Labels
The nutrient that gives a blend away
A proprietary blend withholds the one thing a reader wants: how much of each ingredient is in the capsule. Most of the time it succeeds. Occasionally a label hands the whole thing over in a single row, while following every rule exactly.
A nutrient with a Daily Value must be declared separately, with its weight, even inside a proprietary blend. Where it arrives as a compound — a chelate, a salt, an oxide — the declared figure is the elemental weight, a fraction of the compound’s. Divide one by the other and you have recovered the compound’s weight, and with it the blend’s remainder.
What a blend actually prints
The panel this post is about has two rows. The first reads Magnesium (as Magnesium Glycinate from proprietary blend) — 80 mg, 19%. The second reads Proprietary Blend — 575 mg, with six ingredient names indented beneath it and a single dagger where the amounts would go.
That is the whole quantitative content of the panel: two numbers and an order. Five of the six named ingredients carry nothing. On most labels that is where the enquiry ends, which is what a proprietary blend is for.
The standard move here is the division. Federal guidance requires blend constituents “in descending order of predominance by weight”, so the ingredient in position n cannot exceed the total divided by n: 575, 287.5, 191.7, 143.8, 115 and 95.8 mg. That method has a guide of its own.
Those ceilings are correct and nearly useless: 287 mg is wide enough to accommodate a real dose of almost anything. What follows is the other method — the one that applies when a blend contains a nutrient, and which here tightens those figures by a factor of sixty.
The clause most readers skip
Here is the FDA paragraph in full. Everybody quotes the first half. The part that matters here is the last sentence.
FDA — Dietary Supplement Labeling Guide, Chapter IV
“You must identify proprietary blends by use of the term “Proprietary Blend” or an appropriately descriptive term or fanciful name. On the same line, you must list the total weight of all “other dietary ingredients” contained in the blend. Indented underneath the name of the blend, you must list the “other dietary ingredients” in the blend, either in a column or linear fashion, in descending order of predominance by weight. … Dietary ingredients having RDIs or DRVs must be listed separately and the individual weights declared.”
“Dietary ingredients having RDIs or DRVs must be listed separately and the individual weights declared.” A vitamin or a mineral cannot hide inside a blend. It has to appear on its own row, with its own weight and its percentage of the Daily Value.
That requirement is usually read as small: it stops a manufacturer burying an excessive dose of a nutrient in an opaque blend. It is not small, because the row it forces is a window into the rest of the formula — if you read it as a chemist rather than as a shopper.
One more thing on this label, and it is voluntary. The row does not say Magnesium 80 mg. It says “as Magnesium Glycinate from proprietary blend”. Four words nobody had to print are what make the rest of this post possible, and they work against the product.
Elemental weight is not compound weight
A mineral on a Supplement Facts panel is declared as the element: eighty milligrams of magnesium means eighty milligrams of magnesium atoms. But you cannot put magnesium atoms in a capsule. What goes in is a compound, and the compound weighs more than the magnesium in it — sometimes a great deal more.
So the panel prints a number describing part of an ingredient while the blend total describes whole ingredients — two different currencies, with one division between them.
The conversion, in one line
Weight of compound = declared elemental weight ÷ elemental fraction. The elemental fraction is the atomic weight of the mineral divided by the molecular weight of the compound — a number you can compute from the formula, or look up once and keep.
That is the whole technique. It needs nothing that is not either printed on the bottle or a standard chemical constant. And because the compound’s weight comes out of the blend total, what is left is the weight available to every other ingredient combined.
Three compounds, three different answers
The fraction differs for every compound, which is why the form printed beside a nutrient is worth reading. Three common magnesium ingredients, with the arithmetic shown.
| Compound | Formula and molecular weight | Elemental magnesium | Compound needed for 80 mg |
|---|---|---|---|
| Magnesium glycinate | C₄H₈MgN₂O₄ — 4×12.011 + 8×1.008 + 24.305 + 2×14.007 + 4×15.999 = 172.42 | 24.305 ÷ 172.42 = 14.1% | about 567 mg |
| Magnesium oxide | MgO — molecular weight 40.30 | 24.305 ÷ 40.30 = about 60% | about 133 mg |
| Trimagnesium dicitrate | C₁₂H₁₀Mg₃O₁₄ — molecular weight 451.11 | 3×24.305 ÷ 451.11 = about 16% | about 494 mg |
Read the last column. The same declared 80 mg costs 133 mg of blend as the oxide and 567 mg as the glycinate — a gap of more than four hundred milligrams inside a blend totalling 575. Two labels printing an identical magnesium row can describe entirely different formulas, which is why “80 mg of magnesium” compares nothing unless you know the form. Here the form is printed, and that disclosure is what this post depends on.
The worked example: 80 mg inside 575
Now put them together: magnesium glycinate at 14.1% elemental, a declared 80 mg, a blend of 575 mg.
- 80 ÷ 0.141 = about 567 mg of magnesium glycinate.
- 575 − 567 = about 8 mg left for the other five ingredients combined.
- Apply the descending-order rule to that remainder, position by position: at most 7.5, 3.7, 2.5, 1.9 and 1.5 mg.
Every figure here is forced by two numbers printed on the bottle: Magnesium 80 mg and Proprietary Blend 575 mg. Magnesium glycinate is C₄H₈MgN₂O₄, and the magnesium atom is about 14.1% of it by weight, so 80 mg of elemental magnesium needs roughly 567 mg of the compound. The blend is 575 mg. About 8 mg is left, and the FDA’s descending-order rule divides it as shown. The scale is logarithmic because a linear one would render the bottom five bars invisible — which is itself the finding.
Set those against the ceilings the blend total alone allowed — 287.5, 191.7, 143.8, 115 and 95.8 mg — and the gap is the point. Each bound tightens by a factor of roughly forty to sixty-five, and nothing new was disclosed to achieve it.
A derivation this consequential should not rest on one line of reasoning, and it does not. If the arithmetic is right, magnesium glycinate is about 99% of the blend and must therefore be listed first under the descending-order rule. On this panel it is. One chemical fact and one regulatory fact, reached independently, agree.
How wrong could it be?
Every calculation should be readable by somebody trying to knock it down. The 14.1% figure is what the formula gives for the pure anhydrous chelate. A hydrated form would carry water too, lowering the percentage and making the conclusion stronger. A buffered chelate — glycinate blended with magnesium oxide, which is common and legitimate — raises it and makes the conclusion weaker. This label does not say which is used.
| If the magnesium ingredient is… | Weight needed for 80 mg | Left for the other five | Share of the blend |
|---|---|---|---|
| 14.1% | about 567 mg | about 8 mg | 99% |
| 15% | about 533 mg | about 42 mg | 93% |
| 16% | about 500 mg | about 75 mg | 87% |
| 18% | about 444 mg | about 131 mg | 77% |
| 20% | about 400 mg | about 175 mg | 70% |
Read the last column. Across the entire plausible range — pure chelate to heavily buffered — the magnesium ingredient is between 70% and 99% of the blend: the severity moves, the direction does not. That is the shape of a finding worth publishing, and of a question worth asking — which magnesium glycinate, and what is its elemental content? A formulator can answer in a sentence.
When the method fails
It is not a universal tool, and pretending otherwise would be the same error the method exists to expose. Four conditions have to hold.
- The blend must contain an ingredient with a Daily Value. No vitamin, no mineral, no separately declared row, no method. A blend of six botanicals gives you the division and nothing else.
- The nutrient must actually be in the blend. Many labels declare a mineral outside it, in which case its weight says nothing about the blend. Here “from proprietary blend” settles it explicitly, which is unusual.
- The compound must be named. A bare Magnesium 80 mg is compliant and useless: without the form there is no fraction to divide by.
- The nutrient must be a large part of the blend. The method always works; it only matters when the compound is a substantial share of the total. The same 80 mg as the oxide would leave more than 440 mg for everything else and change nothing.
When all four hold, as they do here, a reader ends up with better information than the manufacturer intended to publish — not by breaking anything, but by reading two compliant rows together.
Doing it on any bottle
Find the blend line and read the total
On the same line as the blend’s name. No total means no arithmetic at all.
Scan the rows above it for a nutrient
A milligram figure with a Daily Value percentage. If it also names a compound, you have the sharper method.
Convert elemental to compound
Declared weight divided by the elemental fraction, computed from the molecular formula.
Subtract from the blend total
What is left is the weight every other ingredient has to share. A negative answer means the label is wrong, which is a finding in itself.
Divide the remainder by position
Descending order does the rest, and those ceilings are the real ones.
Check the ordering agrees
The compound should be listed where its weight says it belongs. If it is not, work out why before trusting either figure.
Whether that matters is a separate question. On this product, none of the six has a respiratory monograph at the bodies this desk reads — a different argument entirely. The arithmetic is neutral: it tells you what is in the capsule, not whether it works. Most of the time that is the harder half to find out.
Read the magnesium row before you decide
Thirty capsules, one a day. One amount is printed on this label — 80 mg of magnesium — and it is the amount that tells you what is left of the 575 mg blend for the other five ingredients. The live price and the 60-day return terms are both on the seller’s checkout screen.
60-day window · Questions first? The FAQ page answers most of them.