Women can be healthy at a range of different weights, as long as they don't have too much body fat and aren't carrying too much weight around their waists. If you're worried about your size, check with your doctor to get a more personalized assessment of your body composition and your potential risk for any obesity-related health conditions.
Healthy Weight According to BMI
One of the more commonly used methods for estimating whether you're at a healthy weight is body mass index, with anything between 18.5 and 24.9 falling within the recommended range. If you're a women who is 5 feet 8 inches tall, you have a healthy BMI as long as you weigh between 125 and 158 pounds. BMI doesn't take body composition into account, however, and can underestimate body fat in women or overestimate body fat if you're very muscular. It's possible to be within the normal range for weight but still have too much body fat, which can increase your heart disease risk.
Waist and Hip Circumference and Health
Other simple measurements can help you figure out whether your current weight puts you at an increased risk for health problems. These include your waist circumference and your waist-to-hip ratio. If you carry most of your weight in your abdominal area, it could indicate that you have a lot of fat around your organs, which is called visceral fat. This type of fat is the most associated with increased disease risk, including high cholesterol, diabetes, high blood pressure and heart disease. Women who have a waist circumference of 35 inches or higher or a waist-to-hip ratio of 0.8 or higher may be carrying too much visceral fat. You can calculate your WHR by dividing your waist circumference by your hip circumference.
Waist-to-Height Ratio When You're 5'8"
Another ratio, which you can calculate by dividing your waist circumference in inches by your height in inches, may be even more useful for predicting heart disease risk. The waist-to-height ratio was better than either BMI or waist circumference for detecting an increased risk for heart disease in an analysis of 31 studies published in Obesity Reviews in 2012. If you're a woman who is 5 feet 8 inches tall, your WHtR should be between 0.42 and 0.48. This would be the case if your waist circumference was between 29 and 33 inches.
Diet and Exercise in Your 30s
If you weigh a bit more than you should or your waist is somewhat rounder than is healthy, a combination of diet and exercise changes can help you shed some fat. Although either eating fewer calories or exercising more can help with weight loss, you'll lose more weight and body fat if you do a combination of the two, notes a study published in Obesity in 2012. Exercise is particularly important for losing belly fat. The more aerobic exercise people do, the more belly fat they are likely to lose, according to a review article published in the International Journal of Obesity in 2007. In some cases, people lose belly fat even without losing weight. You should aim for two resistance-training workouts and at least 300 minutes of moderate-intensity cardio each week if you're trying to slim down. It's best to deal with any extra belly fat in your 30s, as your metabolism tends to slow down as you age, making it even harder to lose weight.