Intermittent fasting has had a surge in popularity over the past couple of years thanks to the 5:2 diet and the bulletproof diet, so let’s explore the pro's and con's of intermittent fasting and who should give this a try, and who should not try this style of eating.
What is Intermittent Fasting?
Intermittent fasting as the name suggests involves eating a normal diet some of the time with occasional periods of fasting.
Sometimes this can be a period of greatly reduced calories or it may involve eating the same amount of calories over a day.
The 5:2 diet involves eating your normal diet for 5 days of the week and then choosing two days of the week where you only eat 25% of your normal calories, or about 500 calories a day.
Another option is to only eat between midday and 6-8pm 2-5 days a week.
This means that you get to fast for 16-18 hours but can consume a normal amount of calories during the eating period. The Bulletproof Diet would be a version of this way of eating.
Another option is to do a 40 hour fast 1-4 times a month. This type of fasting can be combined with the other methods for faster results if your aim is weight loss or if you have a condition such as diabetes.
There are a number of other variations of intermittent fasting but this gives you the general idea, and it is good to try out a few different options to see what suits you the best.
The best book on the different types of fasting is "The complete guide to fasting" by Dr Jason Fung and Jimmy Moore
Why Do Intermittent Fasting?
Intermittent fasting is what is known as a hormetic stressor on the body, this means that it is a good stress leading to positive adaption.
Intermittent fasting promotes cellular repair through up regulation of autophagy, this is the way the body cleanses itself from damaged or old cells and proteins, which can reduce the risk of disease and chronic illness.
While improving cellular repair and reducing the risk of chronic disease is a great reason to try intermittent fasting, the main reason that people do intermittent fasting is for weight loss.
It can be a great way to lose weight while still being able to go out and enjoy some treats too.
Other benefits include improved insulin sensitivity (reduce diabetes risk), reduce inflammation and promoting injury repair, reduced oxidative stress and promoting healthy brain function.
Improved cholesterol results and improvement on other blood markers like liver enzymes, HbA1C and CRP are also common.
So intermittent fasting sounds amazing, so let’s look at who should not do intermittent fasting.
Who Should Not Do Intermittent Fasting?
Pregnant women should not do intermittent fasting, this is a time to be nourishing the growing baby with a quality diet, and adequate amounts of calories, it is not a time to be focusing on weight loss.
There is evidence that fasting (or food scarcity/ famine) during pregnancy can cause epigenetic changes in the baby which will lead to metabolic problems later in life. This can lead to storing calories more efficiently and easy weight gain.
Adrenal fatigue is another condition where intermittent fasting can cause more harm than good, adrenal dysfunction is a time when you need to nourish the body and minimise any stressors.
With adrenal fatigue intermittent fasting can lead to short term benefits but the extra stress will lead to a situation where you may take one step forward and two steps backwards …. this means it can lead to sleep disruption, weight gain and immune problems, and people don’t always connect it to the intermittent fasting especially when they felt so good when they started.
Low thyroid function is another time I would be cautious of starting intermittent fasting, I know it can be very tempting to try this approach because it is so good for losing weight and a lot of people with low thyroid problems have weight gain.
If you are going to try this approach it is important to track your TSH, T4 and T3 to monitor any negative changes, extra stress can have an impact on the T4 to T3 conversion.
Eating disorders, if you have had a past history of anorexia or bulimia restricting food can sometimes cause these past issues to resurface.
A better approach in this case would be to eat three quality meals a day and if you need help with weight or other health problems then tweaking the macronutrients may give you better results. It would be best to talk to your doctor or practitioner in this case before trying intermittent fasting.
Children and young teenagers who are growing and usually very active would benefit from more regular meals, and intermittent fasting would have no added benefits for them.
How to Start Intermittent Fasting?
If you would like to try intermittent fasting the easiest way to start is with a 16 hour fast 2-5 days a week, if this works well for you then you can try and 18 hour fast. This means that you would eat all of your meals between midday and 6pm.
The Bulletproof diet is an example of intermittent fasting that does not reduce total calories and is another great way to get started. This is where you start your day with a bulletproof coffee, which may contain anywhere between 300-500 calories from MCT oil and butter.
The fat consumption does not affect the benefits of fasting, if you avoid protein and carbohydrates you still up regulate autophagy, which is the beneficial repair and clean up process of cells.
If you are overweight you will still lose weight on the Bulletproof version of intermittent fasting, but this is also a good option for people who do not have weight to lose and are just doing intermittent fasting for the neurological benefits or longevity and good health.
Another option is to do a full 40 hour fast 1-4 times a month, this can also be combined with other versions of intermittent fasting if you are looking for quick weight loss or have immune, or metabolic issues.
Pro's and Con's Of Intermittent Fasting - Summary
Look for signs of adrenal dysfunction like poor sleep or weight increases, other signs include negative impact on mental and physical performance, or if blood markers show decreased thyroid function.
*in particular decreased T3 with normal TSH
Sometimes it is a good idea to occasionally track macronutrients if you are not sure if you are eating enough calories.
Intermittent fasting can be great for weight loss, health and longevity, but for some people in can have negative health consequences!