Being underweight can make you vulnerable to illness, contribute to feelings of fatigue and weakness, and upset your normal menstrual cycle. Gaining weight in a healthy way takes time, though. In a month, you can expect to add 2 to 4 pounds to your frame. You don't want to eat just any foods that contain a lot of calories to add the weight. Nutrient-dense, high-calorie foods and exercise support healthy weight gain that improves your health and appearance.
Create a Calorie Surplus for the Month
To gain weight, you'll need to eat more calories than you burn daily. A surplus of 250 to 500 calories per day will contribute 1/2 to 1 pound of healthy weight to your body. To determine how many calories you need daily to maintain your current weight, use an online calculator or consult with a dietitian. Then add the 250 to 500 calories to that number to come up with your daily calorie goal for weight gain.
Spread your calories out over three meals and two snacks. This way you don't have to stuff yourself at any one meal, and it becomes easier for you to hit your target intake. Take advantage of every opportunity to fit in calories to help you meet your one-month weight-gain goal.
Increase Calories at Meals
Eating larger portions of healthy foods is an easy way to add calories. For example, cook up an extra 1/3 cup of dry oatmeal at breakfast to add 102 calories; add an extra 1/2 cup of chicken to lunch for 107 calories; have another 1/2 cup of whole-wheat pasta at dinner for another 87 calories; or choose a large sweet potato instead of a medium one to add 60 calories.
If adding portions makes it hard for you to finish your meals, try calorie-dense additions -- foods with lots of calories in a small serving. Put 50 raisins in your morning cereal for another 78 calories; add an ounce of walnuts to your salad for 183 calories; or, before adding sauce, toss whole-grain pasta in 1 tablespoon of olive oil for 124 calories. Extra peanut butter on toast, avocado on sandwiches and cooking cereal in milk are other ways to sneak in extra calories at mealtime.
Snacks Are Important for Weight Gain
Junky snack foods such as chips, cookies and processed snacks do contain additional calories, but overeating the sugar and refined grains poses health risks, such as cardiovascular disease, even if you're slender. Opt for whole-food snacks instead: 1/2 cup of hummus provides about 200 calories; a tablespoon of almond butter offers 100 calories; and a large banana has 120 calories. Dried fruits, nuts and seeds contain concentrated calories that you can easily carry with you so you don't miss a snack.
Milk and 100-percent fruit juice between meals increase your daily calorie intake when whole food isn't practical. Avoid drinking with meals or you might fill up too much to finish eating. Mix dry milk powder into a glass of milk to add extra calories to each sip, or add it to casseroles and smoothies for a little extra calories and protein. The powder contains 80 calories and 8 grams of protein in 1/3 cup.
Extra calories from protein foods help support efforts you make to add healthy muscle mass, as well as calories. An additional ounce or two of meat on a sandwich, cottage cheese as a snack or a scoop of whey protein in a glass of milk are all ways to increase calories and protein intake.
Move to Stimulate Your Appetite
Even though you're trying to take in more calories than you burn, keep moving -- moderate-intensity cardio keeps you healthy and stimulates your appetite so you can eat all the calories you need to gain weight. Aim for the minimum 150 minutes per week recommended by the Centers for Disease Control and Prevention.
Strength training will help you put on healthy muscle mass, which will increase your weight and muscle tone. Don't worry about it making you look unfeminine; you have to train exceptionally hard for the extra muscle mass to turn you into a body builder. Two training sessions per week that address all the major muscle groups in at least one set of eight to 12 repetitions are enough for health and fitness. If you're interested in building size, work up to two or three sets of six to eight repetitions using heavy weights.