Intermittent Fasting: Good or Bad?
Several books about intermittent fasting have recently been released. The Every Other Day Diet: The Diet That Lets You Eat All You Want (Half the Time) and Keep the Weight Off was written by Dr. Krista Varda, an assistant professor of kinesiology and nutrition at the University of Illinois, who began studying the effects of intermittent fasting on mice. Based on her post-doctoral research conducted at the University of California Berkeley, she found that mice ate only 25 percent more on feast days and didn’t compensate for the lack of food provided on fast days.
A second popular book titled The Fast Diet, written by Dr. Michael Mosley and Mimi Spencer, uses the same concept, except you can choose which two non-consecutive days each week to fast. This method of intermittent fasting is also known as the 5:2 approach (five days feasting, two days fasting).
If you choose to intermittently fast, you’ll probably lose weight. Studies have found that on days after fasting, folks don’t tend to overindulge to make up for the calories lost from the fasting days. A December 2014 study published in Cell Metabolism found that mice fed according to this dietary pattern had a number of therapeutic health benefits for diseases such as obesity and type 2 diabetes. However, this study was conducted only in mice, and it's tough to determine if humans would react the same way.
A 2011 study published in the International Journal of Obesity had 107 overweight or obese premenopausal women follow an intermittent-fasting-type plan. Compared with ladies who followed a continuous-calorie-restricted plan, their weight loss was about the same. In addition, after six months, those who intermittently fasted had lost an average of 14 pounds each.
This type of plan promotes a diet high in fiber, especially fruits and vegetables. Eating a diet high in fruits and vegetables is commonly recommended for folks looking to achieve heart health and also to help lower blood pressure.
Keeping hydrated, especially with low-calorie beverages like water and herbal tea, is promoted on this plan. So is exercise, though you’re supposed to continue your regular exercise regimen even on fast days.
Another advantage of intermittent fasting is the simplicity of the rules, which makes it easier to follow. As long as you can count calories and restrain your hunger, you’re good to go.
The Fast Diet (a type of intermittent fasting) rated 28 out of 31 in U.S. News & World Report's rankings for best overall diet. Intermittent fasting is downright dangerous for women who are pregnant or planning on becoming pregnant, children, or people with type 1 diabetes. It’s also not appropriate for anyone with an eating disorder. If you have a medical condition or are taking medications, it is important to speak with your medical doctor before choosing this dieting style.
When compared with the USDA’s Dietary Guidelines this plan falls short on numerous good-for-you nutrients including fiber, potassium, calcium, and vitamin D. This is not very surprising, since on two or more days during the week (depending on the type of intermittent fasting you choose to follow), you won’t be taking in enough food to supply all the nutrients your body needs.
Hunger and lethargy are to be expected on days you fast. Trying to work and concentrate while you’re very hungry is virtually impossible.
Studies have found that one of the best ways to lose weight is by changing lifelong habits. Intermittent fasting doesn’t address healthy habits or direct you in how to make lifelong healthy changes. Although a handful of studies have been done on intermittent fasting, there are still a lot of unexplored questions.
The Bottom Line: Intermittent fasting is another trend that has taken the dieting world by storm. But until further research is conducted, following this plan isn’t recommended.
Toby Amidor, MS, RD, CDN, is a registered dietitian and consultant who specializes in food safety and culinary nutrition. She is the author of The Greek Yogurt Kitchen: More Than 130 Delicious, Healthy Recipes for Every Meal of the Day.