There are many ways to do an intermittent fast, and 5:2 is one of the most popular. Here's what you need to know about the benefits, risks, and challenges associated with this unique fasting schedule.
What is a 5:2 fast?
This type of fasting was popularized by Michael Mosley, a British journalist who published a book titled The FastDiet in 2013. In his book, Mosley describes the 5:2 eating plan, which was developed in response to his own health issues, and explains how it helped him improve his cardiometabolic health.
"For some, this approach may be more appealing than traditional dieting, as there are only two days of the week where there's a focus on reducing caloric intake," says Laura DeCesaris, IFMCP, M.S., D.C., a functional medicine practitioner.
You have the freedom to choose which two days of the week you want to fast, and they don't have to be consecutive. Another major plus of the 5:2 fast is that there is no restriction on which foods you can eat on fasting or non-fasting days since no food groups are off limits.
However, limiting calorie intake to 500 to 600 calories a day on fasting days will be challenging for most people.
Health benefits of 5:2 fasting.
Emerging research finds that 5:2 fasting may lead to a number of health benefits, such as improved metabolic health, weight loss, blood sugar control, and more. Here's a look at the science behind each:
It improves blood sugar levels.
A randomized trial that included 137 adult participants with Type 2 diabetes found that 5:2 fasting helped lower participants' HbA1c levels3. HbA1c, or hemoglobin A1c, is an indicator of your average blood sugar levels over the last two to three months. High HbA1c levels are associated with a greater risk of long-term diabetes-related complications4.
Another smaller randomized trial with 16 young, healthy-weight participants found that 5:2 fasting helped reduce participants' fasting blood glucose levels5. Fasting blood glucose is an indicator of your blood sugar levels several hours after eating. High fasting blood glucose levels can be a sign of insulin resistance, which means your body is not effectively able to use insulin to metabolize the glucose in your blood.
One of the mechanisms by which 5:2 fasting improves your blood sugar levels is by improving your insulin sensitivity. "The 5:2 diet increases insulin sensitivity, which helps ensure blood glucose is distributed to other cells in your body more efficiently," says Krista Varady, Ph.D., a fasting researcher and professor of nutrition at the University of Illinois, Chicago.
It may improve cardiometabolic health.
Varady, who is the lead author of the review, says, "Some studies have shown reductions in LDL cholesterol (the "bad" cholesterol) by 10 to 25%. Other studies have shown increases in HDL cholesterol (the "good" cholesterol) by 5 to 15%."
It may boost liver health.
The authors of the study note that 5:2 impacted the liver by helping people reduce their body weight, body mass index (BMI), blood glucose levels, and cholesterol levels.
It may improve brain health.
However, the authors note that further research is required to substantiate these benefits in humans.
It may promote weight loss.
Is 5:2 fasting effective for weight loss?
However, it's important to note that the amount of weight you can lose on a 5:2 fast varies from person to person. "With any weight loss journey, the amount of weight lost will depend on factors like initial body weight, extent of calorie restriction, exercise, and stress levels, among others," says DeCesaris.
For instance, what you eat on days when you're not fasting can play a major role in determining how much weight you lose. Eating a healthy, balanced, and nutritious diet on non-fasting days can help you achieve your weight loss goals.
On the contrary, eating a lot of calorie-dense junk food on non-fasting days will make it hard for you to lose weight or even cause you to gain weight.
Keep in mind, however, that losing weight too fast is not healthy either. "Rapid weight loss (losing more than 2 pounds per week for the first four weeks) is generally a sign that something is wrong and you're losing muscle instead of fat," says Scott Keatley, R.D., CDN, a nutritionist who specializes in medical nutrition therapy.
What to eat on fasting days.
On days when you're fasting, since you have limited calories to consume, you should spend them wisely on nutrient-dense foods that will help you meet your body's needs. Nutrient-dense foods are high in nutrition but relatively low in calories, essentially giving you the highest bang for your buck if you're restricting calories.
These are some nutrient-dense foods that can help you feel full and satisfied on days when you're fasting:
On the other hand, these are some foods that may be best avoided or consumed in moderation:
- Fast food
- Refined foods
- Highly processed foods
- Sugary foods
- Foods with excess sodium
- Foods containing trans fats or a high percentage of saturated fat
- Sweetened beverages
Sample 5:2 fasting meal plan.
- Vegetable and egg muffins
- Roasted chickpeas
- Carrots and hummus
- Fruit salad
- Green tea
- Black tea
- Black coffee
Tips for the 5:2 fasting plan.
If you're thinking of trying the 5:2 fasting plan, here are some tips that can help you succeed:
It may not be easy for you to suddenly reduce your calorie intake to just a quarter of what you normally eat. It can help to start reducing your intake gradually, so your body has a chance to get used to it.
The first few times you fast, you can reduce your calorie intake to 75% of your usual calorie intake, followed by 50%, and then by 25%.
Experiment with different meal combinations.
On fasting days, try experimenting with different meal types and timings to see what works best for you. For instance, you could try eating three or four small meals per day, or two larger meals instead.
Keep small snacks handy.
You may occasionally feel hungry or low on energy, particularly the first few times you fast. It can be helpful to keep small portions of healthy snacks with you as you go about your day, in case you need to eat something.
Be mindful of your calorie intake.
While 5:2 fasting doesn't restrict any foods, it does require you to be mindful of the number of calories you're consuming on fasting days.
Remember that the calorie count of a dish can vary depending on how it's prepared. A calorie tracker app can help you keep tabs on the number of calories you're consuming per day.
Eat healthfully on non-fasting days.
How long can you do 5:2?
Most studies investigating the benefits and effects of the 5:2 fasting plan do not go more than 24 weeks, so the long-term consequences of this eating plan are still unknown, says Keatley.
He recommends stopping the fast if you're losing weight very rapidly at a rate of more than 2 pounds per week in the first four weeks. You should also discontinue 5:2 if it "starts to become an emotional burden on you, or if you become dependent on it to feel good," he says.
Safety and side effects.
5:2 fasting may be helpful to some people, but it's not for everyone. You should avoid this diet if you are pregnant or planning on becoming pregnant, breastfeeding, under 20 years old, underweight, or have a history of eating disorders.
To ensure your safety while you're on this eating plan, Keatley recommends consulting a health care provider such as a doctor or a dietitian before you start and in case you experience any symptoms or side effects.
Frequently Asked Questions
How much weight can I lose on a 5:2 fast?
Research shows us that people have been able to lose 3 to 7% of their body weight on the 5:2 fasting diet, over a period of three to six months. However, the actual amount of weight lost can vary from person to person, based on factors like their food choices, exercise habits, and lifestyle.
5:2 fasting is an eating plan that calls for significantly restricting your calorie intake two days a week and eating normally on the other five days. It's been shown to lead to weight loss and metabolic health improvements, but it's not for everyone. Consult a health care provider to determine whether it's safe and appropriate for you.
If you're intrigued by fasting but not sure if 5:2 is the right fit, you can explore other types of intermittent fasting here.
Sanjana Gupta has been a health writer and editor since 2014. She has written extensively for platforms like Insider, Livestrong.com, and Verywell Mind. Her work spans various health-related topics, including nutrition, fitness, mental health, medical conditions, and wellness.
Sanjana has a master's degree in digital journalism from New York University. She also holds a master's degree in management from the University of Mumbai.
She balances her love for chocolate with a penchant for fun workouts like aerial yoga and kickboxing.