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Intermittent fasting is one of the most popular diets for weight loss at the moment. ICYMI, that's when you alternate between fasting and feeding regularly. With so many iterations out there like the 16:8 diet, you can really choose the one that works best for you and your lifestyle. Another method you may have heard of is the 5:2 diet. It allows you to eat anything you want for five days a week, but you have to restrict your intake on the other two days.
To be more specific, you eat about 25 percent of what you'd typically have for two days a week. "The daily requirement for calories for women is between 1,600 to 2,400 per day. However, if a woman is physically active, they likely will need higher amounts," says Roxana Ehsani, RD, LDN, a registered dietitian in Miami, Florida. Based on those numbers, that would translate to consuming 400-600 calories on fasting days.
And for the other five days of the week, you do your normal thing. The idea is that you end up consuming fewer calories overall by following the 5:2 diet.
Technically, you can eat whatever you want to get those calories—but the 5:2 Diet Book recommends loading up on plenty of veggies, as well as small portions of lean meat, fish, and eggs. And soups! Low-cal soups (which tend to be filling) are clutch.
Meet the experts: Roxana Ehsani, RD, is a national media spokesperson for the Academy of Nutrition and Dietetics. She regularly appears on morning shows in Baltimore and Washington, DC. She previously served as the sports performance dietitian for Georgetown University's Division I Athletic Department.
Katherine Brooking, RD, is a recognized expert in nutrition and was listed as a "Top 50 Influencer" at Expo West, a large natural food show. She is also the co-author of The Real Skinny: Appetite for Health’s 101 Fat Habits and Slim Solutions.
Will the 5:2 diet really help you lose weight?
Probably—there's a good amount of research to back it up.
Healthy weight loss should be about one to two pounds per week, which typically is when you are in a calorie deficit of 3,500 calories per week (or cut out 500 calories per day)," explains Ehsani. "So if you were to follow the 5:2 diet, you likely will be hitting that 3,500 calorie deficit per week by just following very low calories on two of those seven days out of the week."
One study in the journal Cell Research found that intermittent fasting may help you lose weight, speed up your metabolism, and burn fat more efficiently (although, caveat: the research was done on mice). A 2021 study published in PLOS ONE found people who followed the 5:2 diet lost roughly the same amount of body weight over the course of a year as those who used the traditional dieting approach—five percent of their body weight. However, the study also stated that participants who followed the 5:2 diet felt more positively about their experience than others who followed the traditional diet.
Most people should lose some weight in one to three weeks on the 5:2 diet.
Whether it’s a good long-term weight-loss plan is ultimately a question of your personality. Some people find fasting a couple of days a week to be totally sustainable, says Katherine Brooking, RD, a New York City-based nutritionist. But others aren't okay with eating just 500 calories a day for two days out of the week—or they may overcompensate on “normal” days by eating more than usual. “It really depends on the person,” she says.
Does the 5:2 diet come with any other health benefits?
Besides weight loss, the 5:2 diet also has some other major health and nutrition benefits.
It may help protect against Alzheimer's. One animal study published in Frontiers in Molecular Neuroscience found that intermittent fasting protected mice against developing Alzheimer’s disease by restoring an important part of the blood-brain barrier. And, of course, if you're overweight or obese, losing weight could certainly lower your risk of developing heart disease and certain types of cancer.
It may help you eat more fruits and veggies. "On days a person is fasting, you might be looking for more low-calorie foods to consume," says Ehsani. "Therefore, you might be able to consume more fruits and veggies, and hit your daily recommendations as they are our lowest calorie food."
It may help your blood sugar values. Several studies have found fasting to be beneficial to people’s blood sugar levels, as it can help normalize fasting blood sugar and reduce your hemoglobin A1c. "It may help a person with diabetes or pre-diabetes better manage their fasting and average blood sugar values," says Ehsani. "But, a caveat: If you are diabetic or pre-diabetic, you also are more at risk for low blood sugar drops (known as hypoglycemia), especially on fasting days. So be careful and monitor your blood sugar closely throughout the day."
It may improve cholesterol levels. Some people who followed this diet in a 2015 study in Nutrition Reviews after 12 weeks found that it improved some of their heart healthy markers, lowering both their triglycerides and LDL cholesterol (the bad cholesterol).
So, is the 5:2 diet safe to follow?
It depends. "If you were looking to follow this method of fasting, 500 calories is quite low, and essentially equivalent to one meal per day," says Ehsani.
However, Brooking says that the 5:2 diet is safe for otherwise healthy people to try. It’s def not considered safe for children (since they need fuel for their growing bodies) or pregnant women, who also need the calories, she says.
The 5:2 diet is best for people who already have healthy eating habits, Brooking notes, adding that if you have a history of bingeing or restricting your food intake, you should take a hard pass on this one. Ditto if you suffer from migraines (skipping meals could trigger headaches) or if you tend to go hard at the gym, since you might not get in enough calories to power your workouts.
And while it's okay to put your fast days back-to-back, you shouldn't do anymore than two days in a row. (Worth noting: Most people find it easier to spread their fast days out throughout the week—but you can do them whenever works for you.)
What’s the difference between Fast 800 and the 5:2 diet?
These diets are pretty different. Specifically, the Fast 800 involves more restriction. "The Fast 800 is where you follow a 800-calorie diet for at least two weeks or more depending on your weight loss goals," explains Ehsani. "Once you’ve hit close to your target goal, then you eat 800 calories on two days a week, and follow the Mediterranean diet on the other days of the week."
Not only is the Fast 800 more challenging, it's more restrictive starting off. "It's also promoting quick weight loss, which never is lasting weight loss," she says. "I’d say the 5:2 diet is probably easier to follow and stick with for the long term versus the Fast 800."
The bottom line: The 5:2 diet could be good to try if you want to lose weight. But it’s still a good idea to check in with your doctor to make sure there are no potential issues with your trying it.
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