In short:
- The 5:2 diet means eating normally on 5 days a week and limiting calories to 500–600 kcal on two freely chosen days.
- Studies show that the 5:2 diet is just as effective for lowering body weight as a continuous daily calorie restriction.
- On fasting days, it’s worth favoring protein-rich foods and drinking enough fluids to avoid excessive hunger.
- People with diabetes, pregnant women and anyone with a history of eating disorders should consult a doctor before starting.
The 5:2 diet is one of the most popular intermittent fasting methods: on 5 days a week you eat as usual, and on two freely chosen days you limit yourself to 500–600 kilocalories. The method has attracted wide attention thanks to its flexibility — for most of the week you don’t have to change anything in your nutrition. The guide below will help you understand how the 5:2 diet works scientifically, who it suits and how to plan your first fasting days safely.
How does the 5:2 diet work, and what is the science behind it?
The 5:2 diet falls into the category of intermittent fasting: on five days you cover your normal energy needs, while on two separate days you limit yourself to 500 kcal (for women) or 600 kcal (for men). On fasting days, insulin levels drop significantly, which kicks off fat burning and supports autophagy — the cells’ self-cleaning process.
Harvie et al. conducted a randomized controlled trial comparing 5:2 intermittent fasting with continuous calorie restriction in overweight women. Both methods produced similar weight loss over 6 months, and insulin sensitivity improved equally in both groups (Harvie, 2011).
Compared with other popular approaches — such as A New Direction, the Snake Diet or the Cyclical Ketogenic Diet — the 5:2 diet doesn’t require cutting out carbohydrates entirely or following a fixed macronutrient ratio, which makes it easier for many beginners to stick to.
Who is the 5:2 diet suitable for, and who should avoid it?
The method suits healthy adults with a BMI over 25 who want to lose weight without daily food restrictions. It is nevertheless important to know when to see a doctor before starting.
The 5:2 diet is suitable if:
– You are a healthy adult with no chronic conditions
– You want to lose weight with a flexible method
– You are not pregnant or breastfeeding
Consult a doctor before starting the 5:2 diet if:
– You have type 1 or 2 diabetes — in the study by Carter et al., a clinically significant risk of hypoglycemia was observed on fasting days in patients on insulin therapy (Carter, 2016)
– You are under 18
– You have a history of eating disorders
– You regularly take medication that must be taken with food
For older adults, it’s important to keep in mind that long-term calorie restriction can affect the preservation of muscle mass. If you want to combine the 5:2 diet with strength training, read more here: How to start building muscle mass later in life.
How do you plan your first fasting days step by step?
The key to a successful start is planning ahead. Follow these four steps:
1. Choose your fasting days
Choose two non-consecutive days, for example Monday and Thursday. Fasting on consecutive days is harder to tolerate and hasn’t produced better results in studies.
2. Plan your meals in advance
To split 500 kcal between two meals, you could have, for example: oat flakes with skim milk in the morning (~180 kcal) and grilled chicken fillet strips with a cucumber salad and tomatoes in the evening (~320 kcal). Favor protein-rich foods — protein keeps you full for longer than carbohydrates with the same calorie content.
3. Drink enough fluids
Water, unsweetened green tea and black coffee are calorie-free helpers for taming hunger. The WHO fact sheet on healthy diet recommends that adults consume at least 1.5–2 liters of fluids per day.
4. Adjust your training on fasting days
Intense training is not recommended on fasting days. Light aerobic activity (walking, yoga) is fine. You’ll find training tips for beginners here: How to start gym training?
What results can you expect from the 5:2 diet?
A 2018 systematic review and meta-analysis by Cioffi et al., covering several randomized controlled trials, found that intermittent fasting and continuous calorie restriction produce similar weight loss over 3–6 months — on average 4–8% of starting body weight (Cioffi, 2018). A systematic review by Harris et al. covering 27 RCTs confirmed that the intermittent fasting groups lost on average 4–7 kg more over 6 months than control groups who did not change their diet (Harris, 2018).
In addition to weight loss, studies have observed:
– A reduction in LDL cholesterol levels
– Improved blood sugar regulation in people with insulin resistance
– A reduction in blood pressure in overweight people
Results depend largely on what you eat on the five “normal” days. Overeating during the rest of the week cancels out the positive effect of the fasting days.
References
- Harvie MN, Pegington M, Mattson MP, et al. (2011). The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomised trial in young overweight women. International Journal of Obesity. PMID: 20921964
- Cioffi I, Evangelista A, Ponzo V, et al. (2018). Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. Journal of Translational Medicine. PMID: 30583725
- Harris L, Hamilton S, Azevedo LB, et al. (2018). Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database of Systematic Reviews and Implementation Reports. PMID: 29419624
- Carter S, Clifton PM, Keogh JB. (2016). Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes: A Randomized Noninferiority Trial. JAMA Internal Medicine. PMID: 27136492
Frequently asked questions
Can you drink coffee on fasting days on the 5:2 diet?
Yes, black coffee without sugar or milk has practically no calories and works well on fasting days. Lattes, cappuccinos and sweetened coffee drinks do contain calories, though, and these count toward the daily 500 kcal limit.
Is the 5:2 diet suitable for people with diabetes?
A risk of hypoglycemia has been observed on fasting days in patients with type 2 diabetes who are on insulin therapy. Before starting the 5:2 diet, people with diabetes must consult their treating physician, who can adjust medication doses if necessary.
How quickly will I see results on the 5:2 diet?
In most studies, noticeable results appear after 6–12 weeks. Typical weight loss is 0.5–1 kg per week, which matches recommendations for a healthy pace. In the first weeks, body weight may fluctuate because of changes in water balance.
What should I do if I get unbearable hunger on a fasting day?
Drink plenty of water, herbal tea or black coffee. Split the 500 kcal across three smaller meals instead of two. Protein-rich foods such as eggs, cottage cheese and chicken are more filling than carbohydrate-rich alternatives at the same calorie amount.
Does the 5:2 diet cause muscle mass loss?
In the short term, muscle mass loss is minimal, especially if you eat enough protein on fasting days (0.8–1.2 g/kg of body weight) and combine the diet with regular strength training. Older adults should pay particular attention to this and consider a higher-protein diet on non-fasting days.
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