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: