Buzz
In a single day, my meals included a portion of green beans, a Clif bar, and one homemade sous vide egg bite, totaling just 500 calories. Let me clarify—this isn’t a sign of an eating disorder; it’s simply part of the diet I experimented with. The next day, I resumed my usual intake of around 2000 calories, feeling completely normal.
The 5:2 diet involves fasting for two days each week—for instance, Monday and Thursday. On these days, you consume only 25% of your typical calorie intake. The remaining five days, you eat as usual. By the week’s end, your total calorie consumption matches that of restrictive 1500-calorie diets, but you only need to restrict yourself for two days.
This diet has gained immense popularity in the UK since its introduction in a 2012 BBC documentary. When I first learned about it, I found the concept intriguing. I had previously practiced a form of intermittent fasting that essentially involved skipping breakfast and postponing lunch. This approach helped me focus better in the mornings and encouraged healthier eating habits, though it required some adjustment.
The idea of fasting for an entire day seemed daunting at first, but considering that half of England seems to embrace it (including Benedict Cumberbatch), I decided to give it a shot. With a few extra pounds to shed and a growing frustration with traditional calorie-counting diets, the 5:2 approach felt worth a try.
What motivates someone to try this?
While diets often tout various health benefits, let’s be honest: most people are primarily focused on losing weight. The 5:2 diet is no exception. Beyond weight loss, this diet, along with other intermittent fasting methods, claims to enhance the function of your brain, heart, metabolism, and more.
The biggest draw is that the 5:2 diet only requires commitment one day at a time. Yes, those fasting days can be challenging, but they pale in comparison to the rigid restrictions of the Whole30 diet, which bans bread and sugar for an entire month. It’s also far less grueling than traditional calorie-counting diets, which demand months or even years of constant vigilance for long-term weight loss.
Is it effective?
While the 5:2 diet hasn’t undergone extensive rigorous studies, some preliminary data exists. One long-term study revealed that the 5:2 diet yields results comparable to traditional dieting methods. Additional research on alternate-day fasting supports this, showing similar weight loss outcomes to conventional diets, as highlighted in studies like this one published in Obesity.
However, the diet’s effectiveness varies among individuals, and researchers are still exploring why. A trial published in Obesity Research and Clinical Practice found that white individuals and older adults tended to achieve better results, though factors like access to healthy foods weren’t fully accounted for. Interestingly, men and women experienced similar success rates on the diet.
Beyond weight loss, the additional health benefits are harder to define. It’s well-documented that mice live longer when underfed. Numerous studies have investigated the potential advantages of calorie restriction and whether these benefits can be safely and practically applied to humans.
For instance, fasting is believed to improve the body’s ability to regulate blood sugar. Overeating can lead to insulin resistance, potentially resulting in type II diabetes. Both dieting and exercise appear to counteract this effect, and fasting is thought to amplify these benefits. However, there’s insufficient evidence to confirm this outcome definitively.
The book The Fast Diet, which explains the 5:2 approach, is surprisingly candid for a diet book. Its author, Michael Mosley, a physician-turned-BBC presenter, experimented with various fasting diets for his documentary Eat, Fast, and Live Longer. He chose the 5:2 method as a balanced compromise based on his personal experiences and intuition. Given the lack of definitive evidence on fasting or dieting methods, I find this approach reasonable. If the 5:2 diet is manageable and has a fair chance of success, it’s worth considering.
What does a fasting day feel like?
I start my day craving breakfast, but since I’m limited to 500 calories, I delay eating and opt for beverages like coffee, water, seltzer, or diet coke. This usually helps curb the hunger until later in the day.
If the hunger persists, I turn to vegetables, which are almost calorie-free. A favorite is Trader Joe’s microwave-steamable bag of fresh green beans. Seasoned with salt and pepper, it’s tasty, surprisingly filling, and only 125 calories for the entire bag, which I divide into two snacks—one for the morning and one for the evening.
Typically, I’m fine until around 2pm. If my focus at work starts to waver, I know it’s time for a small meal. While I could prepare a carefully portioned dish, I usually skip the hassle of recipes and cooking. Instead, I grab a Clif bar, which is around 250 calories and as satisfying as a small meal can be. (The Fast Diet offers plenty of recipes if you prefer a more structured approach.)
The evening is the toughest part for me, as hunger really sets in. I often find myself pacing the kitchen, trying to decide how to use my remaining 100-200 calories. I prefer something substantial, like an egg bite, but it’s never quite enough. I remind myself, Tomorrow, I can eat more.
Staying out of the kitchen and avoiding thoughts of food make fasting much easier. Busy workdays are ideal for fasting, while weekends, with their leisurely pace or social gatherings, present the biggest challenges.
Is it possible to exercise while fasting?
Absolutely, you can. I typically planned my workouts and fasting days separately, but one day I decided to experiment by going for a run to document how awful it might feel.
Surprisingly, it wasn’t awful at all. I was amazed: despite only consuming Diet Coke and seltzer all afternoon, I managed to jog for nearly an hour without feeling hungrier than I did at my desk. I maintained my usual pace and even extended my run beyond my initial plan. (Perhaps hunger clouded my judgment? It’s possible.) Afterward, I saved the Clif bar I brought and waited until evening to enjoy a 400-calorie super burrito.
Some claim they feel more energized when they exercise on an empty stomach. I always thought this was something you could adapt to over time, but I didn’t expect to experience it immediately. Whether it was a one-time occurrence or not remains to be seen.
What do you eat on non-fasting days?
On non-fasting days, you’re encouraged to eat “normally.” While nothing is strictly off-limits, it’s wise to focus on vegetables, protein, and moderation, especially if your goal is weight loss or maintaining a healthy lifestyle. Cupcakes are fine, but they shouldn’t dominate your diet.
I tend to feel slightly hungrier the day after fasting, though skipping breakfast is still manageable, even if I went to bed hungry. However, overeating isn’t inevitable. As Dr. Mosley and coauthor Mimi Spencer explain in The Fast Diet, “A 75% calorie reduction on a fast day typically leads to just over a 15% increase on the following day.” They reference this study, which also found that hunger on fast days diminishes by the second week. (Note: this research focuses on alternate-day fasting, not the 5:2 diet.)
Mentally, I struggle with using a diet tracker like LoseIt on non-fasting days. The app sets a daily goal of 1,400 calories, which aligns with fast days but also warns that it might not be enough. On other days, I’m tempted to stick to that limit, which contradicts the 5:2 approach. This left me feeling perpetually underfed and unprepared for the next fast day. Abandoning the tracker helped me regain the 5:2 rhythm effortlessly.
MyFitnessPal allows different calorie goals for each day with a premium subscription. Personally, I prefer to skip the tracker and let my calorie intake adjust naturally.
Is this diet worth trying?
This diet isn’t for everyone. If you’re content with a plan that involves slightly reducing your daily intake, stick with it—you’re not missing out on anything groundbreaking.
However, if traditional calorie-restriction diets feel unsustainable, intermittent fasting might be a better fit. The 5:2 diet was created to make fasting more manageable: you’re allowed some food instead of none, and you can choose fasting days that suit your schedule. While back-to-back fasting days are an option, even Dr. Mosley acknowledges this is too challenging for most.
The authors emphasize that 500 calories isn’t a magical number (600 calories are permitted for men, or 25% of your usual intake). Similarly, the schedule is flexible: you can reduce to one fasting day per week for weight maintenance or increase to three if you’re enjoying the process and want faster results.
One adjustment I found particularly helpful is switching to a 24-hour fast instead of fasting through a night, full day, and another night. This approach is so simple that I’ve accidentally done it. For example, have a large, late lunch around 2pm, skip dinner, and then delay breakfast until 2pm the next day. Voilà—you’ve completed a 24-hour fast.
I managed to shed a few pounds while experimenting with the 5:2 diet, though I wasn’t entirely consistent. Around the same time, I also made other lifestyle changes, such as increasing my exercise routine. While I can’t attribute all the results solely to the diet, I’m pleased with the progress so far.
Your success with this diet will likely depend on your daily routine (do you have a packed work schedule?) and your ability to manage hunger and self-discipline. It’s certainly achievable, and despite its trendiness, it avoids making unscientific claims. If you’re curious to try it, check out the guidelines on the Fast Diet website and explore the forums for helpful advice. Then, choose a hectic day and steer clear of the kitchen.
