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Effects of Manipulating Dietary Protein and Energy Intake on Energy Balance and Thermogenesis in the Pig^1,2,

Michael I. Gurr^,3, Rodney Mawson, Nancy J. Rothwell^*,4 and Michael J. Stock^*,4

Unilever Research Laboratory, Colworth House, Sharnbrook, Bedford MK44 1LQ, U.K. ^* Department of Physiology, Queen Elizabeth College, University of London, London W8 7AH, U.K.

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 kg 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-kg 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 -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.

KEY WORDS: • diet composition • protein intake • energy balance • thermogenesis • thyroid hormones • norepinephrine • -glycerophosphate dehydrogenase

¹ A preliminary description of these experiments was given to the Physiological Society, London, February 1979.

² Address reprint requests to: Dr. M. J. Stock. Department of Physiology. St. George's Hospital Medical School. Tooting, London SW17 ORE, U.K.

³ Present address: Nutrition Department, National Institute for Research in Dairying, University of Reading, Shenfield, Reading RG2 9AT, U.K.

⁴ Present address: Department of Physiology, St. George's Hospital Medical School, Tooting, London SW17 ORE, U.K.

Manuscript received 30 April 1979.