You’ve heard the mantra: Eat frequently—five to seven small meals daily, each including a serving of protein, healthy fat and low-glycemic-index, or fibrous, carbohydrates, such as vegetables. Now I’ve heard that maybe it’s a good idea not to eat those frequent meals and instead engage in “intermittent fasting.” In a simple sense, most folks think of this as basically not eating on occasion. And herein is the problem. IF is different things to different people.
If people told me they were doing intermittent fasting, it would mean that one or two days a week they simply didn’t eat. That’s fasting. Fasting is not skipping dinner. It’s not skipping meal number four of your six meals. Fasting is fasting. It’s not not eating a meal. So until the International Group of Fasting Scientists come up with an agreeable definition, it’ll be like judging a bikini contest; it’s all in the eye of the beholder. That said, let’s at least look at some telling statistics on what happens when humans alter their basic patterns of eating.
A recent study from the International Journal of Obesity looked at the feasibility and effectiveness of intermittent continuous energy with continuous energy restriction for weight loss, insulin sensitivity and other metabolic-disease-risk markers.1 In other words, the subjects either cut their calories evenly over a six-month period or restricted calories for only two days per week over the six-month period. Both diets involved a 25 percent calorie restriction overall. The continuous restriction group cut their calories by 25 percent spread evenly over the week, whereas the intermittent group followed a very low-calorie diet two days per week, cutting calories by 75 percent.
Results: both methods were equally effective for weight loss. Both groups had similar reductions in leptin, free androgen index, high-sensitivity C-reactive protein, total and low-density-lipoprotein cholesterol, triglycerides, blood pressure and increases in sex-hormone-binding globulin, IGF-binding proteins 1 and 2; however, the intermittent group had a lower fasting insulin. So the bottom line is that both seemed to produce similar weight loss, with the intermittent method being better for insulin sensitivity. But that was in fat people. What happens to folks who actually exercise?
In a more relevant study, scientists determined whether Ramadan intermittent fasting affects 5,000-meter running performance and other parameters classically associated with middle-distance performance.2 Ramadan is a month of obligatory daily fasting that starts at dawn and ends at sunset, so that to me is “intermittent fasting.” Two experimental groups participated in two experimental sessions, one before Ramadan intermittent fasting and the other at the last week of fasting. The subjects were 18 well-trained, middle-distance runners. At the end of Ramadan fasting, a decrease in maximal voluntary contraction—i.e. strength—was observed as well as a decrease in performance of -5 percent. There was no effect on running efficiency or maximal aerobic power. The study shows that Ramadan intermittent fasting can result in a detriment to performance.
So should you fast or not? Or shall you stick religiously to six meals a day for the rest of your life?
Editor’s note: Jose Antonio, Ph.D., is the CEO of the International Society of Sports Nutrition (www.theissn.org); also check out his site www.TheWeekendWorkout.com.
1 Harvie, M.N., et al. (2011). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond). 35(5):714-27.
2 Brisswalter, J., et al. (2011). Effects of Ramadan intermittent fasting on middle-distance running performance in well-trained runners. Clin J Sport Med. 21(5):422-7.