What is intermittent fasting?
There always seems to be a new diet craze taking off and intermittent fasting is one that has been getting more and more airtime recently. We thought we would take a closer look.
Firstly, it’s not really a diet as such. There are no specific foods that you should or should not eat. It is more about the pattern of when you eat. In fact, it is often paired with other diets so for example someone might do a Keto diet with intermittent fasting or a vegan might do a plant-based diet with intermittent fasting. Intermittent fasting has been around for a long time in different versions with one popular version being the 5:2 diet – were you eat normally for 5 days and fast for 2. However, this has evolved into more of a 24-hour based approach which is what we will look at here.
The concept of intermittent fasting is based around returning your body to its natural metabolism cycle. Basically, when you eat your liver produces enzymes to help digest the food and this kick starts your metabolism. Eating is not the only thing which starts your metabolism, there are other variables. For example, exposure to sunlight also plays a part. To be clear, during the fast period you should only drink water as anything else, even a cup of black coffee or a vitamin pill will break your fast.
This is a good video explaining the basic science and thinking behind time restricted eating (intermittent fasting), with Dr Rhonda Patrick on the Joe Rogan Experience podcast.
The problem with most of us is that our metabolism never gets a chance to rest because we eat as soon as we wake up, then we eat throughout the day and then we eat before we go to bed! This messes up our metabolism so it doesn’t work as well, and we can start to put on weight and feel more lethargic.
People using intermittent fasting break each 24-hr period into 2 parts, the bit when you eat and the bit when you don’t and together, they need to make 24 hours. So, some examples of patterns a person using intermittent fasting could follow are:
- Eat for 12 hours, fast for 12 hours
- Eat for 10 hours, fast for 14 hours
- Eat for 9 hours, fast for 15 hours
Many people start with a 12-hours on 12-hours off pattern to begin with, and then build up the length of time they fast for. Obviously, it is easiest when most of that 12 hours is taken up by sleeping! For example:
- Wake up at 7am
- Eat between 7am and 7pm
- Fast from 7pm to 7am
If you are going to bed at 11pm, then you are really only fasting while you are awake for 4 hours!
You can of course change the schedule to fit in with your lifestyle, however as sunlight also starts your metabolism, starting your eating cycle in the morning is better than eating from 12 noon until midnight. Your metabolism has adapted to daytime food, night-time sleep. Night-time eating is well associated with a higher risk of obesity, as well as diabetes.
Why does it work?
Eating within a restricted window means you are giving your body a break from eating and the space it needs to digest the food you have put into it and turn this food into energy. During the fast period your insulin levels drop which means your fat cells will release stored sugar to be released as energy. If the insulin levels, go down far enough for long enough then we burn off our fat.
Who is it for?
While there are have been a lot of studies on mice, we don’t have as much human data to go on. We do have some small studies on humans, however and these show that intermittent fasting can be a hard system to stick to – with a high dropout rate of 38% being noted within a study published by JAMA Internal Medicine. It was also noted in the study that those who used traditional low-calorie diets lost about the same amount of weight as those using intermittent fasting.
It can also be dangerous for some people, such as diabetics and those with high-blood pressure or heart disease to try intermittent fasting as they can be negatively affected by skipping meals and limiting calories. It is also not recommended for anyone who is underweight, has an eating disorder, pregnant women or children.
It can be easy to get caught up in the latest trend and it is possible that time restricted eating might work for you, however it is always best to speak with your doctor before considering a new diet or eating pattern such as intermittent fasting.
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