Dynamics of Fat Absorption and Effect of Sham Feeding on Postprandial Lipema

Abstract

Background and Aims Given the importance of postprandial hyperlipidemia to increase risk for atherosclerosis, in the present study, stable isotope-labeled meals were fed to healthy subjects (7 males and 3 females) to investigate the kinetics chylomicron synthesis and the impact of sensory exposure to lipid on metabolism. Methods Subjects performed 2, 24-hr inpatient studies which entailed consumption of a liquid formula evening meal containing 30g of oil (+13C2 triolein) on day 1. Breakfast (day 2) consisted of TAG fed as capsules (30g oil + 13C7 triolein) to avoid activation of mouth taste receptors. Next, modified sham feeding of cream cheese occurred over 2 hrs. In the 2 trials, the stimulus was higher-fat (HF) and lower-fat (LF) cream cheese. A liquid meal was consumed at lunch. Blood sampling occurred intermittently and chylomicron particles Sf >400-TAG, were analyzed by GC/MS. Results 13C2-Label was found in fasting-state lipoproteins and individuals with higher body fat percentages demonstrated greater dilution of meal-TAG from endogenous sources. For both trials, 13 ± 4% of lipoprotein-TAG oleic acid was derived from the previous evening meal. Incremental AUC for TAG during HF was ~2½ times higher than after LF exposure (46 ±15 vs 17 ± 5 μmol/l × hr, P=0.04). The greater HF morning lipemia occurred with elevated glucose, insulin and NEFA peaks following lunch. Conclusions These data support a connection between enteral lipid metabolism and oral fat exposure, resulting in elevated postprandial lipemia. The results suggest that the intestine may participate in a mechanism coordinating oral fat signaling with control of subsequent macronutrient disposal in the body.

Taste of Fat: A Sixth Taste Modality?

“…Nevertheless, a recent study from our lab found that adult subjects who preferentially overeat high-fat foods were all obese individuals unable to detect LA properly during 3-AFC tests (32). Obesity also compromises the activation of the taste-evoked vagal reflex loop (i.e., tongue-NTS-blood axis; FIGURE 4), normally triggered by an oral fat stimulation and leading to early changes in the plasma TG levels (28,127,128,130). Indeed, the TG rise observed in overnightfasted lean individuals subjected to a brief oral exposure to LA (sip and spit procedure) is lacking in obese subjects (32).…”

Getting the label in: practical research strategies for tracing dietary fat

“…It is now recognized that a significant portion of the previous evening meal's TG resides in the enterocyte for 4--16 h after the meal. 23 This lipid will enter the blood at the onset of the next meal---a phenomenon termed the 'second meal effect'. This effect can be reduced by subjects consuming a low-fat evening meal the night before the postprandial study, and such a scheme will maximize detection of the test meal entry.…”

“…Capsules have been used to deliver tracer lipids, 23,43 but one study reported that the recovery of 13 C in breath was 10 times higher when the tracer was fed in the meal than in capsule form. 44 Many investigators have fed only a single isotope-containing meal and therefore measure the acute postprandial response to that meal.…”

“…As demonstrated in Figure 1, for some subjects who absorb meal fat slowly, a second meal may be required to see maximum appearance of the dietary tracer in plasma lipid compartments. 23,46 After two identically labeled meals, the enrichment of chylomicron-TG pool can approach 100% that of the meal. 27 To maximize entry of a label given in a fat-containing breakfast meal, it is not necessary that fat be included in the second meal; rather, the secondary release of chylomicron-TG may be stimulated by providing a meal containing only glucose.…”

“…However, the response to meal fat consumption is also affected by individual differences in absorption that are beginning to be appreciated. 23 We have documented the very large variability of individual subjects to absorb a test meal, 23 and shown in Figure 1 are more recent examples of the absorption rate of a tracer consumed at lunch, as the first meal of the day (time 0). This rise in the lunch label (solid bold line) after the meal can be contrasted with the rise in plasma concentration of TG-rich lipoprotein apoB48 (solid gray line), the marker of chylomicron particle concentration.…”