Dominique Hermier

Lipids in monogastric animal meat.

Meat from monogastric animals, essentially pigs and poultry, is from afar the most consumed of all meats. Meat products from every species have their own characteristics. For a long time, pig meat has been presented as a fatty meat because of the importance of subcutaneous adipose tissue. Actually, when the visible fat is separated, this meat is rather poor in lipids: pieces eaten as fresh meat and without transformation, such as roasts, contain less then 2% total lipids. Poultry meat has always had a reputation of leanness because of its low content in intramuscular lipids. In addition, adipose tissues, localised in the abdominal cavity, are easily separable. The progress in genetics and a better knowledge of dietary needs has allowed to improve growth performances, to increase muscle weight and, in the pig, to strongly decrease carcass adiposity. However, strong contradictions appear between transformers and nutritionists, especially concerning the pig: the former wish to have meat with adipose tissues containing a high percentage of saturated fatty acids and the latter wish meat with more unsaturated fatty acids. The consumer, however, regrets the pigs of yesteryear or the poultry bred on farmyard that had tastier meat. At the same time, however, they request meat with a low fat content, which is paradoxical.

Hormonal and metabolic responses to overfeeding in three genotypes of ducks

Muscovy, Pekin and Mule duck are different in their body weight. To make a valid comparison in the lipid metabolism between these three genotypes, overfeeding was carried out by providing the animals with amounts of food in proportion to their body weight. Under these conditions, Muscovy ducks developed a strong liver steatosis, whereas it was not very pronounced in the Mule ducks and even less in the Pekin ducks. On the contrary, Pekin ducks showed a much marked extrahepatic fattening. At the beginning of overfeeding, there was a similarity in the three genotypes as regards the post-heparin lipoprotein-lipase (LPL) activity and the insulin and glucagon concentrations. After 10 days of overfeeding, the LPL activity dramatically fell in Muscovy and in Mule ducks, whereas it remained steady in Pekin ducks. Compared to values found at the beginning of the overfeeding period, plasma glucagon and insulin shown no evolution, except for the insulin of Pekin ducks which was dramatically higher. Those data suggest that high plasma insulin concentrations measured in Pekin ducks after 10 days of overfeeding can be responsible for the maintenance of the LPL activity, which favors the extrahepatic fattening to the detriment of liver steatosis.

Metabolism in two breeds of geese with moderate or large overfeeding induced liver-steatosis.

Biochemical mechanisms which may control fat deposition in liver and/or peripheral tissues have been studied in Poland and Landes geese. Post-prandial plasma substrates and post-heparin lipoprotein-lipase (LPL) activity were measured in 10-week-old animals. At 23 weeks of age, geese were overfed for 14 days then slaughtered. Hepatic steatosis was more important in Landes geese, while muscle and subcutaneous adipose tissue were less developed. In this breed, fatty liver weight negatively scaled to LPL activity, suggesting that a low LPL activity is a limiting factor of peripheral fat deposition. Consequently, non-catabolized VLDL may return to liver and increase hepatic steatosis. In Poland geese, such a mechanism does not exist. On the other hand, fatty liver weight was positively correlated to very low density lipoproteins (VLDL) and triacylglycerols measured in overfed Poland geese, suggesting that lipids synthetized by liver are better transferred from liver to extrahepatic tissues. Kinetics of post-prandial plasma glucose, triacylglycerols, phospholipids and uric acid were similar in the two breeds. However, the marked decrease in post-prandial plasma glycerol in Poland geese suggests that an extrahepatic tissue lipolysis inhibition could contribute to the higher peripheral fattening in overfed Poland geese and could be a limiting factor of hepatic steatosis in this breed.

Dose effect of α-linolenic acid on PUFA conversion, bioavailability, and storage in the hamster

If an increased consumption of α-linolenic acid (ALA) is to be promoted in parallel with that of n−3 long-chain-rich food, it is necessary to consider to what extent dietary ALA can be absorbed, transported, stored, and converted into long-chain derivatives. We investigated these processes in male hamsters, over a broad range of supply as linseed oil (0.37, 3.5, 6.9, and 14.6% energy). Linoleic acid (LA) was kept constant (8.5% energy), and the LA/ALA ratio was varied from 22.5 to 0.6. The apparent absorption of individual FA was very high (>96%), and that of ALA remained almost maximum even at the largest supply (99.5%). The capacity for ALA transport and storage had no limitation over the chosen range of dietary intake. Indeed, ALA intake was significantly correlated with ALA level not only in cholesteryl esters (from 0.3 to 9.7% of total FA) but also in plasma phospholipids and red blood cells (RBC), which makes blood components extremely reliable as biomarkers of ALA consumption. Similarly, ALA storage in adipose tissue increased from 0.85 to 14% of total FA and was highly correlated with ALA intake. As for bioconversion, dietary ALA failed to increase 22∶6n−3, decreased 20∶4n−6, and efficiently increased 20∶5n−3 (EPA) in RBC and cardiomyocytes. EPA accumulation did not tend to plateau, in accordance with identical activities of Δ5- and Δ6-desaturases in all groups. Dietary supply of ALA was therefore a very efficient means of improving the 20∶4n−6 to 20∶5n−3 balance.

Plasma lipoprotein distribution in the turkey (Meleagris gallopavo)

The plasma lipoprotein profile has been determined in fasted 7-week-old male turkeys. Lipoprotein classes were subfractionated by density gradient ultracentrifugation. According to phospholipid concentration over the density gradient, an initial peak was visible in the usual LDL density range, whereas two peaks were detected in that of HDL. As density increased, the lipid composition of particles showed an increase in cholesteryl esters and decrease in triglycerides. VLDL were recovered in the first fraction (d<1.013) on the top of the gradient and IDL in fractions 2-5 (d=1.013-1.028 g/ml). The LDL and HDL populations in the density range 1.028-1.090 (fractions 6-12) differ from that found in the other bird species analyzed under the same experimental conditions. LDL predominated in fractions 6-8 with mostly beta-motility and apoB100 as the major protein component. HDL predominated in fractions 10-12 (d=1.055-1.090 g/ml) and corresponded to the first HDL peak (HDL-(A)), with mostly alpha-mobility and apoA-I as the major protein component. Both LDL- and HDL-like particle populations were present in fractions 6-12, making the separation between the two classes of lipoproteins difficult. The second peak in the HDL density range (HDL-(B), d=1.076-1.146 g/ml) contained only HDL-type particles above d=1.090 g/ml. This points out the specificity of the lipoprotein distribution in the turkey that is unique among animals. The density limit at d=1.048 g/ml is a good compromise for the separation of LDL from HDL; however, the presence of HDL-like particles in the LDL density range, and the existence of two, and even three HDL subclasses should be taken into account in the design of further metabolic studies.

Effect of dietary fats on hepatic lipid metabolism in the growing turkey

The influence of dietary fatty acids on hepatic capacity of lipid synthesis and secretion was investigated in 7-week-old male turkeys. They were fed 10% of either lard (rich in saturated and monounsaturated fatty acids) or linseed oil (rich in polyunsaturated fatty acids, especially 18:3n-3). Fattening was identical with both diets (0.15-0.20% of abdominal adipose tissue), but the proportion of muscle Pectoralis major was lower with linseed oil (6.6 vs. 7.4%). Specific activities of lipogenic enzymes (ME, G6PDH, ACX, and Delta9-desaturase) were not influenced by the diet, however, FAS activity was lower with linseed oil (14.3 vs. 25.4 nM NADPH fixed/min). Fasting concentrations of lipoproteins synthesized and secreted by the liver, VLDL and HDL, were also lower with linseed oil, as well as plasma concentrations of phospholipids and cholesteryl esters. However, when VLDL catabolism was inhibited by injection of an antiserum against LPL, VLDL concentration was identical in both groups (100-120 mg/l), whereas that of phospholipids and cholesteryl esters, that are transported by HDL mainly, remained lower with linseed oil. Thus, in the growing turkeys, and contrary to mammals and the chicken, feeding n-3 polyunsaturated fatty acids did not decrease hepatic triglyceride synthesis and secretion, nor fattening. By contrast, in this species, n-3 polyunsaturated fatty acids appear to influence mostly HDL metabolism, with a negative impact on muscular growth.