Intermittent fasting has been practiced for millennia. Mostly due to lack of food and dressed up within religious observance, although some ancestors advocated it for health including Plato and Aristotle.
We do know that human beings never had regular access to food (every 3-5 hours) and there is evidence that we become more creative if we haven’t eaten for 12-16 hours. (In the old days, we had to be even better at finding food!)
Therefore intermittent fasting is known to be safe, especially in people with chronic illnesses such as type II diabetes (those with type I diabetes are the only exception and they would need to talk to their endocrinologist).
There is a growing body of anecdotal evidence that those with metabolic dysregulation do well with intermittent fasting. It seems to help reset insulin sensitivity and regulate hunger (over time). People with PCOS, metabolic syndrome, CFS and other diseases are having a surprising amount of success. These people usually struggle the most to lose weight or remain healthy on conventional diets. There is some suggestion that it doesn’t work for everyone, so we are still collecting evidence.
There are a number of ways to achieve intermittent fasting and everyone is a little different as to which one will work for them.
The traditional method is “anytime” – ie whenever food was scarce!
More recently research has been done on “every other day”. They advocate that fasting every 48 hours helps regulate hunger throughout the week.
The 5:2 diet has been promoted recently and involves choosing two non consecutive days of the week to fast.
The 4:3 is the same principle with fasting 3 days each week (getting close to every other day!)
Lastly the 16:8 diet is where people eat all their food every day within a 6-8 hour window and fast for the other 16-18 hours. This sounds easier but is surprisingly difficult if you are used to a late dinner or supper!
How to fast?
You need to eat a healthy diet all the time (fasting and non-fasting days), but don’t under-eat on non-fasting days. Aim for a “normal” food intake those days – this is especially important if you are used to eating a reduced calorie diet every day. This isn’t an excuse to binge on refined carbs, sugars and fats on all the other days. They remain treat foods (less than once per month)!
On a fast day you aim to eat approximately ¼ of your normal calorie intake. This would be 400 calories for a small woman and 600 for a large man. The rest of us are somewhere in between, but it doesn’t have to be exact.
You can drink as much water, herbal tea, black tea, black coffee, soda water etc as you like. However, don’t drink too much coffee or tea as the caffeine also messes up insulin and cortisol secretion.
The original authors of studies on this suggest eating one 400-600 calorie meal per fast day. Having experimented myself, I would agree, this is much more pleasant than eating three really small meals.
Some people prefer to have their meal at lunchtime and others at dinnertime. We tend to be hungrier in the evening, so most people prefer dinner.
The other option is to eat 3 very small meals per fast day. I found this increased insulin secretion and made me constantly hungry.
The other main tip for fasting is to choose a day when you know you will be really busy – especially for the first month (while you get used to it). If you are in your office with no distractions then you will think about food constantly and be miserable! You don’t have to use the same days every week – look ahead and think about which days will be busiest and easiest to fast during. Don’t pick a day with only yourself for company (at first), nor a day when it’s the office party that night!
Suggested fast day routine:
One method is to have 500-1000mls herbal tea during the first part of the morning (ie instead of breakfast) and then continue to drink tea or water through the day. Different flavours of herbal tea help psychologically break up perceived monotony.
Go for a walk or do something different at lunchtime. Listen to an audiobook so you are distracted. Do not hang out with colleagues who are all eating, nor stay in the same place you normally have lunch or all your habits will kick in.
Around 3-5pm have a “snack” – something like a tea or coffee with milk (a bit of milk – not a large latte!!).
Then cook dinner in the evening as normal. You can either plan a 400-500 calorie meal, or just stick to foods we know are low calorie – such as a large plate of leafy greens, or half a cup homemade porridge or muesli (no added sugar or oil). Alternatively, especially if you are part of a busy family, have a normal dinner and eat a half portion.
Although many people find fasting hard initially, it gets easier after the first few weeks, and you may learn to find comfort in the discomfort, or even enjoy the fast day.
The main side effects of fasting (as reported in the literature – mostly newspapers) are
- Bad breath – not true. Clean your teeth as normal. This is not a ketogenic diet so there should be no change to your smell at all.
- Abject misery – this is psychological, not due to the fast. Many people think about food all the time and make themselves miserable. Keep yourself distracted. If you are hungry – imagine the little insulin molecules going to the liver to get more glycogen out for you. Drink tea/water; listen to audiobooks/podcasts; go to a movie (don’t look at the snack counter). Insulin is Pavlovian – so as soon as you start thinking about food it gets released….making you feel hungry. It’s a real feeling, but it isn’t because you need food. The insulin will find glycogen if you give it half an hour or so (and stop thinking about food – it just encourages the insulin!!)
- Reduced energy – again, psychological. All the research suggests humans have increased energy when fasting and you can do your normal exercise regime on a fast day. There is some evidence that we are more creative when we fast.
The other big problem is, as with any diet, you can use it to tap into other unhealthy psychological problems. This is not something to be rigid about, or to become obsessed with. It’s treading that fine line between discipline and habit versus obsession and compulsion. If you have a “bad” fast day – you eat too much, or forget and eat breakfast, or all your colleagues had potluck lunch and you felt you had to join in….that’s all OK. It’s about picking yourself up and starting again the next day. Don’t feel guilty or be mean to yourself. You can still congratulate yourself for thinking about making a change and starting to make plans. This brings you closer to actually making change. See it as a fun, self-experiment!
Intermittent fasting is still being trialled, so there are not yet guarantees that it will work for everyone, but it is looking promising. Keep in touch with your doctor especially if you think it may not be working.
This website has a nice summary of some of the pros and cons.