The 5:2 diet

What is the 5:2 diet?

The 5:2 diet is a form of intermittent fasting that works by the week rather than by the day. On five days you eat as you normally would. On the other two, which aren't in a row, you eat very little: about 500 to 600 calories, roughly a quarter of what most adults need. Researchers call it intermittent energy restriction or whole-day fasting ³. Unlike a daily eating window, the low days aren't about the clock; they're about calories.

Day	What you eat
Monday	A low day: about 500 to 600 calories, often in one or two small meals
Tuesday	Your usual meals
Wednesday	Your usual meals
Thursday	A low day: about 500 to 600 calories
Friday to Sunday	Your usual meals

What the research shows

Longer trials found much the same. In Norway, 112 adults with abdominal obesity lost a similar amount of weight over a year with two low days a week or with daily calorie cutting, about 8 to 9 kg, but people on the low days reported more hunger ². In Australia, 137 adults with type 2 diabetes followed either two days of 500 to 600 calories a week or a daily calorie target for 12 months, under close medical care; their long-term blood sugar improved by a similar amount ⁴.

Keeping it up is the hard part. In a London trial of 300 adults with obesity, 74% of those given simple 5:2 instructions were still following them after 6 weeks, but only 22% after a year. Their weight loss, about 2 kg, was no better than with standard advice on diet and activity, though they rated the 5:2 diet more highly ⁵.

5:2 or a daily eating window?

	5:2	A daily window, such as 16:8
How it works	Two low-calorie days a week	Every meal within a set number of hours each day
What you track	Calories on the low days	The clock
Hunger	Concentrated on two days	A little, most days, often easing after the first weeks
Results in trials	Similar to daily calorie cutting	Similar to daily calorie cutting

A 2025 review of 99 randomized trials found that neither did better than cutting calories every day ³, so choose by what fits your week. If you'd rather not count calories, a daily window such as 16:8 needs only a clock. If you'd rather eat normally most days and accept two hard ones, 5:2 may suit you better. For the same idea taken further, see alternate-day fasting.

Can you do 5:2 with Fasting Tracker?

Not directly. Fasting Tracker times fasting windows; it doesn't log food or count calories, and it has no 5:2 or calorie-day mode, so it can't tell you when you've reached 500 calories. If you follow 5:2, you'll need to plan your low-day meals some other way. You can still use the app around it:

• On a low day, time the fast between your meals. Many people find it easier to put their 500 to 600 calories into one or two meals, with a long fast before them.
• On your normal days, a free plan such as 13:11 or 14:10 can keep late-night snacking in check.
• If you're an experienced faster and your doctor agrees, you could time a 24-hour fast, dinner to dinner, with Pro. That's not the same as a 5:2 low day: the trials tested days of 500 to 600 calories, not days without food.
• Add a note to a fast, such as "low day", and follow your weight trend from Apple Health in the app.

Who should be careful

Low-calorie days can make blood sugar fall too far if you take insulin or other medication that lowers it. In the diabetes trial, medication was reduced at the start, and about a third of people on those medicines still had a low or high blood sugar event in the first two weeks ⁴. Stop and eat if you feel shaky, sweaty, faint or confused.

Sources

1. Harvie MN, Pegington M, Mattson MP, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. Int J Obes (Lond). 2011;35(5):714-27. doi.org/10.1038/ijo.2010.171
2. Sundfør TM, Svendsen M, Tonstad S. Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial. Nutr Metab Cardiovasc Dis. 2018;28(7):698-706. doi.org/10.1016/j.numecd.2018.03.009
3. Semnani-Azad Z, Khan TA, Chiavaroli L, et al. Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials. BMJ. 2025;389:e082007. doi.org/10.1136/bmj-2024-082007
4. Carter S, Clifton PM, Keogh JB. Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes: A Randomized Noninferiority Trial. JAMA Netw Open. 2018;1(3):e180756. doi.org/10.1001/jamanetworkopen.2018.0756
5. Hajek P, Przulj D, Pesola F, et al. A randomised controlled trial of the 5:2 diet. PLoS One. 2021;16(11):e0258853. doi.org/10.1371/journal.pone.0258853
6. Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11(4):873. doi.org/10.3390/nu11040873