As far as intermittent fasting strategies go, the 5:2 method is super popular. The diet allows for five days of regular eating and two days of fasting. Fasting days restrict calories down to 500 for women and 600 per day for men.
Unlike other diets, the 5:2 method does not prohibit any foods or food groups. The only restriction is keeping your calories limited to 500 to 600 per day during the two fasting days per week.
The Benefits of 5:2 Fasting
1. Weight Loss
Intermittent fasting reduces overall calorie consumption throughout the day by limiting the amount of time you're allowed to eat each day. This schedule can be just as effective as calorie restriction for weight loss, according to an October 2014 review published in Translational Research. The study evaluated intermittent fasting one to three days per week, which models the 5:2 fasting diet plan.
Other research, published December 2019 in The American Journal of Clinical Nutrition, found that 5:2 fasting is more effective for weight loss than the Mediterranean or paleo diets. The study allowed 250 people to choose which of the three diets they wanted to follow and monitored their progress after a year. Although the 5:2 fasting group lost slightly more weight, the average weight loss was only about 9 pounds in 12 months.
A 5:2 fast might also help you break through a weight-loss plateau, a common concern for many dieters. The body has metabolic processes in place to slow down or completely stop your weight loss after an initial drop. But switching from periods of energy balance to energy (calorie) restriction — which fasting achieves — allowed subjects to lose more weight and fat than calorie restriction alone in a February 2018 study published in the International Journal of Obesity. If you've stalled out on your current weight-loss attempt, IF may help you kick the plateau.
2. Improved Blood Sugar Control
An estimated 100 million U.S. adults are currently living with prediabetes or diabetes, according to the Centers for Disease Control and Prevention. Diabetes, while a serious disease, can often be managed through diet and exercise in conjunction with medications to control blood sugar levels.
Restricting the number of hours you eat per day has a direct effect on your blood sugar and insulin levels. Every time you eat carbs, your body releases insulin, which allows that carbohydrate to be used as energy by your cells. When you scale back two days per week on the 5:2 fasting diet, your body produces less insulin. The Translational Research review found participants who used intermittent fasting had reduced blood sugar and insulin levels, which may reduce the risk of developing prediabetes or diabetes.
3. Anti-Aging Effects
One of the newer areas of research looking at intermittent fasting shows that it may help reduce the effects of aging in the body, at least in small animal studies.
Specifically, a study published in June 2011 in Mechanisms of Aging and Development found a calorie-restricted diet using alternate-day fasting — similar to a 5:2 fasting plan — increased the lifespan of lab rodents. Researchers measured molecules associated with age-related heart failure in rats and concluded alternate-day fasting may provide a cardio-protective effect.
Worth noting: The research in this area is very new and only being conducted in animals at this point. The promising results may lead to a better understanding of how to reduce aging in humans.
Who Shouldn't Do 5:2
While 5:2 fasting has some clear potential benefits for weight loss and blood sugar control, it also has some downsides. Restricting your intake to 500 to 600 calories two days a week isn't right for everyone. If you have a history of an eating disorder, are taking medications or have a condition like diabetes, heart or kidney disease, struggle with hypoglycemia or are pregnant or breastfeeding, the 5:2 diet may not be appropriate. It's always important to check with your doctor before beginning 5:2 fasting or any type of fasting diet.
The 5:2 fasting plan is flexible in that it doesn't require calorie or macro counting, but it does limit your calories two days a week. Depending on your work schedule or personal obligations, capping your food intake can be difficult. Plan ahead for days where you have big events, like a wedding to attend or an important presentation at work. Aim to fast on days with less going on.
Common adverse symptoms with intermittent fasting include dizziness, headache, hunger, fatigue and weakness. These symptoms are usually present in those just beginning and may resolve over time. If you notice continued symptoms, it's important to stop fasting and consult a medical professional to make sure this is the right approach for you.
Also keep in mind that you shouldn't take on a 5:2 fast for more than three months. "I do not recommend remaining in a calorie-restricted state for more than three months at a time to avoid rebound weight gain, disordered eating and other potentially negative side effects of long-term calorie restriction," says Robert Santana, RD, owner of Weights & Plates Strength & Nutrition Center in Phoenix, Arizona.
How to Get Started With a 5:2 Fast
1. Select Your Fasting Days
The first step is to determine which days will be normal eating days and which will be fasting days. You will want to make sure you avoid doing two fasting days back-to-back.
The first couple of weeks, experiment with different days of the week to see what fits best with your schedule and what's least disruptive to your energy needs throughout the week. If you are active and exercise regularly, it's a good idea to plan to exercise on normal eating days to make sure you can still crush your workouts.
2. Ease Into It
If you've never fasted before, start small: Begin with one fasting day or one reduced-calorie day per week. If you find the 500-calorie restriction is causing side effects like low blood sugar, fatigue and headaches, up your calories to 800 and see how you feel. There's no need to rush down to the 500-calorie-a-day limit right off the bat.
Space your low-calorie meals throughout your fasting days, too. When you're only getting 500 calories for women and 600 for men, that energy should not be eaten all at once. Spreading those meals throughout the day will reduce your risk of dizziness, headache and fatigue.
3. Enjoy Nutrient-Dense Foods
To get the most out of a 5:2 diet, eating nutrient-dense foods is a must. Whole grains, fruits, veggies, lean protein and healthy fats deliver plenty of vitamins and minerals, even for limited calories.
Plus, they all help keep you feeling fuller longer — especially lean protein. "Protein can help counteract hunger due to a greater increase in satiety than carbohydrates or fats. Couple this with a high fiber intake and hunger becomes much easier to manage," says Santana.
- International Journal of Obesity: "Intermittent Energy Restriction Improves Weight Loss Efficiency in Obese Men: The MATADOR Study"
- Centers for Disease Control and Prevention: "New CDC Report: More Than 100 Million Americans Have Diabetes or Prediabetes"
- Mechanisms of Aging and Development: "Alternate-Day Fasting Reverses the Age-Associated Hypertrophy Phenotype in Rat Heart by Influencing the ERK and PI3K Signaling Pathways"
- Translational Research: "Intermittent Fasting vs Daily Calorie Restriction for Type 2 Diabetes Prevention: A Review of Human Findings"
- The American Journal of Clinical Nutrition: "Intermittent fasting, Paleolithic, or Mediterranean diets in the real world: exploratory secondary analyses of a weight-loss trial that included choice of diet and exercise"