This might be happening for different reasons.  It’s possible that previously eating less has caused you to feel full more quickly or that your body is no longer absorbing nutrients as efficiently. The best way to increase or maintain your weight is by increasing the amount of calories you eat throughout the day by having three meals and two to three snacks. Meals should be balanced and consist of a portion of grains, protein, fruit/vegetable and fat. If you’ve already been eating three meals and three snacks, you can start adding in or increasing foods that might have greater energy density like butter, oil, and nut butters. If you are feeling too full on foods you might try drinking more calories. There are calorie-rich supplemental drinks you can buy such as Ensure and Orgain, that can help increase intake throughout the day.