Although
stearic acid is a
saturated fatty acid, its influence on plasma
cholesterol acid other health variables is neutral; possibly owing in part to poor absorption. Reduced absorption of
stearic acid from particular
triacylglycerols,
cocoa butter and novel
fats formulated with short- and long-chain
acid triacylglycerol molecules (Salatrims) has been attributed to high intakes. However, the circumstances and causes of poor
stearic acid digestion from
triacylglycerols are unclear; published data were therefore collected and analysed, with emphasis on human studies. Of twenty-eight studies conducted in adults, most are in men (>90%). The assertion that reduced absorption is due to a high intake of stearoyl groups is not supported: dietary intakes of stearoyl of 0.05-0.65 g
stearic acid equivalent/kg
body weight (cf typical intake of 0.2 g
stearic acid equivalent/kg
body weight in the Western diet) indicate that the 'true' digestibility of stearoyl is 0.98 (SE 0.01) g/g, with apparent digestibility less than this value at low intakes owing to endogenous
stearic acid excretion and to inter-publication variation of unidentified cause. The neutral health impact of
stearic acid must be due to factors other than availability. Exceptions include
cocoa butter, Salatrims and
tristearin, for which digestibility is an additional factor. The efficiency with which human subjects digest stearoyl from
cocoa butter still remains uncertain, while the digestion of total long-chain fat from this source is 0.89-0.95 g/g, high in comparison with 0.33 g/g for
Salatrim 23CA and 0.15 g/g for
tristearin in their prepared states. Salatrims contain the highest proportion of long-chain
fatty acids that are
stearic acid-rich other than
tristearin, which is the main component of fully-hydrogenated soyabean and
rapeseed oil. Analysis shows that apparent digestibility of
stearic acid is associated with stearoyl density within the
triacylglycerol molecule and that, in Salatrims, the occurrence of
short-chain fatty acids in place of long-chain
fatty acids increases this density.
Soap formation appears not to be a major factor in the reduced digestion of
stearic acid from
tristearin under regular dietary circumstances, but both microcrystallinity and reduced digestibility of tri-, di- and monostearoylglycerols appears to be important. Solubilisation of high-melting-point
tristearin in low-melting-point
oils improves the digestibility of its
stearic acid, particularly when emulsified or liquidized at above melting point. However, without such artificial
aids, the digestive tracts of the rat, dog and man have a low capacity for emulsifying and digesting
stearic acid from
tristearin. Reduced digestibility of
stearic acid from
Salatrim 23CA also appears to be attributable to reduced digestibility of di- and monostearoylglycerols and is particularly due to remnants with the 1- or 3-stearoylglycerol intact after initial hydrolytic cleavage. Short-chain organic
acid in
Salatrim 23CA, which is readily hydrolysed, leaves such remnants. Unlike
tristearin,
Salatrim 23CA melts at body temperature and mixing it with low-melting-point
oils is not expected to cause further disruption of microcrystalline structures to aid digestibility of its stearoyl groups. The low digestibility of stearoyl in
Salatrim 23CA, together with the occurrence of short-chain organic
acids in this product, account for its relatively low nutritional energy value (about 20 kJ (5 kcal)/g) compared with traditional
fats (37 kJ (9 kcal)/g) and low fat value (<20:37 kJ/kJ; <5:9 kcal/kcal) relative to traditional
fats. In part these differences are because of minor effects of
Salatrim 23CA on the excretion of other fat and
protein, due to the bulking properties of this poorly-digestible fat.