The 5:2 diet: two 500-calorie days a week, planned step by step

1. Understand how the 5:2 diet works across a week

Each week has two fast days and five ordinary ones. On a fast day you eat roughly a quarter of your usual energy: the popular version sets 500 calories for women and 600 for men, and the year-long diabetes trial below used 500 to 600 for everyone. On the other days you eat normally, without counting.

Two days at a quarter of your intake trim the week by around a fifth, about the same as eating 20% less every day, as long as the normal days stay normal.

A 5:2 fast day still includes food, which sets it apart from a water fast and from alternate-day fasting, where the low days come every other day. With 5:2, dinners out and weekends mostly stay as they are.

2. Read what trials found against daily calorie restriction

The fair comparison for 5:2 is ordinary dieting, where you eat somewhat less every day. Several trials ran exactly that test:

• Harvie, 2011. In Manchester, England, 107 premenopausal women with overweight or obesity ate about 650 calories on two days a week or about 1,500 every day for six months. They lost 6.4 kg (about 14 lb) and 5.6 kg (about 12 lb) on average, a gap small enough to be chance. Insulin resistance fell a little more on the two-day plan.
• Harvie, 2013. The same team compared two low days a week, also low in carbohydrate, with about 1,430 calories every day in 115 women with a family history of breast cancer. Over three months the two-day groups lost more body fat (3.7 kg against 2.0 kg), and insulin resistance improved more. The authors called for longer studies.
• Carter, 2018. In Adelaide, Australia, 137 adults with type 2 diabetes ate 500 to 600 calories on two non-consecutive days and their usual diet otherwise, or 1,200 to 1,500 calories daily, for a year. HbA1c, the long-term blood sugar marker, fell by 0.3 points on 5:2 and 0.5 on daily restriction, which counted as equivalent. Weight fell by 6.8 kg (15 lb) on 5:2 and 5.0 kg (11 lb) on daily restriction, a gap that could have been chance. Of the 137, 97 finished.
• Headland, 2016. A review of trials lasting six months or more pooled six head-to-head comparisons and found neither approach better for weight. Most had fewer than 50 people finishing, so long-term effects are unclear.
• Semnani-Azad, 2025. A network meta-analysis in The BMJ pooled 99 trials with 6,582 adults. Against daily restriction, whole-day fasting, the family 5:2 belongs to, showed no clear difference in weight. Only alternate-day fasting edged ahead, by about 1.3 kg, in shorter trials.

So 5:2 gives about the same weight loss as daily calorie restriction. These are group averages, and your own result can land well above or below them. Some people find two hard days easier than seven careful ones; others find the opposite.

3. Decide whether 5:2 suits you

5:2 suits people with a predictable week who would rather be strict twice than careful every day. It fits badly if cutting back tends to tip you into overeating.

Your situation	5:2?	Why
Daily calorie counting wears you down and your weeks look alike	Good fit	You only count on two days, and trials found weight loss similar to daily dieting
Long shifts on your feet, or hard training most days	Possible, with care	Put fast days on your lightest days and keep hard workouts for normal ones
Diabetes treated with insulin or a sulfonylurea such as glipizide or glimepiride	Only with your doctor adjusting doses	In the 2018 trial these doses were lowered at the start, and 35% of people on them still had low or high blood sugar events in the first two weeks
Other diabetes treatment, blood pressure pills, kidney or heart disease	Ask your doctor first	Doses set for normal days may need a check for fast days
Pregnant, breastfeeding or under 18	No	Your energy and protein needs are higher, and the trials enrolled adults
A history of an eating disorder, even years ago	No	Strict days followed by free days can restart a cycle of restricting and bingeing

4. Pick two fast days with a normal day between them

Choose two weekdays with at least one normal day between them, as the diabetes trial did. Monday and Thursday is the classic pair: Monday follows a weekend of bigger meals, and Thursday leaves Friday night free. Tuesday and Friday work too.

Then check the week ahead:

• Skip days with a work lunch or a child's birthday party. Moving a fast day beats eating 500 calories at a steakhouse.
• Avoid your hardest training day. A long run belongs on a normal day; a walk suits a fast day.
• If you work shifts, a day off is often the easier fast day.
• If a fast day falls apart at 4 p.m., eat a normal dinner and make it up later that week, keeping a normal day between the two.

Once a pair works, keep it every week. In FastTrack you can mark Monday and Thursday in the fasting-days picker, and auto start and stop runs the timer on those days without you touching it.

5. Plan a 500 to 600 calorie day from the grocery store

Five hundred calories go furthest as protein and vegetables, which fill a plate for very few calories. Many people skip breakfast and split the budget between lunch and dinner, with a snack if the afternoon drags. A day from regular grocery store food:

Time	What you eat	Calories, roughly
7 a.m.	Black coffee, plain tea or water, as much as you like	0 to 5
12:30 p.m.	1 can (5 oz) tuna in water, drained, on 3 cups chopped romaine with cucumber, cherry tomatoes and 1 tbsp light vinaigrette	190
3:30 p.m.	3/4 cup plain nonfat Greek yogurt with 1/2 cup blueberries	140
7 p.m.	2 eggs scrambled in cooking spray with two big handfuls of baby spinach	160
For a 600-calorie day, add	1 cup canned vegetable soup with dinner (check the label)	100

That comes to about 490 calories, or about 590 with the soup, and roughly 55 g of protein. Swap in 4 oz of skinless rotisserie chicken breast for the tuna, or a big bowl of homemade vegetable soup for the eggs.

Fat is where fast days quietly go over: one tablespoon of olive oil is about 120 calories, so measure oil and dressing with a spoon. For a plate you did not plan, the meal scan in FastTrack estimates calories and macros from a photo.

6. Get through the fast day and keep the other five normal

Many people find the first two or three fast days the hardest. Hunger tends to rise around your old meal times and often passes if you drink something and stay busy; black coffee and plain tea add next to nothing. Our guide to hunger while fasting has more ways through the late-afternoon slump.

The evening is the weak spot. Eat dinner at your usual time, close the kitchen after the dishes and go to bed at your normal hour.

On the five normal days, eat the way you usually do, dessert included; in the diabetes trial people simply kept their usual diet on those days. Where 5:2 tends to go wrong is the morning after, when the fast day becomes a reason to eat double. Start with an ordinary breakfast, like oatmeal with a banana or two eggs on toast, and keep lunch and dinner at their usual size.

7. Know when to stop and check in after six weeks

Many people notice hunger and a dull headache on their first fast days. Stop the fast day and eat a normal meal if you notice any of these:

• Dizziness or lightheadedness, especially when you stand up.
• Fainting, or feeling close to it. Talk to your doctor before the next fast day.
• Shakiness, sweating, a pounding heart or confusion if you take insulin or a sulfonylurea. Check your blood sugar and treat a low the way your care team showed you.
• Urges to binge, or eating far past full on normal days.
• Missed periods, or weight dropping much faster than you planned.

If you are pregnant, breastfeeding, under 18 or have had an eating disorder, skip 5:2. With diabetes medication, plan it with your doctor first.

After six weeks, weigh yourself on a normal-day morning, since the scale reads low after a day of little food. If the number is moving and fast days feel routine, keep going. Once you reach a weight you want to keep, the 2013 Manchester trial held weight and insulin resistance steady for a month with one low day a week. If you dread every Monday, a daily eating window may suit you better, and our overview of the types of intermittent fasting compares the options.

Where the 5:2 diet leaves you

5:2 is calorie restriction with an unusual weekly shape: two days at 500 to 600 calories and five ordinary ones. In trials it matched daily dieting for weight loss, with averages that hide big differences between people. Keep a normal day between the two fast days and eat as usual on the rest. On diabetes medication, start with your doctor.