It’s hard to say. The term doesn’t refer to one specific diet, but to a range of ways to restrict the window of time in which you eat. Some say this is in order to give your body time to repair cells without bombarding those cells with new protein. Others say it lets your body start burning fat instead of freshly supplied glucose from food. And there’s no set window of restriction, either. Some people alternate days of complete fasting and eating normally. Others do all their daily eating in a span of just a few hours. Still others eat normally on weekdays and fast on weekends. When you do eat, what do you eat? All this is up to you!
A 2003 study showed that intermittent fasting helped neurons resist excitotoxic stress, which is a type of neuron death associated with Alzheimer’s and epilepsy. One little caveat: the study was done on mice, not people!
Positive Effect on Blood Sugar
Some studies suggest that intermittent fasting decreases blood sugar and insulin in obese people. For average-weight and thin people, the results weren’t quite as promising.
Positive Effect on Cholesterol
Again, though, the results were split by weight. A study done on obese people showed a decrease in overall blood cholesterol, but another study on average-weight people showed an increase. A study of Ramadan fasters not controlled for weight showed an increase in HDL (“good”) cholesterol and also a decrease in homocysteine, a risk factor for heart disease. So
Weight Loss For Some
Studies have shown that intermittent fasting-- most often the type tested alternates moderate calorie restriction days with severe calorie restriction days-- promotes weight loss in obese people at least as well as does moderate daily calorie restriction. Studies of overweight (not obese) people who ate only before sunrise and after sunset during Ramadan and restricted themselves to 2000 calories a day also saw a decrease in body weight and BMI. For non-overweight folks, data on weight loss with intermittent fasting is sparse. This is probably because they shouldn’t be trying to lose weight anyway!
What About Calorie Restriction?
This isn’t really a drawback, just something to consider: not all intermittent fasting plans are created equal! Of course, you have to decide the length of your fasts. But there’s another important part of the plan to think about: are you going to restrict calories? During “fasting” times, will you restrict yourself to 500 calories a day, or 15% of your usual caloric intake, or maybe no food at all? During “non-fasting times,” will you still limit the number of calories that you eat so you don’t overcompensate for your fasts, or will you eat as much as you want? Findings so far make sense: without a net decrease in calories consumed, weight loss is less likely.
If you’re compressing the time frame during which you eat-- even if you eat as many calories overall as usual-- you’re less likely to feel full. So, which type of person are you: does hunger make you feel more alert, do you get confused and hangry, or do you fall somewhere in between?
Maybe Not a Good Idea If You’re Skinny
There’s not much research about the effects of intermittent fasting on normal-weight or thin people. One study compared a standard diet with alternate-day fasting for thin men and found no change in body weight, blood sugar, or metabolism. Another observed normal-weight adults who ate all their daily calories in one meal. They lost fat mass and had lower levels of cortisol, a hormone linked to stress, but their blood pressure and overall cholesterol increased, and so did their hunger.
What You Eat Is Important
If you eat a bunch of junk food anytime you’re not fasting, why make an effort toward better health in the first place? Maybe you decide to try intermittent fasting and see how you feel. Good! But first, make sure you’re eating a healthy foods, which most nutritionists agree means reaching for fruits, veggies, nuts, and seeds more often than processed foods.