Introduction

Type 2 diabetes (T2D) and obesity is a significant risk factor for atherosclerotic disease, particularly when visceral adipose tissue (VAT) accumulation is involved1,2. Elevated VAT levels have been associated with endothelial dysfunction, inflammatory markers, and incident cardiovascular disease3. This metabolic risk is evident even in patients with normal body weight4. Hepatic fat also contributes to cardiovascular risk and insulin resistance5,6.

Numerous interventions have been employed to manage obesity and T2D, with the objective of mitigating their complications2. However, certain drugs may pose potential dangers such as rosiglitazone for T2D and sibutramine for weight reduction in obesity7,8. Furthermore, the costs of medications and treating disease-related complications impose significant financial burdens in low- and middle-income countries9. Therefore, lifestyle and dietary changes remain fundamental recommendations in major practice guidelines for managing obesity and T2D. Lifestyle interventions have shown considerable efficacy in preventing and controlling T2D10,11. Demographic factors, dietary patterns and physical activity levels were found to be associated to abdominal obesity.. A previous study demonstrated that the risk of visceral fat decreased with an increased consumption of fruit and vegetable and decreased consumption of carbohydrate12. The Mediterranean diet, characterized by low in animal protein and saturated fats, high in fibers and antioxidants, and with an omega-3 to omega-6 fatty balance, has been suggested to be effective in the prevention and management of fatty liver13 with some supporting evidence for the management of abdominal fat14. However, adherence to Mediterranean diet cannot be demonstrated to have effect on the prevention or changes of abdominal obesity15. Among 13 clinical trials evaluated the effect of Mediterranean diet plus caloric restriction, only 3 of them demonstrated beneficial effect of the intervention group compared to the control group14. Some of these studies also included lifestyle modification mainly increased physical activity. They mentioned that the effect of diet pattern on visceral fat may be varied which is influenced by the degree of physical activity and age group of the study population12,14,15,16. Therefore, their impact on reducing cardiovascular risk requires further investigation17. Diet interventions, such as reducing high glycemic index (GI) carbohydrate consumption, implementing caloric control, and increasing vegetable and fruit intake, are effective in improving control of obesity and T2D and reducing complications10. Dietary changes and physical activity can also lower the risk of developing T2D and its complications18. A Korean study indicates that healthy subjects who are in the top 10th percentile of visceral fat had a higher risk of T2D and prediabetes with the Odds ratio of 15.919. Reduction in visceral fat and hepatic fat has been shown to be associated with the reduction in cardiovascular risk20,21.

The 3G rice used in this study is a blend of 3 rice varieties in a 1:1:1 ratio. It comprises 2 soft-cooked, whole grain, intermediate GI rice varieties (“Riceberry,” a high-antioxidant purple rice, and “Hom Malaiman,” an aromatic brown rice) and the low GI rice “Pink + 4” (a hard-cooked, fragrant white rice with high amylose content)22. This combination enhances the soft-fluffiness and the dietary fiber content of 3G rice when cooked. The GI of the rice, determined through tests conducted at the Food Innovation and Resource Centre, Singapore Polytechnic, Singapore, is 5223.

This research utilized magnetic resonance imaging (MRI) to evaluate the impact of diet intervention on visceral and hepatic fat, key indicators of cardiovascular risk, in patients with obesity or T2D.

Results

Study population

Out of 121 screened patients, 86 were randomized, with 43 individuals allocated to the diet intervention group and 43 to the usual diet group. During the study period, 6 patients from the usual diet group withdrew, and 1 patient was lost to follow-up. A total of 43 patients in the diet intervention group and 36 in the usual diet group completed the 12-week follow-up visit (Fig. 1). Their mean age was 47.5 ± 11.0 years (range 30–72 years), and 17.7% of the participants were male. Number of patients with obesity was 41 (95.3%) in diet intervention group and 40 (93.0%) in usual diet group. BMI was 30.1 ± 5.2 in the diet intervention group and 29.1 ± 4.0 in the usual diet group (p = 0.324).

Fig. 1
figure 1

CONSORT diagram of the study population.

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Table 1 details the baseline characteristics of patients in both groups. No significant differences were observed in their characteristics. Baseline hepatic fat was 7.9 ± 7.2% and baseline visceral adipose tissue was 12 629 ± 5819 mm2. Hepatic fat was classified as normal, mild, moderate, and severe in 51 (59.3%), 25 (29.1%), 4 (4.7%), and 6 (7.0%), respectively.

Table 1 Baseline characteristics of patients in the diet intervention and usual diet groups.
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Study outcomes

Table 2 displays the changes in clinical parameters, laboratory results, VAT area, and hepatic fat percentage between the baseline and 12-week follow-up visits for the 2 groups. Patients in the diet intervention group demonstrated significant reductions in body weight, BMI, waist circumference, VAT area, and hepatic fat percentage compared to the usual diet group. Figure 2 depicts the changes from baseline to 12 weeks in body weight, BMI, VAT area, and hepatic fat using vertical scattered plots. The diet intervention group exhibited a greater reduction in the primary outcome variables than the usual diet group (P < 0.001 for all).

Table 2 Changes in clinical parameters, laboratory values, and measurement outcomes of patients with diet intervention and usual diet.
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Fig. 2
figure 2

Scatter plot of changes from baseline to 12 weeks in (A) body weight (B) body mass index (BMI) (C) visceral adipose tissue (VAT) and (D) hepatic fat. Adjusted p-value for multiple comparisons at p < 0.025 for VAT and hepatic fat.

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Both groups experienced a significant reduction in body weight and BMI (Table 3). However, the extent of body weight reduction was greater in the diet intervention group than in the usual diet group (2.9 ± 2.6 vs. 0.8 ± 1.8 kg, P < 0.001; Table 2). Similarly, BMI reduction was greater in the diet intervention group (1.1 ± 1.0 vs. 0.3 ± 0.7 kg/m2, P < 0.001; Table 2). However, there was a significant reduction in VAT area and hepatic fat only in the diet intervention group. The diet intervention group showed a VAT area reduction of 1467.9 ± 1467.6 mm2, whereas the usual diet group exhibited a reduction of 179.4 ± 1575.7 mm2 (P = 0.001 for the difference between groups). The diet intervention group had a hepatic fat reduction of 1.6% ± 3.4%, while the usual diet group experienced an increase in hepatic fat of 0.4% ± 2.2% (P < 0.001). Figure 3 presents an example of a patient in the diet intervention group. It demonstrates significant changes in the VAT area and hepatic fat percentage.

Table 3 Comparisons of body weight, body mass index (BMI), visceral adipose tissue (VAT) area, and hepatic fat at baseline and 12 weeks in the diet intervention and usual diet groups.
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Fig. 3
figure 3

An example image presenting visceral adipose tissue (VAT) and hepatic fat changes of a patient in the diet intervention group with a significant reduction in VAT area and % hepatic fat (HF). Color scale indicates % hepatic fat. (A) baseline (B) after diet intervention.

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Linear regression analysis, adjusted for baseline data of each outcome, indicated that diet intervention was significantly associated with reductions in body weight, BMI, VAT area, and hepatic fat relative to the usual diet group. Figure 4A,B illustrates the effects of diet intervention on body weight, BMI, VAT, and hepatic fat percentage as a forest plot of adjusted differences between groups (diet intervention and usual diet) from multiple regression analysis.

Fig. 4
figure 4

Effect of diet intervention on body weight (BW), body mass index (BMI), body fat mass, visceral adipose tissue, and hepatic fat shown as a forest plot of adjusted differences between groups (diet intervention and normal diet) from multiple regression analysis. (A) adjusted for baseline (B) adjusted for baseline, age, sex, and body mass index. Adjusted p-value for multiple comparisons at p < 0.025 for VAT and hepatic fat.

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Comparison of physical activity levels of patients in diet intervention and usual diet group demonstrated that patients win the usual diet group had more duration of moderate intensity (89.9 ± 111.4 vs. 154.4 ± 125.1 min per week, p = 0.018), similar level of vigorous intensity (17.7 ± 36.5 vs. 19.0 ± 31.9 min per week, p = 0.871), and step count (5868 ± 3171 vs. 5341 ± 2694 steps per day, p = 0.434).

Sensitivity analysis

The sensitivity analysis on the interaction of obesity and diabetes on the study outcomes was to determine whether the effect of diet intervention on changes in visceral fat and hepatic fat was consistent for both obesity and T2D group or not. The results indicated that there was no significant interaction (interaction p = 0.854 for visceral fat change and p = 0.611 for hepatic fat change).

To assess the impact of the intervention, we compared the changes in the grading of hepatic fat. Specifically, we examined the proportion of patients in each group who experienced a reduction of at least 1 grade in VAT and hepatic fat. Among the 33 patients with abnormal hepatic fat at baseline (classes 2–4), 60% (12 patients) in the diet intervention group achieved a decrease of at least 1 class in hepatic fat, whereas only 7.7% (1 patient) in the usual diet group showed a similar improvement (P = 0.003).

We analyzed the percentage changes in the clinical outcome variables to determine whether the changes in body weight influenced those in the VAT area and hepatic fat. The results revealed that the percentage changes in VAT area and hepatic fat in the diet intervention group exceeded the percentage changes in body weight and BMI compared to the usual diet group (Table 4).

Table 4 Percentage change in selected parameters between patients in the diet intervention and usual diet groups.
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We performed additional analysis on the changes of visceral fat and hepatic fat with the adjustment of body weight change. The results showed that the effect of diet intervention on hepatic fat reduction remained significant with the adjusted reduction of − 2.51% (− 3.95 to − 1.07%), p = 0.001 and borderline significant for visceral fat reduction, − 654 mm2 (− 1354 to 46 mm2), p = 0.067.

We also analyzed the data on actual caloric intake and composition at baseline 12-week and changes. The results are shown in Table 5. Patients with diet intervention had a significant reduction in total calories as well as calories from carbohydrate and fat but the calories from protein significantly increased.

Table 5 Data on actual caloric intake and composition at baseline 12-week and change from baseline to 12-week.
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Compliance and satisfaction with diet intervention

Compliance with the diet intervention was assessed through a questionnaire. The results revealed that 32.6% (14 patients) reported 100% compliance without consuming extra snacks, 60.5% (26 patients) achieved ≥ 90% compliance, and 83.7% (36 patients) achieved ≥ 80% compliance.

Satisfaction with the diet intervention was also evaluated via a questionnaire. The participants rated various aspects on a scale from 1 to 5, with 5 indicating the highest level of satisfaction and 1 indicating the lowest. Participants expressed satisfaction with the diet intervention. Specifically, they rated it favorably in terms of health benefits (4.3 ± 0.6), color (4.1 ± 0.8), appearance (4.0 ± 0.8), odor (4.0 ± 0.6), taste (4.0 ± 0.8), cleanness (4.0 ± 0.8), amount (3.8 ± 0.9), diversity (3.6 ± 0.7), and softness (3.6 ± 1.0).

Discussion

This is a randomized clinical study comparing diet intervention with usual diet for 12 weeks. Low caloric diet was applied in both groups. The 12-week diet intervention resulted in greater visceral and hepatic fat reductions than those in the usual diet group. Additionally, patients in the diet intervention group experienced larger body weight, BMI, and total body fat mass reductions than those in the usual diet group. While patients in the usual diet group experienced significant reductions in body weight and BMI, there was no corresponding significant decrease in their VAT and hepatic fat. Despite the greater body weight reduction in diet intervention group, the main results on the reduction of hepatic fat and VAT were mainly preserved after the adjustment of body weight change.

Numerous studies have highlighted the link between visceral fat, hepatic fat, and cardiovascular disease3,4,24. Increased levels of VAT and hepatic fat can lead to endothelial dysfunction25 and elevated inflammatory markers26, contributing to atherosclerotic disease1,6. These effects are particularly pertinent in Asian populations. Previous research has shown that increased VAT is associated with metabolic risk factors in the Japanese population, even among individuals with normal body weight4. Moreover, the prevalence of abdominal obesity in Asian Indians is approximately 70%, which exceeds the prevalence of obesity defined by BMI27. At any given BMI, Asian Indians tend to have more abdominal obesity, insulin resistance, hyperinsulinemia, hypertension, and diabetes than Caucasians26,28.

Adopting a healthy diet and engaging in physical fitness can promote reductions in body weight and visceral fat16. The Mediterranean diet, rich in fiber from fruits, vegetables, legumes, and whole grains while limiting foods high in saturated and trans fats (e.g., fatty meats and highly processed foods), has been associated with lower abdominal fat gain over 10 years in the Spanish population29. However, the impact of the Mediterranean diet on the incidence of abdominal obesity remains inconclusive. The AdolesHealth study on European adolescents indicated that adherence to the Mediterranean diet did not influence waist circumference or body fat changes based on bioimpedance measurements15. A systematic review assessing the effects of the Mediterranean diet on central obesity demonstrated that 13 out of 18 studies showed a significant reduction in central obesity14. The explanation for the inconsistent results of healthy diet on VAT among many studies may be related to the characters and age group of study population, type of intervention, and degree of physical activity. Our study included participants with obese or T2D and record their physical activity. We tested the interaction of obese and T2D on study outcome and showed that there were no significant interactions. Therefore, the results of our study indicate the health benefit of diet intervention based on a low glycemic index, high fiber and low sodium. Mediterranean diet that is claimed to be rich in fiber had the fiber content of approximately 14 g per 100 kcal30 which is equivalent to the fiber in the food tat we provided to the participants in the diet intervention arm. Diet with high fiber promote benefits in the reduction of risk of T2D, visceral fat, gut microbial variability, and reduction of systemic inflammation31. Based on the result of a previous study, daily sodium content of the Mediterranean diet32 is higher than the sodium content of diet intervention arm in our study. Besides, the low glycemic index carbohydrate used in the diet intervention group of our study promote the health benefits of patients with obesity and T2D33.

We analyzed the percentage change in clinical outcomes to examine whether the reduction in VAT area and hepatic fat could be attributed solely to changes in body weight. The results indicated that the diet intervention group exhibited a more substantial percentage change in VAT area and hepatic fat than the percentage change in body weight and BMI seen in the usual diet group. This finding suggests that the diet intervention had a more pronounced effect on reducing VAT and hepatic fat beyond weight reduction alone. Besides, we performed additional analysis on the changes of visceral fat and hepatic fat with the adjustment of body weight change. The results showed that the effect of diet intervention on hepatic fat and VAT reduction remained the similar.

It is crucial to emphasize that obesity treatment should not solely focus on weight reduction. Instead, equal attention should be given to reducing visceral and hepatic fat, as they are associated with cardiovascular disease to a greater extent than BMI and other types of adipose tissue24,34. Our study demonstrated that while there was a reduction of − 0.8 ± 1.8 kg in body weight in the usual diet group, it did not lead to a significant decrease in VAT and hepatic fat. Conversely, the diet intervention group showed greater reductions in hepatic and visceral fat alongside weight reduction than the usual diet group. This disparity might be due to a need for more substantial weight loss to observe significant effects on visceral and hepatic fat. An alternative explanation could be that 3G rice has additional beneficial effects on individuals’ metabolic profiles beyond weight reduction alone. Further research is warranted to verify this concept and provide conclusive evidence on the effect of specific diets on VAT and hepatic fat reduction. We believed that nutritional counseling may have some impact on weight reduction since participants in usual diet group.

Mediterranean diet has a high proportion of nuts, legumes, olive oil, fruit and vegetables, cereals, fish, monounsaturated fatty acid/saturated fatty acid (MUFA:SFA) ratio, moderate consumption of dairy products and wine, and low consumption of meat and meat products35. It has been shown that Mediterranean diet is associated with a reduction in cardiovascular risk and a lower rate of mortality in patients with cardiovascular disease36. 3G rice has been developed with the purpose on the low glycemic property23. Besides, it has the antioxidant property and the softness in the texture22. Due to the high fiber content of Mediterranean diet and 3G rice, the absorption of glucose is lower and slower. Low glycemic index is the main action of benefit of 3G rice. The main glucose benefit of the Mediterranean diet is by the improvement of insulin sensitivity35. In fact, the component of the Mediterranean diet may be low glycemic index or high glycemic index which has differential effect on the glucose absorption37. Since some components of Mediterranean diet are limited availability in many Asian countries and are considered costly. Moreover, alcoholic intake using wine is restricted in many Asian groups. 3G rice may be more suitable in population who live in the countries with rice is the main component of carbohydrate in the diet.

Intermittent fasting is another method of diet intervention in patients with obesity or T2D38,39. The benefit of intermittent fasting is related to the benefit on the weight reduction. However, it is difficult to maintain in the long time39. In an meta-analysis, intermittent fasting can reduce body weight and BMI compared to control and compared to caloric restriction. Intermittent fasting but did not significantly affect fat mass, lean body mass, visceral fat, insulin, HbA1c, lipid profiles or blood pressure38. It has benefit on fasting glucose when compared to control but no benefit when compared to caloric restriction38. Moreover, recent study link intermittent fasting with a 91% increase risk of cardiovascular death40. Therefore, we believed that 3G rice with caloric restriction would be suitable for the countries where rice is the main resource of carbohydrate.

Several limitations should be considered in interpreting the study results. First, we only reported intermediate-term results after 12 weeks of diet intervention. Consequently, there are no data on the intervention’s long-term effects. Second, the study did not demonstrate the effects of diet intervention on traditional cardiovascular risk factors, such as serum glycemic levels or lipid profiles. These effects might need more extended follow-up periods to be observed. Third, participants in the usual diet group also experienced significant reductions in body weight and BMI, possibly influenced by the nutritionists’ diet and exercise education during the study period. However, the diet intervention group showed larger body weight and BMI reductions than the usual diet group. It seems to be a limitation that the control group only is subjected to a relatively limited intervention. We realized that the study could be performed by the assessment of the intervention in all patients without the control group. But we intended to have the control group for the comparative purpose and for the demonstration of the effect of intervention in comparison to usual diet. Fourth, the drop-out rate in the non-intervention group was 7 in the usual diet group (16%) vs none in the intervention group (0%). The drop-out in the usual diet group might be related to their expectation to receive diet intervention from randomization. When they were randomized into usual diet group, their willingness to remain in the study is lost. We also analyzed the data of the participants who withdrew from the study or lost to follow-up and found that the demographic and baseline data were similar to the main study population. Therefore, the drop-out should not have much effect on the results of the study. Fifth, the benefit of diet intervention group is not only from 3G rice. Diet intervention also include high fiber, low sodium diet, increased consumption of fruits and vegetables and a negative caloric balance. So there are multiple interventions towards reduction of VAT and hepatic fat. Sixth, female accounts for 82.3% of the study population which may limit the generalizability of the findings. Seventh, we provided diet for the diet intervention group but the food was provided to the usual diet group. We believed that participants who were randomized to usual diet group should continue taking their own usual diet. If we try to provide diet to the usual diet group it might not reflect the usual diet. However, we have recorded food intake in the food diary before and during the study period in the control arm and record the extra food intake in the intervention arm. We also analyze the food content and caloric intake of both groups before and during the study. Finally, there might be discrepancy in behavior could be influenced by participants’ expectations of being assigned to the diet intervention group, potentially introducing bias in the behavior of the usual diet group participants.

In conclusion, the 12-week diet intervention effectively reduced VAT, hepatic fat, body weight, and BMI compared to the usual diet. While the usual diet group also experienced a significant reduction in body weight and BMI, it did not show a corresponding reduction in VAT and hepatic fat. Notably, the diet intervention group achieved greater body weight and BMI reductions than the usual diet group. These findings underscore the importance of addressing visceral and hepatic fat reduction alongside weight reduction in the management of obesity and its associated cardiovascular risks.

Materials and methods

Study population

The study included patients aged 30–80 with obesity or T2D. We studied subjects with age between 30 and 80 based on the increased risk of visceral and hepatic fat increased after age 30 and continue to the 7th decade of 200% in male and 400% in female41,42. The exclusion criteria were as follows: (1) current or recent hospitalization within the past 3 months; (2) allergy to 3G rice or its components; (3) regular consumption of 3G rice or related products; (4) chronic kidney disease stage IV–V; (5) pregnancy or breastfeeding; and (6) inability to comply with the study protocol, such as inaccurately recording food diaries. The Institutional Review Board of Siriraj Hospital authorized the study protocol (approval number Si 778/2021). The trial was registered with the Thai Clinical Trials Registry (registration number TCTR20211207003; 07/12/2021). Prior to participation, all individuals provided written informed consent. The methodology was this study was in accordance with the principles set forth in the Declaration of Helsinki and the International Conference on Harmonization for Good Clinical Practice Guidelines. Sample size was calculated from a previous study43 the expected reduction in visceral fat of − 16 ± 2 cm2 in intervention arm and − 5 ± 3 cm2 in usual diet arm. The assumption was based on the power of 90% and a significant level at 0.05. The enrollment started January 2022 and the follow-up was conducted through January 2023. The trial was stopped after complete the funding period.

Due to differing associations between body mass index (BMI) and health risks in Asian populations compared to Europeans, this study adopted the obesity definitions for Asians recommended by the International Obesity Task Force in 2000. “Overweight” was defined as a BMI ≥ 23 kg/m2, and “obesity” was defined as a BMI ≥ 25 kg/m2,44,45.

Study protocol

After providing informed consent, each participant underwent 2-week screening process to assess the ability to record the food diary and whether the participant can comply with the study protocol. The instructions were given for recording a food diary to assess individuals’ ability to track food intake. Patients had to record food diary of 3 days (2 days during Monday to Friday and 1 day from Saturday or Sunday). Within 2 weeks after the screening visit, patients were randomized by the nQquery Advisor 6.01 (Statistical Solutions Ltd., Saugus, MA, USA) into 2 groups: a “diet intervention” group and a “usual diet” group. Random allocation sequence was kept by a research assistant as the sequential numbered code that could not be reached by the research nurse and investigators. The research nurse explains the study to the participants, enroll and consent, and assign the participants to the intervention.

Diet intervention

Participants in diet intervention group received food with 3G rice from investigators. The food was delivered to the participants on a daily basis. Patients in the usual diet group have to consume their own food based on white rice. However, nutritional counseling was provided in both groups. Negative caloric balance was applied in both groups which is included in the provided food in the diet intervention group and included in the nutritional counseling in usual care group.

The total daily caloric intake prescribed for each participant was personalized. The caloric requirement calculations were based on the recommendations of the Dietary Reference Intake for Thais (year 2020) and considered an individual’s age, sex, body weight, and daily activity level46. The carbohydrate to protein to fat ratio was maintained at 45–50:20–30:20–35, with a minimum daily protein intake of 1.2 g/kg of body weight and at least 14 g of fiber per 1000 cal. With obese patients, the goal was to achieve a daily negative energy balance of 400–500 kcal46,47.

Participants in the diet intervention group were instructed to consume only the food prescribed by the investigators. The intervention involved a carbohydrate-based dietary product named “3G rice,” a mix of 3 rice varieties with a combined GI of 5223. Additionally, they were requested to limit snacks to less than 100 kcal daily. An investigator (WT) calculated the caloric requirement of each patient and instructed the product preparation team on the corresponding personalized meals. A daily meal package was delivered to the diet intervention participants once daily.

Participants in the usual diet group received standard diet and healthy lifestyle education. It included information on a diet with low cholesterol, low sugar, and low salt and instructions on maintaining a negative caloric balance for overweight or obese patients. However, the participants did not receive food provisions. The diet suggestions were based on the food consumption recommendations of the Dietary Reference Intake for Thais46.

Both groups received basic diet education and weight reduction education for obese patients. A nurse from the research team made telephone contact every 2 weeks with participants in the 2 groups to inquire about the weekly food intake and provide diet education. In the case of the diet intervention group, the nurse also monitored the degree of compliance with the intervention, and recorded the type and number of extra snacks.

The food diary record was a self-reported account of all foods and beverages consumed by each participant over 3 consecutive days. These data were analyzed with INMUCAL Nutrients software (version 4.0; Mahidol University, Bangkok, Thailand) to determine the quantities of various food components. The food diary data were analyzed at baseline (during screening and before randomization), at 6 weeks, and upon program completion (12 weeks after randomization).

Nutritional counseling

The nutritional counseling of the usual diet group contains the content of diet sugar control, increase consumption of vegetable and fruit, and the instruction for a weight reduction of 5–10% or negative caloric balance of 400–500 kcal for those who are overweight or obese (99% of the study population were overweight or obese) with the information on daily caloric requirement. The participants need to arrange the diet for their own.

The nutritional counseling for the diet intervention group provides a similar instruction as in the usual diet group plus but the investigators made the diet and send to the participants on daily delivery focus on high fiber low salt, and negative caloric balance of 400–500 kcal. The caloric requirement calculations were based on the recommendations of the Dietary Reference Intake for Thais (year 2020)46 and considered an individual’s age, sex, body weight, and daily activity level.

Image acquisition

Images for VAT assessment

We utilized the Philips Ingenia 3 T 3D 2-point Dixon gradient echo volumetric interpolated breath-hold examination technique in breath-hold mode. The acquisition sequence settings were as follows: axial plane matrix size, 400 × 352; resolution, 1 × 1 mm2; repetition time, 5.2 ms; echo time (TE) 1, 1.96 ms; TE2, 3.3 ms; number of slices, 5; slice thickness, 5 mm; distance factor, 10%; section gap, 0.5 mm; and acquisition time, 16 s. The acquisition focused on the intervertebral disk between lumbar vertebrae levels L2 and L3, covering the region from mid-L2 to mid-L3.

Images for hepatic fat assessment

The mDIXON Quant method utilized a 6-echo 3D gradient echo sequence with the following parameters: repetition time, 10 ms; TE1, 7.5 ms; ΔTE, 1.25 ms; fly back, none; echo train length, 6; water fat shift, 0.309 pixels; field of view, 400 × 350 mm; acquisition matrix size, 1.75 × 1.75 mm; reconstruction matrix size, 0.78 × 0.78 mm; slice thickness, 2.5 mm; and total acquisition time, 19 s. To avoid T1 saturation, a very low flip angle of only 3° was applied.

Image analysis

Visceral fat image analysis was performed using ImageJ software (version 1.53 k; National Institutes of Health, Bethesda, MD, USA). The adipose area was semiautomatically obtained after contour drawing with the automatic thresholding method, and the area was provided in square millimeters (Supplementary Fig. 1). The areas of superficial subcutaneous adipose tissue, deep subcutaneous adipose tissue, and VAT were averaged for 3 slices obtained from the same acquisition images.

The hepatic fat analysis utilized the 3-point IDEAL Dixon method and was quantified with semiautomatic Hippo Fat software. The hepatic fat percentage was calculated using the following formula:

$$Hepatic\, fat \,percentage = \frac{{SI_{fat} }}{{SI_{fat} + SI_{water} }} \times 100$$

where SIfat and SIwater represent the averaged signal intensity on the reconstructed fat and water images, respectively. Images were independently analyzed by 1 radiological technologist with more than 10-year experience blinded to the intervention group who documented the percentage of fat in all 8 hepatic segments using a circular region of interest of 200–300 mm2 in area. A larger region of interest (800–1600 mm2) was obtained for the right and left lobes of the liver. Care was taken to select only representative regions while avoiding blood vessels or regions with artifacts.

Record of physical activity

We recorded physical activity by Mi Smart Band 6 (Xiaomi Communications Co., Ltd., Hefei City, China) for the whole duration of the study. The heart rate data was recorded every minute. We calculated the duration that participants spend on moderate and vigorous intensity based on the recommendation of ESC in the 2021 ESC cardiovascular prevention guideline (moderate and vigorous intensity = heart rate 64–76% and > 76% of predicted maximal heart rate, respectively)48. Step count per day was also recorded.

Data collection

The following data were collected at baseline and after 12 weeks of diet intervention: age, sex, body weight, height, BMI, waist circumference, blood pressure, and heart rate. Clinical laboratory tests included fasting plasma glucose, hemoglobin A1C, lipid profile, alanine aminotransferase, serum creatinine, electrolyte levels, and serum uric acid.

Outcomes

The primary outcomes, evaluated at the 12-week mark of the diet intervention, were changes in VAT area and percentage of hepatic fat. Secondary outcomes were changes in body weight, BMI, and blood chemistry.

Statistical analysis

Descriptive statistics were analyzed and presented as the means and standard deviations for continuous data and numbers and percentages for categorical data. Continuous data were compared using Student’s t-test for unpaired data, while categorical data were analyzed using the chi-square or Fisher’s exact tests. Paired t-tests were used to compare changes in the primary and secondary outcome variables between baseline and 12 weeks. The association between the intervention and primary outcomes was assessed using a linear regression model adjusted for the baseline results of each outcome. Similar analyses were conducted for the associations between the intervention and body weight or BMI.

Sensitivity analysis was performed by (1) analyzing the interaction of obesity and diabetes on the study outcomes, (2) analyzing the percentage changes in clinical outcomes to determine whether changes in body weight explained the changes in VAT area and hepatic fat, and (3) comparing changes in hepatic fat grades at 12 weeks relative to baseline. Hepatic fat was graded as class 1 (“normal”; < 6.4%), class 2 (“mild”; 6.4%–17.4%), class 3 (“moderate”; (17.4%–22.1%), and class 4 (“severe”; ≥ 22.1%)49. The use of threshold of 6.4% was based on the result of a previous study comparing percentage of hepatic fat compared to histopathology49. The threshold of 6.4% had 86% sensitivity and 83% specificity to diagnose grade 1 or higher steatosis compared to the histopathology. Sensitivity analysis based on VAT grading was not performed due to the lack of a universally accepted grading system for visceral fat. We also performed additional analysis to determine whether the effect of diet intervention on visceral fat and hepatic fat change independent on body weight change by adjusting the effect of diet intervention on outcomes adjusting for body weight change.

The analyses were performed using IBM SPSS Statistics (IBM Corp, Armonk, NY, USA). P values < 0.05 were deemed statistically significant. The p-values were adjusted for multiple comparison testing for the analysis between groups (diet intervention vs. usual diet) of these two outcomes (VAT and hepatic fat) with the use of significant p-value at p < 0.025.