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Find Out Why Some Are Fasting to Slim Down

Find Out Why Some Are Fasting to Slim Down

  • February 15, 2021
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For original article click here

The 5:2 diet is a popular intermittent fasting method that involves reducing your food intake on two days of the week. Also called the fast diet, this eating program allows you to eat normally for five days, then on two days of your choice, you significantly restrict calories.

Because no foods are off limits, diets like the 5:2 plan are appealing to many people who are trying to slim down or improve their health. But the 5:2 is one of the more restrictive versions of intermittent fasting, so it may be difficult for some people to follow. 

“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

Intermittent fasting has been around for hundreds of years as a religious, spiritual, and political act. As far back as ancient Greece, philosopher Pythagorus fasted and encouraged others to do so, as did Hippocrates and the Renaissance doctor Paracelsus.

Still today, major religions of the world fast during sacred times. Those who practice Judaism, for example, observe several fasts throughout the year, while Christians fast on certain days during Lent. Political figures like Mahatma Gandhi have used fasting as a means of political protest.  

The practice of fasting has recently became popular for health and fitness reasons. Following low-carb, paleo, keto, and commercial diet trends, intermittent fasting has become the next big thing. There are several different ways to do intermittent fasting, including the warrior diet, water fasting, and more.

The 5:2 diet became popular when Dr. Michael Mosley, a UK-based journalist wrote a book called The Fast Diet . Mosley did his original training as a doctor in London. In the book, he outlines the program where you fast for two days of the week and eat normally during the other days.

There have 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 improve weight loss, help manage or prevent diabetes, and improve heart health. Study results have been mixed and study authors often remark that conducting research is complex.

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.” However, as interest in these program has increased, more studies have been conducted.

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 last 10 weeks.

Another published 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.

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, one third participated in a program of daily calorie restriction (75% of energy needs every day), and one 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 in 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.

Part of the appeal of the 5:2 diet is its simplicity. There are no complicated meal plans to follow and you don’t have to measure portions or count calories.

The 5:2 diet allows you to eat “normally” during most of the week. You restrict your caloric intake on two days of the week.

On the fasting days you reduce your calorie intake to 500 calories (for women) and 600 calories (for men). During the other five days you eat normally. However, in the book, Mosley explains that 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 can’t necessarily over-indulge on your non-fasting days. Instead, you are encouraged to eat reasonable portions of a wide range of foods.

How Many Calories Do I Burn Each Day?

You are generally free to eat whatever you want on the 5:2 diet. That’s one of the major appeals of intermittent fasting—there are no “good foods” or “bad foods.”

Instead of focusing on the content of foods (such as how many carbs or how much protein a food has), the 5:2 diet focuses largely on meal timing

That said, you should aim to consume nutritious foods on any eating plan. The 5:2 diet will work best if you fill up on vegetables, fruits, lean proteins, whole grains, and healthy fats. The healthy fats and protein are especially important on fasting days, as they’ll provide your brain and body with extended energy. 

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 keep you full. 

You can drink anything you want on your regular eating days, but on fasting days, you should stick to water in order to stay within that day’s calorie limit. 

Compliant Foods

  • Whole grains

  • Vegetables

  • Fruits

  • High-fiber foods

  • Healthy fats

  • Lean protein

  • Red meat

  • Beverages

Non-compliant Foods

  • Beverages other than water (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 the 5:2 diet. Load your plate with different colors to benefit from a range of healthy nutrients.

Fruits: Fruit has a healthy place in almost any diet. You can enjoy citrus fruits, starchy fruits, berries, and more on the 5:2 diet. 

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. Try out these lean protein options for better health

Red meat: While it’s best to stick to lean protein most of the time, a few servings of red meat each week won’t hurt. Try incorporating lean ground beef or a lean cut of steak

Beverages: You can drink anything you want on your normal days, but it’s best to stick to zero-calorie beverages on your fasting days. Try to drink water, black coffee, and herbal tea on your low-calorie days. 

On five days of the week, eat as you normally would. This doesn’t mean you should eat more than usual — if you eat more on “normal” 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 your normal days, you may even gain weight. 

So try your best to keep your normal days normal.

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 ab out 25% of your normal calorie intake.

Since you have a limited number of calories to work with, 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 consume 500 calories on your fasting day, you could eat 200 calories at breakfast, 100 calories at lunch, and another 200 calories at dinner. You could also try eating 250 calories at lunch and 250 calories at dinner. 

As far as choosing the fasting days themselves, that’s 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

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. If you feel overwhelmed with hunger, irritability, or any of the other side effects, try helping them pass with these tactics: 

  • 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

Most of these fasting side effects will go away if you just stop focusing on them. Over time, your body should become used to fasting. 

It’s definitely not easy to shift from eating normally every day to eating only 500–600 calories on two days. Instead of taking such a big leap, you can try 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. Keep reducing in smaller increments until you’re eating the recommended 500–600 calories on fasting days. 

All eating plans and diets come with a unique set of pros and cons. Here are some pros and cons to consider before trying the 5:2 diet. 


  • No foods are off-limits

  • You get to choose your fasting days

  • Intermittent fasting is associated with certain health benefits


  • Hard to start

  • Possibility of over-eating

  • Hunger and other side effects

  • Not ideal for all populations

No foods are off-limits: Many people like intermittent fasting because, despite having to restrict calorie intake, it helps them break free from a diet mentality. If you’ve struggled in the past by labeling foods as “good” or “bad,” the 5:2 diet might help you welcome new foods into your eating plan. By focusing on the time of eating, rather than the eating itself, you might find it easier to make healthy choices. 

You get to choose your fasting days: On the 5:2 diet, you’re free to choose your fasting days based off of your schedule. Most people choose to fast during the week, when it’s easier to stick to a routine. On weekends, you might find yourself at social events or family gatherings where it’s hard to stick to your fasting protocol.  

Intermittent fasting may provide 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. However, research findings have been mixed with some studies indicating potential harms (such as the side effects listed).

Hard to start: Even though the 5:2 diet might be sustainable once you’re used to it, it requires some serious dedication in the beginning. You’ll deal with severe hunger and other side effects (more on that below) for the first fast, and possibly the first few fasts. Once you make it past the initial adverse effects, though, your body should adapt and you should feel fine. 

Possibility of over-eating: Restricting calories always presents the risk of over-eating. You may feel so hungry after your fasting days that you intentionally or unintentionally eat more than you need the next day. Not only can this result in the unpleasant side effects of over-eating, but you may not reach your health or weight loss goals. 

Hunger and other side effects: As mentioned earlier, you’ll likely experience side effects when you start the 5:2 diet. These side effects include severe hunger, fatigue, weakness, headaches, irritability, mood swings, feeling cold, trouble focusing, and difficulty falling asleep. 

Not ideal for all populations: The 5:2 diet (and intermittent fasting in general) isn’t for everyone. Some people should avoid the 5:2 diet, including those who: 

  • Have battled an eating disorder or 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

When you’re shopping for an important product or service, you always check out the competition, right? Well, when you’re “shopping” for a diet or eating plan, you should make an effort to look at other similar diets. 

This section covers how the 5:2 diet compares to the federal dietary recommendations, as well as three other similar diets. 

How Intermittent Fasting Compares to Other Diets

The federal dietary recommendations include five food groups: fruit, vegetables, grains, dairy, and protein. The key recommendations in the federal guidelines include:

  • “A variety of vegetables from all of the subgroups—dark green, red and orange, legumes (beans and peas), starchy, and other
  • Fruits, especially whole fruits
  • Grains, at least half of which are whole grains
  • 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
  • Oils
  • 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 recommendations. These guidelines are based off of decades of science, and they’re informed by some of the most experienced and trusted scientists and health professionals in the country. 

No matter what eating plan you follow, you must know how many calories you should be consuming each day in order to reach your weight goals. Ultimately, weight loss comes down to calories in versus calories out — you must eat fewer calories than you burn in order to lose weight.

Most people need around 2,000 calories per day, but women and children may need less, while men may need more. Very active people also usually need more than 2,000 calories. Factors that play a role in your calorie needs include: age, height, weight, genetics, and physical activity level.

The 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. Learn more about the Warrior Diet

The 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 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 the Eat-Stop-Eat diet, 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 the 5:2 diet.  

Intermittent fasting is backed up by a lot of 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 health professional if you have questions or concerns. 

What Is Intermittent Fasting?

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