The energy cost of fat and protein deposition in the rat

Abstract

I. Measurements were made of energy balance by direct calorimetry, and of nitrogen balance in groups of lean and congenitally obese ('fatty') Zucker rats at body-weights of 200 and 350 g given a highly digestible semisynthetic diet at 14.0 or 18.4 g/rat per 24 h. 2.Losses of food energy and N in faeces were very small. The fatty rats lost much more N in urine than did lean rats. Despite this the proportion of gross energy that was metabolized was 0.92 for both fatty and lean rats.3. In all trials, fatty rats lost a smaller proportion of metabolizable energy (ME) as heat and deposited less as protein than thin rats but deposited much more as fat. 4.The amounts of ME required to deposit I kJ of protein and I kJ of fat respectively were shown by regression analysis to be 2 . z~ (fo.16) and 1.36 (k0.06) kJ respectively. These values agree extremely closely with recent, more tentative, estimates based on assumptions as to maintenance requirement which the present experiments were able to circumvent. It may be concluded with confidence that the energy costs of depositing I g of protein or fat are almost identical at 53 kJ ME/g.The energy cost of fat and protein deposition is simply the increment of food energy (usually expressed as metabolizable energy (ME)) required to promote a defined increment in body protein or fat.The energy cost of fat deposition can be measured with precision in adult animals since, in these circumstances, energy retention as protein is small and the amount of ME required to maintain energy balance (so-called ' maintenance requirement ') does not differ much between successive measurements made of metabolic heat production at different levels of ME intake. There is general agreement that in simple-stomached species such as the rat and the pig the energy cost of fat deposition ranges from about 1.4 kJ ME/kJ fat deposited for foods consisting predominantly of carbohydrate to 1-15 for foods rich in triglycerides (ARC/MRC Committee, 1974).The energy cost of protein deposition has been more difficult to assess. First, even during rapid growth the amount of energy deposited as protein is small relative to that deposited as fat or dissipated as heat. Second, the division of ME between maintenance requirement and that for protein and fat deposition changes continuously during growth and these changes are linked in such a way that changes in maintenance, protein and fat deposition show marked autocorrelation. Kielanowski (1965) recognized this when first he used multiple regression analysis in an attempt to partition ME intake between maintenance, protein and fat deposition and since then a series of reports has used his approach to describe the efficiencies of protein and fat deposition in pigs (Kielanowski

Oxidation of intracellular and extracellular fatty acids in skeletal muscle

“…At the end of the period, the average body wt gain was 1.1 g and food intake (regular chow with 4.5% fat) was 23.7±0.6 g. Metabolizable energy from dietary fat is estimated to be 92% [51]. Various body components that utilize fatty acids as fuel are estimated: muscle 130 g (40% of body wt), liver (3% of body wt) and heart 1.2 g. Liver, heart and oxidative red muscle (5% of total skeletal muscle mass [52]) are assumed to utilize fatty acids at a rate twice that for gastrocnemius as determined using the present method.…”

Body weight gain in free-living Pima Indians: effect of energy intake vs expenditure

“…For weight loss, 9 kcal/g FM and 1 kcal/g FFM lost were used. [24][25][26] Thus, the formulas used for calculation of the total energy intake were as follows:…”

Fat balance and serum leptin concentrations in normal, hypothyroid, and hyperthyroid rats

“…Net energy expenditure was calculated from energy expenditure excluding the total cost of storage. The total cost of storage was determined, taking into account that the energy loss in storing 1 kJ of protein is 1.25 kJ, 22 while the corresponding …”