5 Reasons To Avoid Intermittent Fasting

At the same time, no one plan works for everyone, and that includes IF. Even Fung notes certain people shouldn’t do IF, including pregnant or breastfeeding women, underage people, and malnourished folks. He advises others like people with type 1 diabetes to proceed cautiously with fasting. While you can usually work with a credentialed health care expert and modify fasting to your condition, I’ve found people with these five issues should think twice about, and—in one case—absolutely avoid intermittent fasting:

When you fast, your gallbladder doesn’t release bile. As your liver continues to deliver bile, it becomes concentrated. Breaking your fast means your gallbladder could forcefully release sludge or small stones from that buildup that could get stuck in the bile duct. If you have gallbladder issues, proceed cautiously with IF. One study1 showed that among people with gallstone disease, a long overnight fast increased hospitalization risk.

Here’s my one big thumbs-down for fasting. A systematic review of IF’s potential harms mentioned eating disorders, and writer Emily T. Troscianko asked whether IF is "A Fast Route to Disordered Eating?" in an intriguing Psychology Today essay. If you have bulimia or otherwise struggle with other psychological eating disorders, IF could exacerbate those problems. An eating disorder is one condition with which you absolutely should not do fasting. Rather, always work with your doctor when struggling with any sort of disorder.

Fasting can keep your stress hormone cortisol ramped up, stressing your already-overworked adrenals. One study2 with 16 young, healthy female volunteers who fasted for 48 hours had elevated cortisol levels, suggesting fasting could create additional stress. You’re probably not going to fast that long, but beware if you have adrenal fatigue or your adrenals are already overworked from chronic stress—fasting could make your condition worse.

Your thyroid performs many functions, including balancing energy, body temperature, and emotions. When this tiny gland isn’t working correctly, numerous problems can result. Triiodothyronine (T3) is your active thyroid hormone. Studies show3 fasting decreases T3, so if you have mild to moderate hypothyroidism, you might want to reconsider intermittent fasting.

If you don’t fall into those conditions and want to try IF, start out slowly. Have a big dinner, close up the kitchen for the night, and then have breakfast as late as possible the following morning. That creates about a 12-hour or longer fasting window—most of it while you’re sleeping—that helps your body dip into those fat stores. Gradually increase that fasting time, but if you feel nauseous or otherwise unwell, please eat something. Don’t risk your health!