Effects of diacylglycerol ingestion on postprandial hyperlipidemia in diabetes

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Abstract

Background

We previously reported that diacylglycerol (DAG) as compared with triacylglycerol (TAG) suppressed increases in postprandial lipids in healthy volunteers. This study was to investigate the effects of DAG on postprandial lipids, particularly remnant lipoproteins in diabetics.

Methods

Emulsified DAG oil or TAG oil with a fatty acid composition similar to DAG oil was orally administered (30 g fat/m2 of body surface) to moderately controlled six diabetics, with hemoglobin A1c (HbA1c) below 8%, after fasting for at least 12 h in a randomized crossover manner. Serum cholesterol and TAG, lipids in remnant-like particles (RLP), and other lipid parameters including serum ketone bodies were measured prior to and 2, 4, and 6 h after fat loading.

Results

DAG loading significantly suppressed increases in postprandial serum TAG and lipids in RLP as compared with TAG loading. The incremental area under the curve (IAUC) for serum TAG and that for lipids in RLP with DAG loading were also significantly smaller than those with TAG loading. However, changes in serum levels of insulin, free fatty acids, and ketone bodies during fat loading were essentially the same for DAG and TAG.

Conclusions

This pilot study suggests that substituting DAG intake for TAG may be beneficial to moderately controlled diabetics due to its effect in reducing postprandial hyperlipidemia.

Introduction

A greatly enhanced risk for coronary heart disease (CHD) has been reported in diabetes [1], [2]. Lipid abnormalities in diabetes, including elevated plasma triacylglycerol (TAG), low cholesterol in high-density lipoproteins (HDL), an increase in small, dense low-density lipoproteins (LDL), and postprandial hyperlipidemia contribute to this increased risk [3], [4], [5], [6]. Among them, postprandial increase in remnant lipoproteins (remnants) has been recognized as a powerful CHD risk not only for diabetic but also for nondiabetic subjects [7], [8], [9], [10], [11], [12].

Remnants are the metabolites of TAG-rich lipoproteins, such as chylomicrons (CM) and very-low-density lipoproteins (VLDL), and are formed in the circulation by the effect of lipoprotein lipase. These remnants are readily incorporated into endothelial macrophages, leading to the accumulation of cholesterol in these cells, consequently forming a premature atherosclerotic lesion [9], [12], [13], [14].

Therapeutic approaches to reduce remnant levels in the postprandial phase are believed to be important for the management of patients with diabetes and also with metabolic syndrome [5]. We have previously reported [15] that the substitution of diacylglycerol (DAG) oil intake for TAG oil significantly suppressed postprandial increases in serum TAG and lipids in remnants measured by the method of Nakajima et al. [16] in healthy male volunteers. Therefore, we had an interest whether this favorable effect of DAG intake on postprandial hyperlipidemia can be applied to diabetic subjects without any serious adverse phenomenon.

Diacylglycerol is a natural component of various edible oils and consists mainly of the 1,3-species. The intake of DAG has been reported to reduce fasting serum TAG concentration and hemoglobin A1c (HbA1c) levels in type 2 diabetics and to prevent the accumulation of body fat in experimental animals and in humans [17], [18]. Decreased activities of enzymes of fatty acid synthesis and increased activities of enzymes involved in the β-oxidation pathway by DAG ingestion have also been reported [18].

The objectives of this study were to investigate the effects of oral DAG loading on postprandial changes in serum lipids, related parameters including ketone bodies, and changes in remnants in moderately controlled diabetics.

Section snippets

Subjects

The subjects were six patients with type 2 diabetes mellitus (five females and one male; aged 46–70 years) who had moderately controlled HbA1c levels that were <8%. The study was performed in accordance with the principle of the Helsinki Declaration. The subjects were fully informed concerning the study and gave their informed consent. The clinical characteristics of subjects are shown in Table 1. All of them were not receiving insulin therapy, but they were medicated as follows: one was taking

Changes in serum lipids and apolipoproteins

Table 3 shows changes in serum lipids, LDL-C, HDL-C, and RLP lipids. Serum total cholesterol, LDL-C, and HDL-C did not change during TAG or DAG loading. However, serum TAG increased, peaking at 4 h after the loading with either oil and decreased at 6 h. Increases (Δ: shown in the parentheses in Table 3) in serum TAG from the initial value were significantly smaller during DAG loading than those observed during TAG loading (p=0.005), as determined by two-way ANOVA. No significant difference in

Discussion

The effects of DAG loading on postprandial changes in serum lipids and lipid parameters in diabetic patients were examined. Although the subject number of this study was small, the findings again showed the suppressed postprandial increases in serum TAG, RLP-TAG, and RLP-C in the DAG intake when compared with TAG intake in diabetic subjects as previously reported in healthy volunteers [15].

Increased fasting RLP-C concentrations have been reported in individuals with impaired glucose tolerance

Acknowledgement

A part of this study was supported by Health and Labor Sciences Research Grants for Comprehensive Research on Aging and Health (H15-Choju-012), Japan.

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    Current address: Department of Food and Nutrition, Toita Woman's College, 2-21-17 Shiba, Minato-ku, Tokyo, 105-0014 Japan.

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