Eating vegetarian or vegan: which blood values should you check?

Why a plant-based diet needs attention

A well-composed plant-based diet supplies most nutrients amply. There are, however, a few nutrients that occur mainly in animal products or are absorbed less well from plants.

That is not an argument against eating plant-based, it is a matter of knowing what to watch. Those who drop meat and dairy without replacing anything run into the same handful of deficiencies over time.

Blood testing is a tool here, not a goal. It shows where you stand now, so you can adjust deliberately instead of supplementing on instinct.

Vitamin B12: the most important one

Vitamin B12 in a usable form comes almost exclusively from meat, fish, eggs and dairy. Plant sources such as seaweed or fermented products do not supply a reliable amount.

Your liver holds a substantial store, so a deficiency only shows after months to years. That explains why people sometimes eat plant-based for years without complaints and still turn out to be deficient.

Complaints that can fit a deficiency are fatigue, tingling in hands or feet, trouble concentrating, a sore tongue and low mood. If a deficiency persists for a long time, nerve damage can occur that does not always fully recover.

If you eat fully plant-based, supplementing B12 is the starting point. Vegetarians who use dairy and eggs sit in between and benefit more from a measurement to see whether their intake is enough.

Iron and ferritin: absorption is the bottleneck

Iron is plentiful in pulses, wholegrains, nuts and green vegetables. The issue is not the amount but the absorption: iron from plants is taken up less well by your gut than iron from meat.

What improves absorption is vitamin C with the meal, for example peppers, citrus or kiwi. What hinders it is tea, coffee and large amounts of dairy close to the meal.

Ferritin is the value reflecting your iron stores and the first to fall. Menstruating women, athletes and growing teenagers carry the greatest risk, because their consumption is higher.

Watch one thing: ferritin rises temporarily with inflammation or infection. A result taken just after flu or a hard training session can therefore mask a deficiency.

Vitamin D, zinc, iodine and calcium

Besides B12 and iron, these values deserve attention:

• Vitamin D: comes mainly from sunlight and oily fish. In the Netherlands the value comes out low for many people in winter, plant-based or not.
• Zinc: found in pulses, nuts and seeds, but absorption is hindered by phytates in those same foods. Soaking, sprouting and sourdough help.
• Iodine: in the Netherlands iodine comes mainly from iodised bakery salt and dairy. Anyone baking their own bread without iodised salt and using no dairy misses an important source.
• Calcium: without dairy you need fortified plant drinks, tofu, nuts and green vegetables. A blood value says little about your intake here, because your body regulates it tightly.
• Omega 3: for the long-chain fatty acids, algae oil or oily fish are the sources. This is not a standard test.

Iodine, copper and selenium are available at Bloodworks as separate additions through Bloodworks Select. For calcium and omega 3, a blood measurement tells you less than a critical look at your diet.

When should you measure?

Measuring is mainly useful at these moments:

• six to twelve months after switching to a fully plant-based diet
• with complaints such as persistent fatigue, breathlessness on exertion, tingling or hair loss
• around conception or during pregnancy, in consultation with your GP or midwife
• if you use supplements and want to know whether your dose suits your situation
• periodically, for example once every one to two years, to follow trends

For children eating plant-based a different route applies: always consult your GP or a dietitian, because requirements differ per age and growth counts.

Practical: how to get a usable result

If you use supplements, you mainly measure their effect. If you want to know where you stand without them, discuss with your doctor whether you can pause them temporarily. Never do that during pregnancy or with an established deficiency without consulting first.

High-dose biotin, often found in supplements for hair and nails, can interfere with certain laboratory measurements. Always report what you take.

At Bloodworks you have this tested without a referral, at one of the more than 800 affiliated collection points across the Netherlands. The Vitamins, minerals and electrolytes package measures nine values in one draw: vitamin D, vitamin B12, folate, magnesium, calcium, ferritin, zinc, sodium and potassium.