As you enter your forties, you are also entering perimenopause, when levels of your sex hormones progesterone and estrogen decline. Besides regulating your menstrual cycle and reproductive functions, these hormones also impact restful sleep and relaxation. A decrease in progesterone and estrogen levels may lead to sleep disturbances, restlessness, and insomnia.1 Because changes in sleep patterns have been associated with weight gain, sleepless nights may make weight loss increasingly difficult.2
Hormonal changes are one of the main reasons that women tend to lose more muscle as they approach menopause. Diet and exercise also play a role.12 On average, adults lose 3 to 8 percent muscle every decade after age 30.13,14 By the time you reach 80, you may have about 30 percent less muscle than you had at age 20.15,16 Muscle loss over time can lead to slower RMR, increased fat, weight gain, weakness, and fractures.17
Changes in your activity levels are one of the main reasons that losing weight after 40 may be more challenging than before. Like many women, you may be putting others first and simply not finding time to exercise. You may also notice that your joints can no longer handle the same activities as before. However, a lack of exercise can lead to muscle loss and fat gain.
If you eat healthy and exercise regularly and still can’t lose weight, your thyroid might not be working like it should. This happens in about 5% of people, and it's most common in women and people over 60. In addition to weight gain, it can also cause fatigue, joint or muscle pain, and depression. Medications can help, so get it checked if you think it might be an issue.