Several systematic reviews and meta-analyses have shown that ethnic minorities with diabetes have worse glycemic control than NHWs, which likely contributes to the higher risk of microvascular complications seen in these populations [22–24]. The proportion of diabetic ethnic minorities with poor glycemic control, defined as glycemia above a specific threshold, was significantly higher among NHBs, Hispanic Americans, Native Americans, and Asian Americans and Pacific Islanders [22]. Although discussed more in the context of using HbA1c as a diagnostic criteria for diabetes, recent studies have suggested that non-glycemic factors may contribute to the higher HbA1c at similar levels of fasting glucose seen in NHBs, Hispanic Americans, Asian Americans, and Native Americans, compared to NHWs [18]. However, HbA1c is similarly associated with prevalence and risk of microvascular and macrovascular complications, and mortality, among NHB and NHWs with diabetes [25–27], lending credence to true differences in glycemia between the two race/ethnic groups.

Hypertension is an important risk factor for diabetic nephropathy/end-stage renal disease (ESRD) and peripheral arterial disease and likely contributes to the higher prevalence of these complications in certain ethnic groups. NHBs have a higher prevalence of hypertension than NHWs [10]. Mexican American women have a higher prevalence of hypertension than NHW women; however, the prevalence of hypertension is similar among men in the two race/ethnic groups [10]. Native Americans and Alaska Natives have a lower prevalence of hypertension compared to NHWs and NHBs; however, there are regional differences [10]. Studies of blood pressure control and hypertension prevalence comparing NHWs to Native Americans and Asian Americans with diabetes are lacking. Research to date from clinical trials indicates that control of reversible risk factors, including hypertension, is equally effective in lowering the risk of nephropathy and cardiovascular disease in minority and NHW populations [28].

In a prior systematic review comparing low-density lipoprotein cholesterol between minority populations and NHWs with diabetes, Hispanic Americans had slightly lower low-density lipoprotein cholesterol than NHBs and NHWs. In this review, there were no studies comparing lipid control in NHWs with Native Americans and Asian Americans with diabetes [29]. While NHBs have lower triglycerides than NHWs [25], which may explain their lower risk of macrovascular disease, they generally have a higher prevalence of low high-density lipoprotein cholesterol, a strong cardiovascular risk factor [30].

While some studies have shown no differences in SMBG by race/ethnicity, several have shown lower rates among NHBs, Hispanic Americans, and Asian Americans, compared to NHWs. Two studies found no difference in SMBG frequency in Native Americans compared to NHWs [31]. There are several barriers to SMBG, including inconvenience and intrusiveness, pain, lower socioeconomic position, education level, social class, and living in a high poverty area, many of which are disproportionately prevalent in ethnic minority groups [31].

As summarized above, ethnic minorities are less likely to engage in leisure-time physical activity, which can contribute to worse glycemic control and a propensity to developing microvascular complications [10].

Native Americans and Alaska Natives have a higher prevalence of smoking that NHWs [10], which can contribute to their higher risk of peripheral arterial disease and amputations. NHBs and NHWs have similar smoking rates, while Mexican Americans have significantly lower smoking rates. Therefore, smoking may not explain ethnic differences in peripheral arterial disease in these populations.

In Peek’s review of 17 studies of patient interventions within the healthcare organization that sought to improve dietary habits, physical activity, and self-management activities, those that were culturally tailored were more effective in lowering HbA1c than general QI interventions (−0.69 % versus –0.1 %) [37]. Also, peer support and 1:1 interventions were more effective than online and computer-based approaches. In a systematic review and meta-analysis looking exclusively at randomized controlled trials of patient interventions targeting NHBs, most of which were culturally adapted and included peer providers, two of 22 increased patient attendance at screening visits, and 20 of 22 promoted diabetes self-management [38]. In a meta-analysis of eight studies, interventions resulted in a significant 0.83 % reduction in HbA1c [38].

In Peek’s review, provider interventions including education, continuing medical education, computerized decision support, in-person feedback, and problem-based learning improved process measures [37]. The majority of these studies were conducted in NHBs with diabetes. Interventions involving computerized decision-support reminders and chart audit and individual’s feedback resulted in improved HbA1c and treatment modification [74–76, 92].

Healthcare organization interventions in minority populations have included systems for rapid turnaround HbA1c, circumscribed appointments, support staff (e.g., nurse case management, community health worker, pharmacist), and increased follow-up through home visits or telephone/mail contact [37, 38]. In Peek’s review, 14 studies with interventions targeting the healthcare organization resulted in a mean HbA1c reduction of 0.34 %. Ricci-Cabello et al. included five healthcare system intervention trials in NHBs in their systematic review and meta-analysis and found the two most highly effective interventions in improving HbA1c, and frequency of therapy intensification included rapid turnaround HbA1c [77, 86].

Multi-target interventions target all aspects and components of healthcare delivery, including patients, providers, and the healthcare system. Five of these studies have targeted NHBs with diabetes and used various approaches. Three studies showed an improvement in HbA1c [55, 79, 88]. All of these interventions included patient education and self-management support and nurse case management, two included treatment algorithms [79, 88], and two involved collaboration with a physician in treatment decisions (one an endocrinologist [88] and one an unspecified physician [79]). While two additional multi-target interventions showed improvement in process measures and non-glycemic clinical outcomes [89, 90], they did not improve glycemic control. One study involved patient interventions and provider-focused QI interventions focusing on system changes surrounding the physician visit [89] and the other involved nurse case management and community health workers using evidence-based clinical algorithms with feedback to primary care physicians [90]. Finally, one study focusing exclusively on Native Americans in the Indian Health Service included provider guidelines, a multidisciplinary team, diabetes registry/tracking system, and flow sheets [91]. Compared to podiatric screening and patient education, the multi-target intervention resulted in a significant reduction in amputation rate [91].

The largest analysis of the Mediterranean diet was the Prevention with Mediterranean Diet (PREDIMED) study. The trial enrolled 7,447 persons in Spain at high cardiovascular risk with either diabetes or three cardiovascular risk factors. Participants were randomized to one of three diets: a Mediterranean diet supplemented with extra-virgin olive oil, a Mediterranean diet supplemented with mixed nuts, or a control diet (advise to reduce dietary fat) and were followed for 4.8 years for the development of the primary end point of major cardiovascular events. Mediterranean diet with extra-virgin olive oil and Mediterranean diet with nuts were associated with 30 and 28 % reductions in major cardiovascular events [94]. Among participants with diabetes in the Mediterranean diet groups compared to control, there was a 29 % reduction in major cardiovascular events. The Mediterranean diet also reduces HbA1c. In 215 overweight Italian individuals with newly diagnosed diabetes, Mediterranean diet vs. low-fat diet was associated with a 0.6 % and 0.4 % lower HbA1c at 1 and 4 years, respectively, with a 37 % reduction in antidiabetic medication use [95]. In 259 Israeli participants, a low-carbohydrate Mediterranean diet versus a traditional Mediterranean diet or American Diabetes Association diet was associated with greater reductions in HbA1c and cardiovascular risk factors [96]. Notably, the majority of the improved glucometabolic findings with the Mediterranean diet remained significant with adjustment for weight loss. Although, the Mediterranean diet has not been assessed in a clinical trial among US ethnic minorities, observational findings in the Multiethnic Study of Atherosclerosis (MESA) (42 % white (NHW), 12 % Chinese American (CA), 26 % NHB, 21 % Hispanic American) reveal that participants with greater adherence to a Mediterranean dietary pattern had lower insulin and glucose independent of racial/ethnic group [97]. These results suggest a likely beneficial effect of the Mediterranean diet on improved glucose metabolism among US racial/ethnic minorities with diabetes, although intervention trials in these populations are needed.

The Adventist Health Study 2 assessed the role of vegan and vegetarian diets in the USA. Among 73,308 NHB and NHW participants with no history of cancer or cardiovascular disease, there was a 12 % reduction in all-cause mortality over 5.8 years [98], 30–50 % lower diabetes prevalence [99], and 40–60 % lower diabetes incidence in the vegetarian versus non-vegetarian groups [100]. These findings lend credence to improved glucose metabolism with vegetarian dietary patterns. In individuals with diabetes, a small (n = 99) multiethnic (NHW 44 %, NHB 44 %, Hispanic American 4 %, and Asian American 8 %) clinical trial of a low-fat vegan diet or American Diabetes Association diet for 72 weeks revealed greater reductions in HbA1c and cardiovascular risk factors in the low-fat vegan group [101].

The Dietary Approaches to Stop Hypertension (DASH) diet encourages the intake of fruits, vegetables, whole grains, and low-fat dairy products in combination with sodium restriction [102]. The DASH diet was initially studied in a multiethnic trial with 65 % ethnic minorities (35 % NHW, 60 % NHB, 5 % other minority groups) and significantly lowered blood pressure among all participants with twofold greater reductions among racial/ethnic minorities [102]. Further studies revealed that components of the DASH diet may also improve insulin sensitivity [103]. The DASH diet is recommended for all Americans including those with diabetes [93].

Exercise interventions improve glycemic control in diabetes in majority of NHW studies [109]. A meta-analysis examining the effects of exercise interventions (mean 3.4 sessions/week with 49 min/session) on glycemic control in individuals with diabetes revealed mean HbA1c reduction of 0.66 % (p < 0.001) in people with diabetes, even with no significant change in BMI [109]. Higher levels of exercise intensity are associated with greater improvements in HbA1c and fitness [110]. Clinical trials have provided strong evidence for the HbA1c lowering value of resistance training in NHW older adults with type 2 diabetes [111]. There are limited data on glycemia in response to exercise in NHB, Hispanic Americans, and Native Americans with diabetes. Among individuals without diabetes in the HERITAGE Family Study, a 20-week trial of thrice weekly exercise in NHB and NHW, NHB had a greater increase in fasting glucose with exercise compared to NHW, although there were reductions in fasting insulin in both groups [112]. A multiethnic (52.7 NHW, 43.5 % NHB, 3.8 % Hispanic American) randomized clinical trial examining the effect of aerobic exercise, resistance training or combined aerobic exercise, and resistance training on HbA1c levels in 221 participants with diabetes found that aerobic exercise alone or resistance training alone had no effect on HbA1c, only the combined group revealed significant reductions in HbA1c (−0.34 %, p = 0.03) and improvements in cardiorespiratory fitness over 9 months [113]. They lacked the power to examine racial/ethnic differences. Potential components of improved glucose metabolism with physical activity are skeletal muscle mitochondrial mass, mitochondrial function, and aerobic capacity [114, 115]. The racial/ethnic differences of aerobic capacity with physical activity were tested in a 6-month trial of aerobic exercise training in NHB and NHW postmenopausal women. The NHW women had a greater increase in cardiorespiratory fitness with sustained resting metabolic rate, whereas in NHB women, resting metabolic rate declined over the course of the trial, suggesting a perturbation in mitochondrial function [116, 117]. A study of exercise capacity and all-cause mortality in NHB and NHW men with diabetes found that exercise capacity is a stronger and more graded predictor of mortality for NHW than for NHB men [118]. The high-fit compared to low-fit NHW and NHB men had a 67 % and 46 % reduction in mortality risk, respectively [118]. These studies reveal that there is a benefit to physical activity in US racial/ethnic minorities, but the type (aerobic vs. resistance) and intensity of the physical activity need to be further characterized. A recent meta-analysis of step counters to improve physical activity and HbA1c in individuals with diabetes underscores this point. Data from 11 randomized clinical trials using step counters (pedometers) revealed that step counter use is associated with a significant increase in physical activity (1,822 steps/day), but no change in HbA1c [119].

Elevated body mass index and adiposity are the most important predictors of diabetes [120–122]. Obesity is also an independent predictor of clinical cardiovascular disease [123–125]. Mortality for diabetes, myocardial infarction, and stroke was similar for each of these conditions, but when any two are combined, the risk is multiplicative [126], reinforcing the importance of improving weight in individuals with elevated weight. The underlying relationship between obesity, cardiovascular disease, and diabetes has been reviewed and is potentially mediated through the adipokines released from visceral fat [127–130]. In this section we will review the data on nonsurgical and surgical interventions to promote weight loss in diabetes and improve glycemia with the goal of long-term reduction in morbidity and mortality.

Bariatric surgery procedures are associated with diabetes remission due to hormonal changes and weight loss [137]. Hormonal changes include reduction in ghrelin and increases in glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP). Lower levels of ghrelin postsurgically decrease appetite stimulation through a decrease in stimulation of orexigenic neurons neuropeptide Y/agouti-related peptide. Postsurgically levels of glucagon-like peptide-1 and glucose-dependent insulinotropic peptide increase exerting effects on the enteroinsular axis with potent insulinotropic activity. The long-term weight loss occurs due to decreased food (energy) consumption caused by the reduction in appetite and anatomical constraints. The surgical procedures currently performed include laparoscopic adjustable gastric banding (LAGB), laparoscopic vertical sleeve gastrectomy (LVSG), Roux-en-Y gastric bypass (RYGB), biliopancreatic diversion, and biliopancreatic diversion with duodenal switch (Fig. 14.1). In the USA, RYGB was the most commonly performed procedure but with wide adoption of LVSG; LVSG has surpassed RYGB and is performed in one half of bariatric surgical procedures [139]. The type of procedure is important for individuals with diabetes as diabetes remission varies greatly across procedures. Meta-analyses and reviews report remission rates of 48 % (29–67 %) for LAGB, 84 % (77–90 %) for RYGB, 72 % (55–88 %) for LVSG, and 99 % (97–100 %) for biliopancreatic diversion with duodenal switch [140, 141]. Recent analysis of the two most popular procedures have shown diabetes remission rates ranging from 27 to 75 % for LVSG versus 42–93 % for RYGB [142]. In the STAMPEDE trial, diabetes remission rates at 1 and 3 years of follow-up were 12 and 5 % with intensive medical therapy alone, 42 and 38 % in RYGB group, and 37 and 24 % in the LVSG group (Table 14.6). The diminishing rates of diabetes remission over time noted in STAMPEDE are also seen in other studies of LVSG and RYGB at a rate of 7–15 % per year [137]. Given the current popularity of LVSG, longer-term comparative effectiveness data on LVSG are needed. However, bariatric surgery experts believe the effect of LVSG on weight loss and comorbidity improvements seems to be somewhere between those of RYGB and LAGB [151]. Five-year outcomes from RYGB among mostly NHW participants found that shorter diabetes duration, lower HbA1c, younger age, higher serum insulin levels, and nonuse of insulin were associated with higher remission rates [152].