Intermittent fasting: Everything you need to know

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Intermittent fasting has become a new lifestyle for many people over the last decade. Although there are some great studies that prove its effectiveness, most studies have been done on rats. Of course, other studies that were conducted with people have also shown weight loss effects. However, these effects were not greater than any other diet out there. Let’s take a look.

What is intermittent fasting?

Intermittent fasting is an eating pattern where you cycle between periods of eating and not eating. For example, you can have dinner one day but then, you shouldn’t eat until the following day dinner time. However, there are different ways of fasting and their schedule rules vary.

The 16/8 Fast

The 16/8 fasting method is when you fast (not eat) for 16 hours and then eat for 8 hours. This can be any given time, choose wisely and consider your lifestyle. Normally people would eat from midday until 7 or 8pm and fast for 16 hours. However, there is no point in you doing the same if you do nightshifts and sleep most of your day. Choosing your 8 hour time slot is entirely dependent on your lifestyle, there is no actual set rule for this.

This fasting method is said to be a little easier than other methods because you get to eat for 8 hours a day. But let’s check out the other methods.

The 5:2 Fast

This fasting method is okay, it is a little harder than the first one we mentioned. The rules for this one are that you eat normally for 5 days of the week but you choose two days where you fast. On the two days where you fast you should consume no more than 25% of your maintenance calories. Maintenance calories are the amount of calories you require to maintain your current weight. Check out our macro-nutrient calculator to help you calculate your maintenance calories.

Once you have this calculated, you can then multiply you’re your figure by 0.25 (%) to give you the amount of calories you need to consume on the two given days.

Due to the calories being so low, we would not recommend to do this method of fasting for two consecutive days. Maybe spread them out and mix them between the 5 days of normal eating.

The 24 hour fast

This is probably the most difficult fasting method. The rules for this one are that you should eat NO calories for 24 hours. For example, one day you’ll have your dinner, then you need to wait until the following dinner time to eat again.

We would not recommend this method for more than 2 days a week. Some people do it for 2 or more consecutive days but any more than 3 days can suppress your metabolism. This will only hinder your weight loss in the future.

How does Intermittent Fasting work?

Intermittent Fasting does not magically make you burn fat. It works in exactly the same way as any other diet- thanks to the caloric deficit. Caloric deficit refers to consuming less calories than your body requires to maintain your current weight. Again, check out our macro-nutrient calculator to find out how many calories you’d need to lose weight.

Can intermittent Fasting make you gain weight?

Let’s use an easy example of the 16:8 fasting method.

Let’s assume we have calculated your maintenance calories to be 2,000 calories per day, and this is how many calories you need to maintain your current weight.

You have began your week with your fasting day, skipped breakfast and decided you’ll eat at dinner time. By the time it gets to dinner, you may be starving so you’ll eat a normal portion or maybe even bigger than normal. In addition to your dinner, you may still feel hungry and have some snacks. A wee packet of crisps or something. Let’s say, you fasted but at dinner time over the remaining 8 hours you ate 2,000 or more calories.

Let’s assume that you’ve fasted for your 16 hours but in the 8 hour period you ate at your maintenance calories. YOU WOULD NOT HAVE LOST ANY WEIGHT because you’d still have consumed the same amount of calories your body needs to maintain your current weight.

Another example..

Intermittent fasting can also make you gain weight. Using the previous example, say you were so hungry you decide to binge on your favourite snacks. You’ve fasted so why not right? Well hold on a second.

If you eat more than your 2,000 calories per day during your fasted days and/or non-fasted days  your WILL GAIN WEIGHT. You’d still have eaten more calories than your body requires to maintain your weight.

Intermittent fasting is really no magic. If this isn’t suitable for your lifestyle, don’t torture yourself. Simply, reduce your daily calories and you’re ready to lose weight. Also, intermittent fasting is also not sustainable. We would not recommend doing it for more than 2-3 days every couple of weeks.

So how can Intermittent fasting help you lose weight?

Let’s use the previous example, if you actually manage to fast, whichever method you choose, you would have reduced your overall calorie intake. Understanding that your body doesn’t lose weight from day to day but rather from an average calorie intake over 3-7 days. If, on a couple of days you don’t consume calories or reduce them to 25% of your maintenance calories, you’d have reduced your overall average calorie intake.

Health Benefits of Intermittent Fasting

Weight loss and fat loss

Some scientific studies have proven successful weight loss. For instance, one study done by Trepanowski et al (2017) compared weight loss between two groups. One group of people fasted using 5:2 method and the other group simply ate in a caloric deficit.

The study found that both groups lost approximately the same amount of weight. So, what can we take from this? Intermittent Fasting may help with weight loss, but it is not a superior method to any other diets.

Moreover, another study done by Johnstone (2015) analysed the effects of intermittent fasting on weight loss, hunger and adherence. At this point, we are sure we wouldn’t need to remind you that adherence is the key to any weight loss success. Without adherence, there is probably no point in attempting the diet. Nevertheless, this study reported success in weight loss. However, hunger and appetite increased which followed by binge eating.

Effects on your metabolism

Effects of intermittent fasting on metabolism are a little more complex and includes a few different variables. For example,  how fast is your metabolism at the moment? How many days are you planning on fasting? Do you have any medical conditions or take any medications that may affect weight loss?

All these things need to be taken into account. It is easy to assume that everybody will respond similarly to fasting but this is certainly not the case.

Anyway, there was a study done by Mansell et al (1990) which examined the effects of fasting on metabolism. The study reported that your resting metabolic rate increased by approximately 3.6%. This means that when you were sleeping or just relaxing, your body would be burning more calories than it would normally.

Another study..

There was another study that looked into the effects of fasting on metabolism. This study was done by Zauner  et al (2000), and it reported a significant increase to metabolism as well. It is also noteworthy to know that this study suspects that the increase in metabolism occurred due to decrease in blood sugar. Therefore, it may be fair to say that if you drink tea or coffee, you should avoid or at least try to limit the amount of sugar you use.

May reduce the risk of type two diabetes

One of the driving factors of type 2 diabetes is insulin resistance. Insulin resistance is the name given to cells in our body which do not respond well to a hormone called insulin. This hormone is normally released in response to carbohydrates and sugary foods consumption because it helps to lower blood sugar levels by pushing the sugars into body tissues like muscles.

A study done by Antoni et al (2017) found that insulin sensitivity greatly reduced in the fasted group. However, fasting can be difficult to sustain and it is not a long-term solution. We would recommend looking at other ways to reduce the risks of diabetes. For example, watermelon and pomegranate have shown to greatly reduce the risk of diabetes.

Any difference between women and men?

However, studies where women were involved have shown different results. In a study done by Heilbronn et al (2005) studies the effects of fasting on insulin sensitivity in both women and men. This study shown that insulin sensitivity reduces greatly among men but it remained unchanged among female participants. More studies may be required to draw up a conclusive answer, but this study may indicate that fasting may affect women and men differently in regards to insulin sensitivity.

May relieve stress

The study mentioned above, also found that stress levels were reduced. In addition, another study found that fasting also reduced oxidative stress levels (Johnson et al, 2007). Oxidative stress levels occur when there is an imbalance between free radicals (inhaled toxins) and antioxidants in our body. This leads to stress as our body struggles to fight and detoxify our body from those free radicals.

Reduces Inflammation

A study done by Johnson et al (2007) found that fasting improved resistance to oxidative stress as well as reduced inflammation. The participants had asthma, and this study showed that fasting may help reduce the symptoms.

Supports a healthy heart

As you may know, one of the biggest driver of heart disease is bad cholesterol. Well, there was a study done by Varady et al (2009) looked into the effects of fasting on cholesterol and blood pressure. In this study, bad cholesterol decreased and good cholesterol remained unchanged. In addition, systolic (high) blood pressure reduced.

May reduce the risk of cancer

There was a study done by Lee et al (2012) that examined the effects of fasting on different tumour cells. It was found that fasting may be as effective or even replace some of the chemotherapy drugs. Other studies show similar results. Therefore, although more studies are required on humans since most have been conducted in a tube or on rats, the results are promising.

Fasting may support and protect your brain

Some studies have shown significant improvements to brain health. One study done by Lee et al (2000) found that fasting enabled and encouraged formation of new brain cells. A different study found that fasting may even help with Alzheimer’s disease. For instance, Duan et al (2003) found that fasting reduced progression of Alzheimer’s disease. Other studies also show similar results. However, more studies may be useful because most were done on mice instead of people, so the results may vary.

May increase lifespan

A study conducted by Goodrick et al (1982) found that growth duration in rates was slower by 75% and the lifespan increased by 83%.  In addition, another study done by Sogawa (2000) found that lifespan increased significantly in female mice. This shows that fasting may help you live longer. However, no tests were yet conducted on human participants.

Is Intermittent Fasting superior to other diets?

The short answer here is no. The only reason why fasting works is due to the caloric deficit just like any other diet. We would say that fasting is even harder than an ordinary diet.. for some people. Anyway, there was a study done by Akasheh et al (2019) which compared fasting and ordinary calorie restricted dieting. After 6 months, the group which ate an ordinary calorie restricted diet lost MORE weight than fasted group.

Pros and Cons

Pros Cons
– May work better with your lifestyle
– Weight Loss
– You may feel better
– Plenty of health benefits
– Feeling of accomplishment
– Not sustainable
– Difficult to adhere to
– Not superior to any other diet
– May lead to binge eating
– May suppress your metabolism if you over do it.

Our recommendation

If you are a beginner, it may be worth having a look at the book below. This has a step by step guide to help you prepare yourself for fasting as well as plenty of healthy recipes that you can eat through your fasted and non-fasted days.

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Antoni, R., Johnston, K., Collins, A. and Robertson, M. (2017). Effects of intermittent fasting on glucose and lipid metabolism. [online] Available at: [Accessed 28 Nov. 2019].

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