How to lose weight by fasting: Intermittent fasting methods explained

We explain how fasting to lose weight works, and talk you through the most popular diets, including the 6:8 and 5:2 diets

Fasting to lose weight: a healthy meal
(Image credit: Louis Hansel @shotsoflouis on Unsplash)

Fasting as a way to lose weight has been around for quite a while, but has seen a resurgence in popularity in recent years thanks to a combination of social media and celebrity endorsement. The basic concept is very simple: you build set periods of not eating anything, or cutting back your intake severely, into your usual diet. However, there are plenty of variations on the theme, such as the '5:2 diet' or the '16:8 diet', that might make it a bit more difficult for beginners to choose the best type of fasting to lose weight.

In this article, we'll try to explain the most popular fasting methods and also list some good practices when it comes to losing weight through fasting. It is important to note that if you have any medical condition that you may think would affect your fasting weight loss journey, you should consult a medical professional before you start a fasting diet. And make sure you're eating healthily when you're not fasting, too.

What is intermittent fasting and is fasting good for weight loss?

Intermittent fasting is a calorie controlled diet where instead of restricting the amount or type of food you can eat, you restrict the time when you can eat. A recent meta study looked at the findings of individual researches and concluded that “all 27 [intermittent fasting] trials found weight loss of 0.8% to 13.0% of baseline weight with no serious adverse events” and “intermittent fasting shows promise for the treatment of obesity”.

How can you lose weight with fasting when you don't restrict the type of food you eat? Fasting not only teaches people to be more disciplined with food, but by only allowing yourself to eat within a certain time frame, you can also significantly reduce the amount of calories you consume. Gone are the days when breakfast was the most important meal of the day!

As well as reduced calorie consumption, during fasting, weight loss is further helped by your body going into 'ketosis', a metabolic state in which you use fat for fuel as opposed to carbohydrates. Since there are no dietary fats available – you haven't eaten anything after all – your body will tap into the fat reserves and use that as fuel. This can help get rid of belly fat faster than just reducing calories.

Fasting to lose weight: a healthy meal

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Fasting to lose weight: The 16:8 diet

The 16:8 diet is probably the most popular way of intermittent fasting and also the most researched: in this version, the daily window for food intake is reduced to eight hours, which means you fast for the remaining 16 hours. When during the day the eight-hour eating window is, that's up to you entirely: for example, famous actor and health-enthusiast Terry Crews' regime involves a 2-10pm eating window.

As he puts it: “Within the times I don't eat, the fasting period, which is a 16-hour fasting, I drink amino acids drinks. I'll have coffee, maybe tea. Sometimes I'll have a little coconut oil on a spoon that makes you feel a little satiated.”

The 16:8 diet doesn't have to be done every day, although the more often you follow it, the sooner the results will show. Eight hours a day is more than enough for any adult to consume their recommended calorie intake, therefore the 16:8 diet can be considered a sustainable diet. According to Healthline, “in addition to enhancing weight loss, 16/8 intermittent fasting is also believed to improve blood sugar control, boost brain function and enhance longevity.”

Fasting to lose weight: The 5:2 diet

Following the 5:2 diet involves five 'regular days' where there is no restriction on food intake and two 'restricted calorie' days when food intake is reduced to 500 (for women) or 600 (for men) calories a day in a week. This type of fasting is said to be easier to follow, but has been researched less than the 16:8 diet.

The main benefit of the 5:2 diet is the reduced calorie intake on fasting days, although if the 500-600 calories are consumed throughout the day, ketosis might not be achieved and fat loss might be less substantial and take longer than following a frequent 16:8 diet regime.

Alternate day fasting

Alternate day fasting is a version of fasting where people fast every other day while eating normally on alternating days. Just like with the 16:8 diet, you are only allowed unsweetened tea, coffee and water when fasting, while there is no restriction on what to eat or drink on normal days.

A study cited on the NHS website states that by following this diet, "volunteers lost weight, reduced their body fat and lowered their blood pressure and heart rate." However, as the article points out, participants in this study “were all healthy and with a body mass index (BMI) that ranged from healthy to overweight, so it's unclear how well intermittent fasting would work in obese people."

Fasting to lose weight: a healthy meal

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Top tips for fasting to lose weight 

There are a few bits of extra advice to be aware of if you're trying to lose weight by fasting. During fasting, tea and coffee are allowed without restriction and drinking more water is even recommended as it can help both digestion and the feeling of satiety. Creamers, milk and sugar are not recommended with hot drinks when fasting as they contain calories and can throw the body out of ketosis (when following the 16:8 diet).

Exercising is recommended when fasting, as regular exercising can help metabolism and improve cardiovascular health too. Fasted cardio could aid the weight loss process, but any heavy resistance training is recommended to be done during the eating window.

Although following a fasted diet most usually doesn't involve restrictions on what type of food you can eat when not fasting, it is recommended you keep a healthy, balanced diet nevertheless to improve overall health, as well as drinking plenty of water. Try including more protein-rich food items with every meal, such as fish, lean meat or nuts, and fibrous vegetables like broccoli, avocado and kale or spinach.