Over the past decade, intermittent fasting has become one of the most talked about approaches to eating. Among the different styles, the The 5:2 diet, sometimes called the five two diet plan, 2 by 5 intermittent fasting or the 5 2 2 diet, is known for being flexible and achievable because you only restrict calories on two days a week.

But what exactly is the 5:2 diet, how does it work, and is it safe for Australians who want to lose weight and improve their health? This guide explains the science, the health benefits and the practical details, including how nutritionists suggest approaching it safely.

What is the 5:2 diet?

The 5:2 diet is a form of intermittent fasting that divides the week into two types of days:

• 5 days of regular eating - you eat in a broadly normal way, ideally following a balanced, varied diet.
• 2 fasting days - calorie intake is limited to about a quarter of your usual needs, which for most people is roughly 500 calories for women and 600 cals a day for men.

On fasting days you don’t avoid food completely. Instead, you spread a small calorie allowance across one, two or three simple, nutrient dense meals. Many people follow a five two diet plan where they fast on non-consecutive days such as Monday and Thursday and eat normally on the other days. A consistent pattern helps your body adapt, so most nutritionists recommend choosing the same fasting days each week.

For many Australians, the 5:2 structure feels more realistic than daily restriction. Busy professionals, parents and active people often find it easier to manage two lower calorie days than to count every calorie all week. Experts from the University of Sydney highlight that this pattern can be a sustainable option as long as the non-fasting days are built around healthy, minimally processed foods and regular activity. 

How does the 5:2 diet work?

The main principle behind the 5-2-2 diet is overall calorie reduction. For example:

• If you normally eat 2,200 calories per day, that is about 15,400 calories per week.
• Under a five two diet plan, you might eat 2,200 calories on five days (11,000) and 600 cals a day on the two fasting days (1,200).
• That gives a weekly total of 12,200 calories, which a reduction of about 3,200 calories.

Over time, this reduction can result in weight loss. BBC Good Food also notes that after several hours with limited energy intake, the body begins to switch from burning incoming food to drawing on stored body fat, which further supports weight management.

Most experts advise that fasting days should not be back to back. Leaving at least one regular eating day between them helps with comfort and long term adherence. For example Monday and Thursday, both for comfort and for adherence over the long term.

Is the 5:2 diet good for you?

The potential benefits

1. Weight management – Studies show it can be as effective as daily calorie restriction, but easier for many to stick with.
2. Metabolic health – Evidence suggests it may improve insulin sensitivity and cholesterol levels.
3. Flexibility – You choose which days to fast, making it adaptable to social and work schedules.
4. Simplicity – No complicated rules; just focus on two lower-calorie days.

The considerations

• Hunger and fatigue are common on fasting days, especially when starting out.
• Overeating on non-fasting days can undo progress.
• It may not suit people with demanding physical jobs, athletes or those with medical conditions

Nutritionist advice: For Australians with busy or high energy lifestyles, the 5:2 diet can work well. Professional guidance helps ensure fasting days remain nutritionally balanced.

Health benefits supported by research

Although the 5:2 diet was popularised by Dr Michael Mosley, a growing number of studies now focus on intermittent fasting and similar models. Findings suggest benefits for weight, metabolic health and long term disease risk when the diet is followed correctly.

Weight loss and body composition

Intermittent fasting patterns such as the five-two diet plan have been shown to support weight loss in a similar way to continuous calorie restriction. People often find this structure easier to follow because they only focus on restrictions two days a week. Evidence also suggests that weight loss may include reductions in abdominal fat while preserving lean muscle, provided protein intake is adequate.

Blood sugar and insulin

Many studies report improvements in fasting insulin, insulin sensitivity and post meal glucose responses. These benefits often occur even with modest weight loss, making the diet appealing for people managing early metabolic concerns.

Heart and metabolic health

Intermittent fasting can help lower triglycerides, blood pressure and inflammatory markers in some individuals. Results vary depending on diet quality, physical activity and adherence to the recommended calorie levels.

These improvements can vary widely between individuals, and diet quality on non fasting days remains one of the strongest predictors of results.

Studies on the 5:2 diet and intermittent fasting

Several Australian research groups have investigated the five two diet plan and related fasting approaches, offering locally relevant evidence for the 5-2-2 diet.

Monash University: The SWIFt Study

A major Australian trial from Monash University focused on 250 night shift workers who followed two variations of the 5:2 diet that included fasting days at around 600 cals a day. Participants recorded:

• Meaningful weight loss
• Improvements in insulin resistance
• Lower blood pressure

This suggests the five two diet plan can suit people with irregular working hours, including shift workers.

Source: https://www.monash.edu/medicine/news/latest/2025-articles/new-monash-study-supports-intermittent-fasting-for-night-shift-workers

University of Sydney: Charles Perkins Centre

Researchers at the Charles Perkins Centre at the University of Sydney developed a “healthy 5:2 diet” pattern that emphasised nutrient dense food choices on all days. Adults with overweight who followed this plan achieved:

• About 8% reduction in body weight
• About 16% reduction in total body fat after six months
• Improvements in metabolic markers when non fasting days were built around whole food options

Source: https://www.sydney.edu.au/charles-perkins-centre/news-and-events/news/2023/10/20/the-healthy-5-2-diet.html

University of Sydney: Intermittent fasting and metabolic health

Further analysis from the University of Sydney noted that while 5-2 intermittent fasting can support weight loss, the expected anti-inflammatory improvements may be limited if the five regular days are dominated by highly processed foods. The quality of the diet on non fasting days strongly influences results.

Source: https://www.sydney.edu.au/news-opinion/news/2023/02/10/intermittent-fasting-leads-to-weight-loss--not-improved-health.html

Victoria University (Melbourne): 5:2 diet combined with exercise

Researchers at Victoria University studied the five-two diet plan across 16 weeks in overweight adults. The fasting only group achieved:

• Around 4.1 kg weight loss
• A drop of about 1.4 kg per square metre in BMI levels
• Significant reductions in total body fat

The findings suggest that even without structured exercise, the 5:2 diet can support measurable improvements in weight and body composition.

Source: https://vuir.vu.edu.au/42287/

What does 600 calories a day look like?

When people first hear “600 calories,” it sounds extreme. But with careful planning, you can create satisfying meals.

Example 600-calorie day (for men):

• Breakfast: 2 boiled eggs with spinach (150 cals)
• Lunch: Vegetable soup with lentils (200 cals)
• Dinner: Grilled salmon with steamed broccoli (250 cals)

Example 500-calorie day (for women):

• Breakfast: Greek yoghurt with berries (120 cals)
• Lunch: Salad with grilled chicken breast (180 cals)
• Dinner: Stir-fried vegetables with tofu (200 cals)

Tip: High-protein, high-fibre foods help you feel full while staying within calorie limits.

How to succeed on the five-two diet plan

Pick your fasting days wisely

Many Australians choose Monday and Thursday, leaving weekends free for socialising. Others prefer weekdays when routines are more structured.

Stay hydrated

Water, black coffee, and herbal teas can help curb hunger.

Plan your meals

Preparing fasting-day meals ahead reduces the risk of grabbing high-calorie snacks.

Eat mindfully on non-fasting days

While you don’t need to restrict calories on the other five days, overeating can undo progress. Focus on balanced meals.

Combine with movement

Light exercise like walking, yoga or pilates works well on fasting days. Save more intense workouts for non-fasting days.

Nutritionist insight: Who should avoid the 5:2 diet?

The diet isn’t recommended for:

• Pregnant or breastfeeding women
• Children and adolescents
• People with a history of eating disorders
• Those with certain medical conditions (e.g., diabetes) without medical supervision

A dietitian or nutritionist can help assess whether the 5:2 diet is right for you, tailoring it to your health needs.

Investing in yourself: Beyond numbers on a plate

The 5:2 diet isn’t just about calories. It’s about building resilience, discipline, and balance. By practising mindful eating and learning how your body responds to fasting, you invest in both personal growth and physical health.

Bark makes it easy to connect with trusted Australian nutritionists and dietitians who can design a personalised five two diet plan, ensuring you get results safely and sustainably.