Similar to spot reduction, spot weight gain is impossible; you cannot tell your body where to store fat. The only way to thicken your thighs is by gaining weight all over. Eventually the size of your legs will increase. Your fast metabolism may be seen as a blessing by many, but if you desire to gain weight in your legs, it can be an obstacle. Adjusting your diet and performing targeted muscle-stimulating exercises can help you get thicker thighs.
Increase your portion sizes so you consume more calories. Eat more food during breakfast, lunch and dinner, and snack frequently between meals. If you dislike eating large meals, consume up to six regular-sized meals over the day so you still get the extra calories.
Ban all low-calorie, non-fat and sugar-free food products from your diet. Replace them with calorie-dense, full-fat, nutrient-rich products. Eat foods such as dried fruits, cheese, nuts, peanut butter and avocados. Drink mixed-fruit juices and whole milk, or make your own smoothies with fruit and full-fat yogurt.
Consume foods that digest slowly so your metabolism is forced to slow down. These would include whole-wheat bread, oatmeal, brown rice and cereals high in fiber.
Add more calories to foods during food preparation. Add cheese to eggs, and make an omelet in butter. Add peanut butter to buttered toast. Prepare soups and mashed potatoes with dried milk powder. Add butter to vegetables or rice. Have dips, sauces and gravies with your meals.
Drink shakes that are high in nutrients and calories.
Avoid cardiovascular exercise -- you want to hold on to the calories you consume. Perform strength-training exercises instead, two days a week. Exercise all body parts so you build and maintain muscle tissue and avoid the extra calories from storing as fat in undesired areas of your body.
Perform leg-strengthening exercises such as squats. Hold a dumbbell in each hand, next to your body. Stand with your feet hip-width apart. Bend your knees to 90 degrees as you lower your body down while holding the dumbbells next to your body. Visualize sitting in a chair. Place all your weight on your heels. Push yourself back up to the beginning position. Repeat the exercise 12 times for a total of three sets.
Include split squats in your exercise routine. Hold dumbbells in your hands, next to your body. Step forward with your right leg as your come up on the ball of your left leg. Bend your knees and lower yourself straight down to the floor. Aim to reach the floor with the left knee. Push yourself back up to the beginning position and complete 12 repetitions before switching legs. Perform three sets.