Metabolism of dietary fat

Fats ingested from food undergo digestive decomposition in the small intestine by fat-decomposing enzymes known as lipases. Fats are converted principally to 2-monoacylglycerol (2-MAG) and fatty acids and are absorbed into the surface of the small intestines. After absorption, those materials are resynthesized to triacylglycerol (TAG) in small intestinal epithelial cells and form lipoprotein particles termed chylomicron. When chylomicron passes through the lymph ducts and enters the blood, it is decomposed by lipoprotein lipases (LPL) present in capillary vessels of adipose tissue and other tissues. Fatty acids thus generated are incorporated in muscle and adipose tissue. Partially decomposed lipoprotein particles that remain are termed remnants. These remnants are absorbed primarily by the liver and metabolized.

When foods containing fat are ingested, the level of serum triacylglycerol rises temporarily. Recently, a symptom of sustained elevation of postprandial serum triacylglycerol has been reported and is termed "postprandial hyperlipidemia". An emerging relationship has also been shown between the onset and progression of arteriosclerotic lesions and the elevation of remnant lipoproteins levels in the blood. Those remnant lipoproteins are intermediate metabolites created by metabolization of lipoproteins abundant in triacylglycerol.¹⁾

Suppressive effect of diacylglycerol (DAG) on postprandial serum triacylglycerol elevation

Time-course changes in postprandial serum triacylglycerol levels were compared in a double-blind crossover study. Healthy adult male subjects ingested either DAG or TAG oil with similar fatty acid composition, at a dosage of 10g, 20g or 44g per 60kg body weight. The study showed that postprandial serum triacylglycerol levels were significantly lower following DAG ingestion versus TAG ingestion (Figure 2).²⁾

Figure 2

Changes in serum triacylglycerol concentrations after ingestion of　diacylglycerol or triacylglycerol emulsion.

Values are means ± SD from baselinee

*:	Significantly different from the corresponding values for the triacylglycerol emulsion, p<0.05

(Student’s t test for paired values)
Taguchi H. et al., J. Am. Coll. Nutr., 19, 789-796 (2000)

Yanagita et al. investigated quantitative resynthesis of TAG in the small intestine and quantitative secretion to the lymph. Rats were subjected to administration of ¹⁴C oleic acid DAG oil or TAG oil, and time-course changes were studied comparatively. The results showed that quantitative reduction and delay in TAG resynthesis in the small intestine were noted in the DAG oil administration group compared to the TAG oil administration group.³⁾

Tada et al. reported a suppressive effect on elevation of remnants following DAG ingestion. Six healthy male subjects ingested either DAG oil or TAG oil at a dosage of 30g/administration/m² body surface, and the results showed that RLP-C and RLP-TG (remnant-like lipoprotein particle fraction cholesterol and triglycerides) values were significantly lower in DAG oil ingestion versus TAG oil ingestion, indicating that postprandial elevation of remnants was suppressed(Figure 3).⁴⁾

Figure 3

Changes in serum concentrations of RLP after ingestion of diacylglycerol or triacylglycerol emulsion.

Values are means ± SD, n=6
P values for significant main effect by the two-way ANOVA between DAG and TAG

Source:

Tada N. et al., Dynamics of postprandial remnant-like lipoprotein particles in serum after loading of diacylglycerols

Clin. Chim. Acta. 311, 109-117 (2001), with permission from Elsevier

Suppressive effect of diacylglycerol (DAG) on body fat accumulation

38 healthy male subjects age 27-49 underwent 4 months ingestion of DAG oil or TAG oil, and changes in body fat were studied comparatively with double-blind controlled design. Total fat intake per day was restricted to 50g, and 10g of total fat intake (the average dietary oil intake among Japanese individuals is 10-12.5g) was substituted by DAG oil or TAG oil. Both groups demonstrated a reduction in body weight and body fat resulting from dietary restriction, but body weight and BMI after 4 months was significantly lower in the DAG oil ingestion group versus the TAG oil ingestion group. Visceral fat calculated from CT images also demonstrated a statistically significant reduction in the DAG oil ingestion group (Figure 4).⁵⁾

Figure 4

Changes in anthropometric values and body composition of men who consumed food products containing either diacylglycerol or triacylglycerol oil for 16 wk.

Values are means ± SEM, n=19

Change:

wk16 value ? wk0 value

**:	Significantly different from the TAG oil group, p<.01

Source:

Nagao T. et al., J.Nutr., 130, 792-797 (2000) American Society for Nutritional Science

Maki et al. performed human efficacy studies among subjects comprising obese or overweight volunteers in the US. 127 male and female subjects (U.S. residents with BMI 30 or greater) underwent 6 months ingestion of DAG oil or TAG oil, and changes in body fat were studied comparatively. Diet during the study was a diet 500-800kcal less than appropriate daily consumption, and an intergroup comparative study was carried out with a randomized double-blind controlled design. The results showed a statistically significant difference between the DAG and TAG oil ingestion groups with regard to body weight and body fat reduction (Figure 5).⁶⁾

Figure 5

Changes in body weight and fat mass among subjects assigned to diacylglycerol oil or triacylglycerol oil treatment groups.

Values are means ± SEM, DAG Oil group;n=63, TAG Oil group;n=62
p-values for significant main effect by repeated ANOVA between DAG and TAG
Maki K.C.et al., Am.J.Clin.Nutr., 76, 1230-1236 (2002)
Reproduced with permission by the American Journal of Clinical Nutrition.
(C)　Am J Clin Nutri.　American Society for Clinical Nutrition.

Application of DAG to dietary treatment for disease

The application of DAG to dietary treatment in diabetes has been studied.
Tada et al. administered DAG at 30g/m² body surface area to 6 diabetes patients and reported that postprandial serum triacylglycerol levels were suppressed to significantly lower levels compared to administration of TAG oil with a virtually identical composition.⁷⁾ Yamamoto et al. performed a 3-month single-blind controlled ingestion study on subjects comprising diabetic patients with hypertriglyceridemia and reported a distinct reduction in serum triacylglycerol and in glycohemoglobin (HbA1c)(Figure 6).⁸⁾ Teramoto et al. reported usefulness of DAG oil among patients on hemodialysis (Figure 7).⁹⁾

Figure 6

Serum metabolites in diabetic patients before and 12wk after the substitution of diacylglycerol oil for triacylglycerol oil.

Values are means ± SD, n=8

Source:

Yamamoto K. et al.,J.Nutr., 131, 3204-3207 (2001), American Society for Nutritional Science

*,**:

Significantly different from before, *P<0.05; **P<0.01

Figure 7

Effect of diacylglycerol on abdominal fat areas measured by CT scan in patients on hemodialysis.

Values are means ± SE, n=10

*,**:

Significantly different from before, *P<0.05; **P<0.01

Source:

Teramoto T. et al., J.Japanese Soc.Clin.Nutr., 21, 35-38(2000)(in Japanese)

Reference:

Teramoto T. et al., Clin.Nutr., 23, 1122-1126 (2004)

The foregoing results demonstrate a suppressive effect by DAG oil on postprandial elevation of serum triacylglycerol levels and on body fat accumulation.

References

1)	Zilversmit D.B., Atherogenic nature of triglycerides, postprandial lipidemia, and triglyceride-rich remnant lipoproteins, Clin. Chem., 41, 153-158 (1995)
2)	Taguchi H. et al., Double-blind controlled study on the effects of dietary diacylglycerol on postprandial serum and chylomicron triacylglycerol responses in healthy humans, J. Am. Coll. Nutr. 19, 789-796 (2000)
3)	Yanagita T. et al., Comparison of the Lymphatic Transport of Radiolabeled 1,3-Diol eoylglycerol and Trioleoylglycerol in Rats, Lipids, 39, 827-832 (2004)
4)	Tada N. et al., Dynamics of postprandial remnant-like lipoprotein particles in serum after loading of diacylglycerols, Clin. Chim. Acta, 311, 109-117 (2001)
5)	Nagao T. et al., Dietary Diacylglycerol Suppresses Accumulation of Body Fat Compared to Triacylglycerol in Men in a double-blind Controlled Trial, J. Nutr. 130, 792-797 (2000)
6)	Maki K.C. et al., Consumption of diacylglycerol oil as part of a reduced-energy diet enhances loss of body weight and fat in comparison with consumption of a triacylglycerol control oil, Am. J. Clin. Nutr., 76, 1230-1236 (2002)
7)	Tada N. et al., Effects of diacylglycerol ingestion on postprandial hyperlipidemia in diabetes, Clin. Chim. Acta., 353(1-2), 87-94 (2005)
8)	Yamamoto K. et al., Long-term ingestion of dietary diacylglycerol lowers serum triacylglycerol in type II diabetic patients with Hypertriglyceridemia., J. Nutr., 131, 3204-3207 (2001)
9)	Teramoto T. et al., Significant effects of diacylglycerol on body fat and lipid metabolism in patients on hemodialysis, Clin. Nutr. 23, 1122-1126 (2004)

For more information, see also “Diacylglycerol Oil”, AOCS Press (2004) ISBN 1-893997-77-4

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