Studies that use protein or are related to protein
A low-protein (LP) diet has been associated with amelioration of renal function in glomerulosclerosis (GS). However, the mechanisms involved are still unclear. We have used a mouse transgenic for bovine growth hormone (GH), which develops progressive GS and exhibits consistently elevated levels of circulating GH and insulin-like growth factor (IGF)-1, to study the effect of dietary protein restriction. LP (6% protein) and normal-protein (NP, 20% protein) diets were maintained for 30 weeks in mice with established GS of mild/moderate degree.
Voluntary intake of protein, fat and carbohydrate (CHO) was modified by feeding young rats either a control purified diet [% metabolizable energy (ME): protein 21, fat 7, CHO 72], a control diet plus sucrose solution (20%) to drink (final intakes 17, 6 and 77% ME as protein, fat and CHO, respectively) or a low protein diet substituted with either CHO (8, 7 and 85% ME as protein, fat and CHO, respectively) or fat (8, 20 and 72% ME as protein, fat and CHO, respectively).
Weanling (22-day-old) rats fed a low protein (8% casein) diet consumed the same amount of energy as controls (22% casein diet), but intake corrected for body size (kJ/kg0.75) was increased in the former group. Weight gain and the efficiency of gain (g gain/MJ) were markedly reduced in low protein fed rats. Resting oxygen consumption (VO2) was elevated by 15% in the low protein group but this difference was completely abolished by beta-adrenergic blockade with propranolol.
Previous studies in this laboratory with young Fischer 344 male rats have shown that the post-initiation development of aflatoxin B1 (AFB1)-inducedgamma-glutamyltranspeptidase positive (GGT+) hepatic foci was markedly inhibited by low protein feeding, even though the energy intake was greater. This dietary effect, however, did not necessarily apply to hepatic tumor development. Thus, the present investigation was undertaken to examine this dietary effect upon the development of hepatic tumors and, is so doing, to determine the correlation of foci development with tumor development.
The development of hepatocellular, putatively preneoplastic, gamma-glutamyl transpeptidase positive (GGT+) foci and tumors induced by aflatoxin B1 (AFB1) has been shown to be reduced in male F344 rats fed a diet containing 6% protein (as casein). This reduction occurs despite increased energy intake, when compared with animals fed a diet containing 22% protein.
The effects of successive administration, withdrawal and readministration of high protein diets (20% casein) on the promotional growth, remodeling and regrowth of aflatoxin B1-induced preneoplastic liver lesions (foci) were examined. Weanling male Fischer 344 rats were given 10 intragastric doses of aflatoxin B1 at a level of 250 micrograms/kg body weight over a 2-wk dosing period (initiation). The subsequent 12-wk period was subdivided into four feeding periods, each lasting 3 wk (promotion).
Amino acids modulate the secretion of both insulin and glucagon; the composition of dietary protein therefore has the potential to influence the balance of glucagon and insulin activity. Soy protein, as well as many other vegan proteins, are higher in non-essential amino acids than most animal-derived food proteins, and as a result should preferentially favor glucagon production.
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