Specialty Corner: Medical Nutrition Therapy for Pre-Diabetes, Diabetes, and Obesity in Adults

Medical nutrition therapy (MNT) by trained registered dietitian nutritionists (RDN) is an integral part of a multidisciplinary health care team. Research has shown that this therapy is clinically beneficial and cost effective.^1,2,3 For patients with cardiometabolic disease, in particular diabetes and obesity, it is essential for optimizing quality of life and prevention of manifest cardiovascular disease. This article provides information on dietary plans and counseling aligned with best practices for cardiometabolic disease, and how nutrition services are structured and incorporated into clinical practice. 

 

 

The dietitian first assesses the patient’s clinical status, goals of care, current dietary patterns and specific food preferences. Potential barriers to behavior change are identified, such as access to healthy food choices, financial limitations, and wavering motivation to change. Next, the dietitian develops a specific eating plan according to clinical practice guidelines for diabetes care, weight loss, and other relevant diagnoses, incorporating lifestyle modification into the plan.^5,6,7 

 

 

General recommendations for a healthy diet include limiting highly processed foods, limiting fatty meats, and decreasing added sugars.⁸ Two well researched and accepted healthy dietary patterns are The Mediterranean Diet and the Dietary Approaches to Stop Hypertension (DASH) diet.

 

The Mediterranean Diet is distinct for its large amounts of fruits, vegetables, nuts, legumes, fish, whole grains, and extra virgin olive oil; moderate intake of red wine; and low amounts of dairy products, and red or processed meat.9 The positive physiologic effects are attributed to the large amounts of antioxidative, and anti-inflammatory nutrients found in the diet.¹⁰

 

The DASH Diet is also mostly plant-based with low-fat dairy and lean animal proteins to be eaten in small amounts daily. Daily sodium is limited to 1500 mg and alcohol is not recommended. The diet also includes a recommended number of daily servings for each food group, providing clarity and direction to those implementing the diet in their daily lives.¹¹

 

It is helpful for providers to counsel patients on diets that are popular with the general public but not aligned with best practices. Carbohydrate-restricted diets are helpful for patients with diabetes however, there is no evidence that very low (<10% of total daily energy (TDE)) carbohydrate is needed or helpful. When very low carbohydrate intake is combined with high fat (>30% of TDE) content in the diet (“Ketogenic Diet”) as a general weight-loss plan, there is generally an initial considerable weight loss. However, studies have shown that this dietary pattern may be associated with marked elevation in LDL-cholesterol, which increases risk for atherosclerotic cardiovascular events and cardiovascular mortality, and is not an easily sustained diet.^12,13

 

Intermittent fasting with daily time-restricted feeding such as 16 - 24 hours of fasting or 2 - 4 days a week of full-day fasting is also used for weight loss due to the net energy deficit. Current research on long-term consequences, benefits, and risks is not fully understood. Adverse effects include unmet nutritional needs, problems with taking certain medications with food, and hypoglycemia in patients with diabetes.^14,15 

 

 

Definitions of overweight and obesity   

Standard definitions of overweight and obesity are BMI >25 and obesity >30, respectively. However, this can be misleading as it does not consider different body types, such as a very muscular athlete or morphologic characteristics of certain ethnic groups. A better categorization of body morphology as a predictor of cardiovascular risk is central or abdominal obesity measured by waist-to-hip ratio but most easily assessed by waist circumference. Population specific waist circumference parameters are predictive of increased cardiovascular risk. High risk thresholds for men and women respectively (in inches) include 40/35 in the U.S., 37/31.5 in Europe, and 35.5/31.5 for those of Asian ancestry.¹⁶

 

Specific diets for weight loss  

There has been much debate over the optimal diet for weight loss purposes, and no one diet has been identified as “best.” An energy or calorie deficit is typically required for weight loss.¹⁷ Very low-calorie diets, defined as having under 800 calories per day are not recommended for health and sustainability reasons, as these types of diets often result in weight cycling (“yo-yo dieting”) which is associated with negative cardiometabolic impacts.¹⁸ 

 

Exercise and physical activity for weight loss 

Physical activity increases energy expenditure and plays a central role in a weight loss plan.¹⁹ Aerobic exercise in particular improves cardiovascular health, reduces incidence of diabetes and hypertension, and increases overall mood and sense of well-being.²⁰ The World Health Organization 2020 guidelines recommend 150 - 300 min of moderate-intensity, or 75 - 150 min of vigorous-intensity physical activity, per week.²¹ Resistance training should also be included in an exercise regimen as this builds muscle mass and increases resting metabolism.²²

 

Diet and exercise are the cornerstones and optimal methods for weight loss. However, when goals are not achieved and a patient has obesity-related co-morbidities, other options are considered. Medications that are FDA-approved as obesity treatment include phentermine/topiramate, naltrexone/bupropion, orlistat, and more recently GLP-1 receptor agonists, which were originally developed for treatment of diabetes. Side effects and drug interactions are among concerns with these medications and there can be significant weight regain, sometimes higher than baseline weight, with medication discontinuation. Bariatric surgery may be considered for patients with a BMI >40 or >35 and obesity related co-morbid conditions, in particular diabetes, but there are risks and long-term side effects of all procedures.^23,24

 

 

Dietary modification along with exercise and weight loss can help prevent development of type 2 diabetes in patients who have prediabetes (HbA1c 5.7 ---> 6.4 and oral glucose tolerance test 140-199 mg/dL after two hours).²⁵ Specific diets used are similar to those for patients with diabetes and include lower-carbohydrate and higher protein programs. In a CDC diabetes prevention program focusing on diet and other lifestyle changes, HbA1c was lowered by 0.28% at one year compared to 0.16% in the control group.²⁶ Lifestyle interventions remain the preferred approach to reverse prediabetes and have the strongest evidence for effectiveness.²⁷ 

 

Dietary treatment for Type 2 diabetes 

An eating plan for patients with Type 2 diabetes should be highly individualized and consider the presence and dosing of exogenous insulin. Special attention should be given to avoid hypoglycemia in patients taking insulin, especially when progressing with an exercise regimen. Key components of a diabetic dietary plan include training to understand the different food groups, how to read nutrition labels, education on types of carbohydrates (simple versus complex), portion sizes for carbohydrate-rich foods, and the importance of distributing carbohydrate intake across meals and snacks within the context of an overall healthy dietary pattern.^6,7

 

Additional evidence-based strategies in diabetes management include carbohydrate counting, the plate method, and carbohydrate food lists.^28,29 Evidence suggests there is no ideal mix of macronutrients for diabetes and obesity management.⁷ Continuous glucose monitors have emerged as an effective tool for improving HbA1c and glycemic time in range and may motivate individuals with diabetes to take a more active role in their blood sugar management.³⁰

 

 

Methods by which to structure a nutrition service vary greatly depending on where the service is “housed” (for example, within an existing lipid clinic or other outpatient clinic) as well as available resources and support at individual institutions. An example of a fully integrated service is at Georgia Heart Institute, part of the Northeast Georgia Health System. Patients who are referred to the lipid clinic are automatically scheduled for appointments with a dietitian and exercise physiologist, both part of the clinic’s Lifestyle Team. For the first appointment, the patient has 30 minutes with the lipid specialist and 30 minutes each with the dietitian and exercise physiologist, for a total of a 90-minute appointment. Follow up occurs at three months with the lipidologist and 1 - 2 more visits (or more as needed) with the Lifestyle Team, who also keep regular communication with the patients via phone calls and messages. Current evidence-based best practices in diabetes and obesity management advise a high frequency of counseling (>16 sessions over 6 months) to produce desired health outcomes. 

 

The protocol at the Georgia Heart Institute is an example of a comprehensive, multi-disciplinary program. However, many institutions and practices may not have adequate staff or infrastructure to allow this type of service. Options include outsourcing nutrition therapy or having a patient seek exercise counseling at a local YMCA or YWCA or sports center. The Academy of Nutrition and Dietetics offers a digital database of qualified RDNs who are licensed to practice medical nutrition therapy in various locations.³¹

 

 

Third party coverage for medical nutrition therapy varies. Medicare reimburses for patients with diabetes or CKD stage 3A or greater, providing a certain number of hours per year, with additional visits for any change in status (new diagnoses or treatment regimen). Medicaid coverage varies by state. Commercial insurance plans tend to follow Medicare regulations but may also cover visits if a patient meets other criteria, which can include overweight and obesity categories, or any cardiovascular disease risk factors (including metabolic syndrome). 

 

When nutrition therapy is not covered, the clinic’s billing and coding specialist may instruct how to incorporate time spent on counseling into the clinic note documentation as well as how to code and bill to optimize reimbursement for the clinic visit.  

 

Nutrition therapy is an integral part of medical care, in particular for those with cardiometabolic diseases such as prediabetes and obesity. Primary and specialty health care providers should discuss dietary strategies with their patients and refer to a registered dietitian nutritionist for counseling and development of a management plan. Professional medical organizations must continue to lobby for expanded reimbursement for these services and medical institutions seek ways to support integrated medical nutrition services for their patients.