Metabolic rate and physical development in children at risk of obesity.

Children of obese (group O) and normal-weight (group N) parents who took part in a study of metabolic rates and food intakes when 3-5 years old were restudied 12 years later. There were striking differences between the sexes. Among the 15 adolescent boys, parental obesity predicted more rapid growth (but not adiposity) and an earlier decline in resting metabolic rate (RMR)/kg body weight, and childhood energy intake/kg body weight was not predictive. Among the 10 girls, the opposite pattern was observed; childhood energy intake/kg predicted both body size and adiposity, and parental obesity had less predictive value. The sex differences are consistent with the earlier maturation of girls, and the growth differences with the hypothesis that a low RMR/kg body weight is associated with a precocious pattern of growth and development in children predisposed to obesity.

Protein and energy metabolism in starvation reconsidered.

Current concepts of the metabolic changes during starvation have been heavily influenced by recent studies on grossly obese subjects undergoing therapeutic fasting. It has been suggested that during prolonged starvation the central nervous system develops the ability to utilize ketone bodies, and that the consequent reduction in gluconeogenesis leads to an adaptive sparing of protein catabolism. However, our analysis of classical studies on starvation shows that during prolonged starvation in normal subjects the fraction of total energy expenditure derived from protein (the P ratio) remained unchanged. Although urinary nitrogen was reduced during the progress of the fast, we conclude that this is secondary to the general reduction in metabolic rate, rather than to a specific sparing of protein.

The nutritional role of indispensable amino acids and the metabolic basis for their requirements.

Short-term balances and metabolic studies suggest that current estimates of adult indispensable amino acid (IAA) requirements are too low. In addition, the observed biological value of protein is less than that predicted from its amino acid score. We propose that these discrepancies reflect the fact that IAA requirements are complex, and can only be defined under specific artificial conditions. This is because consumption of protein usually results in oxidative losses of IAA and nitrogen, which are important to the organism and variable according to dietary composition. It is likely that the age-related fall in the current values for IAA requirement primarily reflects different dietary designs in the original balance studies, which induced different rates of oxidative losses. A new model for amino acid utilization is proposed which takes account of such losses, and factors that influence them are reviewed. We propose that dietary IAAs serve an important transient function prior to their oxidation, exerting a regulatory influence on maintenance and growth which we call the anabolic drive. The model also allows for diurnal cycling of body protein, in which oxidative losses of amino acids occurring during the postabsorptive phase must be balanced by net protein deposition during feeding if overall balance is to be attained. Diurnal cycling is likely to be nutritionally sensitive, influenced by the anabolic drive and could affect the relationship between total protein and IAA requirements. We argue that oxidative losses should be included in the requirement; this will account for apparent discrepancies in the observed efficiency of protein utilization. We propose that IAA requirements (R) can only be unambiguously defined in terms of Rmin, a value obtainable under artificial conditions when oxidative losses, Lr, are minimal (Lr min); current estimates of adult requirements may be close to this level. An operative requirement of practical value, Rop, will only be defineable when the value to the organism of the oxidative losses induced by usual diets, (Lr op), can be evaluated.

Energy intake in children at high and low risk of obesity.

This study compared 7-d energy intakes of 37 young children at low (Group N) and high (Group O) risk of subsequent obesity, as judged from parental obesity. The energy intake of Group O was 16 per cent lower than Group N (P = 0.02). Although the intakes of all the children considered together and also Group N children alone showed the usual wide variability and absence of correlation with body size, the intakes of Group O children were significantly correlated with their weight and height (r = 0.5). The results confirm a previous study and suggest that, since basal metabolic rate and body weight are known to be correlated, attention should be focused on differences in expenditure in investigations of the aetiology of childhood obesity.

Basal metabolic rate of Indian men: no evidence of metabolic adaptation to a low plane of nutrition.

Basal metabolic rate (BMR) was measured in 58 men of a rural Indian population who had low body weight and body fat stores. Comparisons of subgroups of subjects of different socio-economic status and different nutritional status showed no evidence of differences in BMR when corrected for differences in body weight and body fat content. This suggests that metabolic adaptation did not account for differences in absolute BMR between subgroups of this population. The BMR values agreed well with values predicted by equations based on BMR measurements in Asian men of higher body weight, but were below values predicted by the new FAO/WHO/UNU prediction equations by an average of 12.1 per cent (P less than 0.0001). This overprediction could be a reflection of allometric or climatic influences on BMR rather than evidence for metabolic adaptation to a low plane of energy nutrition.

The effect of dietary protein and energy restriction on heat production and growth costs in the young rat.

1. The effect of dietary protein and energy restriction on heat production and growth costs has been examined in rats fed on a marginal (MP) or high (HP) protein diet, containing 9.2% or 22% respectively of the gross energy content as casein. Diets were given either ad lib. or at approximately 25, 50 or 75% of the ad lib. intake. 2. Heat production (kJ/kg body-weight (W)0.75 per d) was increased by 23% in rats fed on the MP diet ad lib., as compared with their HP controls (P less than 0.01). 3. Factorial analysis of the data showed that the overall cost of energy deposition (kJ/kJ; Ee) was elevated on the MP diet (MP 1.7, HP 1.28; P less than 0.001). Maintenance requirements (kJ/kg W0.75 per d) for zero energy balance were unchanged (MP 562, HP 573). 4. The partial energy cost of protein deposition (Ep) varied with dietary manipulation. If the partial energy cost of fat deposition (Ef) was assumed constant at 1.25 kJ/kJ, and maintenance requirements were assumed to vary with metabolic body size (W0.75), Ep was elevated on the MP diet. On both diets, Ep was reduced at low energy intakes. 5. The significance of these results is discussed in the context of current approaches to the analysis and interpretation of findings describing dietary induced changes in the rate of heat production.

The Oxylog oxygen consumption meter: a portable device for measurement of energy expenditure.

The Oxylog (PK Morgan, Kent, UK) is a recently developed portable device for measurement of oxygen consumption and energy expenditure in man. It incorporates a turbine flowmeter and two polarographic oxygen sensors and is powered by rechargeable batteries. Two instruments were modified for operation at low ventilation rates and used in simultaneous Oxylog and Douglas Bag measurements of resting metabolic rate (RMR) in nine healthy subjects. The coefficients of correlation between RMR measured by the two methods were +0.904 (p less than 0.02) and +0.934 (p less than 0.01) and the standard errors of the mean percent error in energy expenditure were +/- 2.0% and +/- 2.7% for the two instruments respectively. This suggests that the Oxylogs are sufficiently accurate for many field studies of energy expenditure.

Obesity in boys: the distinction between fatness and heaviness.

An anthropometric survey of approximately 2350 boys aged 1-8 years was conducted as part of a study of pre-school child growth. It was shown that there was no close relationship between obesity measured as fatness from the triceps skinfold and the development of heaviness as judged by weight-for-height. It is suggested that the study of obesity in children should involve classification into sub-groups identifiable as the heavy but not fat, the fat but not heavy and those who are both heavy and fat. This may help in understanding the nature of obesity and its implications in future disease.

The effect of catabolic doses of corticosterone on heat production in the growing rat.

The effect of corticosterone treatment on energy balance and heat production was investigated in growing rats. Animals were treated with daily subcutaneous injections of a vehicle containing 0, 50 or 100 mg corticosterone/kg for 5 d. Measurements of digestible energy intake and urinary energy losses showed that corticosterone treatment resulted in a depression of metabolizable energy intake due to elevated urinary energy losses resulting from massive glucosuria. Measurements of the metabolizable energy intake and the change in carcass energy indicated that at 50 mg/kg energy deposition and heat production were reduced, whilst at 100 mg/kg energy deposition was completely abolished with heat production increased. Postprandial oxygen consumption was unchanged at 50 mg/kg and increased at 100 mg/kg. Factorial analysis of these results based on reported values for the energy cost of protein and fat deposition indicated that (a) the depression of total heat production at 50 mg/kg could be entirely accounted for by the concomitant suppression of growth, and (b) the elevation of total and postprandial heat production at 100 mg/kg reflected a specific influence of corticosterone on thermogenesis. The significance of these findings is discussed in the light of reports that corticosterone in low doses suppresses heat production.

Essential fatty acid requirements in infancy.

The view expressed by Cuthbertson that essential fatty acid needs of human infants have been overestimated is contested. In our view Cuthbertson's assessment of essential fatty acid requirements of infants is too low because 1) consideration of the omega3 fatty acids is omitted; 2) the biological value of long-chain essential fatty acids is wrongly assessed; and 3) the significance of variations in composition of random human milk samples is misunderstood.