What Is the 5:2 Diet?

Oatmeal served with berries and almonds

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At Verywell, we believe there is no one-size-fits-all approach to a healthy lifestyle. Successful eating plans need to be individualized and take the whole person into consideration. Prior to starting a new diet plan, consult with your healthcare provider or a registered dietitian, especially if you have an underlying health condition.

The 5:2 diet, also known as the Fast Diet, is an intermittent fasting protocol that involves reducing your food intake on two days of the week. The method became popular in 2013 when Michael Mosley, a British television journalist and former medical doctor, wrote the bestseller, "The Fast Diet." The book outlines the protocol that allows you to eat normally for five days and restrict calories for two days.

But fasting is not a new concept. In fact, the practice dates as far back as ancient Greece. The philosopher Pythagoras fasted and encouraged others to do so, as did Hippocrates and the Renaissance doctor Paracelsus. Mahatma Gandhi fasted on several occasions as a means of both political and spiritual protest. Fasting is also prevalent among different religions during sacred times. Those who practice Judaism, for example, observe several fasts throughout the year, while many Christians fast on certain days during Lent and Muslims during Ramadan.

In recent years, the practice of intermittent fasting has emerged as a wellness trend among health and fitness enthusiasts. Other variations of intermittent fasting include the Warrior Diet and water fasting (both of which are not recommended), the 16:8 diet, alternate-day fasting, and others.

There have also been a few key areas of scientific interest with regards to intermittent fasting. Researchers have been particularly interested in whether or not plans like the 5:2 diet can promote weight loss, help manage or prevent diabetes, and improve heart health. However, study results have been mixed and authors often cite the complexities of the research.

Intermittent fasting protocols like the 5:2 plan are appealing to many people trying to lose weight and improve their health because, for the most part, no foods are off-limits. But the 5:2 is one of the more restrictive versions of intermittent fasting, limiting calories to just 500–600 per day on fasting days. This could make the diet difficult for some people to stick with for the long term. 

The 2021 U.S. News and World Report Best Diets ranks the 5:2 diet (or Fast Diet) number 30 in Best Diets Overall and gives it an overall score of 2.4/5. Learn more about the 5:2 diet and intermittent fasting to decide if this eating pattern is a healthy choice for you.

What Experts Say

“The 5:2 diet is one of the most popular intermittent diets and it’s likely you’ll lose weight while following it because you are reducing your overall calorie intake. It’s a highly regimented diet and can be hard to follow, especially on fasting days.”

Kelly Plowe, MS, RD

What Can You Eat?

On fasting days, the 5:2 diet restricts calories two days of the week to just 500 a day for women and 600 a day for men. On the other five days, you eat normally. But according to "The Fast Diet" book, eating "normally" means that you eat the number of calories your body needs to perform daily functions (also known as TDEE or total daily energy expenditure). That means you shouldn't necessarily overindulge on your non-fasting days. Instead, you are encouraged to eat reasonable portions of a wide range of foods.

A large part of the appeal of the 5:2 diet is its simplicity. There aren't any complicated meal plans to follow and you don't have to measure portions or count calories. That said, you should aim to consume nutritious foods on any eating plan to promote both weight loss and weight maintenance.

Both protein and healthy fats are important on fasting days, as they’ll provide your brain and body with sustained energy. While it’s best to stick to lean protein most of the time, a few servings of red meat on occasion won’t hurt. Try incorporating lean ground beef or a lean cut of steak, for instance. Fruit generally has a healthy place in any diet; enjoy citrus fruits, starchy fruits, berries, and more on this eating plan.

On fasting days, you should also try to eat high-volume, low-calorie foods to fill up space in your stomach. Foods high in fiber, such as carrots and broccoli, are good choices that will help keep you full. You can drink anything you want on your regular eating days, but on fasting days, you should stick to plain water or zero-calorie beverages like black coffee and herbal tea in order to stay within that day’s calorie limit.

Instead of focusing on how many carbs you're eating or how much protein certain foods have, the primary focus of the 5:2 diet is meal timing. 

What You Need to Know

If you eat more than you normally would during the five days to compensate for the lost calories on fasting days, you might not lose weight. And if you overeat high-calorie, high-sugar, or overly processed foods on those days, you may even gain weight. 

On fasting days, you should experiment with timing to see what works best for your brain and body. Some people function best with a small breakfast, while others prefer to wait as long as possible to eat their first meal. You should aim to consume about 25% of your normal calorie intake.

Since you have a limited number of calories to work with on your fasting days, you should try to spread them out as much as possible. Eating high-volume foods will help with that. For example, if you're trying to keep your fasting day to 500 calories, you could eat 200 calories at breakfast, 100 calories at lunch, and another 200 calories at dinner. You could also try two meals instead of three, eating 250 calories at breakfast or lunch and then 250 calories at dinner. 

It is definitely not easy to shift from eating normally every day to eating only 500–600 calories on two days. Start by slowly reducing your calorie consumption on fasting days. For example, during the first week, reduce your intake from 2,000 calories to 1,500 calories. The next week, try eating just 1,000 calories. Continue to gradually reduce your intake until you’re eating the recommended 500–600 calories on fasting days. 

Keep in mind there’s a good chance you’ll experience side effects on fasting days if you’ve never tried fasting before. Side effects of fasting include:

  • Hunger
  • Headaches
  • Irritability
  • Fatigue
  • Trouble focusing
  • Loss of productivity
  • Sleepiness 
  • Mood swings
  • Nausea 
  • Weakness

These side effects are normal, usually minor, and typically go away once your body becomes used to fasting.

What to Eat
  • Whole grains

  • Vegetables

  • Fruits

  • High-fiber foods

  • Healthy fats

  • Lean protein

  • Red meat (on occasion)

  • Beverages

What Not to Eat
  • Beverages other than water, black coffee, or herbal tea (on fasting days)

  • No foods are technically off-limits

Whole Grains

Whole grains are rich in fiber and vitamins, and they help keep you full and satisfied. Carbohydrates are also great brain food, so whole-wheat breads, pastas, brown rice, quinoa and other delicious grains have a healthy place in the 5:2 diet. 

Vegetables

Broccoli, cauliflower, leafy greens, Brussels sprouts, sweet potatoes, squash—all these veggies and more are fair game on this plan. Load your plate with different colors to benefit from a range of healthy nutrients.

High-Fiber Foods

Beans, legumes, lentils, sprouted grains, and oatmeal are all examples of high-fiber foods that will keep you full and provide your body with essential nutrients, especially on your fasting days.

Healthy Fats

Be sure to include nuts, seeds, olive oil, avocados, oily fish, and other sources of omega-3s and omega-6s in your 5:2 diet plan. These will give your body energy when it runs out of glycogen stores

Lean Protein

Foods like chicken breast, ground turkey, eggs, and fish can provide you with sustained energy and the protein your body needs for muscle growth and cellular repair. Choose lean protein options for better health

Sample Shopping List

Like any balanced diet, the 5:2 diet will work best if you fill up on vegetables, fruits, lean proteins, whole grains, and healthy fats. The following shopping list offers suggestions for getting started on this plan. Note that this is not a definitive shopping list and you may find other foods that work better for you.

  • Dark leafy greens (spinach, kale, Swiss chard, bok choy)
  • Veggies (broccoli, cauliflower, Brussels sprouts, bell peppers, eggplant, carrots)
  • Fresh and frozen fruits (grapefruit, oranges, berries, bananas, apples)
  • Healthy fats (avocados, walnuts, almonds, chia seeds, olive oil)
  • Whole grains (rolled oats, quinoa, barley, amaranth, brown rice)
  • Legumes (black beans, lentils, chickpeas, soybeans)
  • Protein (tofu, lean meat, chicken, ground turkey)
  • Fresh or frozen fish and other types of seafood (salmon, halibut, shrimp)
  • Dairy products (cheeses, yogurt, cottage cheese)
  • Eggs

Sample Meal Plan

When you fast on the 5:2 diet is entirely up to you. One common protocol consists of the following schedule: 

  • Sunday: Normal
  • Monday: Fast
  • Tuesday: Normal
  • Wednesday: Normal
  • Thursday: Fast
  • Friday: Normal
  • Saturday: Normal

The following three-day meal plan provides an example of a Sunday through Tuesday 5:2 fasting protocol. In this instance, Monday would be designated as the fasting day and limited to about 500 calories, as outlined below. If you're following a 600-calorie diet, you can round out the plan with a 100-calorie snack such as a small piece of fruit, a serving of popcorn, or half an English muffin, or add a small side of cooked whole grains such as a half-cup of cooked quinoa to your main dish at dinner.

Also, note that this meal plan is not all-inclusive. If you do choose to follow this dietary pattern, there may be other meals that you prefer. Just remember to drink water or other zero-calorie beverages on your fasting days.

Sunday

Monday

Tuesday

Pros and Cons

Pros
  • No foods are off-limits

  • You get to choose your fasting days

  • Intermittent fasting is associated with certain health benefits

Cons
  • Hard to start

  • Hunger and other side effects

  • Possibility of overeating

  • Not suitable for some populations

As with all eating plans and diets, the 5:2 protocol comes with a unique set of pros and cons. Many people like intermittent fasting because, despite having to restrict calorie intake, it helps them break free from a diet mentality if they're trying to lose weight. Still, the eating pattern has its drawbacks.

Pros

  • Customizable: By focusing on the timing of eating, rather than the eating itself, you might find it easier to make healthy choices. On the 5:2 diet, you’re free to choose your fasting days based on your schedule. Many people fast during the week when it’s easier to adhere to a routine, especially if you frequent social events or family gatherings on weekends.
  • No forbidden foods: Because no foods are technically off-limits, this may make it easier to socialize with others. It will also leave you feeling less deprived on non-fasting days.
  • Improved health: Intermittent fasting is associated with a number of health benefits including weight loss and improved cardiovascular and metabolic health.

Cons

  • Difficult adjustment phase: While the 5:2 diet might be sustainable once you’re used to it, it requires some serious dedication in the beginning. You’ll likely deal with severe hunger and other side effects such as fatigue and irritability during the first few fasts. Once you make it past the initial adverse effects, though, your body should adapt and you should start to feel normal.
  • Risk of overeating: Restricting calories always presents the risk of overeating. Not only can this result in the unpleasant side effects of overeating, but you may not reach your health or weight loss goals as a result.

The 5:2 diet (and intermittent fasting in general) isn’t for everyone. Certain groups should avoid the 5:2 diet, including those who: 

  • Have had an eating disorder or a history of disordered eating
  • Are pregnant
  • Are actively growing, such as pre-teens and teenagers
  • Have nutrient deficiencies, such as iron-deficient anemia
  • Are trying to conceive or have known fertility issues
  • Have hypoglycemia 
  • Have type 1 diabetes

Is the 5:2 Diet a Healthy Choice for You?

If you're not sure whether the 5:2 diet is the right intermittent fasting program for you, there are other protocols similar to this plan to consider. Here's how they compare:

  • Warrior Diet: This intermittent fasting protocol involves fasting for 20 hours each day and eating all or most of your food within a 4-hour window in the evening. However, this plan lacks sufficient evidence and is not recommended by nutrition experts.
  • 16:8 protocol: One of the most popular intermittent fasting methods, the 16:8 protocol involves consuming all of your calories for the day in an 8-hour window and then fasting for the remaining 16 hours. This method works well for beginners because 16 hours is typically a doable fast, especially if you count your sleeping hours. 
  • Eat Stop Eat: On this plan, you’ll observe a complete 24-hour fast once or twice a week. For example, if you stop eating at 8 p.m. on Sunday night, you wouldn't eat again until 8 p.m. on Monday night. Like the 5:2 diet, you’re free to choose your fasting days on the Eat Stop Eat diet.
  • Alternate-day fasting: This intermittent fasting protocol involves an ongoing cycle: Fast one day, eat normally the next, and so on. You can eat 500–600 calories on your fasting days on this diet. Ultimately, alternate-day fasting ends up as a 4:3 diet, versus a 5:2 diet.  

When compared to federal guidelines for a healthy, balanced diet, the 5:2 diet is somewhat aligned, especially on non-fasting days. The U.S. Department of Agriculture's 2020–2025 Dietary Guidelines for Americans recommends consuming a variety of nutrient-dense foods including fruit, vegetables, grains, dairy products, and protein. The key recommendations in the federal guidelines include:

  • "A variety of vegetables; dark, leafy greens, red and orange, legumes (beans and peas), starchy, and other fruits, especially whole fruits
  • Grains, at least half of which are whole grain
  • Fat-free or low-fat dairy, including milk, yogurt, cheese, and/or fortified soy beverages
  • A variety of protein foods, including seafood, lean meats and poultry, eggs, legumes (beans and peas), and nuts, seeds, and soy products
  • Healthy oils, including those found in fish and nuts
  • Limited saturated fats, trans fats, added sugars, and sodium"

Since the 5:2 diet doesn’t specify which foods you should and shouldn’t eat, your best bet is to plan your meals around the USDA's recommendations. These guidelines are based on decades of science, and they’re informed by some of the most experienced and trusted health and nutrition experts in the country. 

To stay on track with your weight loss goals, it's helpful to know how many calories you should be consuming each day. Ultimately, weight loss comes down to calories in versus calories out—you must eat fewer calories than you burn in order to create a calorie deficit to lose weight.

Many people need around 2,000 calories per day for weight management and about 1,500 a day for weight loss, but women and children may need less, while men may need more. Very active people also usually need more than that—but other factors that play a role include age, height, weight, genetics, and physical activity level. Use this calculator to help determine the right number of calories to meet your goals.

Nutrient-dense whole foods are strongly encouraged on both fasting days and non-fasting days to promote weight management and overall health. While 500–600 calories on fasting days is much lower than the recommended daily intake, some of those calories and nutrients can be made up for on non-fasting days.

Health Benefits

Until recently, evidence in support of intermittent fasting was limited. As one researcher notes, "scientific evidence for the health benefits of intermittent fasting in humans is often extrapolated from animal studies, based on observational data on religious fasting (particularly Ramadan), or derived from experimental studies with modest sample sizes."

But as interest in intermittent fasting has continued to increase, more science has emerged. Clinical trials have suggested that intermittent fasting may aid in weight loss, help in the management of type 2 diabetes, and possibly even reduce the risk of cognitive disease. Here's a closer look at some of the recent research.

Weight Loss and Heart Health

One recent study published in The American Journal of Clinical Nutrition found that the 5:2 plan is a viable option for obese individuals seeking to lose weight and improve cardiovascular health. But the study was small in scope (16 study participants) and only lasted for 10 weeks.

A 2021 review assessed more than 1,100 healthy subjects and determined that intermittent fasting was more effective than calorie restriction at reducing the risk of heart disease. However, the researchers noted that further research is still needed to determine the safety of intermittent fasting for certain groups such as those with diabetes or those with an eating disorder, in addition to determining any long-term implications for overall health and longevity.

Type 2 Diabetes

A 2017 study looked at the effects of intermittent fasting on study participants with diabetes. Authors of the short-term observational study concluded that the fasting program may improve key outcomes including body weight and fasting glucose. But they also noted that their findings were exploratory, and a larger, longer study is necessary.

Health Risks

Despite some of the research in support of intermittent fasting, the findings are still mixed. A long-term study published in JAMA compared the 5:2 approach to daily calorie restriction. Researchers followed 100 participants for one year. A third of the participants followed the 5:2 diet, another third participated in a program of daily calorie restriction (75% of energy needs every day), and the remaining third made no dietary changes.

The 5:2 diet group had the highest drop-out rate among the three groups. And while both the daily calorie restriction group and the 5:2 group lost weight, there was no significant difference in the amount lost. Additionally, there were no significant differences between the intervention groups in blood pressure, fasting glucose, fasting insulin, insulin resistance, C-reactive protein, or homocysteine concentrations at six months or at one year. And at the end of the study, the 5:2 fasting group had low-density lipoprotein cholesterol levels that were significantly elevated.

Side Effects

Studies have flagged potential harms and side effects of intermittent fasting such as severe hunger, fatigue, weakness, headaches, irritability, mood swings, feeling cold, trouble focusing, and difficulty falling asleep.

In addition, some people may feel so hungry after their fasting days that they intentionally or unintentionally eat more than they need the next day. But if you indulge in unhealthy processed foods on your regular eating days, you might gain weight and even increase your risk for developing certain forms of chronic disease. To reap the most benefits from intermittent fasting, choose healthy, whole foods to meet your calorie intakes whenever possible.

If you feel overwhelmed with hunger, irritability, or any of the other side effects, try these tactics to find some relief: 

  • Drink more water
  • Take a nap
  • Stay busy with work or errands 
  • Take a stretch break 
  • Take a shower or bath
  • Meditate 
  • Call a friend

Proponents of intermittent fasting claim that most of the fasting side effects will subside once your body becomes accustomed to fasting. 

A Word From Verywell

Intermittent fasting is backed by a lot of emerging science. It may help you reach your weight, health, and fitness goals, but you should always be skeptical and cautious when considering diet plans. Make sure to thoroughly research the 5:2 diet before starting it, and always talk to a healthcare professional if you have questions or concerns. 

Remember, following a long-term or short-term diet may not be necessary for you and many diets out there simply don’t work, especially long-term. While we do not endorse fad diet trends or unsustainable weight loss methods, we present the facts so you can make an informed decision that works best for your nutritional needs, genetic blueprint, budget, and goals.

If your goal is weight loss, remember that losing weight isn’t necessarily the same as being your healthiest self, and there are many other ways to pursue health. Exercise, sleep, and other lifestyle factors also play a major role in your overall health. The best diet is always the one that is balanced and fits your lifestyle.

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Article Sources
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  1. Collier R. Intermittent fasting: the next big weight loss fad. CMAJ. 2013;185(8):E321–E322. doi:10.1503/cmaj.109-4437

  2. Welton S, Minty R, O’Driscoll T, et al. Intermittent fasting and weight loss: Systematic reviewCan Fam Physician. 2020;66(2):117-125.

  3. Grajower MM, Horne BD. Clinical management of intermittent fasting in patients with diabetes mellitusNutrients. 2019;11(4). doi:10.3390/nu11040873

  4. Dong TA, Sandesara PB, Dhindsa DS, et al. Intermittent fasting: a heart healthy dietary pattern? Am J Med. 2020;133(8):901-907. doi:10.1016/j.amjmed.2020.03.030

  5. Stockman M-C, Thomas D, Burke J, Apovian CM. Intermittent fasting: is the wait worth the weight? Curr Obes Rep. 2018;7(2):172-185. doi:10.1007/s13679-018-0308-9

  6. U.S. News & World Report. Best Diets 2021. The Fast Diet.

  7. Mosley M, Spencer M. The FastDiet. New York: Atria Books; 2013.

  8. Harvie M, Howell A. Potential benefits and harms of intermittent energy restriction and intermittent fasting amongst obese, overweight and normal weight subjects-A narrative review of human and animal evidenceBehav Sci (Basel). 2017;7(1):4. Published 2017 Jan 19. doi:10.3390/bs7010004

  9. Bernard BN, Louise LC, Louise D. The effects of carbohydrates, in isolation and combined with caffeine, on cognitive performance and mood-current evidence and future directionsNutrients. 2018;10(2). doi:10.3390/nu10020192

  10. Dong TA, Sandesara PB, Dhindsa DS, et al. Intermittent fasting: a heart healthy dietary pattern? Am J Med. 2020;133(8):901-907. doi:10.1016/j.amjmed.2020.03.030

  11. U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2020–2025 Dietary Guidelines for Americans. Ninth Edition. December 2020.

  12. Patterson RE, Laughlin GA, LaCroix AZ, et al. Intermittent fasting and human metabolic health. J Acad Nutr Diet. 2015;115(8):1203–1212. doi:10.1016/j.jand.2015.02.018

  13. Varady KA, Bhutani S, Church EC, Klempel MC. Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. Am J Clin Nutr. 2009;90(5):1138-43. doi:10.3945/ajcn.2009.28380

  14. Arnason TG, Bowen MW, Mansell KD. Effects of intermittent fasting on health markers in those with type 2 diabetes: A pilot studyWorld J Diabetes. 2017;8(4):154–164. doi:10.4239/wjd.v8.i4.154

  15. Zhang J, Zhan Z, Li X, et al. Intermittent Fasting Protects against Alzheimer's Disease Possible through Restoring Aquaporin-4 PolarityFront Mol Neurosci. 2017;10:395. Published 2017 Nov 29. doi:10.3389/fnmol.2017.00395

  16. Allaf M, Elghazaly H, Mohamed OG, et al. Intermittent fasting for the prevention of cardiovascular diseaseCochrane Database Syst Rev. 2021;1:CD013496. doi:10.1002/14651858.CD013496.pub2

  17. Trepanowski JF, Kroeger CM, Barnosky A, et al. Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults: a randomized clinical trial. JAMA Intern Med. 2017;177(7):930-938. doi:10.1001/jamainternmed.2017.0936

  18. Trepanowski JF, Kroeger CM, Barnosky A, et al. Effect of alternate-day fasting on weight loss, weight maintenance, and cardioprotection among metabolically healthy obese adults: a randomized clinical trial. JAMA Intern Med. 2017;177(7):930-938. doi:10.1001/jamainternmed.2017.0936

  19. Gramza-Michałowska A. The effects of ultra-processed food consumption-is there any action needed? Nutrients. 2020;12(9). doi:10.3390/nu12092556

Additional Reading
  • Barnosky AR, Hoddy KK, Unterman TG, Varady KA. Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings. Translational research: The Journal of Laboratory and Clinical Medicine. 2014;164(4):302-11.

  • Martin B, Mattson M, Maudsley S. Caloric restriction and intermittent fasting: Two potential diets for successful brain aging. Ageing Res Rev. 2006;5(3):332-353.

  •  St-Onge MP, Ard J, Baskin ML, Chiuve SE, Johnson HM, Kris-Etherton P, et al. Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement from the American Heart Association. Circulation. 2017;135(9):e96-e121.

  • Stote KS, Baer DJ, Spears K, et al. A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. Am J Clin Nutr. 2007;85(4):981-8.

  • Zauner C, Schneeweiss B, Kranz A, et al. Resting energy expenditure in short-term starvation is increased as a result of an increase in serum norepinephrine. Am J Clin Nutr. 2000;71(6):1511-1515.