Decoding Popular Diets: Intermittent Fasting

If fasting seems like an extreme and unhealthy approach to weight loss, that's because it generally is.  Depriving yourself of food also deprives you of beneficial nutrients on which the body relies to function.  But what about intermittent fasting, which promotes short bouts of fasting or limited eating interspersed between days of regular eating?  Is it possible to promote health and lose weight (preferably fat!) while engaging in such a program?  In short, we don't know yet, but there's a growing body of research looking into it!  Here's the breakdown so far. 

The premise:  The focus is more on when you eat than on what you eat.  It requires cycling between periods of eating and fasting, often with the goal to maximize fat loss and lose weight.  What's included + what's avoided:  While proponents of intermittent fasting recommend eating sensibly, the foods can vary as the timing of eating and fasting is the key piece of the program. 

The analysis: There are a few methods of intermittent fasting including alternate day fasting, modified fasting and time restricted feeding.  Alternate day fasting includes a day of regular eating followed by a day of complete fasting whereas modified fasting allows limited eating on the "fast days" (usually around 25% of calorie requirements).  The number of fasting days may vary and a day of fasting/restricted eating is usually sandwiched between days of regular eating (read: you don't restrict two days in a row).  Time restricted feeding allows for a specific window of eating each day rather than full days of regular eating or fasting.  For example, you may limit all your caloric intake to a 4-hour window (say, between 12 pm and 4 pm).  I'll focus primarily on modified fasting as this has gained significant traction in the dieting world. 

The changes:  Your food choices may remain the same, although a healthy diet is recommended.  Expect the schedule and structure of your meals to change as you'll face days of limited eating.  A common structure for modified fasting includes 5 days of regular eating with 2 non-consecutive days of restricted eating per week.  

The good:  So far, studies have shown that weight loss and fat-free mass retention with intermittent fasting leads to results similar to a calorie-restricted diet.  What does this mean?  Well, think of fat-free mass as the weight that we want to maintain (muscle as opposed to fat).  And think of a calorie-restricted diet as your basic approach to weight loss - a diet that focuses on cutting calories on a daily basis.  If anthropometric results (weight, body composition) are similar for daily calorie restriction and intermittent fasting, then options for viable weight loss programs expand.  That's great news because some people might find it easier to restrict only 2 days per week rather than 7 days per week.  Intermittent fasters still need to decrease overall calorie intake, aiming to consume 100% of their calorie needs on "regular eating" days (as opposed to eating well beyond their needs on such days).  Finally, although studies are limited, preliminary reports show that intermittent fasting does not negatively affect mood or energy.

The questionable: Overall, research on intermittent fasting is still in the early stages.  Many of the studies are completed in animals, and the (limited) human studies often rely on a small sample size.  Initial analysis of weight and body composition seems promising, but biochemical indicators (think lab results determining blood glucose levels + insulin response) should be analyzed as well.  Additionally, the effects of intermittent fasting on diet quality and variety, sleep, exercise, and social life should be considered.  While not well documented, I do question the potential for disordered eating following a plan requiring fasting.  Additionally, in a world where the word "hangry" (hungry + angry) exists, I worry about the effect of intermittent fasting on mood.  More research will reveal if such concerns are justified. 

The recommendations:  If you're someone who has struggled with patterns of disordered eating in the past, I'd strongly caution against trying intermittent fasting.  For those looking to take a different approach towards weight loss, work with a Registered Dietitian to ensure that you're consuming quality calories, meeting nutritional requirements, and following an evidence-based program (think science over stories!).  More specifically, here's my advice for those seeking diet-based fat-loss and considering intermittent fasting:

  1. Be realistic in deciding if a program like intermittent fasting is right for you by assessing your personality and current eating style.  If the mere thought of fasting makes you hungry (yup, that's me!), then look elsewhere to promote health and lose weight.    
  2. Try altering food quality and quantity before adjusting timing of your meals as more research supports benefits of the former adjustments.  Do a quick analysis of your current diet to determine what changes could be made.  How often do you eat vegetables?  Do you regularly consume excess calories?  Are you drinking sugar-sweetened beverages on a daily basis?  You may be able to make small yet effective alterations to your eating habits rather than implementing a version of fasting.  
  3. If you decide to attempt intermittent fasting (in any form), do so under the guidance of a Registered Dietitian.  In addition to weight loss, monitor lab work and body composition (fat-free vs. fat mass) as these factors influence overall health and provide a more complete analysis of the diet's effects.

Have you tried intermittent fasting?  What was the biggest challenge you encountered?  Did you notice any health improvements?  Let me know in the comments below!