What are the best ways for an underweight 19-year-old male to gain weight?

Weight Gain Strategy for an Underweight 19-Year-Old Male

An underweight 19-year-old male should increase daily caloric intake by 500 kcal/day above current consumption through energy-dense whole foods, combined with resistance training 3 days per week for 60-120 minutes, targeting a weight gain of approximately 0.22 kg (0.5 lb) per week, primarily as lean body mass. 1

Caloric Surplus Implementation

• Add 500 kcal/day above typical intake through structured meal additions rather than simply "eating more," as this produces measurable weight gain of ~0.22 kg weekly over 10 weeks in young athletic individuals 1
• Focus on energy-dense whole foods including nuts (particularly peanuts and peanut butter), full-fat dairy products, lean meats, fish, whole grains, and healthy oils 2, 1
• Prioritize liquid calories over solid foods when possible, as liquids are less satiating and easier to consume in surplus 2
• Consume larger portion sizes at each meal and incorporate calorie-dense snacks between meals 2

Macronutrient Distribution

• Ensure adequate protein intake (1.6-2.2 g/kg body weight daily) to support muscle protein synthesis during resistance training 2, 1
• Include sufficient carbohydrates (5-7 g/kg body weight daily) to fuel training sessions and support recovery 2
• Do not restrict dietary fat; healthy fats provide concentrated calories (9 kcal/g) essential for reaching caloric surplus 3, 1
• The macronutrient source matters: higher carbohydrate snacks may promote slightly more total weight gain (2.7 kg vs 1.6 kg over 10 weeks) compared to higher fat options, though lean mass gains are similar 1

Resistance Training Protocol

• Perform whole-body resistance training 3 days per week for 60-120 minutes to ensure weight gain occurs primarily as lean muscle mass rather than fat 1
• Include compound movements (squats, deadlifts, bench press, rows) that stimulate multiple muscle groups 2
• Progressive overload is essential—gradually increase weight, sets, or repetitions over time 2
• Without resistance training, caloric surplus will result in disproportionate fat gain rather than healthy muscle development 1

Meal Timing Considerations

• Consume higher-calorie breakfasts as this pattern may help with weight management and metabolic health 4
• Distribute the 500 kcal surplus across multiple eating occasions rather than one large meal 2
• Consider a pre-bedtime snack to extend the anabolic window overnight 2

Monitoring and Expectations

• Weigh weekly at the same time of day (preferably morning, after voiding) to track progress 1
• Target weight gain of 0.22-0.45 kg (0.5-1 lb) per week; faster gains likely represent excessive fat accumulation 2, 1
• Expect approximately 1.5 kg of lean body mass gain over 10 weeks with proper adherence to both dietary and training protocols 1
• If weight gain plateaus after 4-6 weeks, increase caloric surplus by an additional 250 kcal/day 2

Critical Pitfalls to Avoid

• Do not rely on "junk food" or ultra-processed foods to reach caloric surplus, as this promotes unhealthy fat gain and poor metabolic health 5, 3
• Avoid excessive fat intake (>42% of daily calories), which was observed in 92.9% of underweight patients and associated with hypercholesterolemia and hypertriglyceridemia 3
• Do not neglect micronutrients—underweight individuals commonly have deficiencies in potassium, calcium, magnesium, iron, B vitamins, and vitamin D that require correction 3
• Avoid inadequate carbohydrate intake (<40% of calories), which was present in 92.9% of underweight patients and impairs training performance 3

Medical Evaluation

• Assess for reversible causes of low body weight including hyperthyroidism, malabsorption disorders, depression, or eating disorders before implementing weight gain strategies 6
• Check baseline body composition via bioelectrical impedance or DEXA scan, as 50% of underweight individuals have skeletal muscle deficiency while 10% have normal or above-average muscle mass 3
• Monitor biochemical parameters including lipid profile, iron studies, vitamin D, and calcium levels, as these are commonly abnormal in underweight individuals 3