Breast cancer remains the most prevalent cancer among women worldwide, with approximately 2.3 million new cases diagnosed in 2020, accounting for about 12% of all cancer cases (1). In Saudi Arabia, the incidence of breast cancer has been alarmingly increasing, with 3,954 new cases reported in 2020, making it the most commonly diagnosed cancer among women in the country (2). The age-standardized incidence rate (ASIR) reached 28.8 cases per 100,000 population in 2020, reflecting a significant public health challenge (3). The rising incidence, particularly in low- and middle-income countries, underscores the urgent need to identify modifiable risk factors for prevention. Diet, a critical modifiable factor, influences cancer risk through mechanisms such as inflammation, oxidative stress, and hormonal regulation (4). Diet quality scores, which evaluate adherence to healthy dietary patterns, provide a comprehensive approach to studying these effects compared to single-nutrient analyses.

The global burden of breast cancer stems from both non-modifiable factors, such as genetics, and modifiable factors, like lifestyle (5). While genetic mutations (e.g., BRCA1/2) account for 5%–10% of cases, most breast cancers are sporadic, suggesting environmental influences (6). Early dietary research focused on nutrients like fats or antioxidants, but inconsistent findings—such as null associations between saturated fat and breast cancer risk shifted focus to dietary patterns (7). Diet quality indices, such as the Healthy Eating Index (HEI-2015), Mediterranean Diet Score (MDS), and Diet Quality Index-International (DQI-I), evaluate overall diet based on fruits, vegetables, whole grains, and limited processed foods (8). These scores, adaptable to regional diets, are linked to reduced chronic disease risk, including breast cancer, especially in postmenopausal women (9).

Physiologically, high-quality diets provide bioactive compounds like polyphenols and fiber, which reduce inflammation and oxidative stress, key carcinogenic drivers (10). Fiber lowers circulating estrogens, potentially reducing hormone receptor-positive breast cancer risk (11). Conversely, prime quality diets high in processed meats and sugars promote inflammation and insulin resistance, increasing risk (12).

Research on diet quality and breast cancer risk shows varied findings, particularly when considering menopausal status and tumor subtypes. The GDQS, a relatively new tool, evaluates overall dietary patterns by emphasizing nutrient dense foods, such as fruits, vegetables, and lean proteins, and penalizing harmful components like processed items and excessive fats (13). A study by Bromage et al. (14) introduced the GDQS, highlighting its utility in assessing diet quality across diverse populations. Similarly, the PDQS focuses on optimal eating patterns for chronic disease prevention, prioritizing whole foods and limiting refined sugars and unhealthy fats (15, 16).

This case-control study aims to investigate the association between global and prime diet quality scores and the risk of breast cancer.

Table 1 summarizes the baseline characteristics and dietary intakes of participants in the breast cancer (n = 125) and control (n = 250) groups. There were no significant differences between the two groups in terms of age, BMI, physical activity, marital status, or smoking history (p > 0.05 for all). However, a significantly higher proportion of breast cancer patients reported a family history of breast cancer compared to controls (11.2% vs. 3.6%, p = 0.026). There were no significant differences in energy or carbohydrate intake between the groups. However, the breast cancer group had lower protein (72.2 ± 13.2 vs. 83.1 ± 14.8 g/day; p = 0.024) and fiber intake (16.8 ± 2.4 vs. 20.8 ± 3.2 g/day; p = 0.037), but higher fat intake (68.1 ± 8.3 vs. 58.2 ± 8.1 g/day; p = 0.041) compared to controls.

The results of Table 2 comparing food group intake and diet quality indices between 125 breast cancer patients and 250 healthy controls revealed statistically significant differences in dietary patterns. Breast cancer patients had a significantly lower total GDQS (p = 0.002) and total PDQS (p < 0.001), indicating a greater deviation from optimal dietary patterns. In terms of food consumption, patients consumed significantly lower amounts of protective foods, including dark leafy vegetables (p = 0.002), other vegetables (p = 0.004), other fruits (p = 0.041), legumes (p = 0.021), fish and shellfish (p = 0.003), and poultry (p = 0.040). In contrast, intake of refined grains and baked products (p = 0.003), sugar-sweetened beverages (p < 0.001), fried foods (p = 0.003), and sweets/ice cream (p = 0.002) was significantly higher among patients. No significant differences were observed for citrus fruits, orange-colored fruits, cruciferous vegetables, nuts, whole grains, oils, red meat, processed meats, eggs, or dairy products.

Table 3 presents an analysis of the relationship between diet quality scores and breast cancer risk, revealing significant inverse associations. After adjustment for age, BMI, physical activity, energy and nutrient intake, family history, and smoking, higher total GDQS demonstrated a strong protective effect. Participants in the highest tertile (T3) of total GDQS had substantially lower risk of breast cancer compared to the lowest tertile (T1) [Adjusted OR (aOR) = 0.397; 95% CI: 0.279–0.653; P-trend <0.001]. Similarly, higher Positive GDQS (reflecting healthy components) were associated with significantly reduced risk in T3 (aOR = 0.413; 95% CI: 0.281–0.711; P-trend <0.001). A significant protective trend was also observed for higher total PDQS (aOR for T3 = 0.455; 95% CI: 0.309–0.761; P-trend = 0.003). In contrast, Negative GDQS and Unhealthy PDQS showed no statistically significant association with risk after adjustment (P-trend = 0.263 and P-trend = 0.374, respectively). Healthy PDQS exhibited a non-linear relationship, with only the highest tertile (T3) showing significant risk reduction versus T1 (aOR = 0.575; 95% CI: 0.363–0.932; P-trend = 0.040).

This case-control study conducted at Shaqra General Hospital provides critical insights into the association between diet quality, assessed using the GDQS and PDQS, and breast cancer risk among women aged 30 years or older. The findings demonstrate that higher adherence to both GDQS and PDQS significantly reduces the risk of breast cancer.

The significant differences in dietary patterns between cases and controls underscore the protective role of specific food groups. Controls consumed higher amounts of fruits, dark green leafy vegetables, legumes, and poultry, while cases reported greater intake of refined grains, processed meats, sugar-sweetened beverages, and fried foods. These patterns are consistent with studies linking Plant-based, nutrient-rich diets can reduce breast cancer risk by decreasing exposure to carcinogenic compounds and increasing intake of beneficial phytochemicals and fiber (20). A 2013 study found that diets high in vegetables and low in processed foods were associated with a 15% lower breast cancer risk, supporting the current findings (21). The significant ORs for favorable GDQS components (OR = 0.235; 95% CI: 0.103–0.533) and healthy PDQS sub-scores (OR = 0.397; 95% CI: 0.185–0.854) indicate that nutrient-dense foods are the primary drivers of protection, though reduced consumption of detrimental foods also contributes (unfavorable GDQS: OR = 0.432; 95% CI: 0.249–0.750). The higher dietary fiber intake in controls aligns with evidence that fiber-rich foods, such as legumes and vegetables, lower breast cancer risk by reducing circulating estrogen levels, a key factor in hormone receptor-positive tumors (22). Conversely, the elevated fat intake in cases, particularly from processed sources, supports findings linking high-fat diets to increased tumorigenesis through metabolic dysregulation and chronic inflammation (23).

Physiologically, high-quality diets mitigate inflammation and oxidative stress, both implicated in breast cancer development (24). Fiber, abundant in the control group’s diet, reduces estrogen levels by binding bile acids and promoting fecal excretion, potentially lowering hormone-driven breast cancer risk (25). Lower intake of processed meats and sugar-sweetened beverages in controls may also decrease insulin resistance and pro-inflammatory cytokines, which are linked to elevated breast cancer risk (26). A 2021 study reported that high-fiber diets reduced inflammatory markers like C-reactive protein in women, supporting these mechanisms (27). The consistency of our findings with these studies suggests that GDQS and PDQS effectively capture dietary components influencing breast cancer risk through anti-inflammatory and hormonal pathways, offering a comprehensive approach to dietary assessment compared to single-nutrient analyses.

The public health implications of these findings are substantial, particularly in the context of rising breast cancer incidence in low- and middle-income countries (28). The strong inverse association between high-quality diets and breast cancer risk supports the promotion of dietary patterns rich in fruits, vegetables, legumes, and lean proteins. These findings align with global dietary guidelines, such as those from the EAT-Lancet Commission, which advocate plant-based diets for chronic disease prevention (8). The adaptability of GDQS and PDQS to local food systems makes them practical tools for tailoring interventions in diverse settings. For example, incorporating affordable legumes and locally available vegetables into dietary recommendations could enhance adherence in resource-constrained regions (29).

The significant differences in fat and fiber intake between cases and controls highlight specific dietary targets for intervention. The higher fat intake in cases aligns with evidence linking saturated fats to increased breast cancer risk through metabolic pathways (30), while the higher fiber intake in controls supports its protective role via estrogen modulation.

To further elucidate these findings, exploring the role of specific micronutrients within GDQS and PDQS frameworks is crucial. For instance, antioxidants like vitamins C and E, prevalent in fruits and vegetables, may neutralize free radicals, reducing DNA damage and subsequent cancer risk (31). In 2016, Cadeau et al. (32) founds that higher vitamin C intake was associated with a 12% lower breast cancer risk, particularly in postmenopausal women. Similarly, omega-3 fatty acids, found in fish and nuts consumed more by controls, may inhibit tumor growth by modulating cell signaling pathways (33). A 2024 study by Zhang et al. (34) reported a 10%–15% risk reduction with higher omega-3 intake, reinforcing the protective potential of these nutrients. Socioeconomic and cultural factors also warrant consideration, as access to nutrient-dense foods varies widely. In low-income settings, cost and availability may limit adherence to high GDQS and PDQS diets, a challenge noted in a study by Van Horn (35).

This study has several strengths. First, we used globally recognized and validated dietary indices (Global Diet Quality Score and Prime Diet Quality Score), which enhance the reliability and comparability of our findings. Second, dietary intake was assessed through face-to-face interviews using a semi-quantitative Food Frequency Questionnaire (FFQ), reducing the likelihood of misreporting. Third, the inclusion and exclusion criteria for both cases and controls were clearly defined, which improves internal validity. However, there are some limitations to consider. The case–control design is inherently prone to recall and selection biases and limits causal inference. Although efforts were made to enhance accuracy, dietary data were self-reported and may be subject to recall bias. Its single-center design, although conducted at a major referral hospital, may limit the generalizability of the findings to other populations or healthcare settings. However, because of the retrospective case–control design, reliance on FFQ data, and potential recall bias or diet changes around diagnosis, these findings should be interpreted as associations rather than proof of causality. Furthermore, despite adjusting for several variables, residual confounding from unmeasured factors such as genetic predisposition or environmental exposures cannot be ruled out.

A high diet quality, as indicated by higher total GDQS and total PDQS scores, was associated with lower odds of breast cancer in this hospital-based case–control study. These findings highlight a potential role of overall diet quality in breast cancer etiology but should be interpreted as observational associations rather than evidence of causal or therapeutic effects.