Terms related to the assessment and estimation of nutrient needs are defined below.

In addition to physical activity, there are disease-specific factors to account for the additional energy requirements conferred by fever, burn, infection, surgery, and trauma [2].

There are several formulas used in the clinic setting to estimate a person’s total energy (caloric) requirements [2]. These are based largely on a person’s height, weight, gender, and age. The result can then be multiplied by a factor depending on a person’s usual energy expenditure . But there is much debate about which formula is superior and about the selection of formulas to be used in specific medical conditions. A few of the most important models for estimating energy requirements in healthy individuals are shown (Appendix 4). However it is calculated, the estimated energy requirement is helpful in determining how much food – and in what composition – is required to best meet needs. The Dietary Reference Intakes (DRIs) , nutrient intake goals set by the Institute of Medicine (IOM) [3], include recommended intake ranges for total energy (Appendix 5). These ranges are known as acceptable macronutrient distribution ranges (AMDRs) and represent the acceptable range of macronutrient intake that is considered healthy. AMDRs are expressed as percentages of recommended total energy intake.

The estimation of nutrient requirements, particularly of micronutrients (vitamins and minerals), is a complex and methodical process based on the available scientific and biomedical evidence. From 1941 to 1989, nutrient requirements were expressed as Recommended Dietary Allowances (RDAs) and were based on conclusions reached from studies that assessed the minimum amount of each essential nutrient required for life [3, 4]. Usually these were balance studies; in other cases, data were derived simply from identifying the average intake of a population. In the 1990s, the DRIs were developed to replace the RDAs (although they still include RDAs) [4]. Over time, increasing attention has been placed on the nutrient intake levels that optimize health vs. those that merely prevent deficiency. DRIs are an umbrella term that consists, in addition to the AMDRs addressed earlier, of five categories of reference values:

Nonessential nutrients are required for life but can, under normal conditions, be synthesized in the body from molecules provided from the metabolism of essential nutrients and other compounds. These include ten amino acids and two pro-hormones. Amino acids required for life but considered nonessential because they can be synthesized if sufficient precursors exist include alanine, asparagine, aspartamine, cysteine, glutamine, glycine, ornithine, proline, serine, and tyrosine. Pro-hormones synthesized in the body include vitamin A and vitamin D; but these are produced in amounts insufficient to meet needs, so dietary sources are required. This is why vitamin A and vitamin D are considered essential nutrients. The ten amino acids considered essential (must be obtained from the diet) are phenylalanine, valine, threonine, tryptophan, isoleucine, methionine, histidine, arginine, leucine, and lysine; these are conveniently recalled using the mnemonic “Pvt Tim Hall ,” wherein each letter stands for one of the essential amino acids. Essential nutrients – both macro- and micronutrients – as well as their common food sources are identified (Table 5.2).