Have some lean protein from lean meat, fish, beans and pulses. Page last reviewed: 30 November Next review due: 30 November This means your periods could be delayed if they haven't started yet or, if they have started, you could miss some. Or perhaps you haven't been eating a healthy, balanced diet. Are you more focused on being thin than being a healthy weight? Underweight adults Underweight adults Keeping your weight up in later life. Have you been eating healthily, or have you been skipping breakfast or lunch and eating snacks on the go? This means you could pick up colds and other infections more easily.