Stearic Acid and Magnesium Stearate

Neil Levin

Most people concerned about the tiny amount of stearic acid in a capsule actually consume far more from healthy food sources, safely. Meat, coconut oil and chocolate (cocoa butter) are particularly rich sources. Additionally, researchers do not consider stearic acid to be a lipid that is harmful to cardiovascular health.

NOW’s magnesium stearate is derived solely from palm oil. It is a magnesium salt of fatty acid [C16 to C18], and contains no trans-fatty acids. It is non-GMO, free from BSE/TSE and may be used, if desired, as part of a vegetarian or vegan diet.

Why use Stearic Acid?

Stearic acid is a waxy oil fraction that acts as a lubricant to fill capsules when a dry powdered ingredient (or ingredient mix) is uncooperative, based on issues involving density, stickiness, flowability under pressure, etc. It is also used as an ingredient that helps tablets hold together and break apart properly.

Stearic acid (also called Octadecanoic Acid) is one of the most common long-chain fatty acids, found in both natural animal and vegetable fats, known also by its structural description of being an 18-carbon chain fatty acid (18:0) with a chemical structure of C36H70MgO4.

What is Magnesium Stearate?

Magnesium stearate is a combination of stearic acid and the essential mineral magnesium. Magnesium stearate contains the equivalent of not less than 6.8 percent and not more than 8.3 percent of MgO (Magnesium oxide), and is a mixture of pure stearic acid and palmitic acid where the content of stearic acid is not less than 40.0% and the sum of the two acids is not less than 90.0%. The British Pharmacopoeia 1993 describes magnesium stearate as consisting mainly of magnesium stearate with variable proportions of magnesium palmitate and magnesium oleate.

NOW uses USP grade stearates tested to US Pharmacopeia standards; known as pharmaceutical grade, the highest purity.

Sources of Stearic Acid

Stearic acid is naturally present in many foods in far greater quantities than in supplements. Stearic acid is also the immediate precursor of oleic acid, an important fatty acid found in healthy olive oil.

NOW uses stearic acid and magnesium stearate that are sourced from vegetable oils obtained from palm and other natural sources. These ingredients are widely considered to be safe, and are suitable for vegetarians and vegans.

An American Journal of Nutrition published review of beef’s effect on cholesterol reported that, “Beef products are the most common source of dietary stearic acid in the United States. Because beef fat is 19% stearic acid, the cholesterol-raising potential of beef is not as great as predicted by its total saturated fatty acid content...Data suggest that lean beef is no more hypercholesterolemic than chicken or fish and, therefore, lean beef need not be eliminated from cholesterol-lowering diets.” 1

Stearic acid is also one of the main fats in cocoa butter, and this particular fatty acid is considered safer than others present in cocoa butter. A report from the University of Texas Southwestern Medical Center confirmed this: “It has been known for some time that cocoa butter, although rich in saturated fatty acids, does not raise total serum cholesterol concentrations as much as expected from its total saturated fatty acid content...In a recent experiment cocoa butter did not raise LDL cholesterol as much as predicted by its total saturated fatty acid content.” 2

The Encyclopædia Britannica reports that, “In nature stearic acid occurs primarily as a mixed triglyceride, or fat, with other long-chain acids and as an ester of a fatty alcohol. It is much more abundant in animal fat than in vegetable fat; lard and tallow often contain up to 30 percent stearic acid.” 3

Researchers at the University of Nebraska noted, “The observation that dietary stearic acid does not raise plasma cholesterol concentration is well documented, although the regulating mechanisms are not completely understood… the data suggest that reduced plasma cholesterol concentration in hamsters fed high 18:0 [ed. note: stearic acid] diets may be influenced by reduced cholesterol absorption and increased excretion of endogenous [ed. note: produced by the body] cholesterol.” 4

The USDA cites this study regarding the use of magnesium stearate as a functional aid in the manufacture of tablets: “Stearic acid is the predominant fatty acid in triacylglycerols of beef fat and coconut oil (present as the ester). The free acid is used routinely in many commercial products in addition to foods. It is used in polymer formulations as an extrusion aid. As the magnesium stearate in tablets, it helps keep the solid ingredients from falling apart in the bottle, and it also enables the tablet to break apart and release the active ingredient when the tablet is swallowed.” 5

For softgel capsules containing liquid extracts, NOW does not typically use stearic acid as an excipient. Other excipients are more suitable for use in a softgel capsule and will appear on the label, such as vegetable oils, lecithin, and natural coloring/opacity agents such as annatto seed extract (red color), carob pod extract (brown), and zinc oxide (opaqueness).

The FDA has affirmed that stearic acid is GRAS (Generally Regarded As Safe) and can be added to foods in accordance with Good Manufacturing Practices (GMP). 6 NOW is a GMP-certified manufacturer.

The FDA’s Select Committee on GRAS Substances has also reported on magnesium stearate safety, concluding that, “There is no evidence in the available information on magnesium carbonate, magnesium chloride, magnesium sulfate, magnesium hydroxide, magnesium oxide, magnesium stearate…that demonstrates, or suggests reasonable grounds to suspect, a hazard to the public when they are used at levels that are now current and in the manner now practiced, or which might reasonably be expected in the future.” 7

Is Stearic Acid Safe?

This science assures us that stearic acid is a safe fatty acid found in healthy foods and that magnesium stearate is a safe analog of stearic acid. NOW uses them only as necessary for the functionality of a particular dietary supplement, in tiny amounts (often less than one milligram, per capsule) compared to the amount of stearates found in common foods.


1 Denke MA. Role of beef and beef tallow, an enriched source of stearic acid, in a cholesterol-lowering diet. Am J Clin Nutr. 1994 Dec;60(6 Suppl):1044S-1049S. Review. PMID: 7977148

2 Effects of cocoa butter on serum lipids in humans: historical highlights. Am J Clin Nutr. 1994 Dec;60(6 Suppl):1014S-1016S. Review. PMID: 7977142

3 "stearic acid." Encyclopædia Britannica. 2006. Encyclopædia Britannica Online. 18 Dec. 2006

4 Schneider CL, et al. Dietary stearic acid reduces cholesterol absorption and increases endogenous cholesterol excretion in hamsters fed cereal-based diets. J Nutr. 2000 May;130(5):1232-8. PMID: 10801924

5 Schmidt, W.F., Barone, J.R., Francis, B.A., Reeves III, J.B. 2006. Stearic acid solubility and cubic phase volume. Chemistry and Physics of Lipids. 142(1-2):23-32.

6 Code of Federal Regulations. Title 21, Volume 3. Revised as of April 1, 2006. CITE: 21CFR184.1090 [48 FR 52445, Nov. 18, 1983, as amended at 50 FR 49536, Dec. 3, 1985; 69 FR 24512, May 4, 2004]

7 FDA Center for Food Safety and Applied Nutrition. Database of Select Committee on GRAS Substances (SCOGS) Reviews. CFSAN/Office of Food Additive Safety. October 2006