Abstract :
Three experiments were conducted in healthy middle-aged volunteers (six males and six females in
Expt 1, six males and two females in Expt 2 and twelve males in Expt 3) with a mean BMI of
27 kg/m2 to determine whether there is a difference between morning and afternoon dietary fat
clearance and utilization, and to determine in what way the fat and starch contents of the meal
influence postprandial blood lipid metabolites over 4.5 h. Over 4 days in Expt 1 each subject
received isoenergetic, high-carbohydrate (L, 5.5 g mixed fat/meal) and moderately high-fat (M, 33 g
mixed fat/meal) breakfasts and lunches, in three combinations (LL, MM, LM), or they fasted at
breakfast time and received a high fat lunch (NM) in a randomized and balanced arrangement.
Each evening a standard meal was given. The following effects were significant (P < 0.05): plasma
triacylglycerol (TAG) responses were greater following M meals; plasma TAG concentrations were
greater in the afternoon than in the morning, following two meals of the same composition, although
the postprandial incremental response was less following lunch than following breakfast and peak
responses were reached much earlier than after breakfase a low-fat breakfast, or fasting at
breakfast time, delayed the peak TAG response to a M lunch. The plasma concentrations of nonesterified
fatty acids (NEFA) and of free glycerol were higher in the afternoon following M meals at
breakfast and lunch, especially in males. This response was reduced, by the L breakfast preceding
the M lunch. Two M meals in succession lowered plasma HDL-cholesterol concentration. In Expt 2
each subject received a very low-fat (VL) breakfast, followed by a lunch of the same composition.
Each of these meals was followed, 110 min from the start of eating, by an infusion of Intralipid 10 %
emulsion at the rate of 1 ml/kg body weight over 60 s. Clearance rates of Intralipid were faster in
the afternoon than in the morning (P = 0.024). In Expt 3 twelve subjects were randomly allocated to
either treatment MM or LM meal patterns, as given in Expt 1. These were given daily for a period of
17 d, during which the change in fasting plasma TAG concentration was similar in both treatments.
On days 1,16 and 17 responses were measured to the M lunch and to a glucose tolerance test (GTT),
conducted 2 h 17 min after lunch. The post-lunch responses con6rmed those found in Expt 1; but
immediately following the glucose dose there was an abrupt increase in plasma TAG that was
greater in treatment LM than in treatment MM (P = 0.025), whereas plasma NEFA concentration
decreased rapidly in both treatments at that time (P = 0.00066).
