The use of lower energy ingredients in diets has become increasingly popular over the last few years, and nutritional and carcass impacts have become necessary to consider as well. Determining the nutritional value of ingredients can be done through literature reviews, laboratory analysis, or estimated from analysis of other ingredients and standard equations. These methods can all give different values, so it is important to be consistent in the method used. The impact on average daily gain varies, as a pig can compensate for lower dietary energy by eating a greater quantity of food. When the fibre increases as well, the pig may not be able to eat enough to keep dietary energy the same and average daily gain may drop. The cost of reduced ADG can be small if excess space is available, but when there is no excess space it may cause a loss greater than the savings on feed. Other impacts of alternate ingredients include decreased carcass weight because of enlarged intestines from fibre, and increased space and transport costs from a lower density feed. As well, low energy diets can increase the iodine value, and result in softer fat. Ways in which to decrease the negative impact of low energy feeds are to switch to a higher energy diet three weeks before market, and the use of enzymes to increase digestibility is still under study. The use of lower energy diets is popular because of the lowered feed costs, but the overall impact and possible areas of increased costs should be considered before incorporating one into a diet.