This study assessed whether human food intake is regulated by negative feedback, directly or indirectly, from carbohydrate stores (glycogenostatic model). Six men were studied on three occasions during 7 d of whole-body indirect calorimetry, throughout which they had ad libitum access to one of three covertly manipulated diets: low fat (20% of energy as fat, 67% of energy as carbohydrate, and 13% of energy as protein; 4.80 kJ/g; LF), medium fat (40% of energy as fat, 47% of energy as carbohydrate, and 13% of energy as protein; 5.59 kJ/g; MF), or high fat (60% of energy as fat, 27% of energy as carbohydrate, and 13% of energy as protein; 7.04 kJ/g; HF). Energy intakes increased with percent fat (F[92,60] = 36.7; P < 0.001), producing average daily balances of -0.27, 0.77, and 2.58 MJ/d during the LF, MF, and HF diets, respectively. Changes in carbohydrate stores were attenuated by autoregulatory changes in carbohydrate oxidation. Carbohydrate balance showed a negative relation to the subsequent day's energy balance (t = 2.696; P = 0.0082) but explained only 5.5% of the variance. The relation for fat was positive (t = 5.245; P < 0.0001), accounting for 19.9% of the variance (stepwise regression). LF, lower-energy diets are more satiating than are HF-higher-energy diets, but carbohydrate stores per se did not entirely account for the change that diet composition had on energy intake. This study suggests that protein and carbohydrate have potential to reduce subsequent energy intake whereas there was no apparent reductive effect due to fat.

OBJECTIVE: This study examined the effects of varying the energy density (ED) of high carbohydrate (HC) diets on food and energy intake (EI), subjective hunger and body weight in humans. DESIGN: Randomised cross-over design. Subjects were each studied twice during 14 d, throughout which they had ad libitum access to one of two covertly-manipulated diets. 2 ) were studied. The fat, carbohydrate (CHO) and protein content (as % energy) and ED of each diet were 21 : 66 : 13% and 357 kJa100 g, (lowenergy density (LED)) or 22 : 66 : 12% and 629 kJa100 g (high-energy density (HED)). A medium fat diet was provided at maintenance (1.6 Â BMR, MF for 2 d) before each ad libitum period. Subjects could alter the amount, but not the composition of foods eaten. RESULTS: Mean EI was 8.67 and 14.82 MJad on the LED and HED diets, respectively. Subjects felt signi®cantly more hungry on the LED diet, than on the HED diet (F 1,160 38.28; P`0.001) and found the diets to be similarly pleasant (72.72 mm vs 71.54 mm (F 1,392 0.31; P 0.579)). Mean body weight decreased on the LED diet at a rate of 0.1 kgad and increased at 0.06 kgad on the HED diet (F 1,131 86.60; P`0.001), giving total weight changes of 71.41 kg and 0.84 kg, respectively, both of which were signi®cantly different from zero (P`0.01). CONCLUSION: Excess EI is possible on HC, HED diets, at least under conditions where diet selection is precluded.Comparison of these results with previous studies, which altered ED using fat, suggests that CHO may be a better cue for hunger than fat.

Although the importance of root production and mortality to nutrient fluxes in ecosystems is widely recognized, the difficulties associated with root measurements have limited the availability of reliable data. We have used minirhizotrons and image analysis to measure root longevity of Prunus avium L., Picea sitchensis (Bong.) Carrière, Acer pseudoplatanus L. and Populus x canadensis cv. Beaupre directly in cohorts of roots. Major differences in the longevity of roots among species were identified. For example, 40% of Prunus avium roots but only 6% of Picea sitchensis roots survived for more than 14 days. Survival analysis of cohorts of roots of Prunus avium and Populus x canadensis revealed differences in the distribution of longevity among cohorts. Genetic, biotic and abiotic factors that may influence longevity are discussed.

The relationships of N input or protein status and the concentrations of serum insulin-like growth factor-1 (IGF-1), plasma fibronectin (FN) and total protein (TP) were examined in three experiments with steers and sheep nourished by intragastric infusion of nutrients. In Expt 1, three steers (340 kg live weight) were infused with three levels of volatile fatty acids (0,300 and 600 kJ/kg metabolic weight (w0'75) per d) and six levels of casein (0, 200, 400, 650, 1500 and 2500 mg N/kg W0'75 per d). Each N treatment was imposed for 5 d. In Expts 2 and 3, five groups of sheep (about 35 kg live weight) were infused with casein at 500 mg N/kg vv0.75 per d for 2 weeks followed by 1500,500 or 50 mg N/kg W0'75 per d in Expt 2, and in Expt 3, with 100 mg N/kg w0 75 per d for 6 weeks or 10 mg N/kg W0'75 per d for 4 weeks. Non-protein energy was maintained constant at 500 kJ/kg w0'75 per d throughout. Daily N balance and total body N content at the end were measured, and protein status was defined as a percentage of cumulative N accretion or depletion in relation to the total body N content at maintenance. It was found that IGF-1 and FN responded rapidly and substantially to altered N input, and that when daily N input was maintained constantly at sub-maintenance, their continuous declines were related closely to progressive protein depletion in the sheep. Plasma TP concentration was independent of N input when N input was altered acutely in the steers, but declined significantly and gradually with severe, chronic body protein depletion in the sheep. Plasma content of TP in the sheep however reduced acutely with a reduction in N input. Plasma volume fell substantially over the first 2 weeks of protein depletion, compensating for the declines in TP content and maintaining TP concentration plateau. The possible implications of the changes in TP concentration and content (concentration x volume) to body protein loss in sheep are discussed. IGF-1: Fibronectin: Protein status: RuminantsThe estimation of changes in total body N can be achieved using some advanced noninvasive laboratory techniques such as neutron activation analysis, tracer dilution methods and some instrument techniques (reviewed by Gibson, 1990 andEllis, 1992). However these techniques cannot easily be applied in practical situations. Several blood biochemical metabolites have therefore been studied as potential indicators of protein status in human subjects and animals (see reviews by Gibson, 1990;Young et al. 1990 central role in the regulation of whole-body protein metabolism by reconstituting absorbed and degraded tissue amino acids, removing N in the body by production of urea, using amino acids in gluconeogenesis, influencing protein synthesis via production of its insulinlike growth factor-1 (IGF-1) and producing and exporting plasma proteins to transport nutrients. It may, therefore, be possible to use the metabolic products which reflect liver function as an indicator of whole-body protein status. Plasma IGF-1 (Baxter, 1986) 1989). The present study ...

Increasing concern over the role of greenhouse gases in global warming has led to a renewed interest in models for predicting methane production in ruminants. For economic reasons it would be preferable if such models could be derived from data obtained in smaller ruminants. The objective of this project is to establish whether differences in methane production exist between sheep and cattle and to measure the magnitude of these differences under various dietary situations.

Increasing concern over the role of greenhouse gases in global warming has led to a renewed interest in models for predicting methane production in ruminants. For economic reasons it would be preferable if such models could be derived from data obtained in smaller ruminants. The objective of this project is to establish whether differences in methane production exist between sheep and cattle and to measure the magnitude of these differences under various dietary situations.