What Is the 5:2 Diet?

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.

In recent years, the practice of intermittent fasting has emerged as a wellness trend. Scientists have also investigated 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.

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 to decide if this eating pattern is a healthy choice for you.

What Can You Eat?

The 5:2 diet restricts calories to just 500 a day for women and 600 a day for men on two fasting days. 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 overindulge on 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.

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, 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, try to spread them out as much as possible. 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 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. Continue to gradually reduce your intake until you’re eating the recommended 500–600 calories on fasting days. 

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, 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

• Breakfast: 3 Greek Yogurt Blender Pancakes topped with 1/4 cup strawberries, 1/2 sliced banana, and a drizzle of honey
• Lunch: 1 3/4 cup Red Curry Lentil Soup With Kale
• Snack: 1 sliced apple with 1 tablespoon peanut butter
• Dinner: 2 cups Roasted Red Pepper and Spinach Pasta

Monday

• Breakfast: 1 cup yogurt with 1/4 cup mixed berries (174 calories)
• Lunch: 1 cup Rainbow Vegetable Soup (72 calories)
• Snack: 6–7 whole almonds (48 calories)
• Dinner: 1 serving Roasted Chicken With Turmeric and Fennel (158 calories); 1/2 cup Lemony Roasted Low-Carb Broccoli (49 calories)

Tuesday

• Breakfast: Savory Spinach and Feta Oatmeal Bowl; 1/2 grapefruit
• Lunch: 2 cups Mediterranean Chopped Salad
• Snack: 1/4 cup homemade Roasted Red Beet Hummus with 3 ounces carrot sticks
• Dinner: 1 serving Honey Mustard Herbed Salmon; 1 1/4 cups Oven Roasted Potatoes; 1 cup fresh arugula drizzled with olive oil

Pros and Cons

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

Customization

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.

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.

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.

Health Benefits

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.

Weight Loss and Heart Health

One 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, 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 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. 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.

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

A Word From Verywell

Intermittent fasting 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.