3 year fellowship following internal medicine residency, a 1-year fellowship following either internal medicine residency or fellowship in cardiology or endocrinology, and certification available to any interested clinician. This review discusses the pros and cons of these approaches. The authors believe that a dedicated cardiometabolic training fellowship has significant advantages over the other options. Introduction Globally and particularly in the United States, rates of obesity, metabolic syndrome and diabetes mellitus have been steadily increasing [1,2]. These conditions are each strongly associated with an increased risk of cardiovascular disease (CVD). Collectively, they represent a growing population of cardiometabolic patients that require interdisciplinary preventive clinical management, benefiting the most when care is coordinated between primary care, cardiology, endocrinology and nutrition and lifestyle specialists. Diabetes mellitus is representative of this growing health burden, with the estimated 34 million US adults with diabetes in 2018 projected to increase almost three-fold by 2060 [3]. CVD remains the leading cause of morbidity and mortality among patients with type 2 diabetes mellitus, with death from heart disease being two to four times greater among patients with diabetes than those without [2,4]. As an ever-greater number of patients are living with cardiometabolic conditions, the focus is being placed on chronic preventive management. It is not uncommon for a patient to be managed by a multitude of specialists, including a primary care provider, cardiologist, endocrinologist, vascular medicine specialist, nephrologist and nutritionist/dietitian. This comanagement often results in confusion for the patient and their providers and can lead to potentially adverse circumstances such as polypharmacy. One aspect of the healthcare structure that can be leveraged to address the needs of cardiometabolic patients is physician training. Historically in the United States, patients with diabetes mellitus and CVD are managed by either generalists trained in internal medicine or by subspecialists in the currently disparate fields of endocrinology and cardiology. With the burden of treating a wide breadth of patient concerns, generalists often seek referral to subspecialists for optimized preventive care. Endocrinologists primarily manage diabetes mellitus and other metabolic diseases, while high-risk patients with diabetes mellitus and CVD are more likely to be managed by cardiologists [5]. These specialists must then rely on their organ-system-specific training from fellowship and continuing medical education (CME), which may not adequately prepare physicians to address every aspect of the cardiometabolic patient [6,7]. Furthermore, skills, such as counseling on lifestyle behavior modification and management of novel cardiometabolic medications, such as sodium-glucose co-transporter-2 (SGLT2) inhibitors and glucagon-like peptide-1 (GLP-1) receptor agonists, remain focal points where physician uptake can be improved through training [8–12]. Currently, it is not clear which specialist will oversee the management of these medications, and as a result, they might never be initiated [13]. Highlighting this issue, a recent study found that among a large cohort of US patients with diabetes mellitus and CVD, 87.8% were prescribed a statin, but only 9.0 and 7.9%, respectively, were prescribed an SGLT2 inhibitor and GLP-1 receptor agonist [6]. While there is a need for focused cardiometabolic medicine training for physicians, no such standardized program exists. Many approaches have been proposed to bridge this training gap and are summarized in the following sections of this review (Fig. 1). Current training model The current framework of cardiometabolic training in the United States is through one of two distinct specialty pathways: cardiology or endocrinology. These follow residency in internal medicine (3 years), with additional subspecialty training in either general cardiology (3+ years) or endocrinology, diabetes and metabolism (2–3 years). Residents in internal medicine participate in inpatient and outpatient clinical rotations each year of training and develop basic clinical management skills necessary to independently conduct primary care for the cardiometabolic patient. Preventive care of chronic conditions such as hypertension and hyperlipidemia are mainly taught in the acute care setting. Lifestyle practices such as smoking cessation, nutritional counseling, and weight management are covered only briefly during residency [14,15]. These skills are primarily built upon following completion of house staff training; however, they are underutilized to the same degree by both resident and attending physicians. Residents practice in clinical teams throughout training, developing essential skills for working in a multidisciplinary setting. The third year of internal medicine residency allows for components of customizable training, affording opportunities to seek out rotations in cardiology and endocrinology to gain further exposure to management of cardiometabolic patients [16]. Advanced concepts in cardiac disease prevention education have traditionally been part of cardiology training programs. Primary and secondary prevention of atherosclerotic CVD is a core learning principle of general cardiology fellowship [17]. All fellows are required to complete at least a 1-month rotation dedicated to CVD prevention, which should include experiences in clinics focused on cardiac rehabilitation, diabetes or endocrinology, hypertension, and dyslipidemia management. Education during this month is focused on learning risk factor modification strategies. This rotation can be substituted with a 3-month or longer training period for those particularly interested in cardiometabolic disease. Approximately ten clinical subspecialty fellowships in CVD prevention exist, ranging 1–2 years of additional training after completion of general cardiology fellowship, though these are not currently accredited by the Accreditation Council for Graduate Medical Education (ACGME) [18,19]. Cardiovascular disease prevention training is not a primary focus during an endocrinology fellowship. The ACGME does, however, require programs to provide education in the core competencies of disease prevention and the ‘prevention and surveillance of microvascular and macrovascular complications,’ which includes CVD [20]. Extensive training in management of type 1 and type 2 diabetes mellitus, lipid disorders, and obesity is provided, including the development of nutritional and lifestyle counseling, preparing physicians to address these aspects of cardiometabolic patient care [21]. Following completion of endocrine fellowship, no subspecialty fellowship training is available to provide additional specialized education in cardiometabolic medicine. To further illustrate the gaps in this current training model, consider the case of the lead author on this manuscript, who is a medical student pursuing residency in internal medicine with interest in caring for cardiometabolic patients. Midway through his residency training, he will have to choose to either (1) become a primary care provider immediately following completion of residency, pursue his own educational materials on cardiometabolic care, and practice with minimal, focused training in cardiometabolic medicine or (2) pursue fellowship training in either cardiology or endocrinology. As is the case with most trainees in this situation, he will likely pursue subspecialty training. If he elects to complete a cardiology fellowship, a majority of his training will be focused on acute and critical care cardiovascular management, with significant time spent on developing procedural skills and postprocedural follow-up. If he elects to complete a fellowship in endocrinology and metabolism, he will be required to complete extensive clinical training in thyroid, bone and neuroendocrine disorders. Even after subspecialty training, he may very likely have to pursue additional CME training in topics such as fatty liver and obesity management to further develop his limited expertise. Either path necessitates training in skills that would be minimally applicable in a cardiometabolic clinic and neither path allows for in-depth training across clinical departments. While this review focuses on the United States, similar gaps exist in training models throughout the world. Though parallels in need for and growing interest in focused cardiometabolic training are common across countries, credentialing and healthcare delivery structures vary. Country-specific surveys of perceptions are needed to elucidate the best avenues for improved training. Alternate 1: cardiometabolic fellowship of 2–3 years following internal medicine residency One proposal is for a dedicated multiyear fellowship track in cardiometabolic medicine. After completion of residency training in general internal medicine, residents would complete an additional 2–3 years of subspecialty house staff training and focus on advanced topics in cardiology and endocrinology [22–24]. The cardiology component would be centered around primary and secondary prevention of atherosclerotic disease. Clinical training would include electrocardiograph interpretation, cardiac imaging (interpretation of echocardiography, stress testing, and noncontrast and contrasted coronary computed tomography), hypertension management, cardiac rehabilitation, vascular medicine, inpatient cardiology consultations and outpatient preventive cardiology clinic. Of note, certain elements classically covered in a cardiology fellowship that would be excluded are interventional cardiology, electrophysiology, critical care medicine, advanced heart failure and cardiac transplantation. The endocrine component would be focused on extensive training in management of type 1 and 2 diabetes mellitus, metabolic syndromes, obesity, hypertension and lipid and lipoprotein disorders. House staff training would involve frequent interactions with endocrine and bariatric surgeons. Advanced topics in glucose management would include basal-bolus insulin administration, insulin infusion pumps and continuous glucose monitoring. Education in obesity medicine would include obesity pharmacology, nutrition therapy and management of bariatric surgery patients. Advanced lipid topics would include education in statin intolerance, moderate to severe hypertriglyceridemia and genetic lipid and lipoprotein disorders. Of note, endocrine training classically covered in an endocrinology fellowship that would be excluded are disorders of the thyroid, parathyroid, hypothalamic-pituitary-adrenal axis, reproductive endocrinology and metabolic bone disease. Advanced concepts in lifestyle modification will also represent a significant portion of cardiometabolic medicine training, with particular focus on diet, exercise and substance use [25]. Topics would include nutrition counseling and coordinating with nutritionist staff, exercise counseling and use of mobile health technology, as well as substance (tobacco, novel tobacco products including electronic cigarettes, alcohol, illicit drug) cessation counseling and pharmacology [26,27]. Complimentary education in behavioral sciences and human psychology would allow trainees to augment these skills. Finally, a cardiomet