Jennifer was a 29-year-old patient with bulimia, a binge-and-purge cycle that affects up to 10 million people, mostly 14- to 40-year-old women. That eating disorder created a yo-yo diet pattern for Jennifer that led to small intestinal bacterial overgrowth (SIBO). When a friend told her about intermittent fasting (IF), Jennifer perked up. In her mind, it permitted her to binge during "feeding" hours, and the results were predictably disastrous: She devoured a pepperoni pizza, a pint of butter pecan ice cream, and a bottle of chardonnay that first day.
A few weeks later I saw Jon, a 44-year-old high-stress office executive who needed to lose about 50 pounds. I enthusiastically recommended IF, yet during a subsequent consultation he complained he was actually gaining weight. A little probing found that while he otherwise fasted correctly about 18 hours daily, he was drinking about eight cups of black coffee while fasting—which curbed his appetite but amped up his stress hormone cortisol—while stockpiling doughnuts and other junk foods for his "eating hours."
As a medical doctor who specializes in gut health, IF’s got one heck of an impressive résumé, and I get amazing results with many patients. Among its benefits, studies show doing it correctly can boost immunity, improve LDL particle size and triglycerides, normalize blood pressure, balance fat-regulating hormones like fat-burning adiponectin and satiety-signaling leptin, and lower inflammation.
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:
1. Food sensitivities.
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 create 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.
2. Gut issues.
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.
3. Binge eating.
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 Collier. "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.
4. Anxiety and stress.
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 believe cells respond to exercise-related stress similarly to IF, which is just another reason to believe that no one diet is right for everyone.
5. Sleep issues.
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.