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The speed of absorption of dietary amino acids by the gut varies according to the type of ingested dietary protein. This could affect postprandial protein synthesis, breakdown, and deposition. To test this hypothesis, two intrinsically 13C-leucine-labeled milk proteins, casein (CAS) and whey protein (WP), of different physicochemical properties were ingested as one single meal by healthy adults. Postprandial whole body leucine kinetics were assessed by using a dual tracer methodology. WP induced a dramatic but short increase of plasma amino acids. CAS induced a prolonged plateau of moderate hyperaminoacidemia, probably because of a slow gastric emptying. Whole body protein breakdown was inhibited by 34% after CAS ingestion but not after WP ingestion. Postprandial protein synthesis was stimulated by 68% with the WP meal and to a lesser extent (+31%) with the CAS meal. Postprandial whole body leucine oxidation over 7 h was lower with CAS (272 +/- 91 micromoles . kg-1) than with WP (373 +/- 56 micromoles . kg-1). Leucine intake was identical in both meals (380 micromoles . kg-1). Therefore, net leucine balance over the 7 h after the meal was more positive with CAS than with WP (P 0.05, WP vs. CAS). In conclusion, the speed of protein digestion and amino acid absorption from the gut has a major effect on whole body protein anabolism after one single meal. By analogy with carbohydrate metabolism, slow and fast proteins modulate the postprandial metabolic response, a concept to be applied to wasting situations

Aging is associated with a redistribution of both fat and lean tissue within the body. Intra-abdominal fat (IAF) accumulates more rapidly than total fat while the loss of lean body mass is mostly due to sarcopenia. Increase of visceral fat plays a major role in the pathogenesis of insulin resistance, which leads to type II diabetes and also to cardiovascular diseases. This review is focussed on the relationships that exist between the accumulation of IAF and insulin resistance during aging. The various methods available for assessing IAF are briefly reviewed; imaging techniques are the only reference methods, and their availability is limited. Insulin resistance that appears with aging is caused by accumulation of IAF, rather than by aging per se. Studies done in type II diabetic patients suggest that the metabolic link between increased IAF and insulin resistance could well be the increased availability and/or oxidation of free fatty acids. Physical inactivity certainly enhances both IAF accumulation and, more directly, insulin resistance. Independent and significant effects of menopause or of sarcopenia on insulin resistance remain to be established. The influence of hormonal changes, reduced fatty acid utilization, and resistance to leptin on IAF accumulation are also discussed. Although it is difficult to determine the independent influence of each of these factors, IAF accumulation seems to be a central and important determinant of cardiovascular risk. The last part of this review is devoted to protein metabolism and focused on the preservation of protein metabolism in the liver during aging.

Trans isomers of α-linolenic acid, which are formed by deodorization of refined vegetable oils, can be found in significant amounts in edible oils. Effects of trans α-linolenic acid on plasma lipoproteins are unknown. We therefore investigated the effects of trans α-linolenic acid on plasma lipids and lipoproteins in healthy European men. Eighty-eight healthy men from three European countries (France, Scotland, UK and the Netherlands) first consumed for 6 weeks a diet with experimental oils ‘free’ of trans fatty acids (run-in period). For the next 6 weeks, they were randomly allocated to a diet with experimental oils ‘high’ or ‘low’ in trans α-linolenic acid. Daily total trans α-linolenic acid intake in the high trans group was 1410 (range 583–2642) mg. Experimental oils were provided as such, or incorporated into margarines, cheeses, muffins and biscuits. The high trans α-linolenic acid diet significantly increased the plasma LDL-:HDL-cholesterol ratio by 8.1 % (95 % CI 1.4, 15.3; P=0.02), and the total cholesterol:HDL-cholesterol ratio by 5.1 % (95 % CI 0.4, 9.9; P=0.03) compared with the low-trans diet. This was largely explained by an increase in LDL-cholesterol on the high-trans diet, while no change was observed in the low-trans group (mean treatment effect of 4.7 % (95 % CI -0.8, 10.5; P=0.10). No effects were found on total cholesterol and HDL-cholesterol, triacylglycerols, apolipoprotein B and A-1, and lipoprotein(a) concentrations. In conclusion, trans α-linolenic acid may increase plasma LDL-:HDL-cholesterol and total cholesterol:HDL-cholesterol ratios. Whether diet-induced changes in these ratios truly affects the risk for CHD remains to be established.

To collect (i) baseline data and (ii) execute a large multicentre study examining the effect of trans alpha-linolenic acid on its incorporation into plasma lipids and on risk factors for coronary heart disease. Male volunteers were recruited and the habitual diet assessed by a 4-d weighed record. Fatty acid composition of plasma and platelet lipids were determined by gas chromatography at baseline. After a 6 week run-in period on a trans 'free' diet, male volunteers were randomised to consume 0.6 % of energy trans alpha-linolenic acid or to continue with a diet 'low' in trans alpha-linolenic acid for 6 weeks. Three European university research departments supported by the research and development departments of the food industry. Male volunteers (88) recruited by local advertisement. Replacement of 30 % of the fat of the habitual diet by margarine, oil and foods. Rapeseed oil was deodorised especially to produce the trans 'free' and 'high' trans foods for this study. The incorporation and conversion of trans alpha-linolenic acid into plasma lipids and platelets was assessed by gas chromatography and dietary compliance was verified by 4-d weighed record. Less trans alpha-linolenic acid isomers are incorporated into human plasma lipids in French volunteers than in Dutch or Scottish volunteers consuming their habitual diets. Trans 'free' alpha-linolenic acid-rich oil can be produced by careful deodorization during refining. The 'high' trans diet provided 1410+/-42 mg/d trans isomers of alpha-linolenic acid, whilst the 'low' trans group consumed 60+/-75 mg/d. The change in plasma lipid and platelet fatty acid composition documented that trans linolenic isomers are incorporated and converted to a trans isomer of eicosapentaenoic acid. Only the 15-trans alpha-linolenic acid is incorporated into plasma cholesteryl esters. The group consuming low trans diet had a slightly higher intake of fat, especially saturated and monounsaturated fat. Trans 'free' rapeseed oil, rich in alpha-linolenic acid, can be produced by careful deodorization. Dietary records show good compliance. Dietary trans isomers of alpha-linolenic acid are incorporated in plasma lipids and converted to long-chain polyunsaturated fatty acids. Their effects on risk factors for coronary heart disease and their metabolism will be reported elsewhere. European Commission (FAIR 95-0594 grant). European Journal of Clinical Nutrition (2000) 54, 104-113

OBJECTIVE: To address whether: (1) bioelectrical impedance analysis (BIA) can provide precise and accurate estimates of total body water (TBW) and extracellular water (ECW) in healthy elderly subjects, that display age-induced changes in body composition, (2) BIA models are improved by introducing variables related to geometrical body-shape and osmolarity. DESIGN: Cross-validation of available BIA models and models developed in the study. SUBJECTS: 58 healthy elderly subjects (31 women, 27 men, 66.8 +/- 4.7 y, mean +/- s.d.) MEASUREMENTS: BIA at 5, 50 and 100 kHz, 18O labelled water measurements of TBW, Br measurements of ECW, anthropometric variables, plasma osmolarity. RESULTS: Published BIA models for estimating TBW, entail various degrees of bias. Precise models (SEE of the models 0.8L at 100 kHz, 1.0 L at 50 kHz) involving height2/resistance, weight, gender, circumferences and plasma osmolarity were established with data from 30 subjects chosen at random. Cross-validation of an independent group (n=28) showed no bias (-1.5 +/- 3.2 L at 100 kHz, -1.4 +/- 3.2 L at 50 kHz, P=NS). CONCLUSION: We conclude that BIA models with increased accuracy and precision for predicting ECW and TBW can be derived in healthy elderly subjects. Repeated measures had a mean difference of 0.2 +/- 1.2 L.

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The present study assessed daily activity, physical capacity and body composition in 11 initially sedentary healthy subjects [5 men and 6 women, mean age 62.8 (SD 2.7) years] before training (T(o)), after completion of 7 (T(7w)) and 14 (T(14w)) weeks of training, and again 6 (T(6m)) and 12 (T(12m)) months after training. The mean daily activity index decreased from T(7w) to T(12m) reaching a lower level than at T(o) [T(12m) - T(o) = -1.5 (SD 4.6) units, P = 0.18]. Mean maximal oxygen uptake (VO(2max)) and its corresponding mean power output (Wdot(max)) were increased by 12.5 (SD 6.6)% (P = 0. 003) and 22.8 (SD 12.8)% (P = 0.003), respectively, at T(14w), and returned to their T(o) levels within 1 year. Mean body mass (m(b)) remained stable until T(6m) but increased significantly by 2.6 (SD 3. 7)% from T(6m) to T(12m) (P < 0.05). Mean fat mass (m(f), from bioelectrical impedance analysis measurements) tended to decrease [-2.0 (SD 4.2)%, P = 0.10] during the training period but increased by 7.8 (SD 10.9)% between T(6m) and T(12m) (P < 0.05). The mean fat free mass did not vary during the study period (P = 0.81) but magnetic resonance imaging (MRI) showed that mean thigh muscle volume decreased between T(7w) and T(12m) to less than at T(o) [T(12m) - T(o) = -2.3 (SD 3.6)%, P = 0.05]. Therefore, this study confirmed the favourable effects of endurance training on the physical capacity and body composition of elderly people, but demonstrated that the training programme would have to be continued to maintain the training-related benefits (i.e. increased VO(2max) and Wdot(max)) which would otherwise be lost within 1 year. After training, m(b) and m(f) were found to be increased. Furthermore, a fast and reproducible MRI protocol was validated for study of small intra-individual variations in tissue volumes in longitudinal studies.

OBJECTIVE:: Whole body protein turnover (PTO) and resting energy expenditure (REE) are both correlated to fat-free mass (FFM), in young and elderly subjects, and REE is positively correlated to PTO in young adults. Thus, the aim of this study was to compare the energetic cost of PTO in young (n=39, 23.4±3.1 y) and elderly (n=41, 67.5±3.6 y) healthy volunteers. MEASUREMENTS:: REE (indirect calorimetry), PTO (13 C-leucine isotopic dilution) and body composition (bioelectrical impedance analysis with age-specific equations) were measured in the postabsorptive state. RESULTS:: Elderly subjects had a higher fatness (30.5±7.1 vs 18.2±5.5%, elderly vs young, P<0.001), a similar REE (0.97±0.13 vs 1.06±0.15 kcal min-1 ), and a lower PTO (1.28±0.22 vs 1.44±0.18 μmol kg-1 min-1 , P<0.001). PTO, REE and FFM were significantly correlated and after adjustment for FFM, REE was positively correlated to PTO (r=0.61, P<0.001). The slope of this relationship was the same in both groups, while the adjusted mean REE was lower in elderly subjects (0.97±0.09 vs 1.05±0.07 kcal min-1 , P<0.01). CONCLUSION:: In comparison with young subjects, the energetic cost associated with PTO in elderly subjects is not different, but the proportion of REE not associated with PTO is lower. INTERNATIONAL JOURNAL OF OBESITY: (2001) 25, 601-605