Dieting often boils down to balance: calories in versus calories out, whole foods versus processed foods, thoughtful meal preparation versus convenience and impulse buys. The principle behind intermittent fasting, including the 5:2 diet, is based on restoring balance to one’s diet. You eat regularly most of the time, but restrict calories other times for better weight management and overall health.
But does this approach work? We’ll walk through the 5:2 diet, its effectiveness for weight loss and who should — or should not — consider this strategy.
What Is the 5:2 Diet?
The 5:2 diet is a type of intermittent fasting protocol.
“(It) involves five days per week of habitual food intake without restriction, with two consecutive or nonconsecutive days of substantial calorie restriction,” explains Candace Pumper, a registered dietitian with the Ohio State University Wexner Medical Center in Columbus.
On the days when you’re restricting calories, you should be consuming between 500 and 800 calories, she adds.
The idea behind this approach is that the human body evolved to cope with periods of food deprivation (think of days when our hunter-gatherer ancestors faced food scarcity).
Now, however, our constant access to high-calorie foods has theoretically had a detrimental effect because we’re no longer stressing out the body with those intermittent periods of reduced calorie intake. Some research has also suggested that the easy influx of calories we have access to is responsible for increases in obesity in the U.S. This has led some scientists to recommend recreating that ancient ebb and flow of calories as the potential key to resolving a host of health problems.
[Read: Calorie Reduction vs Fasting.]
Does the 5:2 Diet Work for Losing Weight?
Scientific data on the effectiveness of the 5:2 diet is relatively limited, but it has worked for some people.
Pumper says that the 5:2 diet “is an effective weight-loss intervention, producing body weight reductions ranging from 4% to 7% over eight to 52 weeks.”
However, she adds, when you compare the 5:2 diet with continuous calorie-restricted diets, studies show no significant difference in weight loss and cardiometabolic risk reduction.
A key determinant of how much weight you can lose with the 5:2 diet depends on how long you can stick with it. Because of the restrictive nature of the diet, following it long term can be challenging for some people.
[Read: Intermittent Fasting: Foods to Eat and Avoid.]
How to Follow the 5:2 Diet
While the scientific evidence may be limited, there are lots of anecdotal reports about people who’ve lost weight and improved overall health by following various intermittent fasting plans.
If you’re interested in trying the 5:2 plan, follow these guidelines to get started:
— Consult a health care professional. Before starting the 5:2 diet, or any fasting regimen, talk with your health care provider, especially if you have underlying medical conditions or concerns about how this change might affect your overall health. Your doctor or a registered dietitian can provide personalized guidance and ensure the approach is safe for you.
— Calculate your calorie allowance. When you fast, you’ll significantly restrict your calorie intake. The recommended daily calorie intake for women on fasting days is typically around 500 to 600 calories. For men, that intake is between 600 and 800 calories. You can adjust these numbers based on your specific needs and tolerance for hunger pangs. To keep in line with the whole fasting idea, though, it’s essential to strictly limit your calories on these days.
— Plan your meals. Planning in advance can help you stay within your calorie allowance on fasting days. Opt for foods that are low in calories but provide a feeling of fullness, such as non-starchy vegetables and lean proteins.
— Stay hydrated. Drink plenty of water, herbal tea and other non-caloric beverages on fasting days. Staying hydrated can help reduce feelings of hunger.
— Consume adequate protein. Protein-rich foods, such as chicken, fish and tofu, can help you feel full and maintain muscle mass during fasting days.
— Avoid high-calorie and sugary foods. On fasting days, those items will gobble up your entire calorie allowance without providing much in the way of satiation or nutrition.
— Be reasonable on regular eating days. On your regular eating days, you can eat normally without specific calorie restrictions. However, it’s still important to prioritize a balanced and nutritious diet. If you’re using the 5:2 diet to lose weight, calories still matter, and you need to keep portions in check on your non-fasting days to continue seeing results.
— Monitor your progress. Keep track of your weight, measurements and how you feel while following the 5:2 diet. Adjust your plan as needed based on your progress and any feedback from your body. If you experience extreme hunger, dizziness or other adverse effects, stop following the plan and talk with your health care provider.
[See: Ways to Shift Your Mindset for Better Weight Loss.]
Foods to Eat on the 5:2 Diet
The 5:2 diet doesn’t strictly limit specific foods or prescribe certain ratios of macronutrients. However, on the days when you’re keeping calories to a minimum, any foods you do consume should be as nutrient-dense as possible. This means you should focus on the following foods:
— Vegetables. Non-starchy vegetables like spinach, kale, broccoli, cauliflower, zucchini and bell peppers are low in calories but high in vitamins, minerals and fiber. They can help keep you full without significantly impacting your calorie intake.
— Lean proteins. Lean sources of protein, such as skinless chicken, turkey, fish, tofu and low-fat dairy, can all be part of the 5:2 diet. Protein helps maintain muscle mass and promotes satiety, so you’ll feel fuller longer, even on the days when you’re restricting your caloric intake.
— Eggs. Eggs are also a good source of protein and healthy fats. A versatile food, you can cook them a variety of ways, and they pair well with non-starchy veggies.
— Legumes. Beans, lentils and chickpeas are rich in fiber and protein, making them filling and nutritious choices for fasting days. But you’ll have to watch the portion sizes as they can add calories fairly quickly.
— Whole grains. Small servings of whole grains, such as quinoa, brown rice or whole-wheat pasta, can provide sustained energy and help you feel full. Again, keep portions small, especially on fasting days, so as not to use your whole calorie allotment on a single food item.
— Low-calorie fruits. Berries, such as strawberries, blueberries and raspberries, are lower in calories compared to many other fruits, and they offer lots of antioxidants and fiber. Small portions can certainly be part of the 5:2 diet approach.
— Low-fat dairy. Low-fat, plain Greek yogurt, skim milk or low-fat cheese are good sources of calcium and protein. Choose the low-fat and plain or unsweetened varieties to keep your calorie intake under your daily limit.
— Soup. Soups and hearty broths are especially good choices on the 5:2 eating plan. A low-calorie, broth-based vegetable soup can be both filling and hydrating on fasting days.
— Herbs and spices. Use herbs and spices liberally to add flavor and interest to your meals without adding extra calories.
Foods to Avoid on the 5:2 Diet
While there are plenty of foods you can eat on the 5:2 diet, there are a few you should seek to limit, especially on fasting days. These include:
— Ultra-processed foods. These foods, including chips, sugary snacks, pastries, fried foods and processed meat products, often contain hidden sugars, fats, calories and other additives that won’t aid in nourishing your body. Skip them to open up more room in your calorie budget.
— Full-fat dairy. Full-fat dairy products also tend to be higher in calories than their skim or nonfat counterparts.
— Sugar-sweetened beverages. Sodas, sweet teas and coffees, energy drinks and fruit juices contain lots of calories and sugar but don’t add much, if any, nutritional support. Skip them, and opt for plain water instead.
— Alcohol. Wine, beer and hard alcohol all contain lots of empty calories and can dehydrate you. Opt out of the hard drinks, especially on fasting days.
— White bread and refined grains. When grains are refined, they’re stripped of much of their fiber and other nutrients, leaving just the calories. Go for whole-grain versions instead to put some of that nutrition back in your diet.
Is the 5:2 Diet Healthy?
Intermittent fasting and the 5:2 approach have been developed as a means of losing weight and improving overall health. But it’s not entirely clear whether it actually works.
“Evidence from animal studies (suggests) that intermittent fasting does have favorable effects on insulin, metabolism and inflammation, but human studies have not supported those findings yet,” says Cathy Leman, a Chicago-based registered dietitian and nutrition therapist.
Benefits of intermittent fasting
While the initial data on the 5:2 intermittent fasting approach is limited, it does show some promise for health benefits.
Preliminary human studies, Pumper explains, suggest the 5:2 diet favorably influences biomarkers of cardiometabolic disease, especially for those with increased risk, by lowering blood pressure, hemoglobin A1c and oxidative stress, among other factors, in the short term.
In addition, she notes that the 5:2 approach appears to contribute to decreases in LDL (bad) cholesterol and triglycerides when clinically significant weight loss (greater than 5% from baseline) is achieved, though “contrasting findings have been reported.”
A reduction in systemic inflammation is another benefit that’s often touted for the 5:2 diet. Inflammation is a common feature of many chronic diseases, including diabetes, obesity and cancer. A diet that helps reduce overall inflammation could then help you manage your risk of developing those diseases — that’s the theory, anyway. But Pumper notes that “lack of data precludes any definitive conclusions about the influence of IF 5:2 on markers of inflammation.”
For some people, Leman adds, the benefit of this approach is simply about being more mindful.
“(It) causes them to put their awareness on their eating habits and to be more deliberate when they’re eating,” she points out.
The 5:2 diet risks
Pumper says that the 5:2 plan is generally safe, but you should weigh the benefits against the risks. Potential risks may include:
— Nutritional deficiencies. Severely limiting your calorie intake can make it tough to meet all your body’s nutritional needs. Over time, this can add up to nutritional deficiencies.
— Overeating. In response to the restriction endured on fasting days, some individuals may be more likely to overeat on non-fasting days, which can negate your efforts and slow or stall your weight loss. This can also set you up for an ongoing cycle of binge-and-purge habits, which can trigger or exacerbate existing eating disorders.
— Hunger, anxiety and irritability. Fasting days can be challenging, and some people may experience excessive hunger, irritability and difficulty concentrating. You may also find that you’re too weak to work out, which could limit your ability to gain health improvements.
— Muscle loss. When your body doesn’t have enough calories coming in to sustain its basic function, it may start breaking down muscle as fuel. That can lead to a loss of muscle mass and a reduction in your metabolic rate; muscle burns more calories at rest than fat, so if you’re losing muscle, you may be turning down your burn rate and making it even harder to lose weight.
— Bad breath. Fasting causes a reduction in the production of saliva, which means there’s not as much saliva to help your mouth flush away odor-causing bacteria. This can lead to halitosis or bad breath.
— Constipation. Your bowels can get backed up on fasting days if you’re not consuming enough fiber to help keep things regular.
— Sleep disruptions. Going to bed hungry can disrupt your sleep and make it tougher to get the seven to nine hours a night most adults need to function optimally.
Pumper also notes that there are several areas that we don’t have much data on at all. For example, “the influence of IF 5:2 on human reproductive health is an underexplored but important issue.”
What’s more, she notes that “to date, no studies have evaluated the influence of IF 5:2 on appetite regulation, gut microbiome diversity and sleep,” all key components of overall health.
Who Should Avoid Intermittent Fasting
Intermittent fasting is not suitable for everyone. The following groups should avoid intermittent fasting, including the 5:2 diet:
— People with diabetes or those who are prone to hypoglycemia.
— Anyone with a history of an eating disorder.
— Anyone with a body mass index of less than 18.5.
— Anyone with a history of bariatric surgery.
— People with kidney disease.
— People with gastrointestinal issues, such as irritable bowel syndrome or inflammatory bowel disease.
— Pregnant or breastfeeding women.
— Children and adolescents under the age of 18.
— People who take certain medications, such as those for diabetes or to control blood sugar.
— Older, frail adults.
Alternate Intermittent Fasting Diets
The 5:2 approach isn’t the only way to manage intermittent fasting. Other protocols include:
— Time-restricted eating. These are typically arranged as 16:8, which refers to a limited time window during each day when you can eat. On the 16:8 plan, you’ll fast 16 hours every day and only consume food during an eight-hour “feeding window.” Because you’re fasting while you’re asleep, this format is often easier to adopt because it simply means extending the time before breakfast or eating dinner earlier before bed.
— Alternate-day fasting. With alternate-day fasting, you’ll follow a similar pattern to the 5:2 approach, except that you’ll have one fasting day followed by a non-fasting day and continue alternating until you stop the plan. Some versions of this plan say that on fasting days, you should consume zero calories, while others say up to 500 calories is OK.
— The 24-hour fast. Also called Eat-Stop-Eat, this version says to fast completely for 24 hours once or twice a week and then eat normally the rest of the week.
— The fasting-mimicking diet. With this approach, you essentially “trick” your body into thinking you’re fasting by removing most of the calories you’d normally eat. The fasting-mimicking period lasts for five days, during which you take in between 700 and 1,100 calories (depending on the day) that conform to a strict macronutrient ratio. You’ll repeat that five-day plan every three to four months until you hit your desired weight.
The Bottom Line
The 5:2 diet is a type of intermittent fasting protocol that may help you lose weight. All foods are allowed on the 5:2 plan, “but basing the diet on a variety of nutrient-dense foods, including lean protein, whole grains, legumes, dairy products, fruits, vegetables and healthy fats, is encouraged in place of highly processed foods,” Pumper says.
Be sure to speak with your health care provider before starting this diet, and take care to plan meals to ensure you’re meeting your basic nutritional needs, even on fasting days. While this approach is not for everyone, it’s generally considered safe and might help you shed excess pounds or improve some health markers.
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