There are a lot of opinions surrounding IF, and there are different ways to do it. So you no doubt have a few questions. How effective is it? What’s the best method? What factors into the timing? How do you fit workouts around fasting? Here’s what the science actually says about it.
What is Intermittent Fasting?
Intermittent fasting has been around for centuries, since ancient hunter-gatherer times, but it’s risen to popularity in the past five years or so. There have been a few catalysts: a 2012 documentary called Eat Fast, Live Longer; as well as a slew of books including The Fast Diet, The 5:2 Diet Book, and The Obesity Code. All of this media, combined with anecdotal success, have created a positive buzz around the trend.
IF is an eating pattern that cycles between periods of fasting and eating. It doesn’t specifically say which foods to eat or avoid, but rather when you should be eating. It’s actually more of an eating pattern than an actual diet per se. Modern IF methods can be summed up by these four types:
- Eat-Stop-Eat: This involves fasting for 24 hours once or twice per week.
- The 5:2 Method: You consume only 500 calories on two non-consecutive days of the week, but eat a normal pattern the other five days of the week.
- Alternate-Day Fasting: You fast every other day. This can be adjusted, but some methods allow 500 calories or fewer on the fasting days.
- The 16:8 method: This involves skipping breakfast and restricting your daily eating period to eight hours, then you fast for 16 hours before eating again. For example, your feeding window might be 12-8 p.m. but within that window, you can fit two or three meals, then fast until 12 p.m. the following day.
The 16:8 method is the most popular and easiest for people to stick to. Overall, no matter what method you choose, as long as you’re reducing your caloric intake, any method should cause weight loss as long as you aren’t over-consuming during the feeding timeframes.
How Does It Affect Your Body and Help You Lose Weight?
Fasting causes a number of reactions in the body that affect your cells on a molecular level. The main idea behind IF is that it helps your body access and mobilize fat stores by adjusting the hormones that influence lipolysis (the breakdown of fats). Without diving too much into the science and mechanisms of how this works, here are a couple of the changes that occur in the body during periods of fasting:
- Increase in human growth hormone: Growth hormone, or somatotropin, is a peptide hormone that stimulates cell growth, cell reproduction, and regeneration in humans. More importantly, it stimulates the production of IGF-1, which positively impacts insulin levels and levels of body fat. Research shows that fasting can cause growth hormone levels to skyrocket, which has benefits for fat loss and muscle gain, among other benefits.
- Insulin sensitivity can improve: Fasting can cause levels of insulin to drop dramatically, which makes your ability to burn body fat more accessible. The idea behind fasting is to allow insulin levels to drop far enough that we burn fat because we have to tap into those energy stores in times of fasting or starving.
Among those benefits mentioned, a recent review of the science of IF in the New England Journal of Medicine. does a deep dive on current research, explaining how IF can improve metabolism, lower blood sugar, decrease inflammation, and improve chronic conditions like asthma and arthritis. There’s even evidence to show it can reduce damaged cells and enhance brain function.