Dynamics of fat absorption and effect of sham feeding on postprandial lipema

Abstract

Background & 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 effect of sensory exposure to lipid on metabolism.

Methods: Subjects performed two, 24-hour inpatient studies that entailed consumption of a liquid formula evening meal containing 30 g of oil (+ (13)C(2) triolein) on day 1. Breakfast (day 2) consisted of triacylglycerols (TAGs) fed as capsules (30 g oil + (13)C(7) triolein) to avoid activation of mouth taste receptors. Next, modified sham feeding of cream cheese occurred over 2 hours. In the 2 trials, the stimulus was either higher fat (HF) or lower fat (LF) cream cheese. A liquid meal was consumed at lunch. Blood sampling occurred intermittently, and chylomicron particles S(f) >400 TAGs were analyzed by gas chromatography-mass spectrometry.

Results: (13)C(2)-Label was found in fasting-state lipoproteins, and persons with higher body fat percentages showed greater dilution of meal TAGs from endogenous sources. For both trials, 13% ± 4% of lipoprotein TAGs oleic acid was derived from the previous evening meal. Incremental area under the curve for TAGs during HF was ∼2.5 times higher than after LF exposure (46 ± 15 vs 17 ± 5 μmol/L/h; P = .04). The greater HF morning lipemia occurred with elevated glucose, insulin, and nonesterified fatty acids peak after 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.

Figure 1. Inpatient study timeline

See methods for specifics of protocol. Abbreviations: CRC, clinical research center; TE, total energy.

Figure 2. Serum concentrations of glucose, insulin, and NEFA

See methods for specifics of protocol. HF sensory exposure, denoted with filled symbols; LF sensory exposure, unfilled symbols. Time points that are significantly different (P<0.05) denoted by asterisks.

Figure 3. Concentrations of serum-TAG and TAG in lipoprotein fractions S_f >400 and S_f 60-400

See legend of figure 2 for details.

Figure 4. S_f >400 lipoprotein-TAG FA labeling (4A) and accounting of the sources of lipoprotein-TAG oleic acid by labeling two consecutive meals (4B)

A) The evening meal fed the night before was labeled with ¹³C₂ triolein and the morning capsules were labeled with ¹³C₇ triolein. B) Sources of the total daylong iAUC of Sf>400 TAG oleic acid were identified from labeling patterns and enrichments of the Evmeal (hatched area), capsules (filled grey area) and the sum minus these two sources.

Figure 5. Pattern of labeling of lipoproteins S_f >400 TAG

Evening meal label data (solid line) and capsule label (dashed lines) are presented for individual subjects from HF and LF sensory exposure. The unit on the Y-axis represents the percentage of S_f >400 lipoprotein-TAG oleic acid that is labeled. Horizontal arrows highlight similar starting enrichment of ¹³C₂ at the beginning of the experiment, asterisks denote cephalic phase peaks, and upward arrows highlight acute increases in use of the ¹³C₂ label at the onset of lunch, 4.75 hr.

Figure 6. Relationships between subject body fat residual Evmeal label, subject body fat %, and residual label and peak capsule enrichment

Data are from the HF (filled symbols, solid regression line) and the LF experiments (unfilled symbols, dashed line). A) Relationship between the residual Evmeal enrichment in S_f>400-TAG in the fasting state during HF and LF sensory tests; B) Subject body fat and the residual Evmeal label in S_f>400-TAG in the fasting state; C) fasting enrichment of Evmeal label in the morning vs capsule label enrichment during HF sensory exposure and D) during LF sensory exposure.