Written by
Louise W Lu, PhD, MPH, BMLS
Written/Reviewed by
Lilly (Yutong) Liu, Registered Dietitian, PhD Researcher in Nutrition, University of Auckland
In our previous article, we explored why calcium, vitamin D3, K2, and K1 must work together to truly support your bones and protect against calcification. It's not just about getting enough calcium—it’s about making sure it goes to the right place.
Shortly after publishing, someone messaged us and asked: “I saw online that eating 300 grams of leafy greens daily gives me over 400mcg of vitamin K1. Doesn’t that mean I’ve already got enough?”
You might be eating plenty of greens—but your body may only absorb less than 10%. K1 absorption depends heavily on fat intake, how the food is cooked, and your gut function.
Yes, vitamin K is found in food—but that doesn’t mean you’re absorbing what you need. In fact, it’s one of the easiest nutrients to overestimate on paper and underestimate in the body.
If you're concerned about bone loss, artery health, or calcium buildup, the synergy between K1 and K2 becomes more than relevant—it becomes essential.
In this article, we’ll break it all down:
- Is 300 grams of leafy greens really enough for your daily K1?
- Do natto and egg yolks truly cover your K2 needs?
- Why are your vitamin K levels low even when your diet seems “perfect”?
- Can food alone meet your K1/K2 needs long-term?
The problem isn’t what you eat—it’s what your body can absorb. And it’s time to take a fresh look at vitamin K.
Jump to section:
- Why K1 from leafy greens is barely absorbed
- Where does K2 come from—and can we eat enough?
- Can your gut bacteria really make enough K1 and K2?
- What to do when food isn't enough: effective K1/K2 strategies
1｜Why 300g of Vegetables Still Isn’t Enough: The Truth About K1 Absorption
Many people assume that eating plenty of green vegetables—like spinach, kale, or romaine lettuce—is enough to meet their daily vitamin K1 needs. But clinical evidence reveals a surprising reality: what we consume and what our bodies can actually absorb are two very different things.
Why does this happen?
- In plants, K1 is tightly bound within the chloroplast matrix, making it difficult to release.
- Unless consumed with a substantial amount of fat and thoroughly chewed and cooked, this K1 remains poorly absorbed by the intestine.
- Individual factors like bile acid secretion and lipase activity also affect K1 absorption.
In short, “What looks like enough” ≠ “What your body can use.” This explains why many people who eat lots of vegetables—or follow a vegetarian diet—can still show signs of low bone density or even mild K1 deficiency on blood tests or coagulation assessments.
2｜Where Can We Get Vitamin K2 from Food?
Many people assume that as long as they eat natto, egg yolks, or animal liver, they’re getting enough vitamin K2. But the reality is far more complicated.
Let’s first take a look at common food sources of K2:
- Fermented foods: natto (highest in MK-7), certain cheeses, sauerkraut, Korean kimchi
- Animal-based foods: goose liver, chicken liver, egg yolk, butter, certain full-fat dairy products (rich in MK-4)
Sounds like a good variety, but here are some practical limitations:
- Natto is rich in MK-7 but is a low-fat food, with only about 5g of fat per 100g—far from enough to aid K2 absorption, which requires fat.
- Animal liver and goose liver do contain MK-4, but are not commonly consumed and often avoided due to cholesterol concerns.
- Fermented dairy products like cheese typically contain very low MK-7 levels (around 1–10 μg/100g), making them poor sources of supplementation.
- Those following a long-term low-fat diet for weight loss
- Individuals with metabolic syndrome (e.g., high cholesterol, high triglycerides) who are advised to restrict animal fat intake
- People at risk of cardiovascular disease (e.g., family history, atherosclerosis) who follow a long-term low-cholesterol diet
- Patients taking lipid-lowering medications (such as bile acid sequestrants or statins)
- People who have had their gallbladder removed: without the concentrated bile release after meals, absorption of fat and fat-soluble vitamins is significantly reduced
- Those with fat malabsorption, insufficient pancreatic enzyme secretion, or bile duct obstruction
In other words, even if you eat natto, eggs, and fermented cheese, if there’s no fat accompanying them—or your body struggles to digest fat—K2 likely won’t reach your bloodstream.
This is also why people with fat absorption issues—due to gut conditions or post-surgery recovery—often experience bone loss or fluctuating blood calcium levels. It’s not a calcium deficiency, but rather a lack of K2 to help direct calcium into the bones.
3｜Can Your Body Convert K1 into K2? And Can Gut Bacteria “Ferment” Enough K2?
You might think: “I eat lots of leafy greens for K1, and my gut bacteria can probably make K2—I should be fine, right?”
Well, not quite. Let’s break down the facts behind this common belief:
01｜Yes, K1 Can Convert to K2—But Only a Little
- Vitamin K1 (phylloquinone) is found mainly in green leafy vegetables like spinach and kale.
- Your body can convert K1 into a short-chain K2 subtype called MK-4, but only in specific tissues like the liver, pancreas, and brain.
- The conversion rate is extremely low—only a tiny fraction of K1 becomes MK-4.
- K1 cannot convert into the long-chain forms of K2 (like MK-7 or MK-9), which are the ones that circulate in your blood and provide cardiovascular and bone health benefits.
02｜Yes, Gut Bacteria Can Make K2—But You Can’t Absorb It
- Certain gut bacteria do synthesize vitamin K2, especially the long-chain forms MK-7 to MK-13.
- Common strains include Bacteroides fragilis, Eubacterium lentum, and Propionibacterium.
But here’s the catch:
- The fermentation happens mostly in the colon (the end of the large intestine);
- Vitamin K absorption, however, occurs in the small intestine (jejunum and ileum);
- So most of the K2 made in your gut is excreted in stool—not absorbed into your bloodstream.
✅ Only under rare conditions like leaky gut or inflammation might trace amounts reach your system—but that’s not a healthy or efficient route.
03｜“I’m Not Deficient in K2” Might Be a Dangerous Assumption
Many people assume they’re getting enough K2:
- They eat greens—so they think K1 is enough.
- They eat natto or fermented foods—so they assume they’re covered for MK-7.
- They have “good gut flora”—so they believe their microbes are making K2 for them.
But in reality, they may be:
- Missing the right forms of K2—like MK-7 or MK-9, which are bioactive in blood;
- Not absorbing K2 properly—especially if on a low-fat diet;
- Overestimating their gut’s ability to supply K2—most of it isn’t usable.
4｜What If Food-Based Vitamin K Doesn’t Work Well?
If you’re eating plenty of greens or natto but still struggling to meet your K1 or K2 needs, supplements can be a smart solution—as long as you choose the right form and take it properly.
01｜Choose the right form: MK-7 is the most stable and absorbable K2
- MK-4 has a short half-life and needs to be taken 2–3 times per day at high doses.
- MK-7 lasts up to 72 hours in the body and is more suitable for daily maintenance.
👉 For most people, MK-7 is the better form—especially the “all-trans” MK-7 derived from fermentation, which is highly stable and bioactive.
02｜Fat-soluble vitamins need fat for proper absorption
- Taking K2 on an empty stomach results in poor absorption.
- Consuming it with low-fat meals like skim milk or vegetable soup isn’t effective either.
✅ The best way is to take it with a fat-containing breakfast (e.g., whole milk, eggs, nuts), or with oil-based supplements such as:
- Omega-3 fish oil or krill oil
- Or choose softgel forms of K2 that include lipid delivery systems
03｜Who should prioritise K2 supplementation?
- People who avoid animal fat and eat mostly low-fat diets (K2 intake likely insufficient)
- Those with low bone density, frequent cramps or joint issues (K2 helps calcium go to bones)
- Anyone with vascular calcification, fat metabolism issues, or family history of hypertension/diabetes (K2 may reduce arterial calcification)
04｜Single-ingredient or combo formulas? Choose based on your needs
| Supplement Type | Best For | Why Choose This |
|---|---|---|
| Pure K2 (MK-7) softgel | Those needing precise control; people taking calcium, fish oil, or D3 separately | Clear dose, easy to customise |
| K2 + D3 + Calcium/Magnesium complex | High-risk for osteoporosis | Synergistic effects for bone health |
| K2 + Omega-3 complex softgel | Those targeting both cardiovascular and bone health | One capsule delivers fat + fat-soluble vitamins together |
Authors:
Lilly (Yutong) Liu
Registered Dietitian, PhD Researcher in Nutrition, University of Auckland
Lilly is a New Zealand Registered Dietitian and PhD candidate at the University of Auckland. She specialises in elderly and post-operative nutrition care through her clinical work with DietRight, and her research focuses on biomarkers and nutrition strategies in pancreatic diseases. With experience in hospital-based nutrition, RedCap data management, and bilingual study coordination, she is committed to delivering evidence-based, culturally informed nutrition solutions.
