Laboratory tests and dietary control strategies for obesity

Laboratory tests

Basic examinations include fasting lipid levels, fasting blood glucose, kidney function, liver function, and thyroid function. If fasting blood glucose exceeds 100 mg/dL (the latest standard for impaired fasting glucose), further testing is required to confirm this, and a glucose tolerance test should be performed. Glycated hemoglobin, fasting insulin concentration, and C-peptide levels can guide the treatment of metabolic syndrome and type 2 diabetes. If the patient has diabetes, urinary microglobulin concentration and glycated hemoglobin should be monitored. An electrocardiogram (ECG) should also be performed, which may reveal weight-related cardiovascular abnormalities such as left ventricular hypertrophy, right ventricular strain, ischemia, or arrhythmias.

Treatment methods

General matters

Weight loss therapy is not suitable for pregnant or breastfeeding women. Other contraindications include unstable mental illness, immune system disorders, and malignant tumors, the latter two of which may worsen the condition due to calorie restriction. Patients who have gained less than 20 pounds (1 pound ≈ 0.45 kg) in adulthood, have no other comorbidities, and have a BMI of 25–25.9 should be encouraged to prevent further weight gain, and they should be guided on how to do so, perhaps simply by increasing their physical activity.

For most patients seeking weight loss, the initial treatment goal is to reduce their baseline weight by 10%. This is not only beneficial to health but also typically achieved in about six months. Once the 10% target is reached, clinicians and patients can decide whether further weight loss treatment is needed.

Dietary control

Weight loss requires restricting energy intake, which can be achieved through dietary adjustments and exercise. One unit of energy is expressed as 1 kilocalorie (kcal), equivalent to the energy required to raise the temperature of 1 kg of water by 1°C. To maintain weight, most people need to consume 1500–2500 kcal (formerly known as "kilocalories") per day. To lose 1 pound in a week, you must reduce your calorie intake by an additional 3500 kcal that week, or reduce your intake by at least 500 kcal per day for seven consecutive days. Methods of weight loss through dietary control include complete fasting, very low-calorie diets (VLCD), low-calorie diets (LCD), balanced deficit diets, and fad diets. Complete fasting and near-complete fasting can be used for rapid weight loss, with a daily calorie intake of less than 400 kcal. These "starvation therapies" are rarely recommended due to serious consequences such as lean body mass loss, water and electrolyte abnormalities, decreased basal metabolic rate, arrhythmia, and malnutrition. VLCD (Vitamin-Defined Fasting) strictly controls daily calorie intake to 400-800 kcal, resulting in a significant reduction in calories. It is suitable for individuals with a BMI greater than 30 or a BMI greater than 27 who have comorbidities and have failed to lose weight through traditional diet control. The term "protein-preserving modified fasting (PSMF)" often refers to this method. VLCD is suitable for rapid and significant weight loss to improve obesity-related life-threatening comorbidities. This method has been used in pre-operative preparation for bariatric surgery, as pre-operative weight loss may significantly reduce surgical risks.

VLCDs are often commercially produced meal replacements (such as milk-ice cream mixes, hot drinks, nutrition bars, and soups) that combine the recommended daily intake of essential nutrients, such as vitamins, into a complete meal replacement. Another approach to VLCDs is to consume meal replacements (usually beverages or nutrition bars) twice a day, with the third meal consisting of high-quality lean protein and vegetables. Yet another method involves a dietitian designing a meal plan using real foods, including weekly menus, food types, and vitamin and mineral supplements. In these latter two approaches, protein intake should be 1–1.5 grams per kilogram of ideal body weight per day, with multivitamin supplementation to prevent insufficient intake. Patients are closely monitored through outpatient visits and laboratory assessments. Potential complications of VLCDs include symptomatic gallstones, arrhythmias, and exacerbation of underlying medical conditions. Other common side effects include orthostatic hypotension, constipation, dry skin, brittle nails, hair loss, and menstrual irregularities.

The LCD diet can result in an average weight loss of 1-2 pounds per week and is suitable for most overweight and obese individuals. It provides 800-1500 kcal per day. It is currently unclear which type of LCD diet is the most effective or healthiest. Traditional LCD is a low-fat formula that includes lean protein, complex carbohydrates, and less than 30% fat. The Adult Treatment Panel II (ATP II, the second report of the Expert Panel on the Detection, Assessment, and Treatment of Hypercholesterolemia in Adults) has proposed a "first step" LCD (500-1000 kcal daily energy deficit) formula: 30% or less fat, approximately 15% protein, and 55% or more carbohydrates. Other recommendations include 20-30g of fiber, 1000-1500mg of calcium, and no more than 2400mg of sodium per day. It is recommended to eat 5-9 servings of fruits and vegetables daily, as these higher-density, lower-calorie foods are more palatable to patients. In addition to aiding weight loss, a diet high in fruits, vegetables, and fiber may reduce the incidence of certain cancers and type 2 diabetes. Currently, only 1% of American children meet all the Recommended Daily Allowances (RDA) guidelines, and only 30% meet the recommended amounts of fruits and vegetables. In a study of children and parents, families that emphasized simply eating more fruits and vegetables saw a decrease in the percentage of overweight children at the end of the study.

Some liquid deficiency diets (LCDs) require patients to avoid certain foods, such as sweets. However, recent research on LCDs advocates for a complete diet, adjusting only the proportions of its components. Underestimating portion sizes often hinders weight loss. While consuming only 3 ounces (about the size of a deck of cards, 1 ounce ≈ 28.35 grams) of fish, poultry, or beef, restaurant portions are often several times larger. Therefore, paying attention to portion sizes can potentially reduce daily calorie intake by several hundred kilocalories. By visually estimating or weighing different foods at home, patients can better manage portion sizes when dining out. These balanced deficit diets are modifications of LCDs, with fewer restrictions on daily calorie intake.

While the medical community has raised objections to low-carbohydrate diets, many recent studies suggest that they are no less effective than traditional LCD diets in terms of weight loss and maintenance, although there is currently no consensus on this dietary approach. This plan does not require calorie counting, does not restrict protein intake, allows for a minimum amount of carbohydrates (20 grams/day, or 80 kcal) during the "induction" phase, and also restricts fat intake.

Health professionals should advise people to resist so-called "trendy" diets, such as those involving coffee enemas for "intestinal cleansing," and single or two types of weight-loss foods like cabbage soup or grapefruit diets, all of which may pose potential risks. These diets can cause nutritional deficiencies, dehydration, and electrolyte imbalances, and their unpleasant taste makes them difficult to stick to, leading to weight rebound.