Fewer calories (kcal) can be derived from fats if their molecular structure is modified so they are not absorbed as well, or if the length of fatty acids on the glycerol molecule is reduced. It is known that short- and medium-chain fatty acids provide fewer calories (kcal) than larger ones, which is why butyric acid, with only four carbon atoms, yeilds fewer calories (kcal) than palmitic acid, which contains sixteen carbons. These two principles are applied in the manufacture of the lipid-based fat replacers known as caprenin and salatrim. Caprenin’s reduction in calories (kcal) is due, in part, to the presence of short and medium fatty acids. This fat replacer is used in candy manufacturing, and currently replaces some of the cocoa butter. It achieves these lower calori values due to its short-chain fatty acids and one long-chain fatty acid, which is only partially absorbed.

Lipid-based fat replacers also include extenders, which replace a larger amount of fat with a smaller quantity of fat. Extenders can reduce the soybean oil content in mayonnaise, sandwich sauces, and spoonable salad dressings by 67 to 75 percent. Adding emulsifiers, which are occasionally lipid-based, is another way to simulate the palatability of fats.

One of the most recent fat replacers on the market is Olestra. This unique compound was discovered by accident by Fred Hugh Mattson, a research chemist for Procter & Gamble. Company researchers were trying to locate an easily digested fat for premature infants, but instead found a compound that the body does not break down at all. Previously known as sucrose polyester, Olestra gained FDA approval in 1996 and is marketed under the brand name Olean. It is made from sugar and vegetable oil in a process in which the three-carbon glycerol molecule in the oil is replaced by a six-carbon sucrose, with six to eight fatty acids attached. This molecule is so large that it moves through the digestive tract before enzymes have time to digest the fatty acids.

Besides being undigested, Olestra is stable during heating and can even withstand the high temperatures of frying. Food companies use it in a variety of snack foods such as crackers, potato and tortilla chips, fried and baked goods, and dairy products.

The venerable protein-based fat replacer that has been used in foods, particularly ground meat products, for many years is isolated soy protein. The USDA allows isolated soy protein at certain percentages to be added to ground meat, poultry products, cooked sausages, and cured pork.

Besides, another protein-based fat replacer, Simplesse, has been allowed in foods. Simplesse is made from the whey of milk or from egg-white proteins that have been reduced to tiny particles through a process called microparticulation. The droplets roll around on the tongue, imparting a smooth, creamy consistency that closely resembles the creamy mouthfeel of fat. The FDA approved Simplesse as a generally recognized as safe (GRAS) substance for use in frozen desserts such as ice cream, cheese foods such as cream cheese and cheese spreads, and other products.

Unfortunately, salad dressings made with Simplesse are more acidic, and frying or baking with it is out of the question because the protein droplets of Simplesse break down when heated. As a result, Simplesse is limited to use in frozen and uncooked food products. In these foods, Simplesse contributes only one-seventh the number of calories (kcal) found in an equal amount of fat. Consumers who are allergic to milk or egg protein, however, are cautioned to avoid Simplesse.

Fibers, gums, pectin, cellulose, and starches bind with water, swell, and impart some of the texture, mouthfeel, and opacity of fat. Fruits can also be used as fat replacers to a certain degree, because they naturally contain fibers, pectins, and sugars. The fiber and pectin of dried fruits such as plums, figs, and raisins provide texture, while their sugars contribute bulk and provide hygroscopic properties, which draw in water and improve the moistness of a product.

One of the big challenges facing the food industry is that of reducing the fat content in foods without diminishing their taste and salability. One food industry survey in the early 1990s revealed that fat- and calorie-reduction was the leading research and development priority for 76 percent of food processors. Cutting back on fat content also affects important functional properties – appearance, texture, flavor, mouthfeel, handling, preparation, and storage stability. Although dietary fat consistently ranks at the top of consumer nutrition concerns, food engineers become exasperated when consumers demand low-fat foods but simultaneously value taste above nutrition when it comes to selecting food products. Nevertheless, approximately 10-15 percent of all new food products are labeled “reduced in fat”.

The number of fat replacers and their usage continues to increase as the food industry tries to meet the consumer demand for better-tasting low-fat food items. Processed foods that currently incorporate fat replacers include dairy products such as cheese, sour cream, butter, and margarine; meat products such as sausages and hamburgers; frozen desserts, including ice cream and yogurt; baked goods such as cakes, biscuits, and muffins; and frostings, sauces, and gravies.

Types of Fat Replacers

There is no official classification of fat replacers or standardization in how they are named. “Fat substitute” was often used interchangeably with “fat replacer”, however, “replacer” is a more general term describing any ingredient used to replace fat that can include substitutes, mimetics (imitators), and extenders. Substitutes physically resemble fats are often lipid-based, and usually replace the fat in foods on a one-to-one basis to duplicate the functional properties of fat. Fat mimetics are water-soluble, often protein- or carbohydrate-based, and imitate the mouthfeel of fat, which makes them useful in improving the texture of low-fat foods, especially cheeses. They do not, however, replace fat by weight, as do the fat-soluble substitutes and extenders.

Several substances have been proposed as possible fat replacers – synthetic fats, microparticulated proteins, starch, fiber, and even dried fruit puree – and research continues on these. Fat replacers, regardless of their name, can also be grouped according to whether their chemical structure is carbohydrate-, protein-, or lipid-based.