Getting enough iron on a vegan low FODMAP diet

A vegan diet can be abundant with nutrients and give you everything you need to thrive at all stages of life (BDA, 2017), but when you have Irritable Bowel Syndrome (IBS) and need to do the Low FODMAP diet it can be difficult!

However, with a bit of thought and planning, and the help of a knowledgeable dietitian, it’s still possible to get all the macro and micro-nutrients you need during the elimination and rechallenge phases of the low FODMAP diet. And to help you, I’m creating this Vegan Low FODMAP nutrition series!

I’m kicking off with iron… a nutrient people often worry about on vegetarian and vegan diets.

Why do you need to eat iron?

Iron is an essential metal that is used by your red blood cells to carry oxygen from your lungs to the rest of your body. If you do not consume enough iron for a prolonged period of time or lose a lot of blood, it can lead to an iron deficiency.

How much iron do you need to eat every day?

Iron is actually highly conserved in the body, and it’s estimated you lose only around 1 mg per day through the natural shedding of skin on your body and in your gut (Abbaspour Abbaspour et al., 2014).

The amount of iron you need depends on your age and sex. Your needs are higher if you have a menstrual cycle or have a baby because you lose iron-containing blood and/or milk in the process. You may need more if you have very heavy periods as this is a common cause of iron deficiency in women (Mansour et al., 2021)

Dietary Iron requirements for adults are (NHS):

• Women aged 19-50 years: 14.8mg/day

• Women older than 50 years: 8.7mg/day

• Men older than 18 years: 8.7mg/day

It’s worth noting that these requirements are based on iron consumed, rather than iron actually absorbed into your body.

Absorbed iron requirements for adults (World Health Organization, 1989):

• Women aged 19-50 years: 2.38mg/day

• Women older than 50 years: 0.96mg/day

• Men older than 18 years: 1.82mg/day

Absorption or “bioavailability” of Heme iron vs. non-heme iron

If you eat an animal-based food the iron in it will be attached to a “heme” protein, as it is in your blood. Heme iron has a bioavailability of 15%-35%, so you only absorb a sixth to a third of the iron in animal-based foods (Hurrell & Egli, 2010).

If you eat a portion of plant-based food, the iron won’t be attached to a heme because plants don’t have blood like humans. Non-heme iron absorption is generally lower at 2 to 20% and is strongly affected by other food components (Hurrell & Egli, 2010).

It’s worth mentioning there is iron in most of the staple foods of a plant-based diet, so if you are eating enough food in general, you are likely absorbing plenty of iron. However, because a low FODMAP diet limits a lot of plant-based staple food, you need to be mindful of what you are eating.

Polyphenols in black tea reduce non-heme iron absorption

It breaks my British tea-loving heart to say it, but black tea has been shown to stop iron from your meals from absorbing so well (Hurrell, Reddy & Cook, 1999). So it is worth enjoying a low FODMAP cup of tea an hour or two before or after your meals. A large mug (250ml) of strong black tea is rated as high FODMAP by Monash University (at the time of writing September 2023), so limiting your tea intake could be good for your iron levels as well as your IBS.

Phytic acid also reduces iron absorption

Phytic acid in legumes, nuts and grains can also limit the amount of iron we absorb from the food. However, normal cooking processes degrade these. For example, the standard way to prepare legumes, such as boiling them for one hour can reduce their phytic acid content by up to 80% (Shi et al., 2018).

Moreover, most low-FODMAP legumes are canned, so inherently low in phytic acid.

Vitamin C increases the absorption of iron

Vitamin C has been shown to increase iron absorption and reduce the negative impact of polyphenols and phytic acid (Siegenberg, 1991). Eating a low FODMAP (medium) size navel orange after an iron-rich meal, or adding a squeeze of lemon as a garnish, will help you absorb the iron better. You will notice a lot of the recipes on the website include a squeeze of lime or lemon for this reason, as well as, adding balance to the tastes.

Pro tip: Add low FODMAP servings of Vitamin C rich plants to your meals or dessert

• Dark green leafy vegetables

• Citrus fruits, e.g. lemons, limes

• Bell (capssicum) peppers

• Strawberries

• Tomatoes

Here are some low FODMAP vegan sources of iron (per 100g):

• 1.2 mg firm tofu

• 1.3 mg canned chickpeas

• 10.4 mg sesame seeds

• 6.4 mg sunflower seeds

• 2.1 mg tempeh

• 1.6 mg spinach

• 3.2 mg hazelnuts (low FODMAP at 15 g)

• 2.3 mg edamame (low FODMAP at 90g)

• 1.5 mg quinoa

• 1.3 mg canned lentils (low FODMAP at 46g)

• 3 mg brazil nuts

Serum ferritin concentrations correlate well with total body iron stores. Personally, my partner and I like to do a Thriva blood test to check our serum ferritin once or twice per year just because we find it reassuring to know for certain that we’re getting enough in our diets without iron supplements (You can get £20 off your first order with my “refer a friend” code: WGYM_IU-UMS).

Because your body conserves iron well, you will not become deficient overnight or even over several weeks if your diet is low in iron. However, it's very important that you do not keep eating a restrictive low FODMAP diet, as it is a short term diet just to identify your personal triggers.

References

Abbaspour N, Hurrell R, Kelishadi R. Review on iron and its importance for human health. J Res Med Sci. 2014 Feb;19(2):164-74. PMID: 24778671; PMCID: PMC3999603.

BDA (2017) British Dietetic Association confirms that well-planned vegan diets can support healthy living in people of all ages. [Access at: https://www.bda.uk.com/resource/british-dietetic-association-confirms-well-planned-vegan-diets-can-support-healthy-living-in-people-of-all-ages.html

Hurrell R, Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr. 2010;91:1461–7S.

Hurrell RF, Reddy M, Cook JD. Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. Br J Nutr. 1999;81:289–95

Mansour D, Hofmann A, Gemzell-Danielsson K. A Review of Clinical Guidelines on the Management of Iron Deficiency and Iron-Deficiency Anemia in Women with Heavy Menstrual Bleeding. Adv Ther. 2021 Jan;38(1):201-225. doi: 10.1007/s12325-020-01564-y. Epub 2020 Nov 27. PMID: 33247314; PMCID: PMC7695235.

Shi L, Arntfield SD, Nickerson M. Changes in levels of phytic acid, lectins and oxalates during soaking and cooking of Canadian pulses. Food Res Int. 2018 May;107:660-668. doi: 10.1016/j.foodres.2018.02.056. Epub 2018 Mar 5. PMID: 29580532.

Siegenberg D, Baynes RD, Bothwell TH, Macfarlane BJ, Lamparelli RD, Car NG, et al. Ascorbic acid prevents the dose-dependent inhibitory effects of polyphenols and phytates on nonheme-iron absorption. Am J Clin Nutr. 1991;53:537–41.