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Compared with triacylglycerol (TAG), dietary 1,3-diacylglycerol (1,3-DAG) is associated with reduced serum lipid and glucose levels. We investigated the metabolism of 1,3-DAG by assaying its intermediate metabolites during digestion and absorption in the rat small intestine. After gavage with TAG emulsion, TAG was digested mainly to 2-monoacylglycerol (2-MAG) and unesterified fatty acid (FFA) in the rat small intestinal lumen. 2-MAG was directly absorbed into the small intestinal epithelial cells and esterified to 1,2(2,3)-DAG, and further esterified to TAG. After gavage with 1,3-DAG emulsion, 1,3-DAG was digested mainly to 1(3)-MAG and FFA in the rat small intestinal lumen with subsequent significant increase of 1-MAG and 1,3-DAG concentrations in small intestinal mucosal epithelial cells, and the 2-MAG, 1,2(2,3)-DAG, and TAG concentrations in mucosal epithelial cells were not significantly different after 1,3-DAG than after TAG gavage, suggesting that the metabolic pathway of 1,3-DAG is different from that of TAG. In intestinal mucosal epithelial cells, we further assayed enzyme levels and gene expression of proteins in the phosphatidic acid (PtdOH) pathway. The glycerol kinase, phosphatidate phosphatase, and diacylglycerol acyltransferase-2 expression and the relative expression of mRNA of enzymes were significantly increased in the 1,3-DAG group compared with the TAG group, suggesting that TAG synthesis from dietary 1,3-DAG was mainly via PtdOH pathways, which may partially account for the effect of dietary DAG on postprandial serum TAG., (© 2018 AOCS.)

Medium chain fatty acid (MCFA) escapes the formation of chylomicrons in the small intestine, resulting in energy expenditure through beta-oxidation. Diacylglycerol (DAG) is susceptible to oxidation rather than being stored in the adipose tissue. This study was conducted to verify the effect of MCE-DAG oil on body fat mass in vivo. Male C57BL/6 mice were randomly assigned to four groups (n = 12) as follows: (1) normal diet (18% kcal from fat), (2) canola oil as a control (40% kcal from canola oil), (3) MCE-DAG10 (10% kcal from MCE-DAG + 30% kcal from canola oil), and (4) MCE-DAG20 (20% kcal from MCE-DAG + 20% kcal from canola oil). The body weight and fat mass of MCE-DAG20 group mice were decreased relative to those of control mice (P < 0.05 and P < 0.001, respectively). Serum triacylglycerol (TAG) was decreased in both MCE-DAG10 and MCE-DAG20 groups (P < 0.01 and P < 0.05, respectively). Hormone sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) were increased in the MCE-DAG20 group relative to the control in white adipose tissue (WAT) (P < 0.05). Uncoupling protein 1 (UCP1) was also increased in the MCE-DAG20 group relative to the control in brown adipose tissue (BAT) (P < 0.05). In summary, MCE-DAG reduced body fat mass likely by stimulating lipolysis in WAT and thermogenesis in BAT.

Diacylglycerol (DAG) supplementation has been shown to be associated with the reduction of fasting serum triacylglycerol (TAG) concentration, although the extent of the association is uncertain. We quantitatively examined the effect of dietary DAG on fasting serum TAG concentration by conducting a meta-analysis of randomized controlled trials. Potential papers were searched from electronic databases of Medline, Embase and Cochrane Library. Information was extracted and the net change of fasting serum TAG concentration was used as the primary outcome to examine the effect of DAG in Review Manager 4.2. Six papers with seven independent studies (298 subjects) were included into the statistic pooling. Meta-analysis with random effect model showed that DAG did not reduce the fasting serum TAG concentration (WMD: -0.07 mmol/L; 95% CI: -0.21 to 0.08 mmol/L; P = 0.37). Sensitivity analysis indicated the robustness of overall results. Fail-safe number analysis indicated that 18 studies with positive effect were necessary to reverse the reported non-significant efficacy of DAG. Weight estimation analysis indicated that the effect of DAG was influenced to some extent by the initial fasting serum TAG concentration. In conclusion, DAG supplementation did not reduce the fasting serum TAG concentration significantly compared with TAG, but some effects were suggested in diabetic patients with hypertriglyceridemia.

Diacylglycerol (DAG) supplementation has been shown to be associated with the reduction of postprandial triacylglycerol (TAG) concentration, although the extent of the association is uncertain. We quantitatively examined the effect of dietary DAG on postprandial serum TAG concentration by conducting a meta-analysis of randomized controlled trials. Potential papers were initially searched for in the electronic databases of Medline, Embase and Cochrane library. Inclusion criteria required the trial to be randomized with DAG as the treatment group, and TAG as the control group. Information was extracted independently by two investigators and the effect of DAG on postprandial TAG concentration was examined in Review Manager 4.2. Seven papers were included in the statistic pooling. DAG supplementation reduced the increment of postprandial TAG concentration significantly at postprandial 2 h (Weighted mean difference (WMD) -0.07 mmol/L; 95% CI -0.13 to 0.00 mmol/L; P = 0.05), 4 h (WMD -0.15 mmol/L; 95% CI -0.24 to -0.06 mmol/L; P = 0.002) and 6 h (WMD -0.14 mmol/L; 95% CI -0.23 to -0.05 mmol/L; P = 0.002). Linear regression showed that the effect of DAG was positively correlated with the daily dosage at 2 h (P = 0.095) and 6 h (P = 0.053) after lipid loading. In conclusion, compared with TAG oil, DAG reduced the postprandial serum TAG concentration at 2 h, 4 h and 6 h postprandial and was positively correlated with daily dosage.

Several studies in animals and humans have reported beneficial effects of diacylglycerol (DAG) on lipid and energy metabolism. We assessed the effect of DAG versus triacylglycerol (TAG) treatment on total energy expenditure (TEE), total fat oxidation (Fox) and respiratory quotient (RQ), and measured the oxidation rate of each oil using a respiratory chamber and the 13C-stable isotope. Eleven healthy subjects participated in a double-blind, randomized crossover study. Subjects consumed an energy maintenance diet consisting of 55% of total calories from carbohydrate, 15% from protein and 30% from fat during both the 3-day pre-chamber and 36-h chamber period. Fifty percent of the fat was test oil, containing either DAG oil or TAG oil. The oxidation rate of ingested test oils was determined by monitoring 13CO2 excretion in the breath from 13C-labeled diolein or 13C-labeled triolein. There were no significant differences in TEE, RQ and total Fox between the DAG and TAG treatment in the overall analysis. In the subgroup analysis, DAG treatment decreased RQ significantly in subjects with a high fat ratio (HFR) compared to TAG treatment. In addition, ingested diolein oxidation in DAG treatment was significantly faster than triolein oxidation in TAG treatment in the HFR group. Enhanced fat utilization with DAG treatment and rapid oxidation of ingested DAG may, at least in part, explain the greater loss of body weight and body fat related to DAG consumption found in the weight-loss studies.

This study examines the effect of diacylglycerol (DAG) oil consisting mainly of 1,3-species on fat oxidation as a possible mechanism for anti-obesity. We examined the following: (1) the long-term (23-week) effects of a DAG oil diet on the development of obesity; (2) the effect of a single ingestion of DAG oil on fat oxidation; and, (3) the short-term (2-week) effect of a DAG oil diet on fat metabolism in rats. Rats fed a DAG oil diet accumulated significantly less body fat compared to rats fed a triacylglycerol (TAG) oil diet, each oil possesses a similar fatty acid composition. More( 14)C-CO(2) was expired and less( 14)C-radioactivity was incorporated into visceral fat after administration of a tracer emulsion containing 1,3-[oleoyl-1-(14)C] diolein compared to [carboxyl-(14)C] triolein. Indirect calorimetry showed respiratory quotients were significantly lower in the DAG oil diet group than in the TAG oil diet group. More( 14)C-CO(2) was expired and less (14)C-radioactivity was incorporated into visceral fat in the DAG oil diet group than in the TAG oil diet group after a single intragastric administration of [carboxyl-(14)C] triolein. These results suggest the following. (1) DAG oil has an inhibitory effect on diet-induced fat accumulation. (2) 1,3-DAG, a major component of DAG oil, is more susceptible to oxidation. (3) A short-term ingestion of DAG oil increases fat utilization at the whole body level and results in increased oxidation of dietary fat. The stimulated fat oxidation might be one explanation for the anti-obesity effect of long-term DAG oil ingestion.

The present study investigated the metabolic fate of dietary TAG and DAG and also their digestion products in the stomach and small intestine. A diet containing 10% TAG or DAG oil, enriched in 1,3-DAG, was fed to Wistar rats ad libitum for 9 d. After 18 h of fasting, each diet was re-fed ad libitum for 1 h. The weights of the contents of the stomach and small intestine were measured, and the acylglycerol and FFA levels were analyzed by GC at 0, 1, and 4 h after the 1-h re-feeding. The amounts of re-fed diet ingested and the gastric and small intestinal content were not different between the two diet groups. In the TAG diet group, the main products were TAG and DAG, especially 1(3),2-DAG. In addition, 1,3-DAG and 1(3)-MAG were present in the stomach, and the 1,3-DAG levels increased over time after the re-feeding period. In the DAG diet group, the main products in the stomach were DAG, MAG, FFA, and TAG. There were significantly greater amounts of 1,3-DAG, 1(3)-MAG, and FFA in the DAG diet group in the stomach compared with the TAG diet group. The amount of FFA in the stomach relative to the amount of ingested TAG plus DAG in the DAG diet group was higher than that in the TAG diet group. Acylglycerol and FFA levels were considerably lower in the small intestine than in the stomach. These results indicate that, in the stomach, where acyl migration might occur, the digestion products were already different between TAG and DAG oil ingestion, and that DAG might be more readily digested by lingual lipase compared with TAG. Furthermore, almost all of the dietary lipid was absorbed, irrespective of the structure of the acylglycerol present in the small intestine.

The inhibitory effects of 1,3-diacylglycerol (DAG) on diet-induced lipid accumulation in liver and abdominal adipose tissue of rats were investigated in the present study. Male Sprague-Dawley rats were given free access to diets containing 7 wt% TAG (low TAG), 20 wt% TAG (high TAG), or 20 wt% DAG (high DAG), respectively, for 8 wk. The body weight of rats in the 20% high-TAG group increased significantly, and the weights of their abdominal adipose tissue and liver also showed a significant increase compared with rats in the low-TAG group. However, the high-DAG diet resulted in both a significant reduction in body weight gain (with a decrease of 70.5%) and an increase in the ratio of abdominal fat to body weight (by 127%) compared with the high-TAG diet. As well, the liver TAG and serum TAG levels of the high-DAG group were significantly lower than those of the high-TAG group. These effects were associated with up-regulation of acyl-CoA carnitine acyltransferase (ACAT) and down-regulation of acyl-CoA DAG acyltransferase (DGAT) in the liver. However, no significant difference was observed in the activities of alanine aminotransferase and aspartate aminotransferase among the groups (P > 0.05). The present results indicate that dietary DAG reduced fat accumulation in viscera and body, and these effects may be involved with up-regulation of ACAT and down-regulation of DGAT in the liver.

Several recent studies have demonstrated that dietary DAG oil rich in 1,3-species suppresses the postprandial increase of serum TAG level and decreases body fat accumulation, compared with TAG oil. To clarify the mechanisms underlying the beneficial effects of DAG, we investigated the metabolic features of DAG in the small intestine with regard to the digestion pathway in the lumen and the TAG-synthesis pathway in the mucosa. When intraduodenally infused as an emulsion, TAG was digested to 1,2-DAG, 2-MAG, and FFA, whereas 1,3-DAG was digested to 1(3)-MAG and FFA. When assessed by the incorporation of [1-14C]linoleic acid in lipids, the mucosal TAG-synthesis was significantly reduced by DAG infusion compared with TAG infusion. However, the mucosal 1,3-DAG synthesis was remarkably increased in the DAG-infused rats. The total amount of mucosal 1,3-DAG was also increased (4.5-fold) after DAG infusion compared with that after TAG infusion. Next, we examined the synthesis pathway of 1,3-DAG. In cultures of the everted intestinal sacs, 1,3-DAG production required the presence of 1-MAG, suggesting that the 1,3-DAG synthesis was due to acylation of 1(3)-MAG in the DAG-infused rats. Furthermore, measurements of DAG acyltransferase activity indicated that 1,3-DAG was little utilized in TAG synthesis. These findings suggest that features of 1,3-DAG digestion and assimilation in the intestine may be responsible for the reduction of the postprandial serum TAG level by dietary DAG.

Diacylglycerol (DAG) is a component of various vegetable oils. Approximately 70% of the DAG in edible oils are in the configuration of 1,3-DAG. We recently showed that long-term ingestion of dietary oil containing mainly 1,3-DAG reduces body fat accumulation in humans as compared to triacylglycerol (TAG) oil with a similar fatty acid composition. As the first step to elucidate the mechanism for this result, we examined the difference in the bioavailabilities of both oils by measuring food energy values and digestibilities in rats. Energy values of the DAG oil and the TAG oil, measured by bomb calorimeter, were 38.9 and 39.6 kJ/g, respectively. Apparent digestibility expressed according to the formula: (absorbed) x (ingested)(-1) x 100 = (ingested - excreted in feces) x (ingested)(-1) x 100 for the DAG oil and the TAG oil were 96.3+/-0.4 and 96.3+/-0.3% (mean +/- SEM), respectively. The similarity in the bioavailabilities of both oils supports the hypothesis that the reduced fat accumulation by dietary DAG is caused by the different metabolic fates after the absorption into the gastrointestinal epithelial cells.