Obesity has become common in critically ill patients as it is in the population at large. Despite large fuel stores, obese patients can become rapidly malnourished and are subject to the same inflammatory and catabolic responses as their nonobese counterparts. The concepts of early enteral nutrition are therefore equally applicable to the obese patient as to the nonobese patient. Monitoring of nutrition support likewise is the same. The main differences in obese versus nonobese patients is that nutrition assessment is somewhat more uncertain, and that hypocaloric high-protein feeding is more often recommended in the obese. The rationale for hypocaloric feeding in obese patients is multipart: (1) energy balance is not necessary to achieve nitrogen balance, (2) energy expenditure is difficult to predict in obese patients and is likely to lead to overfeeding, (3) overfeeding is especially detrimental to the obese patient, and (4) positive outcomes have been observed with hypocaloric high-protein feeding. That nitrogen balance can be achieved without energy balance has been demonstrated in several studies. However, the likelihood of overestimating resting metabolic rate in the obese may be overstated, and the evidence that hypocaloric feeding improves outcome is limited. It is therefore still an open question as to whether hypocaloric high-protein feeding should be standard practice in obese critically ill patients.