Iron is arguably one of the most important minerals for runners. Iron helps transport oxygen throughout the body, something that is obviously an incredibly important function not only for people engaging in aerobic and anaerobic exercise, but for any human being who wants to function.
It is important to note that simply taking iron supplements doesn't necessarily do the trick as it's not just getting the iron into your body, but your body actually absorbing it. There are a shocking number of foods that actually inhibit the absorption of iron. This was really devastating for me to find out, considering that I'd be popping iron supplements and then not be able to poop, and I thought, hey...this constipation is worth it because I'm boosting my iron. But no. Not necessarily. Turns out chugging a cup of coffee with my iron supplement was doing me absolutely no good at all.
So let's begin with why we actually need iron. And remember people, I am not a dietician. This is just information sharing and not medical advice.
What does iron do?
It transports oxygen via red blood cells through the blood. Running uses a lot of iron because of the amount of oxygen required to effectively use your muscles. If iron is a necessary component of building and moving red blood cells, we are not going to get a benefit from heat or altitude training unless we have sufficient iron.
While regular adults are recommended 8 mg of iron daily for men, and 18 mg daily for women, runners can lose up to 3/4 of their iron intake from running and therefore need to up their intake. So a male runner might want to consume more like 14 or 15mg of iron daily, and a woman may want to consume more like 31 or 32mg.
Foods High in Iron:
-6 oz. skirtsteak - 9.3 mg
-3 oz. octopus - 8 mg
-3 oz. oysters - 7.8 mg
-1 cup dried apricots - 7.5mg
-1 cup dried peaches - 6.5mg
-1 cup artichokes - 5mg
-1 cup quinoa - 2.8mg
-1 can tuna - 2.5mg
-1 cup oatmeal - 2.5mg
-1 cup rice -2.4mg
-100 grams tempeh - 2mg
-1 cup acorn squash - 2mg
-5 tablespoons goji berries - 2mg
-1 slice whole wheat bread - 1.1 mg
Also: an array of nuts, seeds, mushrooms, whole grains.
Foods That Aid Iron Absorption:
Ascorbic Acid or Vitamin C- studies show that just 100 mg of ascorbic acid/vitamin C can improve iron absorption by over 4x.
Foods high in Vitamin C:
-1 cup Orange Juice from concentrate - 379 mg
-1 raw yellow pepper - 341 mg
-1 cup frozen peaches - 235 mg
-1 cup red pepper, cooked/boiled - 230 mg, sauteed - 172 mg
-1 cup kiwi - 166 mg
-1 cup oranges - 120 mg
-1 cup lemons - 112 mg
- 1 cup raw jalapeno - 106 mg (I don't know who is going to eat a whole cup of jalapeno)
-1 cup strawberries - 90 mg
-1 cup brussel sprouts - 75mg
Beta-Carotene- this is found in fruits and veggies with a yellow, orange or red hue like oranges, red peppers, beets, sweet potatoes, tomatoes, yellow squash, peaches. It helps the body produce vitamin A.
Foods high in Vitamin A
-1 cup baked sweet potato with skin - 1403 mcg
-1/2 cup carrots - 479 mcg
-1/2 cup cantaloupe - 135 mcg
-1/2 cup raw red peppers - 117 mcg
-1 mango - 112 mcg
-3 oz. salmon - 60 mcg
Taking iron with fruit can lead to up to 3x the iron reserves. The sugar from fruit has a positive impact on the amount of iron stored. This can also be achieved by adding a bit of honey with your iron.
Foods that Inhibit Iron Absorption:
Calcium- This is kind of a bummer, especially for women since we tend to be deficient in both calcium and iron. You can find calcium in dairy products like milk, cheese, and yogurt, as well as sardines, tofu, broccoli, almonds, and figs. Calcium unfortunately inhibits absorption of iron in both the heme (from animals) and non-heme (from plants) form. It is important to note that this doesn't mean that you shouldn't have calcium if you want to absorb your iron. It just means that you need to consume these things at separate meals. Also! 50mg or less of calcium has little impact on iron absorption, but increase the amount to 300mg or 1 cup skim milk, and you will not absorb iron properly.
Foods High in Calcium:
-1 tablespoon poppy or sesame seeds - 126 mg (so everything bagel=two birds with one stone)
-1 oz. chia seeds - 180 mg
-1 oz. parmesan cheese - 331 mg (soft cheeses have way less, Brie is only 52 mg)
-1 cup yogurt - 300mg
-1 can sardines - 330mg
-1 oz. almonds - 80mg
- 1 cup cooked collared greens - 226mg *Spinach is high in calcium, and also high in iron. Which means your body cannot absorb the iron in spinach.
-1/2 cup tofu - 860 mg
Remember! These foods that are high in calcium, are awesome for you...just eat them separate from your iron heavy foods!
Oxalates- found in spinach, kale, beets, nuts, strawberries. These inhibit absorption of iron from plant sources.
Foods High in Oxalates-
-1/2 cup beet greens - 916mg
-1/2 cup spinach - 750 mg
-1/2 cup beets - 675mg
-1/2 cup swiss chard - 660mg
-1/2 cup sweet potatoes - 141mg
Eggs - while great sources of protein, fats, and omega-3's, eggs contain a protein that binds to iron and can inhibit absorption by almost 30%.
Polyphenols - found in apples, black teas, coffee, cocoa, walnuts, blackberries, raspberries, and blueberries. Cocoa unfortunately can inhibit absorption of iron up to a whopping 90%! Coffee can inhibit iron absorption by as much as 60%. Nutritionists suggest consuming these foods at least 2 hours before or after your main iron consumption.
Phytates - found in some nuts like walnuts and almonds, seeds, beans, lentils, whole grains, and can reduce iron absorption by 50 to 65 percent!
So many of the items on these lists have major health benefits, so eliminating them is not an option. Mixing and matching combinations of food that work well together is a priority in order to ensure that the nutrients necessary are actually getting absorbed.
What I gather from this information is that timing is everything. Throwing all the things in a smoothie post-run is still going to happen and be extremely beneficial. But maybe I leave out the spinach, since it doesn't seem to be getting much bang for my buck in there when I have lots of other fruits and veggies that offer similar health benefits. I'll still have my coffee in the morning after that smoothie, since I'm not relying on my breakfast for iron. I am not going to take an iron supplement with said smoothie. I'm also not going to take a calcium & iron supplement simultaneously.
I will rely on my lunch/dinner meals for the majority of my iron consumption/absorption through a combination of sweet potatoes, red meat & fish, peppers, artichokes, grains, brussel sprouts, squash, among others. And utilizing citrus like squeezing lemon juice over my kale salad, or having a fruit salad after an almond butter and strawberry jam sandwich.
My iron levels have not been ideal in the past, and prioritizing this has been really important for me to train optimally. With sub-optimal iron levels, I was tired, experienced headaches, felt some brain-fog, and sluggish. Optimizing nutrition is so important to feel good!
There are lots of great nutritionists out there to follow and seek advice from, including the following: