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Is the 5:2 diet the secret to weight loss?
Curious about the 5:2 diet? As the name suggests, it involves eating 'normally' for five days a week and drastically slashing your calorie intake for the remaining two days. As a form of intermittent fasting, there are no specifications about what you should eat on the 5:2 diet – only when and how much.
Made popular by British TV journalist and former medical doctor Michael Mosley in 2012, the 5:2 diet – also known as The Fast Diet, in reference to his book – claims to facilitate weight loss and improve blood pressure, cholesterol levels, and insulin sensitivity. But is the 5:2 diet effective and is it safe to fast for two days a week?
We spoke to Ulrike Kuehl, nutritionist at Lumen, and Ryan Hodgson, nutrition coach at Hodgson Health, to help you decide whether a fasting schedule is right for you – including how the 5:2 diet works, what you can eat and potential side-effects:
How does the 5:2 diet work?
The 5:2 diet falls under the intermittent fasting umbrella, which describes eating schedules that cycle between fasting and non-fasting over a set period. Unlike other intermittent fasting frameworks, the 5:2 diet restricts your daily calorie intake to around one quarter of your daily needs – 500 calories (women) or 600 calories (men) – twice per week. You can choose any two days, providing there's at least one non-fasting day between them.
For the remaining five days you can eat 'normally'. The idea is that you don't have to count calories or avoid certain foods, nor do you have to follow a specific meal plan or measure out portions. According to The Fast Diet website, eating 'normally' means eating around the same number of calories your body typically burns on a day-to-day basis, known as total daily energy expenditure (TDEE). Non-fasting days are not 'cheat days'.
What can I eat on a 500 calorie fast day?
Typically, you'll need to focus on high-volume, low-calorie foods that fill you up, like fruits, vegetables and legumes. Soup is especially filling – calorie-for-calorie, it's more satiating than melon or cheese on crackers, according to research from the Johns Hopkins University School of Medicine – and it's a great way to consume a variety of nutrients in one go.
While there are no rules for eating on fast days, it's important to include a source of protein, such as fish or tofu, plus healthy fats (like avocados, eggs, Greek yogurt and nuts) for sustained energy. You should avoid refined carbohydrates like white pasta and white rice, which will spike your blood sugar levels and leave you hungry and could even affect your mood.
'On low-calorie days, focus on non-starchy vegetables such as cucumbers, mushrooms, bell peppers and leafy greens,' says Kuehl. 'You also want to add in some lean proteins such as grilled chicken or turkey breast at the right portions. Always make sure you get all your nutrients in – try to eat at least four or five fist-sized portions of vegetables a day.'
When it comes to meal timing, you're free to eat whenever you like. Some people prefer to split their calories across three small meals, while others prefer to consume them all in one go. Some people can't start their day without eating something for breakfast, while others find it easier to wait as long as possible before tucking into their first meal of the day.
There's no physiological advantage to restricting your calories on any particular day of the week, but it pays to be tactical. Where possible, choose 'less active days, but perhaps where you're going to be more distracted,' says Hodgson, who explains that on less busy days, people generally find sticking to such a low calorie intake more challenging.
What can you drink on the 5:2 diet?
You can drink anything you want on the 5:2 diet. However, on fasting days it's probably best to stick to still or sparkling water, black coffee and herbal tea to stay within your calorie limit. Alcohol is allowed, but certainly not encouraged. Drinking on an empty stomach is never a good idea – plus it's high in calories, spikes your blood sugar, and increases food cravings.
'Water intake is essential for low-calorie days, to feel full for longer and maintain metabolic function,' says Kuehl. 'Herbals teas are a great way to stay satiated and hydrated. Vegetable or beef broth are also good to remain hydrated while fuelling up on minerals.'
Does the 5:2 diet really work?
'If you create a caloric deficit, your body will rely on stored fat for energy,' says Kuehl. 'Therefore, the 5:2 diet can be effective in terms of losing body weight. However, if you eat above your caloric balance on the other five days, it would defeat the purpose. Maintaining this caloric balance is essential to matching your energy intake to your requirements.'
Compared to conventional calorie restriction – defined as consuming 20 per cent fewer calories than you burn every day – the 5:2 diet is no more or less effective, according to a study published in the American Journal of Clinical Nutrition. However, if adopting this pattern of eating suits your day-to-day life, you're more likely to stick at it.
'For some people, it seems to be easier to be very disciplined on two days instead of counting calories and limiting food every day,' said Tilman Kühn, leading scientist of the trial. Weight loss is one thing, but staying in shape is another. 'In order to keep the new body weight, people must also permanently switch to a balanced diet,' he adds.
Health benefits of the 5:2 diet
While studies on the 5:2 diet are limited, scientists from Louisiana State University Medical Centre have assessed the health benefits of modified alternate-day fasting, which could be thought of as a 4:3 diet – drastically limiting your calorie intake every other day, and eating whatever you want on the non-fasting days in-between.
Since their trials began in 2003, the team has 'observed health benefits starting in as little as two weeks' relating to insulin resistance, asthma, seasonal allergies, infectious diseases (viral URI, recurrent bacterial tonsillitis, chronic sinusitis, periodontal disease), autoimmune disorder (rheumatoid arthritis), osteoarthritis, menopause-related hot flashes and more.
And in a 12-week study of 32 adults by the University of Illinois at Chicago, dieters following the 4:3 protocol lost 5kg on average – with no change in muscle mass – compared to a control group who didn't diet. They also slashed their triglyceride levels by 20 per cent, leptin levels by 40 per cent, and reduced CRP, a key marker of inflammation.
Of course, your health also depends on the contents of your plate. 'If you focus on whole foods and complex carbohydrates that include a lot of fibre, minerals and vitamins such as whole grains, legumes, and foods that contain healthy fats – extra virgin olive oil, nuts, avocado, seeds – complemented with a sufficient quantity of proteins, the 5:2 diet can definitely be a huge factor in improving your health,' says Kuehl.
Drawbacks of the 5:2 diet
The 5:2 diet is no magic bullet for weight loss and health. Before you commit, there are some commonly-experienced downsides you should be aware of:
⏲️ The 5:2 diet is restrictive: The 5:2 diet may be difficult to stick with long-term. Not only is eating 500-600 calories per day twice a week extremely challenging, but it may create an unhealthy relationship with food and interfere with your body's hunger cues.
⏲️ The 5:2 diet doesn't tackle the issues: 'Restrictive eating doesn't address the underlying reasons why people have gained weight, such as poor relationships with food or poor education surrounding food,' says Hodgson.
⏲️ The 5:2 diet is disruptive: On fasting days, it's unlikely you'll have the energy to focus at work – let alone socialise or workout. Some people find it hard to sleep because of hunger. Bad breath, headaches, constipation and irritability are also common side effects.
⏲️ The 5:2 diet is not for everyone: Certain people, including pregnant or breastfeeding women, people with active eating disorders or a history of disordered eating, and people who are prone to fainting, should avoid the 5:2 diet for health reasons.
⏲️ The 5:2 diet is hard to stick to: 'It may not suit the general population, particularly those who have children or active jobs, as the lower calorie days can affect your mood and energy levels – and then coherence is going to drop,' says Hodgson.
⏲️ The 5:2 diet is still a diet: So you'll need to watch what you eat, even on 'normal' days. If you eat far more than you normally would, you might not lose weight. If you over-indulge on highly processed, high-calorie foods on those days, you may even gain weight.
Who should avoid the 5:2 diet?
The 5:2 diet is not suitable for everyone. Some people should avoid strict dietary restrictions like fasting completely, including:
People with eating disorders or a history of disordered eating
People who are prone to low blood sugar
People who are prone to fainting or dizziness
Pregnant and breastfeeding women
Teenagers and children
People with diabetes
People who are underweight
People who have nutrient deficiencies
Women who are trying to conceive or have fertility issues
🍎 If you have a chronic illness or any concerns about your health, always get the go-ahead from your doctor before starting a new diet or healthy eating plan.
Last updated: 29-04-2021
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