Forget about simply cutting processed foods or carbs from your diet: Celebs like Hugh Jackman and Kourtney Kardashian reportedly aren’t eating much—if at all—some days. Known as intermittent fasting (IF), the goal of the buzzy eating plan is to speed up metabolism, encourage healthy weight management, and improve overall health by following certain time-specific restrictions on eating. But if the idea of severely cutting calories or skipping meals on some days sounds iffy to you, there’s good reason to be hesitant—especially if you’re a woman.
In theory, periods of fasting allow your body to churn through the sugar in your blood, lowering your insulin levels so you eventually use stored fat as energy. Some research suggests that IF might improve blood sugar, pressure, and cholesterol levels, promote healthy weight management, and reduce Type 2 diabetes risk—although most studies so far are in animals.
The calculations on IF benefits, however, may change for women. “In my patients, I’ve seen a lot of females who can’t go above 18 hours of fasting, while the guys can do three-day water fasts,” says Ruvini Wijetilaka, MD, a board-certified internal medicine physician at Parsley Health in New York City. “I’m not saying all fasting is bad. But severe caloric restriction in IF is not beneficial fertility-wise.”
As it’s presented in high school health class, pregnancy seems pretty straightforward: egg plus sperm equals baby. But conception involves a delicate balance of hormones and timing that can be affected by everything from your weight to what you eat (or what you’re not eating). For example, having a very high BMI can mess with a person’s hormone balance, leading to irregular ovulation, explains Aaron Styer, MD, a reproductive endocrinologist and a founding partner and co-medical director of CCRM Boston. People who are underweight can also struggle to get pregnant. “The female pituitary gland can sense calorie intake. Below a certain level, it can create a signal from the brain for ovulation to be reduced or absent,” says Dr. Styer.