Food first is the right default. It is also a claim about absorption — and between what a food contains and what reaches your bloodstream sit three exchange rates nobody mentions.
If I hand you a thousand pounds in one currency and a thousand in another, you have not been given the same thing twice.
The number on the note is real. What it converts to is a different question, and it depends on the exchange rate, where you are standing, and whether the bank will take it at all.
Nutrients work like this, and “food first” is a principle that quietly assumes they do not.
I believe in food first. It is how I practise and it is the right default. But it is stated as though the number on the nutrition label is the amount you receive, and that is not how absorption works. Between what a food contains and what arrives in your bloodstream sit at least three exchange rates — the form the nutrient is in, how it was prepared, and the state of the gut receiving it.
Vitamin B6 is the clearest case. In animal foods it is largely free pyridoxine and its relatives — readily absorbed. In plant foods a substantial proportion is bound to a glucose molecule as pyridoxine glucoside, and that form is roughly half as available. The label counts them the same.
Cooking complicates it further. Heat drives the Maillard reaction, which binds some B6 to lysine and makes it largely unusable. So the same food, cooked differently, delivers different amounts.
Raw animal sources → bananas → cooked animal sources → most plants. Not the order most people would guess.
Iron. Haem iron from meat is absorbed at rates several times higher than non-haem iron from plants, and non-haem absorption is further reduced by phytate, tannins from tea, and calcium taken at the same meal — while vitamin C in the same meal improves it. Same milligram on the label, wildly different outcome.
Vitamin A. Retinol from animal foods is ready to use. Beta-carotene from plants must be converted, at a ratio somewhere around twelve to one by weight, and the conversion varies enormously between individuals because of common genetic differences in the enzyme that does it. Some people convert poorly enough that a carotene-rich diet leaves them functionally short.
Omega-3. ALA from flax, chia and walnuts converts to EPA at single-digit percentages, and to DHA at well under one percent. Which is why the omega-3 index responds to oily fish and barely moves on flaxseed.
Zinc from meat is absorbed considerably better than zinc from legumes and grains, where phytate binds it. Soaking, sprouting and fermenting reduce phytate — which is precisely why traditional preparation methods did those things.
None of this is an argument against plants. It is an argument against reading a nutrient number without asking what form it is in.
For some nutrients, food-first is entirely achievable. For others, meeting the requirement from food alone requires quantities nobody eats.
Potassium. The adequate intake sits around 3,500mg. A banana has roughly 420. That is eight to ten bananas a day, every day — and bananas are one of the better sources.
Vitamin D. Between roughly October and March, the sun in the UK does not get high enough for the skin to synthesise meaningful vitamin D at all. Food sources do not come close to covering it. This is not a failure of diet. It is geography.
Magnesium. Achievable in principle and difficult in practice, because soil depletion and food processing have both reduced the amount arriving.
Omega-3. Requires oily fish several times weekly, sustained. Achievable — and most people do not do it.
So food first holds for some nutrients and is a polite fiction for others. Being clear about which is which is more useful than the slogan.
All bioavailability data assumes a functioning gut.
The figures for how much zinc you absorb from a steak were generated in people with normal stomach acid, adequate pancreatic enzyme output, an intact intestinal surface and a reasonable bacterial population. Change any of those and the numbers no longer apply to you.
Reduced pancreatic enzyme output means protein and fat are not broken down efficiently — so the fat-soluble vitamins riding along with them arrive in smaller amounts. Low stomach acid impairs mineral release from food, particularly iron, zinc and B12. An inflamed intestinal surface has less absorptive capacity. Bacterial imbalance changes what is available and what competes for it.
Which means the food-first strategy can fail for reasons that have nothing to do with the food. Someone eating an exemplary diet, with a compromised gut, is receiving considerably less than their food diary suggests — and if you only look at the diary, you will conclude their diet is fine and look elsewhere.
Manganese is a genuine example of the mineral wheel working against you. It is abundant in nuts, seeds, whole grains, leafy greens and tea — exactly the foods a health-conscious person eats more of. Someone living on green smoothies, nuts and grains can take in a great deal more than a typical diet supplies.
And manganese is not a nutrient where more is better. It shares an absorption transporter with iron, so intake at one end affects status at the other, and low iron increases manganese uptake. It is also one of the minerals where the useful range is comparatively narrow.
The principle generalises. A very plant-heavy diet is a mineral intervention as much as a capsule is — it is just not labelled as one.
A need established through testing. Not suspected from symptoms, not inferred from a questionnaire. Measured.
A gut that can absorb it — or a form chosen to work around the limitation, which sometimes means a different form rather than a higher dose.
A required dose that exceeds what food can realistically deliver. Correcting an established deficiency usually requires more than maintenance, and more than a plate provides.
Then food-first resumes for maintenance, once the deficiency is corrected and the absorption problem addressed. Measure, restore absorption, correct therapeutically, maintain with food. Supplements are a therapeutic intervention with an endpoint, not a permanent subscription.
The second is less discussed and I see it more often. That position is not clinical — it is ideological, and it costs the person months of feeling unwell while the principle is upheld.
The honest position sits between them. Food first as the default and the destination. Supplements as a therapeutic tool with an indication, a dose and an endpoint. And testing as the thing that tells you which situation you are actually in.
A nutrient number on a label is an invoice, not a receipt. What you absorb depends on the form, the preparation, what it was eaten with, and the gut receiving it.
Some nutrients are genuinely hard to obtain from food — potassium by volume, vitamin D by latitude, omega-3 by habit. Knowing which are which stops you blaming your diet for arithmetic.
Enthusiastic dietary change is an intervention. A very plant-heavy or very restricted diet moves the whole mineral pattern, whether or not anyone calls it a protocol.
And if you are doing everything right and still not well, the question is not usually what else to add. It is whether what you are already eating is arriving.
Food first is the right default. It is also a claim about absorption — and absorption is measurable.
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