Editor's Note: Commentary based on Pallazola VA, Davis DM, Whelton SP et al. A clinician's guide to healthy eating for cardiovascular disease prevention. Mayo Clin Proc Inn Qual Outcomes 2019;3:251-67.

The recently released 2019 ACC/AHA Guideline on the Primary Prevention of Cardiovascular Disease has given clinicians a comprehensive, evidence-based resource to inform management of patients at increased risk of atherosclerotic cardiovascular disease. In addition to guidance on risk stratification and medication prescribing, the Prevention Guideline stresses the importance of lifestyle intervention through diet and exercise. However, dietary counseling remains difficult for many clinicians as it seems the landscape is continually shifting.

Popular culture espouses a wide variety of dietary myths and trends, so-called "fad" diets. However, nutrition science has consistently demonstrated that a healthy diet is comprised of high quantities of non-starchy vegetables, fruits, whole grains and legumes plus moderate consumption of nuts, seafood, lean meats, low-fat dairy and vegetable oil. Calorie restriction and portion control must exist in every diet to maintain a healthy weight. However, many physicians and patients need greater specificity regarding food choices.

To provide clinicians with an evidence-based approach to dietary counseling, Pallazola et al. reviewed the available evidence.¹ This review focuses on the basic tenets of a healthy diet, evidence-based dietary patterns, risk factor specific nutritional interventions and integrates tips for dietary counseling of patients.

Carbohydrates
Carbohydrates exist on a spectrum from simple to complex, which differ in how quickly they are digested and absorbed. Complex carbohydrates (legumes, whole grains) should be substituted for simple carbohydrates (white flour/rice, table sugar) given their association with lower cardiovascular disease (CVD) risk, cancer risk and all-cause mortality.

A major source of simple carbohydrates in many diets remains sugar-sweetened beverages (SSBs), and the authors identify one simple intervention that all patients can make regardless of socioeconomic status (SES): eliminate SSBs in their diet in favor of water (plain, carbonated, unsweetened or flavored). Reminding patients that fruit juices, smoothies, and sweet teas are a similar source of refined sugar in addition to concentrated calories is also important. In addition, physicians should be reminded that these beverages have not demonstrated improved health when compared to whole fruit.

Fruits and Vegetables
Whole fruit and vegetables remain staples in a healthy diet and are widely-recommended. Simply consuming a higher proportion of fruits and vegetables is a great place to start with most patients, but if refinement is needed, leafy green vegetables and berry consumption (3 servings per week) have been shown to have health benefits as well. Starchy vegetables (white potatoes, corn, green peas) are rich in complex carbohydrates but calorically dense and should be consumed in moderation. Whole fruit is preferable to dried fruit because whole fruit is both more filling, has a lower sugar content, and is less calorically dense.

Fats
Dietary fats exist on a spectrum of chemical composition that includes trans-, saturated, mono-unsaturated and poly-unsaturated fat. Trans-fats are strongly associated with adverse cardiovascular outcomes and should be minimized. The U.S. Food & Drug Administration (FDA) has taken steps to decrease the amount of trans-fat in food but they still exist in many processed and snack foods (frozen pizza, fast food, crackers, cookies, cakes, frozen pies, etc.).

Saturated fats are similarly found in a variety of processed foods, red meat, cheese, whole milk, and butter and should also be limited in a healthy diet. Reduction has been associated with lower LDL-C levels. Mono- and polyunsaturated fats should be consumed in moderation and can be found in non-tropical vegetable fats and other fats that are liquid at room temperature.

Dairy products are a source of fats but current data suggest either neutral or protective associations with cardiovascular health; skim or 1% milk is still recommended over whole milk. Cooking oils contain varying amounts of unsaturated, saturated and trans fats, with extra virgin olive oil and canola oil generally recommended over butter, margarine, and coconut oil (Table 1).

Table 1: Polyunsaturated, Monounsaturated, total saturated and total trans-fats composition of common cooking oils²

Cooking Oil	Total Polyunsaturated (per 100 g)	Total Monunsaturated (per 100 g)	Total Saturated (per 100 g)	Total Trans-fat (per 100 g)
Canola oil	28.142	63.276	7.365	0.395
Olive Oil	10.523	72.961	13.808	0.000
Margarine (hydrogenated)	20.900	39.300	16.700	0.562
Lard	11.200	45.100	39.200	0.000
Butter (salted)	3.043	21.021	51.368	3.278
Coconut oil	1.702	6.332	82.475	0.028

Meats
Guidelines continue to recommend moderate consumption of lean poultry, seafood and nuts while limiting red meat. Processed meats such as deli/cold cuts, sausage, and bacon have the greatest association with adverse health outcomes and should be minimized. Fish may be especially important because of higher levels of omega-3 fatty acids which are recommended to replace saturated fats; salmon, tuna, and mackerel are good options.

Diet Patterns
These basic principles are incorporated into the dietary patterns with the highest level of evidence to support them: Mediterranean, DASH and the Healthy Vegetarian diets (Table 2). The first two have been linked to lower risk for mortality from coronary heart disease, cardiovascular disease and all causes.

Table 2: Components of the DASH Diet, USDA Healthy Mediterranean-Style Eating Pattern, and USDA Healthy Vegetarian Eating Pattern¹

	DASH Diet (based on 2000 calorie diet)	USDA Healthy Mediterranean (based on 1800 calorie diet)	USDA Healthy Vegetarian Diet (based on 1800 calorie diet)
Grains	6-8 servings daily	6 ounces daily (2 whole and 2 refined) per day	6 ounces daily (3 whole and 3 refined) per day
Vegetables	4-5 servings daily	2.5 cups daily	2.5 cups daily
Fruits	4-5 servings daily	2 cups daily	1.5 cups daily
Nuts, seeds, and legumes	4-5 servings daily	2 cups daily	3 cups daily
Fat-free/ and low-fat dairy	2-3 servings daily	6 ounces daily	3 ounces daily
Lean meats, poultry, and fish	< 6 ounces daily	2 ounces daily	2 ounces daily
Fats and oils	2-3 servings daily	24 grams daily	24 grams daily
Sweets and sugars	≤5 servings weekly	Limit – no quantity specified	Limit – no quantity specified
Sodium	<2.3 grams sodium daily	Limit – no quantity specified	Limit – no quantity specified
Alcohol	≤1 drink daily for women, ≤2 drinks daily for men	Limit – no quantity specified	Limit – no quantity specified

The Mediterranean diet focuses on 1) high leafy green vegetable intake, fruits, whole grains, nuts, legumes and extra virgin olive oil; 2) moderate intake of fish, lean meats, low fat dairy, poultry; 3) low intake of red meats and sweets; 4) wine in moderation.

The DASH diet is similar but has greater allowance for dairy, a sodium intake limit and less emphasis on seafood. The Healthy Vegetarian diet maintains the same principles but substitutes soy products, legumes, nuts and whole grains for meat, seafood and poultry. A vegan diet eliminates all animal-derived products, which has also demonstrated improved health outcomes, but with an increased risk of deficiencies in certain vitamins.

Low-carbohydrate high protein/fat (LCHF) diets have gained in popularity recently and have been associated with weight loss and increased insulin sensitivity but also increased LDL-C levels. They also may be associated with increased all-cause mortality when used for extended periods. The authors of the review feel there is insufficient evidence for clinicians to recommend LCHF for cardiovascular health.

Calorie restriction and carbohydrate reduction, especially in patients with diabetes, remain mainstays of therapy. Patients also need to choose foods with a low glycemic index. The quality as opposed to quantity of fat intake is also important in the development of type 2 diabetes.

Lipid control is strongly tied to the selection of fats and simple substitutions in some cases can make a large difference. The authors say this could be particularly important in ethnic/native diets where these substitutions can greatly reduce their health risks while maintaining the culture of the food. The authors also acknowledge the importance of reduced sodium intake (<2 grams) in patients with high blood pressure.

Conclusions
The above principles provide an overarching construct for healthy diet in all individuals. Unfortunately, understanding which foods to recommend is only part of the equation. The authors provide clinicians with advice on how to approach dietary counseling, especially in patients with lower SES. The best diet is the one the patient can implement and sustain. Many patients will have perceived barriers such as food-access or financial constraints. Simple changes such as eliminating SSBs, decreasing the frequency of fast food or buying low-sodium canned vegetables can be effective. Legumes (especially dried) and frozen vegetables are also low-cost and accessible options to modify diets toward the previously mentioned concepts.

Many patients may feel overwhelmed by needing to completely "overhaul" their diet and physicians may feel overwhelmed by the time such discussion takes. One strategy recommended is to discuss one concept or change per visit. Additionally, clinicians can have patients fill out a simple questionnaire while waiting for their visit. Dietary modification is frequently an incremental process and sustained success takes time.

This current review not only provides the evidence behind certain dietary recommendations but also guidance for commonly encountered hurdles in counseling patients on these changes. It stands as a reminder that we must empower clinicians with the knowledge, and embolden them to carry out the difficult task of counseling patients on the many important changes they can make in their diet and nutrition. Together with the additional strategies laid out in the 2019 ACC/AHA guidelines, these changes can have a transformative impact on the health of individuals and populations.

References

1. Pallazola VA, Davis DM, Whelton SP et al. A clinician's guide to healthy eating for cardiovascular disease prevention. Mayo Clin Proc Inn Qual Outcomes 2019;3:251-67.
2. United States Department of Agriculture Agricultural Research Service. USDA Food Composition Databases. https://ndb.nal.usda.gov/ndb/. Accessed April 29, 2004.

Clinical Topics: Diabetes and Cardiometabolic Disease, Dyslipidemia, Prevention, Lipid Metabolism, Nonstatins, Diet, Hypertension

Keywords: Dyslipidemias, Primary Prevention, Secondary Prevention, Vegetables, Fruit, Dietary Fats, Diet, Mediterranean, Insulin, Glycemic Index, Insulin Resistance, Fatty Acids, Omega-3, Nuts, Weight Loss, Fast Foods, Risk Factors, Vitamins, Diabetes Mellitus, Type 2, United States Department of Agriculture, Seafood, Hypertension, Diet, Vegetarian, Cardiovascular Diseases, Coronary Disease

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