29 April 2021

Why we can’t depend on diet for iron

Clinical Diet

Our diets may now be too deficient in iron to practically meet our needs, leaving us reliant on supplements, one iron expert believes.

While the agricultural revolution led to a food innovation and a subsequent population boom, it changed the composition of what we ate forever.

And this shift in our intake, from a seasonal forager lifestyle to one in which we can eat all sorts of foods from across the globe, regardless of season, may ultimately be leaving us deficient in at least one nutrient.

Associate Professor David Frazer, head of the Molecular Nutrition Laboratory at the QIMR Berghofer Medical Research Institute believes that the common advice to try to get all our nutritional, specifically iron, needs met through our diet may be setting patients up for failure.

“The trouble is, because our foods have changed so much, I don’t think that’s entirely possible any more,” he said.

The average woman in Australia takes in about 10mg of iron per day, and the average man takes in around 12-14mg, possibly due to higher meat intake and food intake in general.

However, the recommended daily intake for women is 18mg per day, leaving a big gap. And Professor Frazer and colleagues believe the RDI should actually be much higher.

“Studies that have been done on hunter-gatherers, and estimates on what we used to eat, range from 80mg per day if you’re on predominantly a vegetarian diet to 120mg, if you’re on predominantly a meat-eating diet,” he said.

“That’s far in excess of what we actually need, and probably explains why our deficiencies are high, considering we’re eating probably one-tenth of that now.”

“It’s hard to see how we would have evolved to be so dependent on something that is so hard to get,” he said, considering that iron deficiency during pregnancy causes cognitive and physical developmental problems and other issues that reduce survival and reproductive capacity. “It just doesn’t make any sense.”

What would make more sense was if humans’ diets throughout the majority of our existence contained much more iron than they do today, he said.

Professor Frazer pointed to the drastic changes in our diets today compared to before the agricultural revolution.

“We’ll go to the butchers or the supermarket and we’ll pick up a nice rump steak or something from a cow that’s been standing out in the field its entire life and never really had to run at all,” said Professor Frazer.

In contrast, forager diets rely more on game meat, which typically comes from prey animals.

“The iron content of the muscle is about twice as much as you will get in a beef steak,” he said.

This is because the endurance needed to be able to outrun a predator, requires game animals to have more mitochondria in their muscles, which includes iron containing proteins.

“You’ve got an electron transport chain, which is made up of iron containing proteins, you’ve got to have more myoglobin, which is another iron containing protein which helps to store oxygen in the muscle,” he added. “So you’ve got all these different components to do with energy production – which a cow just standing out in the field for its entire life doesn’t need.” 

Similarly, fruits and vegetables have been selected over hundreds or thousands of years to be juicier, have more vibrant colours and handle shipping better.

Those features often came at the expense of micronutrient density, said Professor Frazer.

Now, if a pregnant woman were to meet her RDI of 27mg per day, she would need to eat 800g to 1.3kg of steak every day.

Professor Frazer said the common call to meet one’s iron needs through diet may be unrealistic given today’s food components, and an added source of guilt for patients – particularly pregnant women.

“It’s almost seen as a failure to have to take a supplement to top things up, when it’s not really the fault of the person, it’s the fault of the food that we eat. Now, it’s just completely changed,” he said.

Registered dietician Dr Evangeline Mantzioris, at the University of South Australia, agreed that our modern diets may make it harder to meet our iron needs. As well as a shift away from iron-rich game meat, food processing also robbed grains and other foods of many of their nutrients.

Moreover, Western consumers now ate far less organ meat, such as the iron-rich liver and spleen, than before, she noted.

While supplementation was important to address immediate deficiencies, Dr Mantzioris urged patients to aim for a healthy and varied diet that did meet those requirements, as this would have better outcomes in maintaining nutrient levels long-term than relying on supplements.

“If your diet is low in one nutrient, there’s a chance it could be low in other nutrients,” Dr Mantzioris said. “Iron and zinc tend to go together [for example].

“And we’re just talking about nutrients we know about – there’s a whole lot of other phytonutrients in food that we don’t really know about yet.”

Are the current recommendations even enough?

Despite many women not meeting the current recommended daily intakes for iron, Professor Frazer suspects even this guide is set too low.

Dietary guidelines are based on the intake of someone who has a serum ferritin level of 15mcg/L. This makes them iron deficient, having no iron stores, but not anaemic.

The problem is that we now know that people absorb more iron from food when the body’s iron levels are lower, and less when levels are higher.

“So that is close to the maximum of what your absorption is going to be,” said Professor Frazer. But people who aren’t iron deficient will need to consume more iron in their diet if they want to offset what they lose each day. If they stick to the same recommended intake as an iron deficient person, they will progressively lose their iron stores, he said.

“So it actually encourages iron deficiency.”

Small, older studies also suggested that people who had a serum level of 50mcg/L or less felt better when taking a supplement, he said, indicating that the target for ideal iron levels could be much higher than previously believed.

Such targets might not have been difficult to meet if humans evolved with a diet much richer in the mineral. 

Nevertheless, Professor Frazer cautioned that these studies were small, and much more high quality research needed to be done to properly understand our iron needs, and the effects oral supplements have on the microbiome.

Both Professor Frazer and Dr Mantzioris emphasised the importance of getting iron levels checked by a doctor before self-treating, to avoid possible complications.

COVID-19 live update