Proponents of such regimens say these diets may improve sleep and blood sugar control; reduce risk factors for chronic diseases such as cancer, heart disease and diabetes; and may even help you live longer. The appeal is that unlike typical daily diets, part-time dieting plans allow you to eat freely for a few days a week so you don't feel as deprived.

Consider these options.

5:2 diet. This weekly plan has you eating just 500 to 600 calories on two nonconsecutive days and consuming a normal diet the rest of the week. Mark Mattson, chief of the Laboratory of Neurosciences at the National Institute on Aging, who has published two studies comparing the 5:2 diet with daily calorie restriction, found that overweight women on the 5:2 regimen tended to lose more belly fat and less muscle mass than those simply cutting their calories. However, they didn't lose any more weight than normal dieters. Women following the diet also showed greater improvements in blood sugar regulation.

Every-other-day diet. On this plan, "feast days," when you can eat whatever you want, alternate with "diet days," during which you eat a maximum of 500 calories. Choosing high-fiber and high-protein foods for your fast-day meals helps to stave off hunger, according to Krista Varady, associate professor of nutrition at the University of Illinois at Chicago, who has conducted several studies of alternate-day fasting. Like those on the 5:2 diet, people on the every-other-day plan lose a higher percentage of fat and lower percentage of muscle than those on typical calorie restriction diets, Varady says. They also show significant reductions in LDL (bad) cholesterol, blood pressure, insulin and triglycerides (blood fats).

Prolonged nighttime fasting. Also called time-restricted feeding, participants refrain from eating for at least 13 hours overnight. A 2016 study of more than 2,400 women, published in JAMA Oncology, found that prolonged nighttime fasting may have protected those with early stage breast cancer against recurrence. Women on this plan who fasted 13 or more hours per night not only reduced their risk of developing new tumors by 36 percent, they also slept longer and had improved blood sugar regulation.