In healthy subjects the metabolic response to starvation invokes regulatory mechanisms aimed at conservation of protein mass. This response is characterized by a decrease in energy expenditure and a progressive decrease in urinary N excretion. Many non-endocrine diseases induce anorexia and a decrease in food intake. However, in contrast to the metabolic reaction to starvation in healthy subjects, anorectic patients with serious diseases have increased energy expenditure and protein catabolism, associated with profound neuroendocrine alterations. These neuroendocrine changes are induced by two mechanisms. First, afferent nerves inform the central nervous system of tissue injury which results in neuroendocrine activation. Second, tissue injury stimulates the production of inflammatory mediators, which in turn results in neuroendocrine and metabolic effects. Although these metabolic changes enable the organism to survive short-lasting diseases by using endogenous substrates, in protracted serious diseases these changes will result in loss of functioning protein mass and may endanger survival. Moreover, tissue injury alters the metabolic responses to nutrition, reflected in the persistence of catabolism as long as serious tissue injury remains.

The trace element and vitamin requirements of severely-ill injured patients depend on a complex interaction of the status of the patient at the time of admission, ongoing losses and the potential benefit of supplying large amounts of individual micronutrients. Characteristic clinical deficiency states are now uncommon, but subclinical deficiency is of growing concern. The main effects of subclinical deficiency are: (1) an altered balance of reactive oxygen species and antioxidants, leading to oxidative damage of polyunsaturated fatty acids and nucleic acids, and possibly to increased activation of the transcription factor nuclear factor-κB, with increased production of pro-inflammatory cytokines; (2) impaired immune function with increased likelihood of infectious complications. Laboratory tests to optimize intake in such critically-ill patients lack sensitivity and specificity, this situation being made worse as a result of the acute-phase response. Recent studies have indicated the clinical benefit of providing large amounts of certain micronutrients in burned and head-injured patients. Further clinical studies are now required to define optimal levels of provision in different disease states, with a particular emphasis on markers of tissue function and clinical outcome.

While many studies have reported that providing parenteral nutrition (PN) can change nutritional outcomes, there are limited data that demonstrate that PN influences clinically-important end points in critically-ill patients. The purpose of the present paper is to systematically review and critically appraise the literature to examine the relationship between PN and morbidity and mortality in the critically-ill patient. Studies comparing enteral nutrition (EN) with PN and studies comparing PN with no PN were reviewed. The results suggest that EN is associated with reduced infectious complications in some critically-ill subgroups. PN, on the other hand, is associated with increased morbidity and mortality in critically-ill patients. When nutritional support is indicated, EN should be used preferentially over PN. Further studies are needed to define the optimal timing and composition of PN in patients not tolerating sufficient EN. Strategies to optimize EN delivery and minimize PN utilization in critically-ill patients are indicated.

Despite a marked increase in the prescription of oral nutritional supplements (ONS) in the community (Department of Health, 1991–7), there is still uncertainty about the value of their use in patients with different diseases. To answer questions about the effects on ONS on body weight and structure, spontaneous food intake and body function, a critical systematic review was undertaken (Stratton & Elia, 1999a). Eighty-four trials were reviewed (forty-five randomized, thirty-nine non-randomized; 2570 patients; diagnoses including chronic obstructive pulmonary disease, Crohn’s disease, cystic fibrosis, human immunodeficiency virus and acquired immune deficiency syndrome and cancer). Most studies (83 %) were conducted in patients living at home. The supplements were typically mixed macronutrients in liquid form, providing < 0.42–10.5 MJ/d for 1 week–2 years. The studies reviewed in patients with predominantly chronic conditions living in the community suggested that: (1) ONS produce demonstrable clinical (including functional) benefits, but the nature and extent of these benefits varies with the underlying chronic condition; (2) ONS increase total energy intake with > 50 % of the energy from ONS typically additional to that from habitual food intake; (3) improvements in body weight, total energy intake and body function following ONS appear to occur more frequently in individuals with a BMI < 20 kg/m2 than in those with a BMI > 20 kg/m2.

The growing interest in the role of phyto-oestrogens in human health has prompted scientists to evaluate the risk : benefit which would result from consuming high levels of these compounds at different stages of the life cycle. These compounds have been shown to exert a wide range of hormonal and non-hormonal activities in animals and in vitro, and these activities suggest plausible mechanisms for potential health effects in human subjects consuming phyto-oestrogen-rich diets. In addition, experimental and epidemiological data are available supporting the concept that phyto-oestrogen-rich diets exert physiological effects in vivo; however, their relative importance to human health remains to be elucidated. Our understanding of factors involved in their absorption and metabolism, including the role of intestinal microflora, is limited, and these factors together with dose-related effects may well be important in determining clinical efficacy.