26 mai 2025

Folate in a vegetarian diet: real needs, sources and cooking losses

The short version

In Switzerland the reference value for an adult is 300 µg of dietary folate equivalents a day, not the 400 µg still repeated across the internet. The figure was lowered in 2013 by the German, Austrian and Swiss nutrition societies (D-A-CH), because the cardiovascular argument behind the older 400 µg did not survive randomised trials.

A vegetarian plate clears that bar without trying. A 200 g portion of cooked lentils supplies roughly 360 µg on its own. The interesting question is almost never how much folate sits in the raw ingredient, but how much survives the pan and how much your gut actually absorbs.

Two things deserve attention more than the microgram count:

Before and in early pregnancy, food alone is not enough. The WHO and the NHS both recommend a 400 µg folic acid supplement daily, starting before you stop contraception and continuing to week 12.
Folate and vitamin B12 are entangled. For a vegetarian or vegan it is B12 that is the genuine risk, not folate, and heavy folic acid supplementation can blur the picture.

The numbers and sources behind both points follow.

Folate, folic acid, equivalents: three words, three different things

Everyday language treats these as synonyms, which is why most advice on the topic is unreadable. They are not the same.

Folate is the natural form of vitamin B9, the one plants make and that you find in lentils, spinach or asparagus. It is really a family of related molecules with different chemical stabilities.

Folic acid is the synthetic form used in supplements and fortified foods. It does not occur as such in raw foods. It is considerably more stable against heat and oxygen than natural folates.

Dietary folate equivalents are the accounting unit that makes the two comparable. According to the 2025 review in npj Science of Food (Vitamin B9), the bioavailability of food folate is estimated at around 50 %, against roughly 85 % for folic acid taken with a meal and near-complete absorption on an empty stomach. The D-A-CH conversion is blunt: 1 µg of folate equivalent = 1 µg of food folate = 0.5 µg of synthetic folic acid.

There is a consequence people routinely miss. A 400 µg folic acid tablet corresponds to 800 µg of folate equivalents, more than twice an adult’s daily reference. That is not a dosing error, it is a deliberate choice for the periconceptional window. It also explains why nobody should take that dose year-round “just in case”.

How much do you actually need?

Recommendations differ between countries because the biological markers used to derive them differ: red blood cell folate, serum folate, total homocysteine, autopsied liver folate. Here are the official figures, in µg per day.

Reference body	Adults	Pregnancy	Breastfeeding	Upper limit
D-A-CH (Switzerland, Germany, Austria)	300 equivalents	550	450	not set here
ANSES (France)	330 equivalents	600	500	1000 µg folic acid
NHS (United Kingdom)	200	400 µg supplement	–	1 mg folic acid in supplements
United States and Canada	400 equivalents	–	–	–

That 200 to 400 µg spread between wealthy countries with access to the same literature is worth sitting with. It means none of these numbers marks a sharp biological line between health and deficiency. They are population reference points built with different safety margins.

For Switzerland, the applicable value is the D-A-CH one: 300 µg of folate equivalents. Women who could become pregnant should add 400 µg of synthetic folic acid daily on top of a folate-rich diet, starting at least four weeks before conception and continuing through the first third of the pregnancy.

Why Switzerland went from 400 down to 300 µg

This revision deserves an explanation, because it contradicts half the articles you will find online. Krawinkel and colleagues set out the reasoning in the European Journal of Clinical Nutrition (2014).

In 2000, the 400 µg figure rested partly on the idea that lowering blood homocysteine would prevent cardiovascular disease. The randomised trials that followed did not confirm it: bringing homocysteine down to around 10 to 12 µmol/l did not reduce thromboembolic and cardiovascular risk in people who already had such disease. On top of that, intakes below 400 µg turned out to be enough to maintain adequate folate status. The value came down to 300 µg.

Remember the reasoning rather than the number. An observed association between a folate-rich diet and better cardiovascular health does not prove the isolated nutrient produces the effect. Pulses and green vegetables remain excellent, for plenty of other reasons.

What folate does

Vitamin B9 is involved in amino acid metabolism and cell division. Fast-renewing tissues feel a shortage first, which explains the shape of the symptoms.

DNA synthesis and cell division. The central function, upstream of everything else.
Red blood cell formation. A prolonged shortfall produces megaloblastic anaemia: abnormally large red cells that do not work properly.
Neural tube closure in the embryo. This is the one area where extra intake has a solidly demonstrated preventive effect.

The WHO lists folate deficiency alongside iron, vitamin A, B12 and riboflavin among nutritional causes of anaemia, with iron by far the most common.

What folate does not do, on current evidence: prevent cardiovascular disease through supplementation, improve energy in someone whose status is already normal, or compensate for an otherwise poor diet.

Plant sources, in portions people actually eat

Per-100 g tables mislead, because nobody eats 100 g of sunflower seeds. The values below come from USDA FoodData Central and are converted into plausible servings.

Food	µg/100 g	Typical portion	Folate in that portion
Lentils, cooked	181	200 g	362 µg
Chickpeas, cooked	172	150 g	258 µg
Black beans, cooked	149	150 g	224 µg
Asparagus, cooked	149	150 g	224 µg
Spinach, cooked	146	150 g	219 µg
Spinach, raw	194	50 g in a salad	97 µg
Chickpea flour	437	30 g	131 µg
Avocado, California variety	89	half, 100 g	89 µg
Sunflower seed kernels, dried	227	15 g	34 µg

Three things fall out of that table.

First, pulses flatten everything else. One plate of lentils covers the Swiss daily reference by itself. That is why vegetarians statistically show higher folate intakes than omnivores, a pattern confirmed in a 2026 meta-analysis of 59 studies and 48,626 children and adolescents (Critical Reviews in Food Science and Nutrition), which found higher intakes of fibre, iron, folate, vitamin C and magnesium, and lower intakes of B12, vitamin D and zinc.

Second, seeds and nuts are extras, not the main act. Their per-kilo figure looks impressive; their real contribution is small. They earn their place for other nutrients.

Third, variety matters within a single food. The California avocado measures 89 µg/100 g, the Florida one 35. A two-and-a-half-fold gap between cultivars of the same fruit is a good reason to treat nutrition tables as approximations rather than measurements.

What cooking really destroys

Most articles dispatch this in one vague sentence, which is a shame, because it is where the real losses happen. Natural folates are lost through two distinct mechanisms, described in the npj Science of Food review cited above.

Leaching. The vitamin is water-soluble and moves into the soaking or cooking water. It is not destroyed, it has simply relocated. Consume the liquid and you recover most of it.

Oxidative degradation. Heat in the presence of oxygen destroys the molecule. Not all forms are equal: folic acid is the most stable, 5-methyl-THF and THF are highly thermolabile, and an acidic environment speeds their breakdown.

The measured orders of magnitude in vegetables:

boiling: 40 to 50 % loss
steaming: about 40 %
frying: 15 to 30 %
baking: 20 to 35 %

Counted across the whole dish, cooking liquid included, boiling losses fall to 25 to 30 %. In other words, the broth recovers a large share of the damage.

The per-vegetable detail is even more telling. Boiled, spinach loses 36 to 62 % of its folate and broccoli 25 to 56 %. Steamed, the gap widens: 9 to 57 % for spinach against 10 to 30 % for broccoli. Microwaved, 51 % against 17 %. Non-leafy vegetables retain the vitamin better than leafy ones, simply because they expose less surface. Leeks lose 26 % when steamed, cauliflower 8 %, green beans 10 %.

One counter-intuitive finding is worth flagging. Frying destroys 1 to 31 % of the folate in certain leaf vegetables through heat, while boiling costs 10 to 47 %. Except that in the second case the vitamin is sitting in the water. Drink it and boiling becomes the better option again. Our piece on gentle steam cooking covers the same trade-off for other nutrients.

The double-counting trap

Watch out for a common reasoning error. The cooked-food values in the table above already include cooking losses, which is precisely why spinach drops from 194 µg raw to 146 µg cooked. Do not then subtract another 40 %. The loss percentages are for comparing methods against each other, not for correcting a figure already measured on the cooked food.

Freezing, milling and processing

Freezing and thawing rupture cell walls, which releases the vitamin but also lets it escape more easily into water. Boiled, fresh green beans lose no significant amount of folate while frozen ones lose 15 %; fresh spinach loses 47 % against 59 % for frozen. Frozen produce is still a good option, but steam it or use the liquid.

Milling strips out much of the folate in cereals, which concentrates in the germ and the outer layers of the grain. Refined wheat flours contain 21 to 89.5 % less than wholemeal flours. Non-parboiled white rice loses 46 to 79 % relative to brown rice. Oat flakes, by contrast, lose only 16 %, because they keep the whole grain. That is a concrete argument for wholegrain, without any hand-waving about nutrient “synergy”. Our guides to lesser-known local pulses and to pairing grains with legumes take the practical side further.

Pregnancy and trying to conceive: the one case where food is not enough

This is the most important section of the article and the only one that calls for a specific action.

Neural tube defects, including spina bifida, result from incomplete closure of the neural tube during the very first weeks of embryonic development, often before the pregnancy is known. ANSES makes a revealing point: the women affected usually have normal dietary intakes but low serum and red blood cell concentrations.

The protective effect of periconceptional supplementation is among the best established findings in the whole of nutrition. The Cochrane review by De-Regil and colleagues (2015, five trials, 6,708 births) reports a risk ratio of 0.31 with a 95 % confidence interval of 0.17 to 0.58, graded as high-quality evidence.

The operational recommendations:

400 µg of folic acid a day, from the moment you start trying to conceive until week 12 (WHO, NHS). The D-A-CH references add: begin at least four weeks before conception.
5 mg a day where a previous pregnancy was affected by a neural tube defect, or where risk is otherwise raised. That dose is a medical decision, not a personal initiative.
Start the supplement before you stop contraception, since the critical window precedes any pregnancy test.

A folate-rich diet is still recommended alongside, but it does not replace the tablet. This is one of the rare cases in nutrition where the synthetic form beats the food, thanks to its stability and bioavailability.

Deficiency: what it looks like, and who is at risk

The NHS describes a symptom picture shared by folate and B12 deficiency: extreme tiredness, lack of energy, pins and needles, a sore red tongue, mouth ulcers, muscle weakness, vision problems, psychological effects ranging from mild anxiety to confusion, and problems with memory and judgement. Some of these appear even without anaemia.

Inadequate dietary intake is an uncommon cause in Switzerland. The situations that genuinely raise the risk:

Age. Folate and B12 deficiency each affect around 1 in 10 people over 75, and 1 in 20 aged 65 to 74.
Certain medicines. Methotrexate, anticonvulsants, proton pump inhibitors, trimethoprim and possibly sulfasalazine antagonise folate metabolism or absorption. The NHS in fact prescribes folic acid specifically to limit methotrexate side effects.
Very restrictive diets or a poor diet sustained over a long period.
Dialysis, which drives blood folate down.
Pregnancy, through increased requirements.

Diagnosis rests on a blood test, not on self-assessment against a symptom list. If several of these signs persist, the useful next step is an appointment, not a supplement purchase.

The real pressure point for vegetarians is B12

Folate is abundant in a well-built vegetarian diet; vitamin B12 is not. And the two interact.

The NHS is explicit: folic acid doses above 1 mg can mask the symptoms of B12 deficiency, which can eventually damage the nervous system if it goes unspotted. The mechanism is historical. Both deficiencies produce the same type of anaemia, and high-dose folic acid corrects the blood picture without stopping the neurological damage from progressing.

Two honest caveats. Current medical practice no longer relies on anaemia being present to diagnose B12 deficiency, which frequently presents without it. And the 2025 review stresses that the data remain heterogeneous, with no solid evidence of harm from existing fortification programmes.

What this means for you in practice: do not take high-dose folic acid long-term without a reason, and above all, if you are vegetarian or vegan, secure your B12 status through a reliable source. Our articles on B12 needs and reliable sources and on which supplements a vegetarian actually needs go into detail.

Fortified foods: do not count on them in Switzerland

Several countries, including the United States and Canada, mandate folic acid fortification of flour. European countries, Switzerland among them, have been reluctant to make it compulsory. Fortification here is voluntary, with one blunt practical consequence: the folate content of your breakfast cereal depends entirely on the brand, and nothing guarantees consistency between batches.

The only reliable method is to read the nutrition declaration. If folic acid is not listed, it is not there.

A day that hits the reference without trying

Here is a worked example, to show that 300 µg of folate equivalents is not a demanding target.

Breakfast. Oat porridge with a plant drink, a handful of sunflower seeds (15 g, about 34 µg) and fresh fruit.

Lunch. Cooked lentil salad (200 g, about 362 µg) with tomatoes, cucumber, herbs and a lemon dressing. The daily total is already passed at the first course.

Snack. Half an avocado on wholemeal bread (about 89 µg).

Dinner. Steamed asparagus (150 g, about 224 µg) or braised spinach (150 g, about 219 µg), with brown rice and a soup whose broth you actually drink.

Nobody should run this arithmetic daily. It simply shows that if you eat pulses several times a week and green vegetables regularly, the folate question is settled. Our batch cooking guide for beginners sets out a rhythm that makes that sustainable.

Ten common mistakes

Quoting 400 µg for a Swiss adult. The D-A-CH reference has been 300 µg of folate equivalents since 2013.
Confusing µg of food folate with µg of folic acid. The latter counts double in equivalents.
Believing vitamin C improves folate absorption. This widespread claim is not established. What is documented is that folates degrade through oxidation, a process in which ascorbic acid can play a protective role inside the food. That is not the same as an effect on intestinal absorption.
Throwing away the cooking water. The single largest avoidable loss.
Waiting for a positive pregnancy test before starting the supplement. The critical window has already closed.
Taking 5 mg of folic acid on your own initiative. That dose belongs to specific situations, on medical advice.
Subtracting cooking losses from a value already measured on the cooked food. Double counting.
Relying on seeds for folate. The realistic portion is too small.
Assuming your breakfast cereal is fortified. Nothing requires it in Switzerland.
Supplementing folate when the nutrient to watch is B12.

Frequently asked questions

Is a vegetarian at risk of folate deficiency? Unlikely, if the diet includes pulses and green vegetables. Intake data point the other way: vegetarians average higher folate intakes than omnivores. The genuine risk factors are age, certain medicines and very restrictive diets.

Should I eat spinach raw to preserve the vitamin? Raw spinach does contain more folate, 194 against 146 µg/100 g. But a salad portion is 50 g against 150 g cooked, which reverses the outcome. Alternate rather than pick a side.

Is methylfolate better than folic acid? The bioavailability of supplemental 5-methyl-THF is reported as similar to or higher than folic acid at equimolar doses. That said, the data on MTHFR gene variants are not yet sufficient to change intake recommendations for the general population. For neural tube defect prevention, the evidence base rests on trials run with folic acid.

Can you get too much folate from food? The risk is negligible. The upper limits set by ANSES, 1000 µg a day for adults, apply explicitly to folic acid from supplements and fortified foods, not to natural folates.

Do tinned pulses keep their folate? They undergo heat treatment and time in brine, so real losses occur. They remain a valid source: some of the vitamin sits in the canning liquid, and a tin you actually eat beats dried lentils you never cook. Soaking and sprouting offer an alternative for anyone cooking from dry.

What about folate-rich “superfoods”? None of them beats a plate of lentils at 360 µg. Spirulina, wheatgerm and brewer’s yeast do contain folate, but at realistic portion sizes their contribution stays marginal next to pulses.