Both your nutritional needs (the food and water) and your metabolism (how fast your body converts food to energy) change at this age. Your metabolism gets slower. Women lose about half a pound of muscle per year starting around the age of 40. That makes losing weight even more difficult. Some of the changes women experience are due to decreased hormones, reduced activity level, and medical conditions.
Loss of taste. Some medicines alter your sense of taste making you lose your appetite. Ask your health care professional if there are alternatives to the medicine you're taking. You might also experiment with spices to make foods tastier. Also, rotating tastes of each food on your plate, rather than eating one food at once, can help you taste various flavors better. Foods with strong scents also taste better, since taste and smell are linked.
It's a cliché, to be sure, but a balanced diet is the key to good nutrition and good health. Following that diet, however, isn't always that easy. One challenge is that women often feel too busy to eat healthfully, and it's often easier to pick up fast food than to prepare a healthy meal at home. But fast food is usually high in fat and calories and low in other nutrients, which can seriously affect your health. At the other extreme, a multimillion dollar industry is focused on telling women that being fit means being thin and that dieting is part of good nutrition.