Goji berries from Tibet. Moringa powder from India. Ashwagandha from Ayurveda. The list of expensive, exotic superfoods is long.
Yet, one of the most nutrient-rich foods of all has been in every one of our kitchens for centuries. It costs almost nothing. It grows in every garden. Or could grow in every garden. It is one of humanity's oldest cultivated plants.
The onion. And its two special sisters: the red onion and the spring onion.
Our grandmothers still knew this. Onion juice for coughs, onion lard in the ears. Red onions raw on salads. Spring onions fresh from the bed on buttered bread. This was not folklore — it was applied nutritional wisdom that is now fully confirmed by science.
What makes the red onion so special?
All onions are healthy. But the red onion is the queen of nutrients among them. Red onions provide twice as much quercetin as yellow onions — and quercetin is one of the most powerful antioxidants found in nature.
What is Quercetin?
It is a flavonoid — a secondary plant compound that originally serves the plant as protection against pests, UV radiation, and pathogens. When we eat this plant, our body also benefits from this protection.
Red onions contain particularly high levels of anthocyanins — special plant pigments from the flavonoid family that give red onions their deep color. Several population studies have shown that people who consume more anthocyanin-rich foods have a lower risk of heart disease.
The numbers behind this are impressive. A study of 43,880 men showed that habitual intake of anthocyanins correlated with a 14 percent lower risk of non-fatal heart attacks. Another study of over 93,000 women found that those with the highest intake of anthocyanin-rich foods had a 32 percent lower incidence of heart attacks. You can find the source at the end of the article below.
These are not laboratory results — these are observations on living humans, over many years.
The seven wonder compounds of the red onion
A study at the University of Messina has shown that red onions contain seven different flavonoids — the most important of which are quercetin and anthocyanin.
What these substances do in the body:
Quercetin has anti-inflammatory effects and strengthens the immune system. It can help lower blood pressure and reduce LDL cholesterol levels. It interacts with cells in the small intestine, liver, and adipose tissue — thus controlling the body's entire blood sugar regulation.
Anthocyanins give the red onion its characteristic color — and at the same time protect against oxidative stress. They have preventive effects against heart disease, certain types of cancer, and diabetes.
Sulfur compounds (sulfides) inhibit bacterial growth. They maintain the cell membrane of red blood cells, optimize oxygen supply, and inhibit blood clotting — thus onions can prevent thrombosis.
Inulin acts as a prebiotic — it nourishes the healthy bacteria in the gut. A healthy gut is now associated with a reduced risk of diabetes, colon cancer, and even depression.
Vitamin C strengthens the immune system and supports collagen formation — important for skin, bones, and blood vessels.
Vitamin B6 plays a key role in protein and energy metabolism and supports nervous system function.
Potassium regulates blood pressure and is essential for heart function.
A crucial tip when peeling
Here, most people make a mistake that truly hurts — nutritionally speaking.
By peeling too much, removing the two outer fleshy layers, approximately 20 percent of the quercetin and over 75 percent of the anthocyanins are lost. 75 percent of the most valuable ingredients — simply peeled away.
The outermost fleshy layers of the red onion are the most nutrient-rich. Peeling them only as much as necessary is the simplest nutritional optimization there is.
And one more thing: Traditional soaking in water destroys up to 50% of the valuable quercetins. If you want to make red onions milder, it's better to marinate them briefly in lemon juice or red wine vinegar — this preserves the nutrients and even improves their bioavailability.
The spring onion — the complete package
The spring onion is the younger, milder sister of the common onion. And it has a crucial advantage: you eat it whole — from the white root part to the green tip. And precisely in this completeness lies its special nutrient density.
The green of the spring onion provides Vitamin K, which is important for blood clotting, and Beta-carotene, a precursor to Vitamin A. The white part, on the other hand, contains more Vitamin C and sulfur-containing compounds, which are also found in regular onions.
This means: if you only use the white part and throw away the green, you are giving away a significant portion of the nutrients. Both parts have their strengths — and both belong on your plate.
What makes spring onions special:
Spring onions have germicidal and anti-inflammatory properties and relieve cold symptoms. With 25 milligrams per 100 grams, spring onions cover about a quarter of the recommended daily amount of Vitamin C. Spring onions particularly excel in secondary plant compounds, sulfides, and potassium — 276 milligrams per 100 grams — and are extremely low in fat with 0.2 grams of fat per 100 grams.
In addition, there's beta-carotene for eye health, allicin as a natural antibiotic in the digestive tract, polyphenols in the white part that improve blood flow — and all of this with almost zero calories.
Since the plants are harvested very young and consumed soon after, their high mineral content and vitamins are almost entirely beneficial to the body.
This is the crucial point: spring onions are consumed young and fresh — no long transport routes, no months of storage, no nutrient loss due to ripening in cold storage.
The Problem: Not All Onions Are Created Equal
And this is the core of our work at STEINKRAFT.
A red onion with 12 °Brix is not the same as a red onion with 4 °Brix. The numbers on the price tag are identical. The nutritional content is not.
The Brix value — the density of the plant sap — provides direct information about the content of dissolved substances: sugar, but also minerals, amino acids, and secondary plant compounds like quercetin and anthocyanins. A nutrient-rich red onion tastes more intense, lasts longer, and provides the body with significantly more of what it needs.
And the Brix value is no coincidence. It is the result of soil health, mineral supply, and the way the plant is grown.
Field studies from Colombia have shown: If onions are grown with mineral foliar fertilization based on activated calcite, onion weight increases by 44.8 percent. Not because the onion is bloated with water — but because it builds up more dry matter, more minerals, more secondary plant compounds. A denser, more nutrient-rich onion.
What the farmer measures as weight gain and economic profit — we consumers measure as taste, shelf life, and health value.
Why Red Onions and Spring Onions are particularly dear to our hearts
At STEINKRAFT, we have a clear conviction: the healthiest foods are not the most exotic. They are the most original — grown on healthy soils, supplied with natural minerals, freshly harvested, and consumed whole.
The red onion with its anthocyanins and double quercetin content. The spring onion, harvested young and whole, retaining its full nutritional bounty.
These two are our favorites. Also because they are so close. And because they can do so much if given what they need: healthy soil, sufficient calcium, intensive photosynthesis.
An onion that gets this tastes different. Smells different. Lasts longer. And does more for the body. That's the difference between foods that fill you up — and foods that truly nourish. And we want to contribute to that.
Do you want to know what this looks like in practice — from paramagnetic soil to the first spray pass with Grünkraft Calcium? The complete step-by-step program for nutrient-rich red onions can be found in the next blog post.
🧅 Growing nutrient-rich red onions — the complete program from soil preparation to harvest
Zeolite is much more than a simple soil additive — what exactly it can do and how it works, you can find in our Zeolite shop with all products.
Why microorganisms are better than any organic fertilizer — this blog article explains it.
Sources: Università di Messina, Flavonoid study red onions | Study 43,880 men, anthocyanin intake and heart attack risk | Study 93,600 women, anthocyanin-rich diet and heart attack | German Institute of Human Nutrition 2024, anthocyanins and insulin sensitivity | Zentrum der Gesundheit, Red Onions | AOK, Spring Onions | EatSmarter, Spring Onions | UMID Colombia S.A.S., Field study onion cultivation Valle del Cauca 2018
