Starting a weight loss journey is tough. Because it really is that. It’s a journey of trial and error, mistakes, backward steps, and navigation through a complicated network of information and guidance. It’s rarely ever a straight road that gets you exactly where you want to be on the first go. It is frustrating when you try a tactic that doesn’t work and ends up delaying your progress.

Intermittent fasting is a relatively recent approach to weight loss. It describes different eating methods such as the 5:2 diet or the 8-hour eating window. Either way, by prolonging the time you go without eating, fasting is used to encourage weight loss in adults.

Like everything, it helps to understand the science behind this before deciding if it’s something you want to do. This way, you can focus your efforts on approaches that are actually going to work for you and your weight loss.


What is intermittent fasting?


Intermittent fasting is described as regular, scheduled periods of consuming little or no food. It’s an umbrella term for several approaches.

The 5:2 diet is a common form of intermittent fasting. It involves eating normal (or calorie maintenance) amounts 5 days a week, then restricting down to just a few hundred 2 days of the week. These 2 days are considered fast days and can be planned for when they will have minimal disruption to your week.

The 16:8 diet involves reducing your daily eating window to only 8 hours within a day. You can choose when these 8 hours are, but you shouldn’t eat anything during the remaining 16 hours. For example, this could mean you eat only during the hours of 9am and 5pm.

Similarly, there’s also the morning fast, whereby you don’t eat your first meal until 12pm. In this way, you fast completely for the morning and push your eating window back into the day.

There are also many more aggressive and unconventional fasting approaches, which are often advised against. These include fasting completely for 24 hours or reducing the eating window to only 4 hours of the day.


How does the body lose weight?


It’s essential to understand the simple science that drives weight loss to understand how fasting can help.
Calorie deficit. These two words are the most important ones when it comes to advising weight loss. You probably hear them all the time, but it’s helpful to translate what those words mean for individuals and their day-to-day lives.

The body takes in energy (or calories) from food. It uses that energy in 4 different ways. Some of these you can control, and others you can’t.

Your BMR (basal metabolic rate) is the energy your body needs every day to just be you. Whatever you’re doing, the body needs this energy to carry out all its important processes like circulation, breathing, synthesising, and transporting. If you lay in bed all day, this is the number of calories your body needs to simply exist. It accounts for around 70% of your total calorie burn.

Your body also burns energy by digesting the food you eat. The technical name for this is the Thermic Effect of Food. After eating, your metabolism increases slightly to help put it away in all the right places. This accounts for around 10% of your total calorie burn.

Those are the first two ways your body burns energy. Now, we get to the two areas you can actually control.

The purposeful exercise that you do in the gym or playing sports will burn a bit of energy. Probably about 5% of your daily total.

On the other hand, general activeness, like walking, standing, and just generally moving accounts for up to 10%. This is why counting steps and remaining active is the easiest and most impactful way to increase daily energy burn.

So, all of these different things will together make up the total amount of energy (number of calories) you burn in a day. If this number is larger than the number of calories you eat, you will lose weight. It’s just about in versus out. That’s what a calorie deficit is. Your body needs to be burning more than it’s consuming for a sustainable amount of time so that it converts fats (and sometimes muscle) into energy to be used for all the different processes.

It doesn’t matter what you eat. Whether it’s McDonald’s every day or only carrots, if the number going in is lower than the number going out, you will lose weight.


What effect does fasting have on the body?


When you stop eating, your body relies on stored reserves for energy. These reserves come from a few places, but ultimately it will start converting fat into energy for use. As soon as you eat something, this will stop, and your body will instead use the energy from the food you’ve just given it instead.

Make sure to ignore the myth of ‘starvation mode’. When you’ve been fasting, your body does not become significantly more efficient at converting and burning fat, nor does it do it at a higher rate.

If you burn 2000 calories and eat 1800 calories throughout the day, without fasting, you will create a calorie deficit of 200 calories that day. If you burn 2000 calories, fast for the morning, and eat 1800 calories in the afternoon, you will still create a calorie deficit of 200 calories that day.

However, some hormonal changes happen when you fast. Your insulin levels will lower. This can aid the fat burning process. It’s an effect that can support weight loss, but it does not cause weight loss. Only a calorie deficit can do that.


How does fasting help you lose weight then?


Fasting can help you lose weight by reducing the total number of calories you can consume across a day or week. It’s a tactic. Some people also claim it helps them to retain muscle whilst dieting, which is often lost. However, this hasn’t yet been scientifically proven.

You might find it easier to reduce the total number of calories you consume in a more sustainable way than other diets by fasting.

For example, the morning fast can remove the habitual eating you might do earlier in the day when you’re not really that hungry, shortening the amount of time you actually eat for and resulting in fewer calories being consumed in total.

The 5:2 diet might allow you more flexibility and enjoyment on weekends, as you can eat normally most of the time and then really focus on your food intake for just two days of the week.

The critical thing to remember is that the time you’re not fasting for still counts, and unfortunately, it isn’t an opportunity to eat massive amounts. If you increase your calories above your maintenance during these times, you will remove any calorie deficit you created by fasting, and weight loss won’t happen.

It’s also crucial to keep in mind that weight loss happens over a sustained period, not overnight. The clock on a calorie day doesn’t reset at midnight. The calorie deficit you create must be sustained over a prolonged period to have a noticeable and significant effect on weight. For this reason, some people prefer to count their calories across a week rather than across a day.


Who should use intermittent fasting?


You could use intermittent fasting if you are looking to lose weight and think this approach to eating will help you to reduce the total number of calories you eat. It’s something designed to make dieting easier. So, if it fits in with you and your lifestyle, then great. If it doesn’t, then go for a different approach.

There’s also a fair amount of caution to observe when intermittent fasting. There’s a risk of dizziness, fatigue, low blood sugar, and headaches. These risks increase the longer you fast for. It’s also crucial to make sure you’re eating a balanced and nutritious diet, regardless of the approach you take.

If you want to know more about fasting or have any pre-existing health conditions that might affect you, it’s important to speak to a qualified doctor or dietician about it. Only they can give you the safe advice you need.


So, intermittent fasting is simply a tactic you can use to help you lose weight. If that’s what you fancy doing. Whether or not you choose to go down this route depends on you and your individual preferences. It can be great for those who find it helpful, but if you don’t, there’s nothing you’re missing out on. Keep putting yourself first.