Effects of Manipulating Dietary Protein and Energy Intake on Energy Balance and Thermogenesis in the Pig

Abstract

Weight maintenance was achieved by feeding either restricted amounts of a high-protein diet (HP) or ad libitum amounts of low-protein diet (LP) to 6 and 20 kp pigs for up to 42 days. In all cases, LP animals consumed approximately three times as much energy as the HP animals but in the 20-kp pigs, almost all (70%) of this excess was deposited in the carcass as fat. In 6-kg pigs fed the LP diet, changes in body energy content accounted for only a small fraction (27%) of the total energy intake; a large difference in energy expenditure was seen between these animals and the HP group, which was attributed to differences in dietary-induced thermogenesis. Six-kilogram LP pigs showed elevated plasma triiodothyronine levels and hepatic mitochondrial alpha-glycerophosphate dehydrogenase activity and an enhanced sensitivity to the in vitro lipolytic effects of norephinephrine (NE) on adipose tissue. These changes are similar to those observed in rats exhibiting dietary-induced thermogenesis and the relevance of these findings to the increased heat production of LP pigs is discussed.

Effects of dietary protein quality on energy metabolism and thyroid hormone Status in growing pigs

“…The present results indicate changes in the same manner when feeding SPI-with the lower biological value in comparison to CAS+ in all periods at both protein levels. The excess of dietary energy, which cannot be deposited as protein, can either be used for fat deposition (KEAGY et al, 1987) or dissipated as heat GURR et al, 1980). In the present study the total efficiency of utilization of ME (energy retention/ME intake) within periods at both protein levels was not significantly different between CAS+ and SPI-.…”

“…Furthermore, the question arises of how an excess of dietary energy can increase either fat deposition or heat production. GURR et al (1980) demonstrated both metabolic pathways in growing pigs. There were, however, essential differences to our trials.…”

“…The excess of dietary energy, which cannot be deposited as protein can either be used for fat deposition (KEAGY et al, 1987) or dissipated as heat GURR et al, 1980). Although several studies were carried out to measure energy balance under these conditions, only a few studies have attempted to investigate the regulatory factors of thermogenesis.…”

“…The decreased energetic efficiency observed in growing rats and pigs fed low protein diets is often associated with a marked rise in T 3 concentration , ROTHWELL et al" 1983, GURR et al, 1980, which is frequently interpreted as an adaptive diet-induced thermogenesis. Some energy dissipating Systems such as the hepatic mitochondrial ct-GP Shuttle (TYZBIR et al, 1981, SAWAYA and LUNN, 1985, KEAGY et al, 1987, as well as the thermogenic activity of brown adipose tissue (ROTWELL et al, 1983) are sensitive to the thyroid hormone Status.…”

Renaissance of brown adipose tissue research: integrating the old and new

“…According to the authors, the 'missing' energy implied a thermogenic process that was triggered by diet, perhaps in a manner similar to that observed in pigs fed a low-protein diet. 13 These investigators went on to show that cafeteria-fed rats had larger brown fat depots and were significantly more responsive to the thermogenic effects of NE injection. As BAT is the dominant site of energy expenditure in cold-adapted rats, and sympathetic activity is the main driver of cold-induced BAT expansion, the clear inference was that BAT is a major site of diet-induced thermogenesis.…”