This guest blog comes from Brian St. Pierre, a Cressey Performance staff member who specializes in nutrition. Keep an eye out for more great things from Brian; he’s got a lot of excellent ideas and is very well-read.

Intermittent Fasting (IF) seems to be newest dietary fad. IF followers will choose a day or two each week, and on those days, they simply won’t eat for 24 hours. It seems simple, and a lot of people like the idea of giving your body and digestive system a break.

It also stands to reason that eating this way will help you eat less calories and make it easier to maintain a healthy body weight. Seems logical, right? Since IF usually leads to decreased calorie consumption it is often compared to Caloric Restriction (CR).

CR has been shown in a plethora of animal studies to lead to significant improvements in many markers of health and an increase in life span. Extrapolating that data, it would seem that if humans cut their calorie intake by 30-40% we would lead longer, healthier lives. Here arises the problem. In the animal studies with rats, researches observed signs of depression and irritability. With primates, it was even worse (researchers quantified the amount of monkey poo thrown for statistical analyses…okay, not really, but it’s an amusing concept for future reference). If they did not consume enough cholesterol, they became violent.

So, angry monkeys aside, if you are willing to be cold, irritable, and prone to depression and flashes of violence, then caloric restriction is for you!

This is supposedly where IF comes in. More animal studies have shown that when animals were forced to fast every other day, but consume all they wanted on the off days, they were able to maintain their body weight, while also sustaining all the life prolonging benefits of CR. They had better glucose tolerance, insulin sensitivity and blood pressure to name a few. It was the best of both worlds!

After these initial animal studies, human researches jumped on the IF bandwagon. People were expecting big things. Unfortunately, they were very disappointed with the results. Research started showing that people following IF, or even purposefully skipping a few meals per day were developing insulin resistance, decreased glucose tolerance, and increased blood pressure. These problems were not tremendous problems and some might argue that in real world IF, where people don’t fast every other day (only once or twice a week), the studied health problems wouldn’t occur.

Even if this is so, there is another problem with which we have to contend. The largest problem is a decrease in thermogenesis. Essentially saying that these people, even though they purposefully consumed as many total calories on IF as the control group, had drastically suppressed their metabolisms. This is why so many people have found such little real world fat loss from IF. In most real world applications – especially because people were eating diets in a significant caloric deficit – the body downregulated its thermogenesis to such an immense degree as to not allow for almost any weight loss. This to me is the final blow.

So, I guess if fasting is your thing, and it’s not causing you any negative health effects, then have it. As for me, I prefer to stick to my low carb diet, eat whenever I feel like it, and receive all the benefits that IF proposes to give – except mine are real, not imaginary or hypothetical.

Note from EC: You can find a rebuttal to this post HERE.