Introduction

Prediabetes is an early and inevitable stage of type 2 diabetes mellitus (T2DM) that is characterized by intermediate hyperglycemia, insulin resistance, and islet β malfunction [1]. Prediabetes affects 374 million people worldwide, with that number anticipating a rise to 454 million in 2030 and 548 million in 2045 [2]. A large clinical trial in China showed that prediabetic patients had a 93% high risk of acquiring T2DM after 20 years if no treatment was given [3]. T2DM causes a variety of health issues, such as diabetic neuropathy, diabetic nephropathy, diabetic retinopathy, and vascularity. T2DM patients have a nearly 3.46-fold higher medical cost than those without complications, implying a greater financial burden [4]. Therefore, effective preventive strategies for patients with prediabetes are urgently needed to reduce the global public health threat of T2DM.

In terms of lifestyle, exercise, diet, and weight loss have currently been recognized as the "golden" treatments for preventing T2DM [5]. A clinical investigation found that regular exercise and a balanced diet improved impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) in individuals with prediabetes from Malmö, the United States, and China [6]. Another Diabetes Prevention Program study found that individuals with prediabetes who made lifestyle modifications regained to normal IFG and IGT levels and had a 56% lower risk of develo** diabetes [7].

The glycated hemoglobin A1c (Hb1Ac) and HOMA indices are used to screen for glycemic status and β-cell function. Hb1Ac is commonly used as a monitoring indicator for diabetes control in clinic and reflects glycemic exposure in the previous 8 ~ 12 weeks [8]. There is a strong relationship between high Hb1Ac level and the risk of develo** diabetes-related complications [9]. Sustained Hb1Ac control was associated with significantly lower odds of being diagnosed with diabetes-related complications five years later [10]. Homeostasis model assessment (HOMA) indices, such as insulin resistance (HOMA-IR), insulin sensitivity (HOMA-IS), and β-cell function (HOMA-β), are often used to quantify β-cell function. In young sedentary female overweight college students, 12-week resistance training may change HOMA-IR and HOMA β [11]. Moreover, Rowan found that a 12-week fitness program that included resistance training, high-intensity interval training (HIIT), or continuous moderate-intensity training would reduce Hb1Ac in prediabetes by only 0.5% [12]. The reason might be related with insufficient physical activity [13]. A high quantity of moderate-intensity exercise and diet management over a 6-month period can significantly enhance oral glucose tolerance and prevent development to T2DM in older adults [14]. Whereas, it is not clear whether moderate-intensity endurance and resistance exercise combined with a MCCR diet can improve Hb1Ac levels and HOMA scores in young adults with prediabetes in a shorter period of time.

The purpose of this study was to compare 1) the effects of an eight-week high volume of moderate-intensity endurance plus resistance training combined with the MCCR diet on reversing Hb1Ac, fasting plasma glucose (FPG), and 2-h post-glucose (2 h-PG) levels, and 2) the effects of a short intervention program on HOMA indices in prediabetic subjects.

Materials and methods

Participants

Twenty-two obese adults between the ages of 18 and 30 (body mass indexes, BMI ≥ 28 kg/m2) from the Haoqian Weight loss training camp were divided into the intervention group (obesity and prediabetes; INT, n = 10) and control group (obesity and normoglycemia; CON, n = 12) based on the American Diabetes Association (ADA) prediabetes criteria [15]. All participants were familiarized with the testing procedures and completion of the entire experimental training sessions. In addition, they did not develop any injuries or illnesses that could have affected their training or test performance during the intervention period. Six participants dropped out of the intervention due to personal reasons (Fig. 1). The INT and CON groups were guided by the following criteria of ADA:

  1. 1)

    INT group: obesity (BMI ≥ 28 kg/m2) and prediabetes (5.6 mol/l ≤ FPG ≤ 6.9 mol/l and/or 7.8 mol/l ≤ 2hPG < 11.1 mol/l and/or 5.7% ≤ Hb1Ac ≤ 6.4%).

  2. 2)

    CON group: obesity ((BMI ≥ 28 kg/m2) and normoglycemia (FPG < 5.6 mol/l and/or 2 h-PG < 7.8 mol/l and/or Hb1Ac < 5.7%) [16] (Table 1).

Fig. 1
figure 1

Flowchart for recruitment

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Table 1 Individual criteria of ADA for prediabetes and diabetes
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The characteristics of the subjects are described in Table 2. BMI was significantly different in the INT and CON groups (p < 0.05). The study protocol followed the Chinese government's ethical guidelines prior to screening and recruiting. A clinical registration number in the study was ChiCTR2100050506. The epidemiological studies were conducted according to the Declaration of Helsinki and reviewed by the Ethics Committee of Wuhan Sports University. All individuals provided written informed consent.

Table 2 Characteristics of the participants
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Methods

Procedure

All subjects received 50 min/time of continuous exercise 5 times/day, 6 days/week for 8 weeks (30 times/week), including 24 aerobic exercise and 6 resistance exercise sessions. Each exercise was done three times a week. The overall time spent on aerobic and resistance exercises was 1200 min/week and 300 min/week, respectively. The workout schedule is detailed in Table 3. Individual tutoring was offered for these subjects under supervision. The Taisin Heart Rate Detection System (DL897) was used to assess heart rate and a rating of perceived exertion (RPE). Subjects must reach 40% ~ 70% of HRmax and be below the RPE score of 13. To guarantee the individuals' safety, the intensity of the exercise was matched to their physical condition.

Table 3 All exercise items of the subjects during intervention
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Participants in two groups were advised to follow a MCCR diet that included meat, shrimp, grains, legumes, vegetables, and fruits. MCCR diet plans were designed by a registered dietitian according to the American Diabetes Association's Complete Guide to Diabetes [17, 18]. They were instructed to eat three meals and two snacks (fruit and milk) per day, to count carbs using 20 g as a unit, and to maintain adequate protein levels. In addition, all participants were advised to consume approximately 220 g of carbohydrates per day and were not permitted to consume alcohol or sugary beverages. According to the Institute of Medicine Dietary Reference Guidelines, the macronutrient dietary composition of the MCCR diet was as follows: 40% ~ 50% from total energy of carbohydrates, 20% ~ 25% from total energy of protein, and < 30% of total energy from fat [19].

Body composition and circumference

All parameters were measured before and after the 8-week intervention during the clinical investigation days. Participants were required to take off shoes, socks, and coats and stand barefoot in the metal area of the X-Scan PLUS II body composition analyzer (JA-WON, Korea) for measuring body composition when they were in a fasting state. Non-stretching tape was used to measure the waist circumference, biceps brachii circumference, and thigh circumference of the participants while they were standing. The measuring tape is placed horizontally on the left side of the body at the hump point of the muscles biceps and left quadriceps to measure the biceps and thigh circumference.

Biomarkers

Blood samples were collected before 10 a.m. and refrigerated at -80 °C. An automated biochemical analyzer was used to measure total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-c), and low-density lipoprotein cholesterol (LDL-c) levels in the blood (Beckman Type Dx800). The glucose oxidase technique was used to assess FPG and 2hPG (the test kit was provided by Tian** ** prediabetes, a big waist circumference had the greatest direct effect in prediabetes among adults aged 50 years and older [35]. The benefits of diet control and exercise on physical function and body composition tend to be crucial for clinical interventions to prevent the development of T2DM in high-risk older adults [36]. Furthermore, 12 months of high-intensity progressive resistance training in older patients with T2DM enhanced skeletal muscle mass and lowered Hb1Ac levels [37], and the amount and frequency of exercise had a greater effect on Hb1Ac than the mode or intensity of exercise [38]. Exercise interventions in older adults with prediabetes require a number of considerations due to their declining physical conditions. According to the survey, 28% of older adults aged 53 were prediabetic, with 32% having physical functional limitation and 56% having lower extremity limitation [39]. As a consequence, exercise prescriptions for the elderly may need to be more personalized, emphasizing exercise volume and frequency over exercise mode and intensity. While moderate-intensity exercise is safe, older adults with T2DM should be medically screened before exercising and have their heart rates and blood glucose levels checked throughout prolonged activities to prevent mishaps.

According to our findings, the present prescriptions might be used to lower the occurrence of T2DM in prediabetic individuals by lowering body fat mass and reversing the Hb1Ac level. Significant effects on insulin and blood glucose were detected in the INT and CON groups, respectively, indicating that the short-term intervention program decreased insulin resistance. As a result, these findings have important implications for the selection of clinical intervention to prevent T2DM development in obese individuals at high risk. This is a pilot study of moderate-intensity, high-volume exercise and dietary restriction in young prediabetic patients enrolled in a weight-loss camp. The further studies will investigate the effects of exercise and dietary interventions on indices of prediabetes and explore association between the HOMA-β index and pancreatic cell function in a larger population of older obese adults.

Conclusion

The MCCR diet combined with an eight-week high volume of moderate-intensity endurance and resistance training is effective in reversing Hb1Ac and improving insulin sensitivity in young, obese adults with prediabetes.