Short-Term Effect of Convenience Meal Intake on Glycemic Response and Satiety among Healthy College Students in South Korea

Rapid economic growth and industrial development in Korea have led to a great change in dietary patterns, and the use of convenience foods has increased with development of food industries and tendency to pursue convenience [1]. Recently, convenience stores have been growing rapidly in Korea because of 24-hour operation and easy access. In previous studies, consumption of convenience foods purchased at convenience stores was high especially among college students [1, 2, 3, 4]. While several studies investigated the utilization and consumption patterns of the convenience foods [1, 2, 3, 4], there was no study examining the relationship between the consumption of the convenience foods and health issues.

It has been known that postprandial glucose concentrations, even within the non-diabetic range, are associated with increased risks of cardiovascular disease [5], diabetes [6], metabolic syndrome [7], and cancer [8]. Therefore, increasing postprandial glucose may be a risk factor of those diseases. There are prior studies showing that blood glucose responses may be different depending on the type and nutritional composition of the meal [9, 10]. These circumstances may cast interest as to whether the consumption of convenience meals has any negative effect on glycemic response. Thus, the purpose of this pilot study was to examine effects of convenience meals purchased at convenience stores on glycemic response and satiety in healthy college students compared to home-made style standard diet.

A total of 10 college students were recruited and 9 of them completed the study (4 males and 5 females). We measured the glycemic and satiety impact elicited by 3 different test meals in male and female volunteers on non-sequential 3 separate days. Subjects were non-smokers, aged 20–24 years, with mean body mass index (BMI) of 21.8 ± 2.8 kg/m² (18.6–24.5 kg/m²), without diabetes, and in good health. The study protocol was in accordance with the Declaration of Helsinki, and each subject gave informed consent prior to the participation.

Subjects were (mean ± SD) 22.0 ± 1.9 years of age with a BMI of 21.8 ± 2.8 kg/m². Although fasting glucose levels were not significantly different at the baseline, glucose levels at 30 minutes and 120 minutes after the type 1 convenience meal intake were significantly higher than those in the standard meal (p < 0.05, p < 0.01) (Figure 1). Glucose response areas (total, left, and right) under the curve were significantly higher after consuming the type 1 convenience meal and type 2 convenience meal compared with those after the standard meal (p < 0.05, p < 0.01, p < 0.05) (Table 1). In the satiety evaluation of these experimental meals, although the type 2 convenience meal (sweet bread and flavored milk) contained over 200 kcal more calorie than the other test meals, mean satiety score of the type 2 convenience meal was lowest at 30 and 60 minutes after consumption (p < 0.01, p < 0.05) (Figure 2).

Figure 1
Blood glucose response. Values are mean ± SD (n = 9). A standard meal contained cooked rice and side dishes, type 1 convenience meal contained kimbap and instant ramen, and type 2 convenience meal contained sweet bread and flavored milk.

SD, standard deviation.

^*p < 0.01; ^†p < 0.05; ^a,bMean for control not sharing the same letter in the superscript differs significantly by Tukey's post-hoc test (p < 0.05).

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Table 1
Area under the curve for postprandial blood glucose after the meals in healthy college students (n = 9)

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Figure 2
Satiety scores. Values are mean ± SD (n = 9) reported in millimeters of visual analogue scale for fullness feeling. A standard meal contained cooked rice and side dishes, type 1 convenience meal contained kimbap and instant ramen, and type 2 convenience meal contained sweet bread and flavored milk.

SD, standard deviation.

^*p < 0.01; ^†p < 0.05; ^a,bMean for control not sharing the same letter in the superscript differs significantly by Tukey's post-hoc test (p < 0.05).

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In the pilot study, we found that within the first 120 minutes after a meal, the type 1 convenience meal (kimbap and instant ramen) led to a significant increase in postprandial glycemia. Also, we found that total glucose response areas under the curve were significantly higher after consuming the type 1 convenience meal, followed by the type 2 convenience meal, and standard meal. We did not control the serving amount of the convenience meals to match with the calorie contents of the standard meal, because we intended to use actual serving size of products currently sold at convenience stores in Korea. Even though we did not tightly control the test meals in terms of calorie contents to match with the standard meals, the type 1 convenience meal and standard meal contained similar calorie. However, there were differences in the composition of carbohydrate, protein, and fat between these 2 meals, which could have partially contributed to the difference in glucose response. For example, high carbohydrate contents of the type 1 convenience meal may cause higher glucose response, as instant ramen and kimbap have high carbohydrate. Another possibility is that it may be caused by low dietary fiber in the type 1 convenience meal. Although we did not measure actual dietary fiber contents of the test meals, we could postulate lower dietary fiber contents of the convenience meals than the standard meal based on their ingredients.

The glycemic response and insulin response are highly associated with postprandial rise in plasma glucose in healthy normal-weight individuals [7]. Postprandial glucose concentrations are associated with increased risk of chronic degenerative diseases, such as cardiovascular disease [5], diabetes [6], and metabolic syndrome [7]. Therefore, a long-term effect of instant ramen and kimbap consumption on increasing glycemic response should be studied.

While the type 2 convenience meal (sweet bread and flavored milk) contained higher energy, carbohydrate, and fat than the standard meal and the type 1 convenience meal, satiety of study subjects on the type 2 convenience meal was lowest for 2 hours after consumption of the test meals. Furthermore, our result showed no pattern between glycemic response and satiety. According to the Roberts' review article [12], short-term studies indicated that consumption of carbohydrate sources with high-glycemic index (GI) might increase hunger and promote overeating compared to consumption of foods with a lower GI. However, Flint et al. [13] found that insulin was associated with short-term satiety regulation, but glycemic response showed no effect. Rolls [14] reported that fat provides a high level of energy in a given volume of food; however, when given in equal volumes, carbohydrate (sugar) and fat have similar effects on hunger, satiety, and subsequent food intake when infused intragastrically or ingested in foods by normal-weight, unrestrained young men. Although more data are needed, our results suggested that convenience meals consisted of breads and beverages with high fat and sugars may induce overeating and increase the risk of obesity.

The standard meal provided lower energy than convenience meals purchased from a convenience store and showed lower postprandial glycemic response but higher scores in satiety. A previous study reported that consumption of boiled white rice with mixed grains shows higher satiety rates compared to the boiled white rice, despite having lower calories [9]. Also, dietary fiber has shown to increase satiety [10, 15], therefore, the improved glycemic response in the standard diet than in the other diets without its effect on satiety may have been counterbalanced by an increase in fiber intake in the standard diet.

This pilot study is subject to limitations. First, the 2 convenience meals may not be representative of all convenience foods available at convenience store, even though we selected these food items based on previous studies [1, 11] and focus group interview. Second, this study examined a single time effect of different meals on glycemic response and satiety. Future studies are needed to investigate long-term effects of convenience meal consumption on glycemic response and health outcome with a large sample size. Third, blood glucose response was only assessed from fingerstick blood samples with one type of glucometer, this would not assure accuracy and reliability of the test. Fourth, the test meal provided to male and female subjects had some differences in total calorieand the composition of carbohydrate, protein, and fat. However, future studies should consider separate studies by gender or studies investigating a smaller variation in the composition of carbohydrate, protein, and fat.

Despite these limitations, this pilot research suggests that convenience meals may increase glycemic response or induce higher calorie intake among college students. Moreover, college students should limit the consumption of convenience foods for their health and have a nutritionally balanced diet.