Diabetes mellitus (DM), particularly type 2 diabetes (T2DM), is a growing global health concern, with a dramatic increase in prevalence in China. T2DM is strongly linked to insulin resistance (IR) and obesity, especially central obesity, which is characterized by excessive visceral fat accumulation. While genetic factors contribute, dietary factors play a crucial role in obesity and T2DM development. Traditional dietary studies often focus on individual nutrients, neglecting the complex interactions of foods within dietary patterns. This study aimed to identify major dietary patterns in middle-aged Chinese adults (40-65 years) and assess their association with body fat distribution, IR, and DM. The rapid socio-economic changes in China have significantly altered dietary habits and lifestyles, underscoring the importance of understanding these relationships within the current context. The prevalence of diabetes was significantly higher in overweight and obese individuals, and higher yet in those with central obesity. Visceral adipose tissue releases more proinflammatory and proatherogenic factors than subcutaneous adipose tissue, leading to oxidative stress and IR. Previous research suggests associations between dietary patterns (particularly Western-style diets) and weight gain, but few studies have examined the link between dietary patterns and body fat distribution. This research aims to address this gap, employing dietary pattern analysis to examine the cumulative effects of combined food items on health outcomes.

Existing literature highlights the complex interplay between dietary habits and the risk of developing type 2 diabetes mellitus and central obesity. Studies have shown a protective effect of high fruit and vegetable consumption against these conditions, likely due to the high fiber content and low glycemic index of these foods, and their potent antioxidant properties. Conversely, Western dietary patterns, characterized by high fat, high energy density, and low fiber, have been consistently linked to an increased risk of glucose intolerance and obesity. The role of specific food groups like red meat, rice, eggs, and seafood in relation to diabetes and obesity remains inconclusive, with studies reporting conflicting findings. These inconsistencies may be attributable to variations in cooking methods, portion sizes, accompanying dietary elements, and genetic differences across populations. This study aims to further investigate these relationships within the context of the changing dietary habits in the Chinese population.

A population-based cross-sectional study was conducted from March to May 2010 in Caihe communities, Hangzhou, China. A total of 1432 Han Chinese participants aged 40-65 years were included, excluding those with a history of stroke, ischemic heart disease, or pre-existing DM. Ethical approval was obtained, and informed consent was secured from all participants. Data collection involved questionnaires assessing demographic information, lifestyle factors (smoking, alcohol consumption, physical activity), and a validated semi-quantitative food frequency questionnaire (FFQ) with 81 items covering 21 food groups. The FFQ assessed food intake frequency over the previous four weeks. Laboratory measurements included a 75g oral glucose tolerance test (OGTT) to diagnose DM, along with serum glucose, insulin, lipid profile (triglycerides, total cholesterol, HDL-c, LDL-c), and glycosylated hemoglobin A1c (HbA1c). Anthropometric measurements encompassed BMI, waist circumference (WC), hip circumference, waist-to-hip ratio (WHR), body fat percentage (Fat%), blood pressure, and visceral fat area (VFA) and subcutaneous fat area (SFA) via MRI. DM was diagnosed based on WHO criteria (fasting glucose ≥7 mmol/L or 2-h glucose ≥11.1 mmol/L), and central obesity was defined as VFA ≥ 80 cm². Factor analysis (principal component with varimax rotation) was used to identify dietary patterns. Statistical analysis included descriptive statistics, Pearson's χ² test, Student's t-test, correlation analysis, linear regression, and multivariate logistic regression to assess the associations between dietary patterns and the outcomes (HOMA-IR, VFA, DM, central obesity). SPSS version 16.0 was used for all analyses, with p<0.05 considered statistically significant.

The study identified four major dietary patterns: vegetable-fruits, rice-meat, seafood-eggs, and sweet-fast. The vegetable-fruits pattern, characterized by high consumption of vegetables, fruits, beans, and whole grains, showed a significant inverse association with HOMA-IR (p<0.001 in both genders) and VFA (p=0.029 in males, p=0.017 in females). After adjusting for confounders, participants in the highest tertile of this pattern had a significantly lower risk of DM (OR: 0.30, 95% CI: 0.13–0.70 in males; OR: 0.28, 95% CI: 0.11–0.72 in females) and a lower risk of central obesity in males (OR: 0.50, 95% CI: 0.29–0.86). In contrast, the sweet-fast food pattern, high in fast foods, desserts, and beverages, was positively associated with HOMA-IR (p=0.002 in males, p<0.001 in females) and VFA (p<0.001 in males). Participants in the highest tertile of this pattern had a significantly higher risk of DM (OR: 2.58, 95% CI: 1.23–5.88 in males) and central obesity (OR: 2.85, 95% CI: 1.67–4.86 in males). No significant associations were found between the rice-meat or seafood-eggs patterns and the outcomes. The associations between dietary patterns and outcomes appeared stronger in males than females.

The findings support the hypothesis that dietary patterns are significantly associated with IR, DM, and central obesity in a middle-aged Chinese population. The protective effect of the vegetable-fruits pattern aligns with previous research emphasizing the benefits of high fruit and vegetable intake for metabolic health. The detrimental effects of the sweet-fast pattern underscore the negative impact of consuming energy-dense, nutrient-poor foods high in added sugars. The lack of association found for the rice-meat and seafood-eggs patterns suggests that the effects of red meat, rice, eggs, and seafood on metabolic health are likely context-dependent and influenced by other dietary components and lifestyle factors. The stronger associations observed in males compared to females warrant further investigation into potential gender-specific physiological responses to dietary patterns. These findings have significant implications for public health interventions aimed at preventing DM and obesity in China. Promoting healthy dietary patterns rich in vegetables and fruits, while reducing the consumption of processed foods, sweetened beverages, and fast food, are crucial for improving metabolic health.

This study provides valuable insights into the relationships between dietary patterns and the risk of DM and central obesity in middle-aged Chinese adults. A vegetable-fruits-rich diet is associated with a reduced risk, while a diet high in sweet and fast foods increases the risk. The findings highlight the importance of promoting healthy dietary habits as a key strategy for preventing these prevalent metabolic disorders in China. Further research is needed to explore the gender-specific differences and potential underlying mechanisms. Larger, longitudinal studies are warranted to confirm the causal relationships and establish the long-term effects of these dietary patterns.

The cross-sectional design limits the ability to establish causality. The use of factor analysis involves subjective decisions, and residual confounding may exist despite adjusting for several covariates. The sample was restricted to a specific region in China, limiting the generalizability of the findings. The study's power might be limited for stratified analysis by gender, and the findings may not apply to other age groups or populations.