The Complete Guide to the 5:2 Diet

The 5:2 diet involves fasting two days per week and eating regularly for the remainder of the time. 

According to some weight-loss “experts,” eating on this schedule profoundly affects your health and body composition.

Better yet, they say, it makes dieting effortless, which means it’s the perfect solution for anyone looking to slim down and improve their health.

Is the 5:2 diet really as simple and effective as they claim?

Or is it just an acceptable but unremarkable way to lose weight?

Here’s what science says.

Table of Contents

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• What Is the 5:2 Diet?
• How to Follow the 5:2 Diet Plan
• 5:2 Diet: Benefits
• What to Eat on the 5:2 Diet Plan

What Is the 5:2 Diet?

The 5:2 diet (sometimes referred to as the 5:2 fasting diet) is an eating protocol that involves restricting your calorie intake to 500 (women) or 600 (men) calories per day on 2 days per week and eating as normal on the remaining 5 days.

British journalist Michael Mosley popularized the diet in the early 2010s when he created a documentary called Eat, Fast and Live Longer and published a book titled The Fast Diet detailing its benefits and how to follow it.

How to Follow the 5:2 Diet Plan

To follow the 5:2 diet, choose two days per week as “fast” days. On fast days, you can eat 500 calories if you’re a woman or 600 calories if you’re a man.

You can choose any two days of the week as your fast days; the only stipulation is that they’re non-consecutive. For example, if you choose to fast on Monday, your other fast day can’t be Sunday or Tuesday. 

Many people like to fast on Mondays because it’s psychologically more manageable to fast at the beginning of the week when your resolve is highest. Likewise, most prefer to forgo fasting on weekends since this is the time you’re most likely to enjoy social dinners and parties, which can make calorie counting more challenging.

On non-fast days, you eat the amount and types of food you typically eat. Don’t eat more on non-fast days to compensate for fast days, though, as this will undermine your progress.

5:2 Diet: Benefits

The most commonly cited benefits of the 5:2 diet are that it helps you lose weight and maintain healthy blood glucose levels and that it’s easier to stick to than other diets.

Are these claims legit? Here’s what science says about each.

Weight Loss

While many people follow the 5:2 diet to lose weight, surprisingly few studies have investigated its effect on weight loss.

That said, the limited evidence we have is promising.

For instance, in a 2022 study conducted by scientists at University College London, researchers found that people who followed the 5:2 diet for a month lost an average of ~4 pounds. 

Another study published in the journal Frontiers in Nutrition found that overweight and obese people with non-alcoholic fatty liver disease who stuck to the 5:2 diet for 3 months lost an average of ~8 pounds.

Importantly, studies that pit the 5:2 diet against more conventional diets that involve maintaining a daily calorie deficit show that both protocols are equally effective at promoting weight loss.

For example, in one study conducted by scientists at the University of South Australia, researchers found that people who followed the 5:2 diet for a year lost ~15 pounds, while those who followed a regular diet for the same time lost ~11 pounds.

This may surprise you if you’ve ever listened to online weight-loss “gurus” wax lyrical about the superiority of fasting for fat loss.

However, the truth is there’s nothing unique about how the 5:2 diet aids weight loss—it simply makes it easier to eat fewer calories than you burn over the course of a week by limiting your calorie intake on two days.

While the 5:2 diet is effective at helping you lose weight, it isn’t necessarily optimal for improving your overall body composition. For instance, in a study conducted by scientists at Swinburne University of Technology, researchers had 17 people lift weights and follow either a continuous diet or the 5:2 diet for 12 weeks.

Both groups gained about the same amount of strength, but those who dieted continuously gained slightly more muscle. During the 12-week study, the differences weren’t statistically significant, though they likely would’ve become more pronounced over a longer period.

Thus, following the 5:2 diet is a viable weight-loss strategy, but it’s probably suboptimal if you want to “recomp” (build muscle and lose fat simultaneously).

Blood Sugar Control

Keeping your blood sugar levels in a healthy range is important because it helps you avoid health conditions, such as heart disease, type 2 diabetes, and metabolic syndrome, and can improve your quality of life, energy levels, and mood.

Many people believe that fasting diets can help you maintain healthy blood sugar levels better than traditional diets. 

According to them, when you eat 3 meals and 1-to-2 snacks daily, your blood sugar and insulin levels remain chronically elevated. Over time, this causes your cells to become less sensitive to insulin, which means glucose stays in your blood for longer.

However, when you refrain from eating for prolonged periods, your insulin levels spend more time at “baseline,” which helps reset your insulin sensitivity.

While there’s plenty of evidence that the 5:2 diet effectively improves blood sugar control, it rarely outperforms regular dieting. 

As such, it’s not clear whether there’s anything inherently special about fasting that improves blood sugar control. It’s equally likely that it occurs because fasting helps you lose weight, which is a proven way to better blood sugar control.

At bottom, following the 5:2 is a feasible way to improve blood sugar control, but it’s likely no more effective than regular dieting. Therefore, you don’t need to follow the 5:2 diet to improve your blood sugar control if you prefer to eat on a more regular schedule.

Adherence

One of the reasons the 5:2 diet is so popular is that many feel it simplifies dieting.

Unlike traditional diets that require you to count the calories in every meal, the 5:2 diet allows you to eat ad libitum (without restriction) most of the time and only monitor your calorie intake on two days per week.

Many people also feel “going hungry” for two days per week is more manageable than the “relentless restriction and self-control” associated with conventional dieting.

(Of course, dieting doesn’t have to feel like punishment. If you want to learn how to diet to lose weight without “starving” yourself or restricting all your favorite foods, check out this article on flexible dieting.)

Furthermore, when you follow the 5:2 diet, you don’t have to pay membership to a weight-loss group, buy pre-made meals, meal replacements, or other fat-loss supplements, or understand complex nutritional information. This makes the 5:2 diet more accessible than most other diet strategies.

For many, this “user-friendliness” makes the 5:2 diet easier to stick to long term, which increases the likelihood that it will help you lose weight.

That said, studies also show that some people find conventional diets just as easy to stick to as the 5:2 diet. Moreover, there’s evidence that some people grow weary of the 5:2 diet very quickly, while others find their initial enthusiasm ebbs after just a couple of months.

In other words, the 5:2 diet can work for some people but probably isn’t suitable for everyone. If you want to know whether it can “work” for you, try it for 2-to-4 weeks and see how you respond. If you enjoy it and it helps you achieve your goals, continue.

However, if you find restricting your food intake on fasting days miserable, don’t feel like you have to persist. There are plenty of other strategies that might be a better fit.

(And if you’d like to know exactly what diet to follow to reach your fitness goals, take the Legion Diet Quiz and in less than a minute, you’ll know exactly what diet is right for you. Click here to check it out.)

What to Eat on the 5:2 Diet Plan

Since you can’t eat more than 500-to-600 calories, it’s unlikely you’ll ever feel “full” on fast days.

That said, if you choose your foods carefully, you maximize your chances of feeling satiated.

Here are some tips to make fasting easier:

1. Prioritize protein: Protein is the most satiating macronutrient, so try to include as much as possible in your 5:2 diet plan. Some good options are fish, particularly when it’s steamed or raw (sashimi); lean white meat, such as chicken or turkey breast; whey isolate protein powder, such as Whey+; low-fat dairy, including Skyr and low-fat cottage cheese.
2. Eat leafy green vegetables: Leafy green vegetables add bulk to meals, which makes you feel fuller, but generally contain very few calories. 
3. Eat raw vegetables when appropriate: Research shows that eating hard-textured foods increases satiety. Eating vegetables raw also helps you avoid eating cooking oil, which can add a significant number of calories to food. If eating raw vegetables sounds unappealing, prepare salads with carrots, beets, radishes, red onions, and similar veg using a mandolin.
4. Dress salads with oil and lemon juice: Dressing salads with oil and lemon juice makes them tastier and helps you absorb nutrients in your food. Oil also contains a lot of calories, so use it sparingly—a teaspoon per dish is usually enough.
5. Use a non-stick pan or low-calorie spray for cooking: Using a non-stick pan or low-calorie cooking spray saves you from using oil for cooking, reducing the calorie content of your meals.
6. Use herbs and spices to flavor your food: 5:2 diet recipes don’t have to be bland. Herbs and spices contain very few calories, so use them to enhance the flavor of your food.
7. Eat oats for breakfast: Oatmeal is highly satiating, full of fiber, and when you prepare it with water, relatively low in calories—one cup of cooked oats contains just 158 calories.
8. Eat plenty of fiber: Fiber helps you feel fuller for longer, so try to eat plenty of fruit, vegetables, pulses, legumes, beans, and whole grains on fast days. Also, keep the skin on fruits and vegetables when possible to maximize your fiber intake.
9. Drink enough water: Drinking enough water quells hunger and may prevent you from overeating at meal times.
10. Avoid high-GI foods: Some research suggests that low-GI foods are more satiating than high-GI foods, so swap starchy white carbs such as white bread and pasta for brown rice and quinoa.