Two studies were designed to compare the effects on post-ingestive satiety of manipulating the degree of saturation of fatty acids, at a fixed chain length (18 C atoms), in a fixed energy (5·68 MJ for males; 3·97 MJ for females), high-fat (55 % energy) lunch meal. Two different groups of twenty subjects (ten males and ten females) took part in each study. All forty subjects were of normal weight and aged between 18 and 36 years. Study 1 compared the effects of fat A (oleic blend, high in monounsaturated fatty acids (MUFA)) with those of fat B (linoleic blend, high in polyunsaturated fatty acids (PUFA)) and fat C (stearic–oleic blend, high in saturated fatty acids (SFA)). Study 2, which was designed to confirm and extend the findings of Study 1, compared the effects of fats A, B and C with those of fat D (a linoleic–oleic blend). Energy and nutrient intakes were monitored for the rest of the day and for the following day. Profiles of hunger, fullness and other sensations were monitored by continuous tracking and end-of-day questionnaires. In each meal the fat content was exclusively composed of one particular type (A, B, C or D) and was divided equally between the main course and dessert. Study 1 revealed a significant effect of fat type (degree of saturation) on intake of nutrients at the following (dinner) meal (smallest F[2,36] 3·38, P < 0·05), on post-ingestive ratings of motivation to eat (smallest F[2,36] 4·18, P = 0·02) and on energy intake over the whole test day (F[2,36] 3·39, P < 0·01). Subjects consumed significantly more energy after consumption of the lunch containing fat A than after the lunches containing fats B or C and there was a trend for these effects to continue into the second day. In Study 2, fat C produced more similar effects on appetite to fat A and there was a tendency for subjects to consume more over the whole test day when they had consumed the lunch containing fat A than when they had consumed the lunch containing fat B. Furthermore, when the data from fat conditions A and B in both studies were combined (n 40) the results of Study 1 were confirmed. Overall, the results of these short-term studies indicate that PUFA may exert a relatively stronger control over appetite than MUFA and SFA.

HDL-phospholipids are determinants in reverse cholesterol transport. They are mostly derived from triacylglycerol (TG)-rich lipoproteins. Chylomicron size is important, therefore, because it is related to the ratio surface phospholipids: core TG and, thus, determines the availability of postprandial phospholipids for transfer to HDL. Eleven healthy young women each ingested four different fat loads supplemented with retinyl palmitate and containing 60 g sunflower oil (SO), oleic–sunflower oil (OSO), mixed oil (MO; (g/kg) linoleic acid 480, oleic acid 380, linolenic acid 13) or beef tallow (BT). At the peak of TG absorption for all loads (4 h) chylomicron diameters, determined by agarose-gel filtration, were larger after SO compared with OSO (P < 0·05) and BT (P = 0·06) and after MO compared with BT (P < 0·05). At 6 h chylomicron size was larger after the vegetable oils compared with BT (P < 0·05 in each case). After each fat load chylomicron size decreased at 6 and 8 h compared with that at 4 h (P < 0·05) except for OSO. Retinyl ester and TG concentrations were lower in chylomicrons after BT than after the other fats but not in the chylomicron-free serum (containing chylomicron remnants), suggesting absorption in the form of very small particles. Compared with the fasting value, the concentration of the Svedberg unit of flotation 20–400 fraction, which contains VLDL and chylomicron remnants, was lower 8 h after MO, the only fat to contain significant amounts of linolenic acid. We conclude that chylomicron size is dependent on the fatty acid composition of ingested fats and the time-course of digestion, being larger for polyunsaturated fatty acid-rich fats and in the early phase of digestion. On the basis of retinyl ester concentration there were no differences between fats in chylomicron-remnant clearance.

Four metabolism trials were conducted. Trials 1 and 2 (Tl, T2) investigated degree of saturation of fats (ratio of unsaturated to saturated fatty acids, U/S) on digestible energy (DE) content. Fats evaluated were rape oil (RO) and tallow (T) for Tl (U/S 15·67 and 0·97 respectively) and RO and palm oil (PO) for T2 (U/S 15·33 and 0·85 respectively). Three fats of intermediary U/S for each trial were produced by blending the two fats in proportions to give U/S of 3·18,2·08 and 1·49 in both trials. Trials 3 and 4 (T3, T4) investigated the effect of free fatty acid (FFA) content of fats on DE value. Fats were soya-bean oil (SO) and soya-bean acid oil (SAO) for T3 (FFA 6·2 and 626·0 g/kg respectively) and T and tallow acid oil (TAO) for T4 (FFA 44·3 and 818·2 g/kg fat respectively). Three fats of intermediary FFA for each trial were formed by blending the two fats in the ratios of 72:25, 50: 50 and 25: 75 in both trials. The FFA content of the blends were 161·2, 316·1 and 471·1 g/kg fat for T3 and 237·8, 431·3 and 624·7 g/kg fat for T4. All trials evaluated five fats by substitution, at 40, 80 and 120 g/kg into a basal diet, in a cross-over design, with 16 gilts of 25 kg initial live weight evaluating 16 diets over four time periods. Diets were offered for 10 days followed by a 5-day collection period using the marker to marker technique. Fat content of food and faeces, with methodology based on acid hydrolysis, allowed calculation of apparent digestible fat (AFD) of experimental diets. Analysis of variance gave effects of fats (P < 0·001 for Tl, T3 and T4 and P = 0·014 for T2), rates of inclusion (P < 0·001 for all trials), and fats × rates (P > 0·05, P > 0·05, P < 0·001, P < 0·01 for T1, T2, T3 and T4 respectively). Extrapolation of the function obtained by regressing AFD of diets (y) on rate of inclusion of fat (x) to × = 1000 generated values for the fats. The product of the coefficient of apparent fat digestibility of fats and their respective gross energies gave DE values for fats which were MJ/kg: T1 RO = 35·8 and T = 31·2; T2 RO = 36·7 and PO = 33·1; T3 SO = 374 and SAO = 32·8 and T4 T = 33·8 and TAO = 28·9. Data for fat blends intermediary between the two fats showed that DE improved exponentially as a function of U/S and that DE declined linearly with increasing FFA content.