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How to Fast

Find out how to modify fasting timing and length to meet your goals.

I fast daily (currently), mostly for the potential benefits to both lifespan and healthspan. How I fast, and how anyone else ‘should’ (or should not) fast is highly individual. As considered in the review in this issue, some people should perhaps not fast, or at the least should not fast aggressively, habitually. People for whom this may be true might include habitual under-eaters, under-eaters with Gilbert’s syndrome, uncontrolled or poorly controlled diabetics who aren’t being monitored by a suitably qualified practitioner, or those seeking to gain large amounts of muscle and failing to do so.

Apart from those instances, and for those wanting to try fasting, there are many different styles available and much discussion as to what is the ‘best’ way to fast. At least in my humble opinion, there simply is no best fasting method. There is simply what works for the individual and remember that what works for an individual is not just determined by their physiology but also by their behaviours within their unique psychosocial environment.

The major points of confusion are commonly:

  1. How long should I fast?
  2. When should I fast? (Particularly, should I fast in the morning or evening)

How long should I fast?

The answer to the first question is somewhat parsimonious. Fast for as long as you need to… Another way to conceptualise this is to think about how long you need to eat, or how many meals you can eat, in order to maintain a healthy body weight (for you). If eating the standard 3-meals per day makes it difficult for you to maintain your body weight, you might want to consider cutting back to 2 meals, or a shorter feeding window. If on the other hand, you are losing weight and you don’t want to, you might consider a shorter fasting window or adding a meal or two to your day. Of course, all of this is predicated on the understanding that you are eating a diet that is based on natural, unrefined foods (to at least 80% of your overall nutrition), and if that’s not the case, then THAT is the first step!

When should I fast?

The debate rages as to whether you should fast early (e.g. miss breakfast) or late (i.e. having a very early dinner or missing dinner), or something in between!

While different studies and expert opinion will provide evidence for either style, the key is what you can stick to. Because there is likely to be a tiny difference between these styles over the longer term, in order to get optimal results, you should choose a style that fits your unique situation. The easiest way to evaluate this is to ask yourself the simple question: Am I hungry when I wake up in the morning?

If the answer is yes, then eat breakfast! Then, either miss lunch  (12:12 fasting)  and have your next meal at dinner or after work, or have lunch and a very early dinner, in order to provide for the fasting window that you want (i.e. 12, 14, 16, or more hours fasting).

If, on the other hand, you aren’t hungry in the morning, there is no good reason to force yourself to eat. Omitting breakfast and then resuming eating either late in the morning, for lunch, late in the afternoon, or even at night, are all good strategies depending on the individual. One of the main considerations again is to a) make sure you are still eating a healthy diet containing plenty of protein and veggies,  and b) make sure that you are taking in enough energy (and macros and micros) to thrive over the longer term.


Remember, that the first priority is always on food quality (natural, whole, unprocessed food) not finetuning fasting windows!

Discover the science behind fasting in All You Need to Know About Fasting

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