Sphingolipids in food and the emerging importance of sphingolipids to nutrition.

Eukaryotic organisms as well as some prokaryotes and viruses contain sphingolipids, which are defined by a common structural feature, i.e. , a "sphingoid base" backbone such as D-erythro-1,3-dihydroxy, 2-aminooctadec-4-ene (sphingosine). The sphingolipids of mammalian tissues, lipoproteins, and milk include ceramides, sphingomyelins, cerebrosides, gangliosides and sulfatides; plants, fungi and yeast have mainly cerebrosides and phosphoinositides. The total amounts of sphingolipids in food vary considerably, from a few micromoles per kilogram (fruits) to several millimoles per kilogram in rich sources such as dairy products, eggs and soybeans. With the use of the limited data available, per capita sphingolipid consumption in the United States can be estimated to be on the order of 150-180 mmol (approximately 115-140 g) per year, or 0.3-0.4 g/d. There is no known nutritional requirement for sphingolipids; nonetheless, they are hydrolyzed throughout the gastrointestinal tract to the same categories of metabolites (ceramides and sphingoid bases) that are used by cells to regulate growth, differentiation, apoptosis and other cellular functions. Studies with experimental animals have shown that feeding sphingolipids inhibits colon carcinogenesis, reduces serum LDL cholesterol and elevates HDL, suggesting that sphingolipids represent a "functional" constituent of food. Sphingolipid metabolism can also be modified by constituents of the diet, such as cholesterol, fatty acids and mycotoxins (fumonisins), with consequences for cell regulation and disease. Additional associations among diet, sphingolipids and health are certain to emerge as more is learned about these compounds.