Peter Faber

Effects of isoenergetic overfeeding of either carbohydrate or fat in young men.

Ten pairs of normal men were overfed by 5 MJ/d for 21 d with either a carbohydrate-rich or a fat-rich diet (C- and F-group). The two subjects in each pair were requested to follow each other throughout the day to ensure similar physical activity and were otherwise allowed to maintain normal daily life. The increase in body weight, fat free mass and fat mass showed great variation, the mean increases being 1.5 kg, 0.6 kg and 0.9 kg respectively. No significant differences between the C- and F-group were observed. Heat production during sleep did not change during overfeeding. The RQ during sleep was 0.86 and 0.78 in the C- and F-group respectively. The accumulated faecal loss of energy, DM, carbohydrate and protein was significantly higher in the C- compared with the F-group (30, 44, 69 and 51% higher respectively), whereas the fat loss was the same in the two groups. N balance was not different between the C- and F-group and was positive. Fractional contribution from hepatic de novo lipogenesis, as measured by mass isotopomer distribution analysis after administration of [1-(13)C]acetate, was 0.20 and 0.03 in the C-group and the F-group respectively. Absolute hepatic de novo lipogenesis in the C-group was on average 211 g per 21 d. Whole-body de novo lipogenesis, as obtained by the difference between fat mass increase and dietary fat available for storage, was positive in six of the ten subjects in the C-group (mean 332 (SEM 191)g per 21 d). The change in plasma leptin concentration was positively correlated with the change in fat mass. Thus, fat storage during overfeeding of isoenergetic amounts of diets rich in carbohydrate or in fat was not significantly different, and carbohydrates seemed to be converted to fat by both hepatic and extrahepatic lipogenesis.

Plasma concentrations of alpha-MSH, AgRP and leptin in lean and obese men and their relationship to differing states of energy balance perturbation

objective  A great deal of attention has focused on the central role of alpha melanocyte‐stimulating hormone (α‐MSH) and its antagonism at the melanocortin‐4 receptor (MC4R) by agouti related protein (AgRP) in the regulation of energy balance. However, very little is known regarding the function of circulating AgRP and α‐MSH in humans. We aimed to determine whether circulating α‐MSH and AgRP are responsive to long‐term perturbations in energy balance, in a manner consistent with their central putative functions.

Effect of an acute fast on energy compensation and feeding behaviour in lean men and women.

AIM: Humans appear to defend against energy deficit to a greater extent than energy surplus. Severe dietary energy restriction resulting in 5–30% weight loss often leads to hyperphagia and weight regain in lean subjects. However, the period of time over which fasting is often endured in Western society are far shorter, ∼1–2 days. This study examined how a 36 h fast effected the subsequent days energy and nutrient intake in a group of 24 healthy, lean men and women.METHOD: Subjects underwent two 2 day treatments, termed ‘fast’ and ‘maintenance’. During the ‘fast’ treatment, subjects were fed a maintenance diet on the day prior to the fast (day −1) to prevent overeating. They then consumed non-energy drinks only, from 20:00 h on day −1 to 08:00 h on day 2 (ad libitum feeding day), thus fasting for 36 h. On the ‘maintenance’ protocol, subjects received a maintenance diet throughout day 1. Throughout day 2 they had ad libitum access to a range of familiar foods, which were the same for both treatments. Body weight, blood glucose and respiratory quotient were used as compliance checks. Hunger was monitored on days −1, 1 and 2 for the fast treatment only.RESULTS: On day 2, average energy intake was 10.2 vs 12.2 MJ/day (s.e.d. 1.0) on the post-maintenance and post-fast periods, respectively (P=0.049). Subjects altered feeding behaviour, in response to the fast, only at breakfast time, selecting a higher-fat meal (P<0.005). Compared to day −1, motivation to eat was elevated during the fast (P<0.05). This continued until breakfast was consumed during the re-feeding period (day 2), when values then returned to baseline.CONCLUSION: These data suggest that a 36 h fast, which generated a negative energy balance of ∼12 MJ, did not induce a powerful, unconditioned stimulus to compensate on the subsequent day.

Use of the cellular model of body composition to describe changes in body water compartments after total fasting, very low calorie diet and low calorie diet in obese men.

Introduction:The cellular model of body composition divides the body in body cell mass (BCM), extracellular solids and extracellular fluids. This model has been infrequently applied for the evaluation of weight loss (WL) programmes.Objectives:(1) To assess changes in body compartments in obese men undergoing fasting, very low calorie diet (VLCD) and low calorie diet (LCD); (2) to evaluate two cellular models for the determination of changes in BCM, fat mass (FM) and body fluids.Materials and methods:Three groups of six, obese men participated in a total fast (F) for 6 days, a VLCD (2.5 MJ per day) for 3 weeks or an LCD (5.2 MJ per day) for 6 weeks. Body composition was measured at baseline and after small (∼5%) and moderate (∼10%) WL. FM was measured using a four-compartment model. Total body water (TBW) and extracellular water (ECW) were, respectively, measured by deuterium and sodium bromide dilution and intracellular water (ICW) calculated by difference. Two cellular models were used to measure BCM, FM and body fluids distribution.Results:After about 5%WL changes in TBW were F=−3.2±1.2 kg (P<0.01), VLCD=−1.2±0.6 kg (P<0.01), LCD=−0.3±0.9 kg(n.s.). The contribution of TBW to total body mass loss was indirectly associated with FM loss. ECW increased during fasting (+1.5±3.1 kg, n.s.), decreased during the VLCD (−2.0±1.5 kg, P<0.05) and remained unchanged at the end of the LCD (−0.3±1.6 kg, n.s.). ICW significantly decreased during fasting (−4.7±3.9 kg, P<0.05) but did not change in the LCD and VLCD groups. The loss of BCM was more significant in the fasting group and it was directly associated with changes in ICW.Conclusions:After a 6-day period of fasting we observed more ICW losses and less fat mobilization compared with VLCD and LCD. The cellular model of body composition is suitable for the characterization of changes in body fluids distribution during WL.

Imposed rate and extent of weight loss in obese men and adaptive changes in resting and total energy expenditure.

OBJECTIVES Weight loss (WL) is associated with a decrease in total and resting energy expenditure (EE). We aimed to investigate whether (1) diets with different rate and extent of WL determined different changes in total and resting EE and if (2) they influenced the level of adaptive thermogenesis, defined as the decline in total or resting EE not accounted by changes in body composition. METHODS Three groups of six, obese men participated in a total fast for 6 days to achieve a 5% WL and a very low calorie (VLCD, 2.5 MJ/day) for 3 weeks or a low calorie (LCD, 5.2 MJ/day) diet for 6 weeks to achieve a 10% WL. A four-component model was used to measure body composition. Indirect calorimetry was used to measure resting EE. Total EE was measured by doubly labelled water (VLCD, LCD) and 24-hour whole-body calorimetry (fasting). RESULTS VLCD and LCD showed a similar degree of metabolic adaptation for total EE (VLCD = -6.2%; LCD = -6.8%). Metabolic adaptation for resting EE was greater in the LCD (-0.4 MJ/day, -5.3%) compared to the VLCD (-0.1 MJ/day, -1.4%) group. Resting EE did not decrease after short-term fasting and no evidence of adaptive thermogenesis (+0.4 MJ/day) was found after 5% WL. The rate of WL was inversely associated with changes in resting EE (n = 30, r = 0.-42, p=0.01). CONCLUSIONS The rate of WL did not appear to influence the decline in total EE in obese men after 10% WL. Approximately 6% of this decline in total EE was explained by mechanisms of adaptive thermogenesis.

The effect of rate and extent of weight loss on urea salvage in obese male subjects

It is well established that in human subjects a proportion of urea production undergoes hydrolysis in the gastrointestinal tract with release of N potentially available for amino acid synthesis. Previous studies have suggested adaptive changes in urea kinetics, with more urea-N retained within the metabolic pool during reduced dietary intakes of energy and protein. We therefore investigated the effect of rate and extent of weight loss on adaptive changes in urea kinetics in two groups (each n 6) of obese men (mean age 43 (sd 12) years, BMI 34.8 (sd 2.9) kg/m(2)) during either total starvation for 6 d or a very-low-energy diet (2.55 MJ/d) for 21 d. Subjects were resident in the Human Nutrition Unit of the Rowett Research Institute (Aberdeen, Scotland, UK) and lost 6 and 9 % initial body weight within the starvation and dieting groups respectively. Changes in urea-N metabolism were assessed by stable isotope tracer kinetics using [(15)N(15)N]urea infused intravenously for 36 h before, during and after weight loss. In response to weight loss, urea production decreased (P<0.01) by 25 % from 278 to 206 micromol urea-N/h per kg within the dieting group only. However, no changes were observed in the proportion of urea being hydrolysed in the gastrointestinal tract (range 20-25 %) or in the proportion of N retained for anabolic purposes (80-85 % urea-N from gastrointestinal hydrolysis) within either group. It was concluded that no adaptive changes in urea kinetics occurred in response to either the different rate or extent of weight loss.

Acute kidney injury and renal replacement therapy in the intensive care unit

BACKGROUND Renal replacement therapy (RRT) is now offered as a routine treatment in most intensive care units (ICU) in the UK for patients suffering from acute kidney injury (AKI). It is important for all ICU staff to understand the underlying principles of the available therapeutic options and the possible complications thereof. AIMS AND OBJECTIVES The objective of this review was to provide an accessible theoretical and practical update on the management of RRT. In addition to a detailed discussion of the underlying principles and indications for the various modes of RRT, we will discuss the assessment of kidney function, possible complications and anticoagulation during RRT, following a review of the current literature. SEARCH STRATEGIES Pubmed, Medline and the Cumulative Index to Nursing and Allied Health Literature were searched using the keywords renal function, RRT, dialysis, renal failure kidney injury, together with intensive care, intensive therapy and critical care. We included only studies published in English from 1998 to 2008 and from these identified and included additional publications. The 12 most relevant publications are referenced in this review. CONCLUSION AKI is associated with increased mortality in ICU, and RRT should be considered early in the disease process. Continuous haemofiltration is the most common modality of treatment in this group of patients, and a detailed knowledge of the management of such patients is required.

Theoretical and practical aspects of anaesthesia for thoracic surgery.

Thoracic surgical procedures account for only a small fraction of all surgery undertaken in the NHS. Thoracic surgery is performed in specialist centres as patients often suffer serious co-morbidities and require vigilant care and observation by staff involved in their treatment. Anaesthesia for thoracic surgery challenges the theoretical and practical experience of all involved. This review briefly summarises the anaesthetic skills and knowledge required to deliver a safe and professional service to patients with thoracic pathology.

Measurement of body composition changes during weight loss in obese men using multi-frequency bioelectrical impedance analysis and multi-compartment models

BACKGROUND The accurate measurement of changes in body composition is important to assess the contribution of fat and fat free mass to total body mass change as a measure of the effectiveness of weight loss programmes. Bioelectrical impedance spectroscopy (BIS) is a rapid and non-invasive technique which could be applied to assess body composition changes. The aim of the study was to evaluate the accuracy of the BIS for the measurement of fat mass (FM), total body water (TBW) and extracellular water (ECW) changes induced by different degrees of caloric deficit in obese men. METHODS Three groups of six, obese men participated in either (i) a total fast (for 6 days); (ii) a VLCD (2.5 MJ/day for 3 weeks); or (iii) LCD (5.2 MJ/day for 6 weeks). FM was measured using a 4-compartment (4-C) model. TBW and ECW were determined by dilution methods, respectively. TBW, ECW and FM were also assessed with BIS. RESULTS Body weight loss in the fasting group was 6.0 ± 1.3 kg over 6 days; the VLCD group lost 9.2 ± 1.2 kg over 21 days and the LCD group lost 12.6 ± 2.4 kg over 42 days. BIS underestimated FM changes (bias = -3.3 ± 3.8 kg) and overestimated changes in TBW and ECW by +1.8 ± 4.8 kg and +2.3 ± 6.4 kg, respectively. The measurement error was consistently larger in the fasting group and the magnitude of the bias interacted significantly with the rate of weight loss. CONCLUSION Rapid weight loss affects the accuracy of the BIS in detecting changes in body composition. A careful interpretation of the results is needed when sizable changes in body water compartments occurs.

Nutritional physiology of the critically ill patient

Nutritional physiology refers to the role of food and nutrition in the function of the body. In the critically ill patient there are numerous points at which nutrition affects function, since all fuels, tissues, and mediators ultimately arise from the food consumed by the individual. There are now evidence-based guidelines for the provision of nutrition support in the critically ill patient. Several actions related to feeding improve outcomes such as infection rate, days on mechanical ventilation, days in the critical care unit, and mortality. These actions include the provision of early enteral nutrition, use of tube feedings supplemented with n-3 fatty acids and antioxidants, and reaching minimum targets for energy and protein intake. The minimum target range is an area of debate currently. This chapter will focus on energy balance, protein and nitrogen balance, and the macronutrient requirements of critically ill patients compared to normal. The potential role of nutrients to modulate inflammatory injury in the critically ill patient will also be examined.