Nutritions - Lipids Lipids in simple words are fats or cholesterol, and sometimes, oils. They store energy and form heat in animal bodies. They form the structure of tissues. Similar functions to proteins, they also form hormones. Fats, which provide 9 calories of energy per gram, are the most concentrated of the energy-producing nutrients, so our bodies need only very small amounts. Fats play an important role in building the membranes that surround our cells and in helping blood formation. Once digested and absorbed, fats help the body absorb certain vitamins. Fat stored in the body cushions vital organs and protects us from extreme coldness and heat.