What is the Intermittent Fasting Diet?

How to optimize health and fitness by incorporating periods of fasting in your diet

Nearly everything we hear about healthy eating habits says that breakfast should never be skipped. It’s not like this is crazy advice, plenty of research has shown that starting the day off with a nutritious meal yields several important health benefits including a decreased risk for diabetes and heart disease, improved cognitive function, and weight maintenance.

So, with so much science standing behind the age old adage that touts breakfast as the most important meal of the day, could it really be possible that removing it from the picture completely might provide similar health benefits?

Proponents of intermittent fasting (IF) think so, and while the research behind this method of dieting is still infantile, some studies have shown that it may be an effective way to improve health and fitness, and for many who implement IF into their daily routine it has proven an effective fat loss and muscle-building tool.

Although commonly referred to as a “diet,” IF is actually less about reducing calories and more about optimizing the timing of your meals. Essentially, you eat a normal amount of food every day only within a smaller time frame than what is considered typical.

The goal is to maintain a “fasted state” which will encourage your body to use your stored fat as an energy source rather than the glucose from a recently consumed meal.

There are several different ways to apply IF but the most common method, which was popularized by Martin Berkhan on his website Lean Gains, follows a daily cycle that calls for 16 hours of fasting followed by an 8-hour “feeding” period. For many who follow IF, this means fasting from about 8 p.m. until 12 p.m. the next day (essentially skipping breakfast) and eating all of their allotted calories during the remaining 8 hours of the day (about 12 p.m. to 8 p.m.)

The idea behind IF stems from the same “caveman” theory that argues in favor of following the “Paleo” diet, which maintains that optimal health can be achieved by eating similarly to the way our ancestors did. IF takes this beyond simply copying what they ate by also recommending that we follow how they ate, which was much less frequently than we do in modern times since food was less readily available and not as easily accessed.  

Ultimately, the purpose of IF is to teach the body to use fuel more efficiently. When paired with healthy sleep habits, regular exercise and the consumption of nutrient-dense, whole foods many people who practice IF have found that it’s an effective way to reduce body fat percentage.

“With intermittent fasting, I have been able to increase strength, reduce body fat, and maintain good health while spending less time eating each day,” health and wellness blogger James Clear wrote in a blog post about his experience with the diet.

Additionally, a few studies support its effectiveness as a method for weight loss and several others suggest that it may help reduce the risk for cardiovascular disease and cancer and improve insulin resistance.

Although many of these studies suggest that IF can be beneficial for human health, women should take into consideration that the study referring to improved insulin resistance mentioned above only found this to be true for men and found that IF could actually have an adverse effect on insulin tolerance for women.

“Overweight women may experience metabolic benefits, whereas normal weight women do not,” Stefani Ruper wrote on her blog in a post reviewing the available literature about IF and how it applies specifically to women.

Although IF may be an effective tool for some, for others it may not be the best option, especially those who might have  a hard time  getting used to such a dramatic change in their eating habits and people with diabetes, hypoglycemia, or other conditions that effect insulin sensitivity.  

Dr. John M. Berardi summed it up best in his personal review of IF on Precision Nutrition after testing it for 6 months:

“Intermittent fasting can be helpful for in-shape people who want to really get lean without following conventional bodybuilding diets, or for anyone who needs to learn the difference between body hunger and mental hunger. (And for the latter, I only recommend the Trial Fast.) It’s a helpful tool and one I’ll continue to use periodically. But it’s not the end-all, be-all of nutrition or fitness.”

Related: What is the IIFYM Diet?