A recent breakthrough study done at the University of Southern California (USC) found fasting for just three days could reboot your entire immune system.
Add that to the numerous potential benefits of intermittent fasting (IF), a wildly popular alternating eat-and-fast plan that varies wildly according to practitioner.
"Basically, it's a technique that incorporates a weekly fast into your routine," says Yuri Elkaim. "This method is great because it allows you to reap the benefits of fasting without leaving you feeling weak or deprived."
A simple online search will yield numerous bloggers emphatically singing intermittent fasting's praises for fat loss, increased stamina and vigor, improved focus at the gym and at work, breaking plateaus and, with this latest study, immune health.
Many studies do indeed show benefits. One in the Nutrition Journal concluded IF combined with calorie restriction and liquid meals helped obese women lose more fat and improve their cardiovascular disease risk.
Yet not all studies have concluded so convincingly. One in The American Journal of Clinical Nutrition found for women, alternate-day fasting could actually lower glucose tolerance and potentially crash your metabolism.
Women in another study published in that same journal experienced some benefits when they ate just one meal a day, yet they also had significantly increased hunger, blood pressure, and total, LDL-, and HDL-cholesterol concentrations.
Those and other problems coupled with some of my own clients gaining weight doing alternate-day fasting led me to conclude that, far from being a panacea, IF could potentially create these five detrimental consequences.
You can create or exacerbate eating disorders.
People rarely discuss this, but at its most extreme, intermittent fasting's binge-and-purge mentality could trigger or exacerbate bulimia and other eating disorders. The "anything goes" mentality some experts permit during the feeding state could lead someone to overeat, creating guilt, shame, and other problems that only become worse over time. For someone with emotional or psychological eating disorders, IF could become a convenient crutch to amplify these issues.
You might chronically elevate cortisol levels.
"Skipping meals ramps up your stress hormone cortisol, which I consider a dark lord of metabolism," Sara Gottfried, M.D., author of The Hormone Cure, told me. "From an evolutionary perspective, that short-term elevation was a win because it got the body to release fat as energy. Women seem particularly vulnerable to the dangers of intermittent fasting, which can keep cortisol elevated when it should be tapering down and create the an undesired effect of storing fat and breaking down muscle. Have you been around intermittent fasters? Not fun to be around!"
You can create an unhealthy obsession with food.
You've been fasting all morning, your coworker opens her broccoli chicken Chinese takeout at lunch, and suddenly all you can think about is what you'll eat to break your fast at dinner.
Hunger proves a powerful evolutionary mechanism that kept us alive back in the day. With our modern ubiquitous bodegas and snack machines, hunger isn't normally a problem and we rarely confront it. The problem is, when you're starving everything else takes a backseat to eating.
With IF, that could become an obsession with mentally planning your next meal. Everything becomes about food.
You might over-rely on coffee.
Most IF plans allow caffeine, a stimulant that can keep you going for hours when you're not eating. When you're fasting, you might find yourself gravitating to coffee shops more often to get your fix that keeps you going without food. Especially for slow metabolizers, that third cup of dark roast could cut into your sleep cycle. "It is a vicious cycle, as caffeine can disrupt sleep and promote anxiety and depression," writes Mark Hyman, M.D.
Coffee also amps up your stress hormone cortisol. "Cortisol's main job is to raise glucose levels," writes Gottfried in The Hormone Cure. "Even small increases in cortisol, such as those experienced when drinking caffeine, can raise blood sugar and increase insulin resistance."
You could increase food intolerances and inflammation.
Fasting leaves you famished, creating a free-for-all dive into deep-dish pizza and a hot-fudge sundae when you actually eat. Never mind that a major caloric overload and blood sugar spike and crash that ultimately lead to more cravings. Your "break the fast" meal will likely contain gluten, dairy, and other potential reactive foods -- perhaps in massive amounts -- that contribute to leaky gut, paving the way for food intolerances, Candida and other gut issues, and increased inflammation.
One study in the journal Immunology found eating gluten increased inflammation in mice and increased their risk for Type 1 diabetes. (The gluten-free diet showed anti-inflammatory here.) "Inflammation is one of the biggest drivers of weight gain and disease in America," says Hyman.
If you've ever attempted intermittent fasting, have you encountered any of these or other roadblocks? Do you think IF makes an optimal strategy for fast, lasting fat loss? Share your thoughts below.
Sara Gottfried, The Hormone Cure (New York: Scribner, 2013).