Diet Series: Intermittent Fasting

Continuing the series on diet, let’s talk about Intermittent Fasting.  I must say that this seems to be ever more popular these days.  It’s not a new concept and has been around for centuries.  During Ramadan, people who follow the Muslim faith have been practicing this type of diet every year.  But recently it has become more popular in the mainstream media and blogosphere.  Celebrities and athletes have all touted this diet in recent years.

 Overview

 The main concept is to fast for an interval of time, followed by a limited amount of time eating ad lib.  There are several different ‘formulas’ to follow for this diet. Schedules normally will be written out like: 5:2 and 16/8.  The first being that fasting happens 2 days out of the week and eating normally the other 5. Sometimes it can be written out 4:3 instead (fast 3 days of the week).  The 16/8 means that fasting occurs for 16 hours of the day and ad lib eating occurs during a finite 8-hour period (Typically between 9 and 5).  During fasting, there is a limited amount of glucose and carbohydrate load, so the body is forced to use up the stored nutrients in the body (typically stored by the liver).  Once those stores are exhausted, then the body starts to break down fatty acids to ketone bodies and burn fat.  This is the same process that the ketogenic diet tries to capitalize on, except this way is through fasting, instead of just loading it chalk full of protein and fat all the time.  This conversion to breaking down fatty acids and ketone bodies occurs about 8-12 hours after initiating the fast, so fasting would need to last at least that long to benefit. 

Most of the studies were conducted on cyclists practicing Ramadan.

- actually this is a photo of me cycling near the Des Moines river.

Benefit 

This is another diet that results in weight loss consistently.  Again, this isn’t something new, as several different religions practice some sort of fasting within their practices.  Thus, this is slightly easier to follow than some diets that are more restrictive in what kind of food that can be eaten during them.  It can be inclusive of other diets too. People can be vegan, paleo, gluten-free, and have no special dietary restriction and still practice intermittent fasting.

The fasting process has been shown to induce changes in the cells and their processes that seem to have a lasting effect.  It has shown to increase production of anti-oxidants, increase DNA repair and resiliency, and have better cellular response to inflammation.  The New England Journal of Medicine has a great article about much of the benefits!  There is evidence in rats that caloric restriction via intermittent fasting can prolong life expectancy. This hasn’t been seen consistently in humans, but increased caloric intake to excess has been linked to increased risk of stroke, Alzheimer’s, obesity, and other causes of mortality. 

With the cellular changes, people become more resilient to stress. There is improvement seen in adults with insulin sensitivity, a decrease in blood pressure, lowering of cholesterol, and improvement in diabetic control. 

Drawbacks 

Considerably less overall drawbacks than Ketogenic diet.  The main one would be the need to fast for prolonged periods of time which initially can cause increased hunger and irritability.  Usually it takes about 4 weeks to get used to it.  Failure will usually be due to this hunger, causing people to throw in the towel.  However, the longer the body keeps up the intermittent fasting periods, it will get used to the lower caloric intake and, hopefully, portion size.  Another drawback is at baseline there is no direction on macronutrients, type of food, or overall caloric intake.  Some sources just say to eat ‘ab lib’ which could still equate to very large calorie intake and binge eating food.  Some more regimented diet plans for IF do have ‘goal’ caloric intake, but this would again lead to increased hunger initially and higher rate of quitting the diet.   

Athletics 

Head to head studies did not show that IF provided much benefit in performance.  There was actually an initial decline in athletic performance, especially in more explosive sports such as sprinting and cycling, as compared to glucose rich diets, without fasting intervals.  After about 10 weeks, this decline corrected back to the baseline for many. There was considerable weight loss in the athletes studied. 

The main thing to take away from the literature is there was no improvement in any type of athletic performance and to expect an initial decline in performance. BUT you might get to this physique a bit quicker…. Or just lose some weight if that’s your goal.

-photo taken by myself in Rome, Italy (actual work done by some ancient Roman sculptor)

Conclusion 

Mixed feelings on this one. There are several benefits that have been noted with intermittent fasting. However, they can easily be undone if still overeating during the non-fasting period, which could increase overall stores of glucose in the body and adipose (fat) tissue making it a zero-sum game overall. But if done right, there are many health benefits to intermittent fasting and it has shown to help with weight loss.  For sports, not a great way to improve performance.  The athlete may be leaner and weigh less afterward, but with the lack of nutrients for most of the day, training and performance would be hindered, at least initially.

For me, I may recommend attempting this diet for my family medicine patients to help lose weight, but for the athletes, I wouldn’t recommend this to during a season while training.  Keep in mind everyone is different and, again, diets need to be tailored to the individual.  

As always, stay safe out there and keep moving!