Intermittent Fasting Can Be Dangerous For Some People. Here's Exactly What You Need To Know

But as Jennifer and Jon prove, no diet works for everyone. And the details on how to do it correctly can be easily misunderstood. Certain people—including pregnant women and those with eating disorders—should not try IF. And even when IF does work for a patient, I always discuss these potential pitfalls and how to remedy them. People with the following issues should reconsider:

Even with the best-designed plan, gluten, dairy, soy, artificial sweeteners, and other food sensitivities could creep into your diet. Studies show non-celiac gluten sensitivities, for instance, can create3 gut and brain problems. That "little dietary leeway" IF provides means these things can easily add up to create leaky gut, weight loss resistance, inflammation, and other problems. IF does not give you license to eat whatever you want during grazing hours, and those problem foods could become roadblocks. Regardless of whether patients are doing IF, I strongly recommend they remove dairy, gluten, and other highly reactive foods from their diet.

I had an IF patient drinking orange juice during her eating hours, unaware of how much fruit sugar she consumed, which fed yeast and unfriendly bacteria in her gut (not to mention that massive fructose burden to her liver). Gas, bloating, and other post-meal problems could mean you’re overeating but might also be hints that you have a gut problem like SIBO. For patients like Jennifer, those issues had been there all along, but IF simply exacerbated them. I had her remove sugar and other gut-unfriendly foods while following the gut-healing protocol I describe in my book Happy Gut.

You might be hungry after fasting 18 hours, but that doesn’t give you license to nose-dive into a bacon double cheeseburger with fries. "Promoters of intermittent fasting will, perhaps unintentionally, encourage extreme behavior, such as bingeing," says Robert Collier4. "Often, they depict people eating heaps of high-calorie, high-fat foods, such as hamburgers, french fries, and cake. The implication being that if you fast, you can devour as much junk as your gullet can swallow during the remaining eating hours." This is just not the way IF is meant to work, and it's important not to lose sight of what a healthy diet really means.

Life comes riddled with stress and anxiety, and fasting can amp up those emotions. For some patients, those feelings arise from the idea that they should be eating rather than actual hunger. But it’s not all in your head: Studies show hunger can increase your stress hormone cortisol, leaving you "hangry" and craving your co-worker’s freshly baked cookies. Caffeine, a staple among patients during "fasting hours," raises anxiety and stress when you overdo it. I recommend switching from coffee to green tea, which contains some caffeine along with the calming amino acid L-theanine. That being said, IF might also cultivate a resilience to stress as some researchers believe4 cells respond to exercise-related stress similarly to IF, which is just another reason to believe that no one diet is right for everyone.

Occasionally a patient doing IF will complain about feeling "wired" before bed. While many reasons could exist for this problem, I first rule out food issues: If they eat a higher-carbohydrate dinner, they likely experience blood sugar crashes that can disrupt sleep. Increasing protein usually helps with this. Avoiding refined carbohydrates and focusing on complex carbohydrates (like sweet potatoes) at dinnertime can also help. For these patients, I recommend a calming pre-bed ritual like deep breathing or gentle yoga along with a natural sleep aid like melatonin or an herbal formula that contains valerian and passionflower to unwind and lower stress hormones.