I was recently made aware of something called a 5:2 diet. People like Jimmy Kimmel from The Tonight Show follow it and claim that it is incredibly effective. What is it all about?

The 5:2 diet involves intermittent fasting. It is also known as the Fast Diet. It was popularised by a British doctor and journalist called Michael Mosley. It became really popular some time around 2012 to 2013. In this diet, you “fast” for two days and eat normally for five days in one week.

In the days that you “fast”, you have to restrict your calorie intake to about 500 to 600 calories per day. Most people find this diet a lot easier to follow and stick to than the ketogenic diet, especially when you eat out a lot and you’re eating Asian foods.

Wait. I only eat less for two days? Can I eat anything I want for the other five days?

Yes. For the five days that you don’t fast, you can eat anything you like from carbs to cakes to pasta. The 5:2 diet does not restrict you from eating certain types of foods, unlike the ketogenic diet or the Atkins diet. It only restricts WHEN you can eat them.

The tough part is the two days when you are restricting your calories. Those two days can be very tough, and many people feel as though they are starving. In those two days, if you are a woman, you have to restrict your calories to 500 a day. If you are a man, this will be 600 a day.

OK, let’s talk about the fun five days first. Can I eat however much I want?

Well, if you are planning on losing weight, it isn’t a good idea for you to eat 10 bags of potato chips and a whole cake every day for those five days! You should be eating normally, meaning breakfast, lunch and dinner – what you eat on a normal work day or what you usually cook for yourself.

You will find that because you are trying to lose weight, you end up watching what you eat during those five days as well because you don’t want to undo the good work you put in for those two restriction days.

I want to give this a try. What days should I restrict calories?

You can choose any two days in a week, but most people find two consecutive days of restricting calories really difficult. So most people choose Monday and Thursday as their calorie restriction days, and eat normally for the rest of the week.

And you should eat “normally” for yourself, not copy what other people are doing because everyone has different metabolism and caloric requirements.

Let’s talk about those calorie restriction days. Is it easy to eat around 600 calories a day?

It is very difficult actually. It requires you to have an in-depth knowledge of how many calories different foods contain so that you can plan your meals accordingly. During those “fasting” days, you should be eating two or three small meals.

But most foods we normally eat contain a lot of calories that are going to add up. For example, if you choose to eat one plate of wonton noodles, that would be around 480 calories. That would mean you can only eat 20 more calories for that day if you are a woman and 120 more for a man!

So you have to really make very difficult food choices. You have to be careful about eating your salads as well. Salads can contain quite a lot of calories, especially if you load up on cheese shavings/cubes, nuts and protein.

Think about halving your food portions – including your salads. A Caesar salad can contain up to 600 calories, especially if you pile on the cheese shavings and grilled chicken or smoked salmon. Drink lots of water! Water fills you up, if only temporarily.

Is this diet medically safe?

Yes. So far. There hasn’t been a lot of research done in the medical world for the 5:2 diet compared with, say, the ketogenic diet. But intermittent fasting has been shown to have many health benefits. This is because there are lower insulin levels, and insulin is a hormone that you want to avoid a spike of because it stores glucose and fat.

Studies have shown that the sweet spot for intermittent fasting comes between 18 and 24 hours of fasting. This is the spot that sees the greatest drop of insulin and the greatest increase in fat burning.

Achieving 16 to 18 hours of fasting is easier than you think! The hours that you are asleep also count, so it can actually be achieved by skipping breakfast and not having lunch until late afternoon. Fasting is extremely good for diabetics!

Of course, there are side effects. Most people report not being able to function or focus well on the job, and on those fasting days, you are probably too weak to exercise hard.


Dr YLM graduated as a medical doctor, and has been writing for many years on various subjects such as medicine, health, computers and entertainment. For further information, e-mail starhealth@thestar.com.my. The information contained in this column is for general educational purposes only. Neither The Star nor the author gives any warranty on accuracy, completeness, functionality, usefulness or other assurances as to such information. The Star and the author disclaim all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.