The fasting diet, better known as the “5:2 Diet”, is perhaps the most talked about diet this year and has been highly praised by some of those who have followed it, but it has been questioned considerably by scientists and healthcare professionals.

Perhaps when they served me this thimbleful of soup, they thought I was on a "fast" day...

Perhaps when they served me this thimbleful of soup, they thought I was on a “fast” day…

What is the 5:2 Diet?

The 5:2 Diet is a form of intermittent fasting which involves severe calorie restriction for two days a week and normal eating the remaining five days. The two days of calorie restriction may be any day of the week and do not need to be consecutive. During the two “fasting” days, women are only allowed to consume 500 calories and men 600 calories per day. These numbers are based on consuming a quarter of your daily calorie allowance, which is considered 2000 calories for women and 2400 calories for men.

The general principal behind the 5:2 diet is that you can eat what you want five days a week, as long as it is within those calorie limits. Apart from restricting your calories on the two fasting days, the diet recommends that you also avoid certain foods on those days, such as refined carbohydrates (rice, pasta etc.), anything high in sugar, as well as alcohol. It recommends drinking anything that has no calories or low calories and focusing more on fresh, raw ingredients as much as possible such as nuts, fruits and vegetables.

The diet claims to promote weight loss and several health benefits like lowering blood cholesterol levels and reducing blood sugar levels.

This mac n cheese is probably not a good idea for a "fast" day

This mac n cheese is probably not a good idea for a “fast” day

How does it work?

The main reason why this diet works is calorie reduction. The maths behind weight loss is quite simple: eat fewer calories than your body needs and you will lose weight; eat more than what you need and you will gain weight. With two days of severe calorie restriction, based on a 2000 calorie diet for women, this results in a reduction of 3,000 calories per week. This follows the well known guideline that simply reducing your intake by 500 calories per day (3500 calories per week) will result in ~1 lb (~0.5kg) weight loss per week. For a woman, reducing the consumption to 1500 calories per day instead of 2000 calories a day will result in a similar reduction in calories as the 5:2 diet.

The 5:2 diet is designed for people who are overweight or obese. This is because following a diet of 2000-2400 calories a day for some men and women would be considered overeating, and would result in weight gain. Greater weight loss in participants who follow the 5:2 diet can be expected to be seen in men and women who require more than 2000-2400 calories per day to maintain their weight, thus resulting in a greater overall reduction in calories per week.

Overall, this diet appears to have worked for many who have followed it, however it can also be difficult to adhere to because of the two fasting days where calories are severely restricted. Rather than following the 5:2 diet, the same results can be achieved by reducing calorie intake by 500 calories per day.

The amount of calories you need is based on several factors including weight, height, age, gender, and physical activity. These can vary greatly among men and women, and therefore the best method for weight loss is to first calculate your basal metabolic rate (BMR). The BMR is the amount of calories you would burn if you stayed in bed all day. Then take the BMR and add an activity factor to determine your total daily calorie needs, this then gives you the amount of calories you currently need to maintain your weight. For weight loss, use this number and subtract 500. Reducing your calorie intake by 500 calories per day is how much is needed for a weight loss of ~1lb (~0.5kg) per week.

(BMR x Activity Factor) – 500 = calories needed daily for weight loss

The calculations above can only provide you with an estimate, however they can give you a good idea of approximately how many calories your body burns, and how many you should consume if you are looking to either maintain or lose weight. This would provide a more constant intake of nutrients as opposed to having two fasting days, as well as a more personalized calculation of calorie requirements.

Written by BKR