Detailed Instant Glucose Fluctuation due to Continuous Glucose Monitoring (CGM)

Bando H, Mima S, Tamura A, Okino Y, Yamada T and Abe Y

Published on: 2025-08-09

Abstract

For Continuous Glucose Monitoring (CGM), detailed blood glucose fluctuation was investigated using FreeStyle Libre 3. The case was 46-year-old registered female nurse, who has been totally healthy with BMI 18.0 kg/m². She has restricted carbohydrate so far for standard low carbohydrate diet (LCD), and then tried various carbohydrate intake and exercise intentionally with instant data from applied with smartphone. When she ate Japanese Udon noodles and tempura, blood glucose acutely to more than 200 mg/dL. Just after that, jumping exercise continuation for 3 minutes as high intensity degree has decreased glucose acutely. Taking bath at night decreased blood glucose.

Keywords

Continuous glucose monitoring (CGM); Free style libre 3; Low carbohydrate diet (LCD); Jumping exercise; Time in tight range (TITR)

Introduction

American Diabetes Association (ADA) has continued important management for diabetes for long and its Professional Practice Committee has presented the 2025 version of Standards of Care (SoC) in January, 2025 [1]. As recent topics, the examining and training of several personalized model can be obtained [2]. In order to obtain the detail analyses of glucose variability, intermittently scanned continuous glucose monitoring (isCGM) and blood glucose monitoring (BGM) have been used for diabetic patients with multiple daily injection (MDI) [3]. As the development of CGM apparatus, several types of CGM have been known such as FreeStyle Libre [4] and Dexcom G7 [5].

Authors and co-researchers have continued clinical practice and research on type 1 diabetes (T1D), type 2 diabetes (T2D), and atherosclerotic cardiovascular diseases (ASCVD) for years [6]. We proposed useful methods of low carbohydrate diet (LCD) including petite-LCD, standard-LCD and super-LCD [7]. Furthermore, various articles about CGM have been published including review and case reports [8,9]. Recently, we have an impressive opportunity of the experience of CGM, in which an expert nurse has a chance to apply Freestyle Libre 3 as a volunteer for further evaluation. Then, its general progress and related perspectives are described in this article.

Case Presentation

Case and Method

In this report, the case has been a registered nurse aged 46 years. She has been healthy for long without no health and medical problems.

She has worked in the out-clinic department, and good at information and treatment for diabetology. Her stature shows 153 cm in height, 42.1 kg in weight with 18.0 kg/m² in BMI. She is interested in healthy meal pattern, and continued standard-LCD method for years. Consequently, she always keeps health with stable condition.

Method included the experience of applied FreeStyle Libre 3 for 7 days in June 2025. She can manage the medical apparatus of Libre 3 well as a volunteer [10]. The purpose for this study was to become a monitor for the apparatus of Libre 3, and to obtain various data of simultaneously changing in blood glucose for various situations of food taking and exercise.

Results

The project of CGM was satisfactory conducted in June 18-23, 2025. The former data of 3 days were summarized in Figure 1. On the first day, her blood glucose during 8-16 o’clock persisted stable without fluctuation. She has taken some mixed nuts and some non-sugar beverages. She had supper from 18 o’clock, eating salad, meats and some carbohydrate food, and then blood glucose has increased to near 150 mg/dL. On 2^nd day, sweetened chestnuts has raised blood glucose enough. Taking Java tea with no carbo kept blood glucose stable. When she takes bath, blood glucose decreased about 50mg/dL. On the 3^rd day, she continued light exercise for 9-12 o’clock, in which blood glucose was stable to decreasing a little bit. She took donuts, grape burns, nuggets, and cheese naan for lunch, where glucose rapidly increased to 160mg/dL.

Figure 1: CGM Results for Various Trials-1.

The latter data of 3 days were shown in Figure 2. When she took hamburger, donut and ice cream continuously in the 1^st day, blood glucose was elevated for several hours. Just after drinking isotonic beverage 500mL with almost zero carbohydrate at 8 o’clock, she developed hypoglycemia to lower than 50 mg/dL. She did not feel any symptom or sign of hypoglycemia at that time. In the 3^rd day, she ate 2 packs of Japanese Udon noodles and 2 pieces of tempura, and then blood glucose increased to more than 200 mg/dL. Just after that, she tried exercise jumping for 3 minutes that was hard working degree. Then, blood glucose decreased acutely.

Figure 2: CGM Results for Various Trials-2.

The authors have worked together in the hospital, and the first author has participated current project for measuring simultaneous blood glucose by FreeStyle Libre 3 (Figure 3). We have meaningful and significant experience for CGM during this project, and we can take most advantage in future diabetic care and nutritional education.

Figure 3: Medical Staffs in the Hospital.

The Arrow Indicates The Sensor Of Libre 3.

Discussion

CGM system has been known and used for years, and it is more convenient with smartphone. All data can be memorized in the smartphone, and sent through the internet. FreeStyle Libre 3 system includes a sensor and an app, which are developed to higher degree for clinical use [11]. The sensor is applied painlessly to the back of the upper arm and streams glucose value automatically to the smartphone, and then the patient or staff can know the level anytime. The benefits would be accurate, painless, affordable, discreet, and real-time glucose readings with a glance at the smartphone.

Recent data have been reported about the precise comparison of CGM apparatus. From the investigation comparing Libre 3 and Dexcom G7, the results showed that the value of MARD was 8.9% in Libre 3 and 13.6% in Dexcom G7 [12]. The former seemed to show more accurate than the latter sensor in all metrics. Thus, CGM becomes more convenient for diabetic patients [13]. With the development of data analytics and Artificial Intelligence (AI), healthcare has given revolution with enhancing well-being, health challenges and system performance [14]. Latest general trend includes precision medicine, rapid drug delivery system (DDS), and so on. The AI application have large potential opportunities, which will develop operational efficiency, better patient care and improved health outcomes.

In this study, the fluctuation of blood glucose in response to various meals was detected with precise degree. She always eats mixed nuts, where blood sugar has remained stable during the period. Interestingly, she consumed 500mL of an isotonic drink with vitamin and almost zero sugar, and then she developed hypoglycemia without symptom or sign. The reasons could be as follows: i) the amount was large as 500mL at once, ii) it was a carbonated drink and quickly absorbed, iii) a small amount of sugar may influence to insulin secretion, iv) she usually restricts carbo food, as standard LCD method, v) secreted insulin has remained and influenced to decreasing blood glucose, and vi) non-diabetic hypoglycemia may be present that would be individualized due to clinical manifestation and possible diagnosis [15].

By taking udon noodles and tempura, she had hyperglycemia. Japanese food is characterized by its high carbohydrate content. The staple food is rice, and bread is also widely eaten. In this case, one pack of udon noodles contains 50-60g of carbohydrates, and then two bowls contain carbo 100-120g. If a healthy person eats this amount, blood glucose will show post-prandial elevation as 100-120 mg/dL [16]. When carbo 1g is ingested, blood glucose rises 1 mg/dL for healthy people, 3 mg/dL for T2D, and 5 mg/dL for T1D. From these, we have recommended the actual LCD tips as petite-LCD, standard-LCD, and super-LCD methods, where carbohydrate includes as 40%, 26%, and 12% of daily energy intake, respectively.

The exercise with jumping for 3 minutes seemed to be high-intensity training [17]. When it was performed during fasting, blood glucose did not decrease. In contrast, during hyperglycemia, the exercise contributed much for decreasing blood glucose. This fact would be beneficial for patient education. For those using CGM, they can at once take some exercise just after discovering hyperglycemia. It would be meaningful to make daily habit for exercising after meal. Similarly to time in range (TIR) ranging 70-180 mg/dL, the novel marker of time in tight range (TITR) ranging 70-140 mg/dL has been proposed. TITR means an ideal range narrower than TIR [18]. From CGM study among blood glucose, TIR and TITR (n = 22,006), many cases were classified into four groups. Compared with highest TIR and TITR group, the lowest glycemic variability was found as 23-30% of the glucose coefficient of variation (CV). It is indeed that TITR means too narrower glycemic range, but it will mean ideal range to maintain for anti-aging medicine in the future.

Some limitations may be present in the article. CGM has been used for evaluation for diabetic patients [19]. However, it is not enough for just examining, but behavioral modification based on the CGM data would be dispensable. In concrete, adequate advices of meal selection and instant exercise would be possible.

In summary, CGM will become more crucial apparatus for patients, caregivers and related people. Meaningful and effective application will be expected, because of obtaining precise data instantly. These continuation will lead to well-being in each person and welfare in the society.

Conflict of Interest

The authors declare no conflict of interest.

Funding

There was no funding received for this paper.

International Journal of Endocrinology and Diabetes