The effects of a diet rich in alpha-linolenic acid vs. one rich in oleic acid on the oxidation of uniformly labeled 13C-alpha-linolenic acid and its conversion into longer-chain polyunsaturates (LCP) were investigated in vivo in healthy human subjects. Volunteers received a diet rich in oleic acid (n = 5) or a diet rich in alpha-linolenic acid (n = 7; 8.3 g/d) for 6 wk before and during the study. After 6 wk, subjects were given 45 mg of 13C-alpha-linolenic acid dissolved in olive oil. Blood samples were collected at t = 0, 5, 11, 24, 96, and 336 h. Breath was sampled and CO2 production was measured each hour for the first 12 h. The mean (+/- SEM) maximal absolute amount of 13C-eicosapentaenoic acid (EPA) in plasma total lipids was 0.04 +/- 0.01 mg in the alpha-linolenic acid group, which was significantly lower (P = 0.01) than the amount of 0.12 +/- 0.03 mg 13C-EPA in the oleic acid group. Amounts of 13C-docosapentaenoic acid (DPA) and 13C-docosahexaenoic acid (DHA) tended to be lower as well. The mean proportion of labeled alpha-linolenic acid (ALA) recovered as 13CO2 in breath after 12 h was 20.4% in the ALA and 15.7% in the oleic acid group, which was not significantly different (P = 0.12). The cumulative recovery of 13C from 13C-ALA in breath during the first 12 h was negatively correlated with the maximal amounts of plasma 13C-EPA (r = -0.58, P = 0.047) and 13C-DPA (r = -0.63, P = 0.027), but not of 13C-DHA (r = -0.49, P = 0.108). In conclusion, conversion of 13C-ALA into its LCP may be decreased on diets rich in ALA, while oxidation of 13C-ALA is negatively correlated with its conversion into LCP. In a few pilot samples, low 13C enrichments of n-3 LCP were observed in a diet rich in EPA/DHA as compared to oleic acid.

Controlled human intervention trials are required to confirm the hypothesis that dietary fat quality may influence insulin action. The aim was to develop a food-exchange model, suitable for use in free-living volunteers, to investigate the effects of four experimental diets distinct in fat quantity and quality: high SFA (HSFA); high MUFA (HMUFA) and two low-fat (LF) diets, one supplemented with 1·24 g EPA and DHA/d (LFn-3). A theoretical food-exchange model was developed. The average quantity of exchangeable fat was calculated as the sum of fat provided by added fats (spreads and oils), milk, cheese, biscuits, cakes, buns and pastries using data from the National Diet and Nutrition Survey of UK adults. Most of the exchangeable fat was replaced by specifically designed study foods. Also critical to the model was the use of carbohydrate exchanges to ensure the diets were isoenergetic. Volunteers from eight centres across Europe completed the dietary intervention. Results indicated that compositional targets were largely achieved with significant differences in fat quantity between the high-fat diets (39·9 (SEM 0·6) and 38·9 (SEM 0·51) percentage energy (%E) from fat for the HSFA and HMUFA diets respectively) and the low-fat diets (29·6 (SEM 0·6) and 29·1 (SEM 0·5) %E from fat for the LF and LFn-3 diets respectively) and fat quality (17·5 (SEM 0·3) and 10·4 (SEM 0·2) %E from SFA and 12·7 (SEM 0·3) and 18·7 (SEM 0·4) %E MUFA for the HSFA and HMUFA diets respectively). In conclusion, a robust, flexible food-exchange model was developed and implemented successfully in the LIPGENE dietary intervention trial.

; on behalf of the investigators of the TransLineE project { Objective: To collect (i) baseline data and (ii) execute a large multicentre study examining the effect of trans a-linolenic acid on its incorporation into plasma lipids and on risk factors for coronary heart disease. Design: 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 a-linolenic acid or to continue with a diet`low' in trans a-linolenic acid for 6 weeks. Setting: Three European university research departments supported by the research and development departments of the food industry. Subjects: Male volunteers (88) recruited by local advertisement. Methods: 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 a-linolenic acid into plasma lipids and platelets was assessed by gas chromatography and dietary compliance was veri®ed by 4-d weighed record. Results: Less trans a-linolenic acid isomers are incorporated into human plasma lipids in French volunteers than in Dutch or Scottish volunteers consuming their habitual diets. Trans`free' a-linolenic acid-rich oil can be produced by careful deodorization during re®ning. The`high' trans diet provided 1410AE 42 mg/d trans isomers of a-linolenic acid, whilst the`low' trans group consumed 60 AE 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 a-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. Conclusions: Trans`free' rapeseed oil, rich in a-linolenic acid, can be produced by careful deodorization. Dietary records show good compliance. Dietary trans isomers of a-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. Sponsorship: European Commission (FAIR 95-0594 grant).

Weight reduction programmes are mainly focused on reducing intake of fat and sugar. In this review we have evaluated whether the replacement of dietary (added) sugar by low-energy sweeteners or complex carbohydrates contributes to weight reduction. In two experimental studies, no short-term differences in weight loss were observed after use of aspartame as compared to sugar in obese subjects following a controlled energy-restricted diet. However, consumption of aspartame was associated with improved weight maintenance after a year. In two short-term studies in which energy intake was not restricted, substitution of sucrose by artificial sweeteners, investigated mostly in beverages, resulted in lower energy intake and lower body weight. Similarly, two short-term studies, comparing the effect of sucrose and starch on weight loss in obese subjects did not find differences when the total energy intake was equal and reduced. An ad libitum diet with complex carbohydrates resulted in lower energy intake compared to high-sugar diets. In two out of three studies, this was reflected in lower body weight in subjects consuming the complex carbohydrate diet. In conclusion, a limited number of relatively short-term studies suggest that replacing (added) sugar by low-energy sweeteners or by complex carbohydrates in an ad libitum diet might result in lower energy intake and reduced body weight. In the long term, this might be beneficial for weight maintenance. However, the number of studies is small and overall conclusions, in particular for the long term, cannot be drawn.

Trans isomers of a-linolenic acid, which are formed by deodorization of refined vegetable oils, can be found in significant amounts in edible oils. Effects of trans a-linolenic acid on plasma lipoproteins are unknown. We therefore investigated the effects of trans a-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 a-linolenic acid. Daily total trans a-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 a-linolenic acid diet significantly increased the plasma LDL-:HDL-cholesterol ratio by 8´1 % (95 % CI 1´4, 15´3; P 0´02Y 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 20´8, 10´5; P 0´10X No effects were found on total cholesterol and HDL-cholesterol, triacylglycerols, apolipoprotein B and A-1, and lipoprotein(a) concentrations. In conclusion, trans alinolenic 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.