A new review finds that whole, minimally processed plant foods offer the strongest metabolic benefits, while refined foods, sugary drinks, and excessive red and processed meat may undermine diabetes prevention and control.

Review: Plant-Based Nutrition and Type 2 Diabetes Mellitus: Prevention, Risk, Metabolic Health and the Role of Legumes, Dietary Fiber, and Red Meat. Image Credit: kimberrywood / Shutterstock

In a recent narrative review published in the journal Nutrients, researchers in Austria summarized evidence on plant-based diets and their associations with metabolic health and type 2 diabetes (T2D).

In 2024, diabetes affected 589 million adults aged 20 to 79 years worldwide, a figure projected to reach 853 million by 2050. T2D is the most common form, accounting for approximately 90% of all diabetes cases. The rising incidence of T2D is associated with the growing prevalence of obesity and is driven by urbanization, sedentary lifestyles, economic development, and unhealthy diets.

Dietary modifications are central to the management and prevention of T2D, with plant-based diets gaining substantial attention in this context. Nevertheless, the optimal composition and contribution of specific food groups in plant-based diets remain unclear. In the present narrative review, researchers reviewed current evidence on plant-based diets and their associations with T2D, with particular emphasis on legumes, dietary fiber, and red and processed meat.

Metabolic health and dietary patterns

Western diets are characterized by increased intakes of refined carbohydrates, ultra-processed foods (UPFs), processed and red meat, and sugar-sweetened beverages (SSBs). They have been consistently associated with insulin resistance, obesity, and metabolic syndrome. A cross-sectional study reported that higher adherence to the Western diet was associated with higher odds of prediabetes and diagnosed or undiagnosed T2D relative to a prudent diet.

Conversely, diets involving whole and minimally processed plant foods, e.g., vegetarian and vegan diets, the Mediterranean diet (MD), and the Dietary Approaches to Stop Hypertension (DASH) diet, are associated with better metabolic health. Meta-analyses indicate that these diets significantly improve glycemic control and lipid profiles and reduce cardiometabolic risk, with HbA1c reductions of approximately 0.36 to 0.53 percentage points compared with control diets.

MD is recognized as a premier strategy for the management and prevention of T2D. High MD adherence is associated with a 30% lower risk of T2D and improvements in body mass index, blood pressure, and low-density lipoprotein cholesterol. These benefits are largely attributed to the high levels of fiber, polyphenols, and monounsaturated fatty acids in the MD, which inhibit inflammatory processes and enhance insulin sensitivity.

Plant-based diets and risk of diabetes

Evidence consistently suggests an association between increased adherence to plant-based dietary patterns and lower T2D risk. A meta-analysis of nine studies involving 307,099 participants and 23,544 incident T2D cases reported a 23% lower relative risk of T2D associated with adherence to plant-based dietary patterns. Prospective studies also suggest that decreasing adherence to these dietary patterns is associated with a higher risk of T2D. Plant-based patterns do not necessarily exclude animal-derived foods and can include predominantly plant-based flexitarian diets. Recent studies differentiate between unhealthful and healthful plant-based diets.

Diets rich in legumes, whole grains, nuts, fruits, and vegetables (healthful plant-based diets) are associated with a considerable reduction in the risk of diabetes. In contrast, those rich in added sugars, SSBs, and refined grains (unhealthy patterns) have fewer benefits and may even elevate metabolic risk. However, the review notes that not all plant-based foods classified as ultra-processed appear to carry equivalent cardiometabolic risk. Legumes and dietary fiber play important roles in insulin sensitivity and glucose metabolism.

A meta-analysis of 41 randomized controlled trials (RCTs) reported that legume intake significantly improved glycemic control, particularly by reducing postprandial glucose and insulin excursions. Their high fermentable fiber content is also thought to modulate the gut microbiota and promote the growth of short-chain fatty acid (SCFA)-producing bacteria, although subsequent effects on HbA1c and fasting glucose remain heterogeneous across studies. Insoluble cereal fibers show the most consistent associations with T2D risk, with a 10 g/day increase in cereal fiber intake associated with a 25% lower risk.

Red and processed meat showed the opposite association. In an analysis of 1.97 million adults, each additional 50 g/day of processed meat was associated with a 15% higher risk of T2D, while 100 g/day of unprocessed red meat was associated with a 10% higher risk.

Low-carbohydrate diets

Ketogenic and low-carbohydrate diets have become popular for their ability to produce rapid improvements in glycemic control, weight loss, and insulin sensitivity. However, there are concerns about their fiber inadequacy, cardiovascular safety, and sustainability. A meta-analysis of 23 RCTs involving 1,357 participants found greater diabetes remission with low-carbohydrate diets at six months, but the advantage was no longer significant at 12 months.

Animal-based, low-carbohydrate diets were associated with a 39% higher risk of T2D, whereas healthy plant-based low-carbohydrate diets emphasizing vegetable protein and unsaturated fats were associated with a 16% lower risk. A network meta-analysis ranked MD, moderate-carbohydrate diets, and low-glycemic-index diets among the most effective approaches for improving fasting glucose and glycated hemoglobin (HbA1c) levels, with vegan and vegetarian diets yielding smaller but significant reductions in HbA1c.

Concluding remarks

Collectively, available evidence indicates that healthful plant-based dietary patterns dominated by legumes, fruits, whole grains, nuts, and vegetables, while limiting processed meat and excessive red meat, are associated with improved glycemic control and a lower risk of T2D. Conversely, unhealthful plant-based dietary patterns dominated by refined grains, added sugars, SSBs, and lower-quality highly processed foods may be associated with increased T2D risk.

Interpretation is limited by the predominance of observational studies, heterogeneous definitions of plant-based diets, reliance on self-reported dietary assessments, and the limited number of long-term RCTs. 

As a narrative review, the study also lacked a predefined protocol and formal risk-of-bias assessment. Future high-quality RCTs are required to determine the optimal composition of plant-based diets for T2D management and prevention and to inform individualized dietary strategies that prioritize food quality and long-term adherence.

Journal reference:

• Frigo F, Fasching P, Brath H (2026). Plant-Based Nutrition and Type 2 Diabetes Mellitus: Prevention, Risk, Metabolic Health and the Role of Legumes, Dietary Fiber, and Red Meat. Nutrients, 18(16), 2672. DOI:10.3390/nu18162672, https://www.mdpi.com/2072-6643/18/16/2672