Adjusted or Ideal Body Weight for Nutrition Assessment

Many of the resting metabolic rate, or RMR, equations that are used today by registered dietitian nutritionists are based on actual body weight. Research evaluating the use of adjusted body weight, or ABW, has been shown to underestimate or overestimate RMR depending on the patient's weight status. Reasoning behind using an ABW with individuals who weigh less than 95% or more than 115% of a standard body weight was based on the assumption that adipose tissue is inert; however, research to justify this assumption lacks evidence.

If RMR cannot be measured by indirect calorimetry, actual body weight and the Mifflin-St. Jeor equation are recommended when estimating energy needs in non-critically ill patients. The Mifflin-St. Jeor equation demonstrated the most reliability in predicting resting energy expenditure, regardless of weight status, according to the Academy's Evidence Analysis Library Adult Weight Management Guideline.

Alternative equations may need to be considered, as is the case with critical illness, mechanical ventilation, ascites, edema and other conditions. Although limited research exists, ABW and ideal body weight (IBW) have been used when assessing energy and protein needs in critically ill patients who have an elevated body mass index and require a hypocaloric and/or high-protein feeding. Estimations of IBW have also been used for people with amputations and spinal cord injuries. Dosing of prescription medications by pharmacists also may warrant use of an adjusted IBW; otherwise, in most other circumstances, RDNs will utilize actual body weight when assessing energy, protein and fluid needs.

References:

• Academy of Nutrition and Dietetics. Nutrition Care Manual. Accessed July 15, 2022.
• Patil PR, Sucher K, Hollenbeck C, Brown E. Evaluating the Use of Adjusted Body Weight for Predicting Resting Metabolic Rate of Overweight and Obese Subjects. J Am Diet Assoc. 2011;111(9):A28.
• Kensinger KM, Molaison EF, Sample AD. Estimation of Resting Energy Expenditure in Obese Populations: A Comparison of the Equations. J Am Diet Assoc. 2011;111(9):A28.
• Academy of Nutrition and Dietetics. Evidence Analysis Library. Adult Weight Management. Accessed December 1, 2014.
• Charney P, Malone AM. Pocket Guide to Nutrition Assessment, 4th edition. Chicago, IL: Academy of Nutrition and Dietetics; 2022.