Since most studies reported moderate- or long-term effects of different composition of macronutrients in the diet rather than the acute effects on blood kinetics, it is not easy to discuss our results comparing with previous studies (Coulston et al., 1983
; Gougeon et al., 2006
; Laaksonen et al., 2005
, Shai et al., 2008
). However, our results are comparable to preliminary evidence that postprandial carbohydrate utilization was increased directly after the administration of a meal or single oral glucose (Liu et al., 1983
In Chinese subjects, Liu et al. (1990
) observed the fasting plasma glucose, insulin and lipids responses to the high-carbohydrate (CHO 80%) and the high-fat diet (Fat 45%). The high carbohydrate diet increased the fasting plasma glucose levels on day 1 (P
<0.01), insulin (P
<0.01) on day 3 and TG levels on days 3 and 5. On the other hand, the high fat diet decreased plasma TG values on day 1 but increased TC on days 1 and 3, but the fasting plasma glucose levels were decreased slightly on day 5 without a significant difference in insulin levels.
In healthy American volunteers, two levels of dietary carbohydrate (40% and 60% of calorie) consumption for 10 days resulted in that no differences were observed in fasting plasma glucose or cholesterol concentrations. However, fasting plasma TG levels as well as insulin were significantly elevated in the 60% carbohydrate diet group, and HDL-cholesterol concentrations were decreased significantly (Coulston et al., 1983
). It is therefore that the levels of dietary carbohydrate may influence the blood measures of lipids, lipoproteins, and insulin which are associated with incidence of coronary heart disease.
Several studies have shown that the amount and nature of carbohydrate in a meal alter postprandial lipid metabolism. Since we compared the influences of relative amounts of macronutrients in the same menu, the latter could not explain our results. Plasma TG concentration was significantly elevated according to the amount of fat consumption (Lopez-Miranda et al., 2007
). Some studies using a very low (5 g) or low (15 g) dose of dietary fat did not significantly increase triacylglycerolaemia postprandially; moderate doses (30-50 g) dose-dependently increased postprandial triacylglycerolaemia (from 0.9 to 1.3 mmol/L above baseline, respectively); and very high doses (80 g and above) exaggerated postprandial triacylglycerolaemia but without dose-dependence (Dubois et al., 1998
; Lopez-Miranda et al., 2007
Data obtained after the addition of glucose (50 g, 100 g) to high fat meal have not shown consistent findings on postprandial lipid metabolism in healthy subjects (Cohen & Berger, 1990
), whereas the addition of sucrose or fructose has consistently been shown to increase postprandial triacylglycerolaemia (Grant et al., 1994
). Therefore, the amount of fat (40.6 g) in the present study was appeared to be enough to stimulate postprandial triacylglycerolaemia, although it is not the usual amount of fat in typical Korean menu. Moreover, the high fat meal was acceptable in the present subjects. All subjects consumed the given menu entirely in recommended time. We found that salad dressing is an easily applicable food item to modify fat consumption in this study.
In healthy subjects, physiological ranges of postprandial hyperglycemia and hyperinsulinaemia as generated by starch foods (bread, pasta, beans) did not induce noticeable alterations in the overall postprandial TG response (Harbis et al., 2004
). Similarly, the experimental menu, high carbohydrate meal used in the present study did not altered postprandial TG response. On the other hand, the third National Health and Nutrition Examination Survey (NHANES III) showed that the quantity and type of carbohydrate consumed in the habitual diet did not contribute to the plasma glucose, serum insulin concentration but inversely associated with serum C-reactive protein (CRP) concentration (Yang et al., 2003
The IGI is a commonly used measure of early insulin secretory capacity (Laaksonen et al., 2005
). This index had moderately high correlation with acute insulin responses that were measured during a frequently sampled intravenous glucose tolerance test (r=0.47-0.61). Sharman et al. (2004
) showed that the short-term hypoenergetic low-fat diet was more effective at lowering serum LDL-C, but the very low carbohydrate diet was more effective at improving characteristics of the metabolic syndrome as shown by a decrease in fasting serum TG, postprandial lipidemia, serum glucose and greater weight loss.
There are several limitations of the current study. A single diet is a poor descriptor of a person's usual intake, because of individual variability. Also, our results must be considered preliminary due to the small number of study subjects. However, there is widespread interest in "high fat diet" and "high protein diet" alternatives to the conventional "high carbohydrate" approach for weight loss recently. Although a diet low in saturated fats and rich in whole grains, vegetables and fruit is recommended in order to reduce the risk of obesity, cardiovascular disease and type 2 diabetes (McAuley et al., 2005
). It is unclear exactly how postprandial glycemia or lipaemia impacts on pathophysiologic conditions such as atherosclerosis, diabetes, and coronary heart diseases. Further studies are expected to investigate the effects of amounts and types of macronutrients in the habitual Korean diets on postprandial response.
In the current study, hyperglycemia and hyperinsulinemia were both induced significantly and acutely by the high carbohydrate meal not by the high fat meal, while gradual hypertriacylglycerolaemia was observed by the high fat meal not by the high carbohydrate meal. In conclusion, macronutrients content in the meal may be an important determinant of postprandial substrate utilization in healthy young individuals.