Nutrition is critical to health. Poor nutrition and a sedentary lifestyle are the main contributors to the rising prevalence of obesity and preventable chronic diseases that impact health. Over half of adults in the United States are overweight or obese and suffer from at least one diet-related chronic health condition including cardiovascular disease (CVD), type 2 diabetes mellitus (T2D), and hypertension, among others.¹ Following a healthy calorie-reduced diet that is practical, sustainable, and consistent with the patient’s lifestyle and social norms is foundational to obesity care. It is also notable that despite excess caloric intake in the US population, nutrient deficiencies among adults with obesity are increasingly recognized as a result of poor food quality.²

Dietary counseling in the office setting can be challenging. Time restraints and low healthcare professional (HCP) confidence in nutrition knowledge can lead to
oversimplification of the recommendations provided. For many patients with obesity, dietary education is not enough to effectively promote and sustain changes in eating habits. As a result, a more deliberate and thorough approach is recommended, often implemented by other clinicians such as a registered dietitian nutritionist (RDN). Multidisciplinary teams for obesity care commonly include an HCP (physician and advanced practice providers [nurse practitioner or physician assistant]), RDNs, as well as behavioral health and exercise specialists. Collaboratively, these disciplines can help HCPs by dedicating their time and expertise to develop, implement, and support an individualized care plan for the patient.³ When these disciplines are not readily available within a practice, a “virtual” care team can be created by identifying specialists in the community or healthcare system that can serve as valuable resources for patients. However, with proper guidance, the HCP should be able to initiate meaningful and effective dietary counseling during a dedicated office visit.

Several tools are available that can facilitate dietary counseling. The US Department of Agriculture (www.choosemyplate.gov/resources/all-resources)⁴ offers online resources to develop meal plans that can be individualized to a specific calorie goal and eating pattern. There are also several smartphone apps and websites that can help with meal planning and dietary tracking (Table 5.1). Depending upon the electronic literacy of the patient, web-based technologies and mobile devices that help HCPs and patients track progress and support dietary change should be routinely considered.

The key principle to achieve weight loss is to create an energy deficit, i.e., to consume fewer calories than are being burned.⁵ This is consistent with the first law of thermodynamics. Yet, as simple as this seems, successful implementation is limited by multiple factors including individual genetic, physiologic, psychological, environmental, and social determinants that can impact energy balance. As a result, long-term success at losing and maintaining weight with dietary intervention alone is challenging.⁶ However, understanding the principles of energy balance and how they impact weight loss can establish a sound foundation on which to help patients succeed.

Individual energy requirements (i.e., calories needed to maintain or to lose weight) are determined by many factors including age (drops as we age), sex (higher for men than women), height (the taller you are, the higher your energy needs), and weight (the heavier you are, the higher your energy needs).⁷ The single largest predictor of energy requirement is muscle mass. Energy expenditure (calories burned) comprises three components:

Both basal and total energy requirements can be measured; however, precise measurement of energy expenditure is impractical in the primary care setting. Several prediction equations, such as the Harris-Benedict equation,⁹ Mifflin-St Jeor equation,¹⁰ and WHO,¹¹ are available to estimate energy expenditure if a more precise estimation is desired for an individual patient. These formulas are often employed by RDNs when calculating dietary requirements. When using one of these equations, the next step is to introduce a caloric restriction for weight loss. Reducing calorie intake by 500 to 750 kcal/day (or 30% of calorie needs) can be expected to lead to weight loss. However, from a practical perspective, use of the American Heart Association/American College of Cardiology/The Obesity Society (AHA/ACC/TOS) recommendations of 1,200 to 1,500 kcal/day for women and 1,500 to 1,800 kcal/day for men is suitable for most patients with obesity as an initial treatment goal. The calorie target can then be adjusted up or down over the first 1 to 2 months of treatment, based on the patient’s weight loss.

Due to biological changes that occur with weight loss, a weight reduction of just 10% of initial body weight leads to a phenomenon called “adaptive thermogenesis.”¹² This term describes the observation that an individual who has lost weight burns fewer calories per 24-hour period, compared to an identical individual who is not weight reduced. For patients, this sobering reality means that, once weight loss stabilizes, the patient must maintain the same (lower) level of calorie intake in order to maintain the weight loss they have achieved. Adaptive thermogenesis appears to persist for at least 1 year after weight loss or longer.¹³ Thus, regardless of which dietary intervention is selected, the patient must be prepared for the weight loss plateau that inevitably occurs after the body’s energy expenditure has dropped to be equivalent with the lower calorie intake that initially led to weight loss.

The most important dietary factor to lose weight is caloric reduction. As long as calories are reduced, the macronutrient composition of food (percent of carbohydrate, protein, and fat) can vary.⁵,¹⁴ Patients and their HCPs can choose a meal plan based upon the presence of comorbid conditions, taste/food preference, family culture, access, affordability, and overall health. Often, patients will benefit from seeing an RDN for individual dietary counseling. In the section below, the composition and research behind several evidence-based healthy eating patterns are discussed, followed by several shorter-term restrictive diets that are commonly used in clinical practice (Table 5.2).