Nutrition therapy that targets optimizing glucose levels, blood pressure, and lipid profiles in individuals with DM is associated with a lower risk of CVD, CHD, and stroke. The ADA advises replacement of saturated fat with unsaturated fats, especially polyunsaturated fat. This has been associated with significant reductions in both total cholesterol and LDL-C. Additionally, replacement of saturated fat with monounsaturated fat from plant sources, such as olive oil and nuts, is associated with lower CVD risk. Replacing saturated fat with carbohydrate is not advised; although this reduces total cholesterol and LDL-C, it also significantly increases triglycerides and reduces HDL-C. Replacing foods high in carbohydrate with foods lower in carbohydrate and higher in fat may improve glucose, triglyceride, and HDL-C levels. However, the replacement of carbohydrate with fat should be with unsaturated fat.

Individuals with DM should consume <2300 mg/day of sodium, which has been shown to have beneficial effects on blood pressure. A serving of fish, particularly fatty fish such as salmon, mackerel, or rainbow trout, at least two times per week is recommended. Fatty fish contains long-chain omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid, which have beneficial effects on lipoproteins and have been associated with prevention of ASCVD. Individuals following a vegetarian or vegan eating plan are encouraged to consume omega-3 α-linoleic acid, which is found in plant foods such as flax, walnuts, and soy, and may provide some CVD benefits. Other dietary recommendations for CVD risk reduction include consuming 8 to 10 servings per day of fruits and vegetables, 2 to 3 servings per day of low-fat dairy products, and limiting alcohol consumption to ≤2 servings per day for males and no more than 1 serving per day for females ( Box 17.1 ).

The Mediterranean diet, which is inclusive of the above dietary recommendations, includes consumption of whole grains; legumes; fruits; vegetables; nuts; fish and olive oil; wine in moderation; and a low intake of meat, dairy products, processed foods, and sweets. This diet has been shown in numerous prospective clinical trials to have beneficial effects on CV health. Additionally, the Mediterranean diet has been shown to have a favorable impact on the CV risk factor profile of individuals with DM.

Cigarette smoking in people with DM heightens the risk of CVD, premature death, microvascular complications, and worsens glycemic control when compared with those who do not smoke. Quitting smoking has been shown to reduce the risk of CVD to that of someone who has never smoked in ~10 to 15 years, with the greatest decline of CVD risk within the first 5 years of quitting.

The ADA recommends including smoking cessation counseling and other forms of treatment as routine components of care for patients with DM who smoke. Assessment of smoking should be completed with every patient and those who smoke should be counseled on quitting. Results from numerous large randomized clinical trials have demonstrated the efficacy and cost-effectiveness of brief counseling in smoking cessation in reducing tobacco use. Patients should also be advised not to use electronic nicotine delivery systems, commonly known as e-cigarettes or “vaping,” or heated tobacco products. There are no rigorous studies that have demonstrated that noncombustible tobacco products are a healthier alternative to smoking or that e-cigarettes can facilitate smoking cessation.

Pharmacologic therapy can assist with smoking cessation and has been shown to be effective in people with DM. For motivated patients, the addition of pharmacologic therapy to counseling is more effective than either treatment alone. Pharmacological therapies, including bupropion and nicotine replacement therapy, can lessen the symptoms of nicotine withdrawal during smoking cessation. Behavioral support programs have also been shown to be effective for smoking cessation. A clinician’s referral and recommendation to participate in a behavioral support program for smoking cessation is more effective than simply providing information about these resources. There is strong evidence that combining pharmacotherapy with behavioral interventions is the most effective way to help smokers sustain abstinence. Community-based behavioral support resources for smoking cessation are listed in Table 17.2 .

Epidemiologic studies and clinical trials have consistently demonstrated the survival benefits of regular exercise, especially walking, in the prevention and treatment of DM. In epidemiologic studies, brisk walking for ≥30 min/day has been associated with a 30% to 40% lower risk of developing DM in females. Two clinical trials demonstrated that regular walking or other moderate exercise in conjunction with dietary changes and modest weight losses resulted in a 58% lower risk for the development of DM in overweight patients with impaired fasting glucose, as compared with usual-care control groups. In the Diabetes Prevention Program, drug therapy with metformin reduced the risk by only 31%.

In a nationally representative sample ( n = 2896) of Americans with DM aged ≥18 years, regular walking was associated with significantly lower risk for all-cause and CV mortality, up to 39% and 54% for walking at least 2 h/week and 3 to 4 h/week, respectively. The inverse association held in multivariable analyses after potential confounding variables (e.g., risk factors, BMI, comorbid conditions) were controlled for. Compared with inactive individuals, the mortality rates were lowest for those who walked 3 to 4 h/week, and for those who reported that their walking involved moderate increases in heart rate and breathing. In the Nurses’ Health Study, in which patients with CVD or cancer at screening were excluded, moderate and vigorous levels of PA were associated with lower rates of overall CV events among females with diabetes aged 30 to 55 years. Similarly, the Aerobics Center Longitudinal Study reported that males with DM who had a low CRF level and were physically inactive had higher mortality rates during follow-up than did their counterparts who were active and fit. The clinical and public health implications of these data are enormous, because the survival benefits of moderate-to-vigorous-intensity PA, often achieved by brisk walking alone, may be even greater than those achieved by contemporary pharmacologic therapies to manage DM.

An inverse association between CRF and the incidence of chronic disease has been established by large, well-designed epidemiologic studies. The findings indicate that these associations are observed at relatively moderate levels of PA or structured exercise and increase in a graded fashion across increasing levels of PA, associated with a significant survival advantage. A systematic review and meta-analysis of 33 PA studies including 883,372 participants reported pooled estimates of 35% and 33% lower risk for CV and all-cause mortality, respectively, among the most physically active cohorts. More recently, researchers estimated the influence of five low-risk lifestyle factors, including ≥30 min/day of moderate-to-vigorous PA, on premature mortality and life expectancy in the US population. During the follow-up period, which extended up to 34 years for some participants, the most physically active cohorts of males and females demonstrated 7- to 8-year gains in life expectancy from age 50 years.

Regular moderate-to-vigorous PA, increased CRF, or both can decrease the risk of initial or recurrent CV events, presumably from multiple mechanisms, including antiatherosclerotic, antiischemic, antiarrhythmic, antithrombotic, and improved psychologic effects ( Fig. 17.2 ). Specific antiischemic effects of regular exercise include reducing the rate-pressure product and associated myocardial oxygen demands at rest and at any given submaximal workload. Decreased vulnerability to threatening ventricular arrhythmias and increased resistance to ventricular fibrillation have also been postulated to reflect exercise-related adaptations in autonomic control, including reduced sympathetic drive and increased vagal tone, as well as increasing the period of diastole as a result of decreased resting heart rate, during which coronary perfusion predominates.

A structured endurance exercise program, increased lifestyle physical activity, or both are sufficient to maintain and enhance cardiorespiratory fitness, which favorably affects multiple atherosclerotic cardiovascular risk factors in patients with diabetes. BP , Blood pressure; CACs , cultured angiogenic cells; EPCs , endothelial progenitor cells; HR , heart rate; O ₂ , oxygen; ↑︎, increased; ↓︎, decreased.

Exercise preconditioning . This phenomenon provides an underappreciated independent and additive mechanism for protecting the heart against acute myocardial infarction. First described decades ago in animal studies, subsequent clinical investigations confirm that exercise preconditions the human heart. The benefits of exercise preconditioning are attributed to a host of endogenous biochemical factors activated within hours to days following the first bout of PA so that an ischemic-resistance phenotype is conferred, and appears to be continuously activated in those who remain regularly engaged in exercise ( Fig. 17.3 ). Accordingly, the phenomenon is distinct from other established exercise-induced adaptations, such as those described in Fig. 17.2 . Most importantly, the immediate benefits of exercise preconditioning can be conferred in males or females, young or old, who engage in even brief bouts of PA that achieve a minimum threshold of 50% V˙O ₂ max.

Exercise ischemic preconditioning prevents myocellular injury and death in multiple animal models. Ischemia-reperfusion injury is a time-dependent pathology, as shown conceptually above by the appearance of ventricular ectopy on the ECG, and later by declines in ventricular pump function. Unremitting ischemia is invariably marked by cardiomyocyte death due to necrotic and apoptotic processes. Exercise preconditioning lessens the magnitude of all facets of ischemia-reperfusion injury ( dashed line ). Protection afforded by exercise is due to the upregulation of multiple cellular mechanisms. Importantly, the mechanisms of biochemical cardioprotection against MI are unique to each phase of injury; for example, the factors preventing ventricular ectopy can be different than the other factors which prevent ventricular pump dysfunction. ECG , Electrocardiogram; MI , myocardial infarction; MRI , magnetic resonance imaging; PVCs , premature ventricular contractions.

Increasing scientific evidence also suggests that aerobic exercise training improves blood rheology in individuals with and without CHD. Endurance exercise has been shown to improve hemostatic/fibrinolytic parameters, with decreases in plasma fibrinogen levels, platelet aggregability, and hematocrit standardized blood viscosity and increases in fibrinolysis. Finally, well-designed studies now highlight the value of regular aerobic exercise in reducing chronic stress, anxiety, and depression.

Collectively, these data and related reports suggest that regular moderate-to-vigorous PA and higher levels of CRF are associated with a reduced risk of developing hypertension, DM, atrial fibrillation, chronic kidney disease, and major adverse CV events, including heart failure, MI, coronary artery bypass surgery, and death. This inverse association of lower incidence of DM has also been noted against the diabetogenic effects of statins. Accordingly, it appears that the risk of DM incidence in dyslipidemic patients treated with statins may be significantly attenuated by achieving moderate levels of CRF.

Aerobic (or endurance) exercise has been the most frequently studied mode of physical conditioning, and the resultant increases in CRF in patients with DM have been consistently associated with improvements in modifiable CV risk factors, independent of weight loss. The most effective exercises for the endurance phase use large muscle groups, are maintained continuously through the exercise session, and are rhythmic in nature, such as walking, jogging, elliptical training, stationary or outdoor cycling, swimming, rowing, stair climbing, and combined arm-leg ergometry. Other exercise modalities commonly used in structured exercise training programs for patients with DM include calisthenics, particularly those involving sustained total-body movement, recreational activities (e.g., golf, doubles tennis, pickleball), and resistance training. The last is a particularly important option, because traditional aerobic-conditioning regimens often fail to accommodate participants who require improved muscle strength or endurance to perform occupational or leisure-time activities. Moreover, studies have now shown that muscular strength is inversely associated with all-cause mortality, independent of CRF levels.

Because of the high prevalence of underlying ischemic heart disease, and the heightened risk for exertion-related CV events and orthopedic injuries, adoption of a moderate intensity (e.g., walking), rather than a vigorous PA program (e.g., jogging, running), may be more appropriate for patients with diabetes, especially those who are middle-aged and older. Due to lack of data and observation hours in varied populations with known or occult CVD, including patients with DM, it is currently premature to conclude that high-intensity interval training is a safe and superior exercise intervention compared with moderate-intensity continuous training. Walking has several advantages over other forms of exercise during the initial phase of a physical conditioning program, including inherent neuromuscular limitations on the speed of walking (and therefore the rate of energy expenditure).

Rule of 2 and 3 miles per hour (mph) . Because most patients with diabetes, many of whom are overweight or obese, prefer to walk at moderate intensities, it is helpful to recognize that walking on level ground at 2 and 3 mph approximates 2 and 3 METs, respectively. For patients who prefer the slower walking pace (2 mph; 3.2 km/h), each 3.5% increase in treadmill grade adds ~1 MET to the gross energy cost. Therefore patients who desire to walk at a 2-mph pace, but require a 4-MET workload for training, would be advised to add 7.0% grade to this speed. For patients who can negotiate the faster walking speed (3 mph; 4.8 km/h), each 2.5% increase in treadmill grade adds an additional 1 MET to the gross energy expenditure. Accordingly, a workload of 3 mph, 7.5% grade, would approximate an aerobic requirement of 6 METs. Use of this practical rule can be helpful to clinicians in prescribing level or graded treadmill walking workloads for their patients with DM.

LIFESTYLE PHYSICAL ACTIVITY

Lifestyle PA involves bodily movement produced by the contraction of muscles that increase aerobic requirements or energy expenditure. In contrast, structured exercise is PA/planned exercise that is performed with an underlying purpose or goal. Despite contemporary exercise guidelines and the Surgeon General’s report, the traditional model for getting people to be more physically active (i.e., a regimented or structured exercise program) has been only marginally effective. Randomized clinical trials have shown that a lifestyle approach to PA among previously sedentary adults has similar effects on CRF, body composition, and coronary risk factors as a structured exercise program. These findings have important implications for public health, suggesting an alternative approach for sedentary people who are not ready to integrate a formal exercise commitment into their daily schedule. The skyrocketing prevalence of overweight and obesity and related sequelae (e.g., DM, metabolic syndrome) suggests the need for “real-world” interventions designed to circumvent and attenuate barriers to achieving an adequate daily energy expenditure. Accordingly, physicians and allied health professionals should counsel patients to integrate multiple short bouts of PA into their day. Nonexercise activity thermogenesis—the spontaneous physical activities of daily living (e.g., fidgeting while sitting, standing while reading, moving the lower extremities while working at the computer)—represents another source of energy expenditure for many people. Standing also elevates lipoprotein lipase, an enzyme that improves fat metabolism while reducing insulin resistance. Thus energy expenditure during nonexercise time may be as critical for preventative health as structured exercise time. Pedometers can be helpful in this regard, as can programs that use them (e.g., America on the Move) to enhance awareness of PA by progressively increasing daily step totals. According to one systematic review, pedometer users significantly increased their PA by an average of 2491 steps per day more than their control counterparts. Although 10,000 steps/day has been the traditional recommendation to improve health, few data are available to support this recommendation. The CARDIA study of 2100 Black and White males and females (aged 38–50 years), with a mean follow-up of 10.8 years, reported that participants taking 7000 or more steps/day, compared with those taking fewer than 7000 steps/day, had a 50% to 70% lower risk of mortality. These findings suggest a viable alternative to a moderate-to-vigorous PA regimen to increase life expectancy.

The Activity Pyramid ( Fig. 17.4 ) has also been suggested as a model to combat America’s increasingly hypokinetic environment. This schematic presents a tiered set of weekly goals to promote improved CRF and health, building on a base that emphasizes the importance of accumulating at least 30 min of moderate-intensity activity on 5 or more days per week.

The Activity Pyramid, analogous to the US Department of Agriculture (USDA) Food Guide Pyramid, has been suggested as a model to facilitate public and patient education for adoption of a progressively more active lifestyle.

Copyright © 1996 Park Nicollet Health, Institute for Research and Education. Reprinted with permission.

INTENSITY AND DURATION

There is some controversy regarding the most appropriate exercise intensity and duration that are needed to optimally physically condition patients with the insulin resistance syndrome. Different risk factors associated with this condition may respond more favorably to different exercise frequency, intensity, and duration. For example, a randomized, controlled trial of previously inactive, overweight males and females with abnormal lipoprotein profiles compared the effectiveness of three different exercise regimens versus controls: high-amount, high-intensity exercise; low-amount, high-intensity exercise; and low-amount, moderate-intensity exercise. Although all exercise groups demonstrated improved responses on a variety of lipid and lipoprotein variables as compared with the control group, the most beneficial changes were noted in the high-amount, high-intensity exercise regimen. Because DM has been associated with increased body weight and fat stores, a sedentary lifestyle, and a low level of CRF, the initial exercise training intensity should approximate at least 40% of the peak V˙O ₂ , or heart rate reserve or 55% of the maximal heart rate. In the absence of data from an individual standard exercise test or a cardiopulmonary exercise test to volitional fatigue, this approximates a rating of perceived exertion (6–20 category scale) of 11 (fairly light) to 13 (somewhat hard), for a minimum accumulated duration of 30 min/day. Over time, in the absence of adverse signs and symptoms, the exercise intensity should be gradually increased, generally corresponding to a rating of perceived exertion up to 15 (somewhat hard to hard), to further improve CRF, based on age-, sex-, and good fitness-adjusted target intensities for training ( Fig. 17.5 ).

Age- and sex-adjusted “good” levels of cardiorespiratory fitness (CRF) for males and females and the recommended training intensity (60%–80% V˙O ₂ R, expressed as metabolic equivalents [METs] ) to achieve these fitness levels. Regression equations signify 70% V˙O ₂ R.

The exercise intensity recommendation can be achieved with a combination of moderate and vigorous PA, which approximates 40% to 59% and 60% to 84% of peak V˙O ₂ or heart rate reserve, respectively. The ACSM/AHA recommends that most adults engage in moderate-intensity exercise training for at least 30 min/day on at least 5 days of the week for a total of more than 150 min/week, or vigorous exercise training for at least 20 min/day on at least 3 days of the week for a total of more than 75 min/week, or a combination of moderate- and vigorous-intensity exercise to achieve a total energy expenditure of >500 to 1000 MET/min/week or more.

FREQUENCY

The frequency of exercise is an important consideration when structured exercise and/or increased lifestyle PA are used to treat the abnormalities associated with DM, especially insulin sensitivity and glucose use. Although even twice-weekly exercise sessions may favorably influence glycemic control, patients with DM should exercise at least 3 days each week with no more than 2 consecutive days without training, because increases in insulin sensitivity decline markedly by 48 h after exercise. Nevertheless, more frequent exercise (i.e., at least 5 days/week) may serve to maximize both the acute glucose-lowering effect and the effect on CV risk reduction.

A summary of exercise prescription and PA guidelines for patients with DM is shown in Table 17.3 , with specific reference to the type of exercise; major goals and objectives; and the recommended intensity, frequency, and duration. It should be emphasized, however, that if these recommended levels of exercise are deemed by the patient to be unrealistic or excessive, the patient should be counseled to achieve more moderate exercise dosages or intensities, because the primary beneficiaries are individuals with and without CVD who are in the least fit, least active subgroup (bottom 20%).

Table 17.3

Exercise Recommendations for Patients with Type 2 Diabetes Mellitus

Type of Exercise a	Major Goals and Objectives	Intensity, Frequency, Duration
Aerobic (large muscle activities)—for example, walking, jogging, stationary or outdoor cycling, swimming	Increase V˙o 2 peak; ADLs	40%–84% V˙o 2 R b or HRR; 55%–89% HR max; RPE 11–16 (6–20 scale)
	Improve glycemic control and coronary risk factors	No more than 2 consecutive days without exercising; four to five sessions per week (or more) may be needed to reduce body weight and fat stores
	Decrease rate-pressure product during submaximal exercise	≥150 or ≥75 min/week for moderate-intensity or vigorous-intensity exercise, respectively; ≥20 min per session
	Induce other cardioprotective benefits (e.g., enhanced nitric oxide vasodilator function, improved vascular reactivity, altered vascular structure, increased resistance to ventricular tachycardia and fibrillation)	For moderate-intensity activity (≤59% V˙o 2 R or HRR and/or ≤69% HR max and/or RPE ≤13), multiple shorter periods of exercise (10- to 15-min exercise bouts) accumulated throughout the day may elicit similar (or even greater) reductions in body weight and fat stores than a single bout of the same duration
		Complement structured exercise with an increase in daily lifestyle activities (walking breaks at work, gardening, household activities); move more, sit less
Resistance training (multijoint exercises, large muscle groups, progressive)	Increase muscle strength and endurance	8–10 different exercises that work major muscle groups; weight loads gradually increased over time
	Increase ability to perform leisure and occupational activities and ADLs	≥2 times/week
	Decrease the rate-pressure product at any given resistance (e.g., during lifting or carrying objects)	Moderate-to-vigorous intensity; one to four sets of 8–10 reps at a weight that cannot be lifted more than 8–10 times, c or 12–15 reps at a weight that cannot be lifted more than 12–15 times (for patients with known CHD), with 1- to 2-min rest periods between sets
	Assist in the maintenance of basal metabolic rate by maintaining or increasing lean body mass over time
Flexibility and stretching (upper and lower body ROM activities)	Improve balance and agility	Static stretches: hold for 10–30 s
	Decrease risk of musculoskeletal and orthopedic injury	2–3 days/week

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