Nutrition, Weight Management, and Behavior Change
Energy balance and macronutrients
Body weight reflects energy intake versus expenditure. A pound of fat stores roughly 3500 kcal, so a 500–1000 kcal/day deficit supports about 0.5–1 kg (1–2 lb) of loss per week. A sensible initial goal is 5–10% of body weight over 3–6 months. General guidance: carbohydrate 45–65% of calories, fat 20–35%, protein about 0.8 g/kg/day for sedentary adults and higher (roughly 1.2–1.7 g/kg) for active individuals. Hydration before exercise is about 5–7 mL/kg four hours out. Practical tools include MyPlate, food labels, waist circumference and BMI.
Behavior change
Know the transtheoretical model stages-precontemplation, contemplation, preparation, action, maintenance-and match strategies to the stage. Supporting constructs include self-efficacy, decisional balance, and the processes of change. Social cognitive theory emphasizes self-monitoring, goal setting, reinforcement and social support. Motivational interviewing uses open questions, affirmations, reflections and summaries, and rolls with resistance rather than arguing. Goals should be SMART, and relapse should be framed as a normal part of the process.
Traps
The 3500-kcal-per-pound figure approximates fat loss, not total scale weight; early rapid loss includes water and glycogen. BMI misclassifies muscular clients. Scope of practice matters-provide general education and refer for medical nutrition therapy. Arguing with a contemplative client usually backfires.
Rule of thumb
A 90 kg client targeting 10% loss needs to lose 9 kg; at 0.5–1 kg/week that is roughly 9–18 weeks of a 500–750 kcal/day deficit.