non-heme iron. As in, animal contains heme iron. If you actually do the measurements, animal products have both heme and non-heme. There is a varying ratio amongst that as well. Maybe a bit too deep for this podcast. But I just thought I would chuck that in there too.

Torwen:

Cool. Now there are obviously negatives as well. Or things that block iron absorption. And decrease availability in the body. The first one I am going to start with is coffee and tea, or polyphenols. They can actually decrease the absorption of iron quite significantly. There was a study that looked at iron-replete adults. So they have enough iron. It looked at a cup of coffee with a hamburger meal. It reduced non-heme absorption by about 39%. Then a cup of tea was about 64%. So it does show that tea is potentially a more potent inhibitor there.

Aidan:

Yeah, absolutely. That was one of the first things I wanted to look at after the calcium thing. Everyone says this inhibits iron. Does it actually? Unfortunately, yes, it does. One very positive thing is keeping coffee and tea around an hour away from meals, either before or after, largely stops this from being an issue.

One of the things that had me curious was this. There are a lot of people who have caffeine in their system for most of the day. I was curious if this has such a big impact. Is this an issue? Is this a big thing? But it actually seems mostly fine if you separate it by an hour. That is kind of odd in a way. If it was about the caffeine specifically, that would be peaking in your blood 30 to 60 minutes later. So that is interesting. But then if you go through the tannins and other polyphenol angle, it might make more sense too.

Torwen:

I think I also saw that it does have a bit of an effect in terms of strength. Specifically, caffeine or coffee strength. So it does seem to be a concentration-dependent effect as well. If you are having lots of caffeine, and it is stronger caffeine, then it makes sense to be more cautious around that hour. If not, a little bit longer.

Aidan:

Now we are going to talk about calcium. Calcium is another one that a lot of people talk about in relation to iron. It is hard to say how much it matters. One of the first times I ever saw this in practice was this. I saw a 12-year-old boy who was low in iron. That is rare enough for males to start off with. But he was having three litres of milk a day. I was like, this checks out. This is the first time I have seen something like that.

This is because calcium and iron compete for absorption. For context, so do zinc and magnesium. All four of them are competing together. So, having too much calcium alongside iron can reduce absorption. This applies to both heme and non-heme iron. For what it is worth, a lot of what we are talking about today is far more relevant for non-heme iron. That could be because there is more room to move on that. The levels of absorption are so low to start off with.

Anyway, in terms of how much this matters, dosages of 300 to 600 milligrams of calcium can often reduce iron absorption by 20 to 50%. If I was to add context on that, that is around one to two cups of milk.

Torwen:

That is similar to what I had as well. It does appear a little bit that the type of calcium potentially matters too. That is if we are talking about calcium supplements. But again, I think it just makes sense to say, let us split those up. Rather than taking them at the same time.

Aidan:

Absolutely. This also has ramifications for how you supplement as well. If you look at a regular multivitamin, you often find that most regular multivitamins are really low in calcium. This is partly why that is the case. There are definitely exceptions to that rule. But that is a factor.

Torwen:

The last one that I have got then are phytates. They are found in a lot of plant-based foods. Whole grains, veggies, beans, all those sorts of things. That makes this a little bit hard. They bind to non-heme iron. And they form insoluble complexes that then further reduces absorption. They can reduce non-heme absorption by up to 50 to 70%, which is another quite significant reduction.

Aidan:

Yeah, it is pretty massive. We were on the fence about whether we include that. I think, I do not know, you were in the Instagram post that we are making. You were on that, no. We did a collab with five people on an Instagram post on this. We decided not to put phytates in. I do not want to scare people off eating fruits and vegetables. And all these good things that are consistently associated with good health.

On the other angle, it is actually one of the biggest inhibitors of iron absorption as well. But you can also get around that by having a higher intake of iron. People who are plant-based are often recommended to have double or triple the amount of iron. That helps them reach their needs. Even if absorption was hard, if you had double it, it would solve that. Another way around that is adding vitamin C once again. That can improve the absorption as well.

Torwen:

And those foods maybe contain both. So it becomes a bit of a double-edged sword in terms of what you are looking at. I think focusing on the positive sometimes makes a lot more difference. More than saying I should cut these foods out completely.

That sounds good. We will wrap up there then. Thank you for tuning into today’s episode. As always, if you are concerned about your iron status, please go chat to your GP. And get some blood tests done. This has been episode 253 of the Ideal Nutrition Podcast. If you liked our episode, please leave a positive review. Thank you.