Firstly I have to hold my hands up and admit that it took me a long time to come round to trying intermittent fasting. Like most personal trainers i’ve been raised on the understanding that we should eat 3-6 equal sized meals evenly spread out throughout the day. So when I first read about intermittent fasting I totally blanked the idea.
As all good diet trends do, intermittent fasting got bigger and its voice louder so I decided to read into the research to see if there was any evidence to support it, before giving it a try.
Intermittent fasting is the practice of going for prolonged periods without food. What can be a bit confusing is there is no one universal method. Over the past 5 years quite a few different diets have emerged, the most popular are:
Eat Stop Eat – (5:2)
On this system you fast for a full 24 hours once or twice per week, eating a sensibly (higher protein, minimal processed food…etc) the rest of the week. Its really flexible, you can choose which 24 hour period you want. This can be breakfast to breakfast, lunch to lunch or dinner to dinner. You just choose a 24 hour period that suits you, for example, have dinner on Wednesday night at 8pm and don’t start eating again until 8pm on Thursday.
Within this system the 5:2 diet books have come out which allows 1 x 500kcal meal during the 24hour fast period. The rest of the rules stay the same.
Lean Gains – (16/8)
This style of fasting is based on a 8 hour feeding period followed by a 16 hour fasted period. Again you can pick your fasted window depending on what you find more manageable for example you could choose to fast from 9pm on Monday night through to 1pm Tuesday afternoon and you eat in the following 8 hour window. The eating during the 8 hour window is a bit more complicated. You should aim to eat a high protein diet and cycle your carbohydrates (eating more carbs on days you train than days of low or no exercise). The diet recommends you train fasted and then eat the bulk of your calories in the first solid meal post workout. So your training should always be at the end of the fast, then you break the fast with your 1st solid meal.
Alternate day fasting (ADF) – (36 hour fast / 12 hour feed)
With this plan you simply eat every other day. So on Monday, you would eat within a 12 hour window, say, 8 AM to 8 PM. Then you’d fast overnight on Monday, and all day/overnight on Tuesday. You’d eat again from 8 AM to 8 PM on Wednesday. And so on. Alternate day fasters are encouraged to make good eating choices, but they’re allowed to eat what they want on the non-fasting days.
Warrior Diet – (20hour fast / 4 hour feed)
On this plan, you would either fast, or eat very small amounts of specifically recommended foods, for the first 20 hours of each day, working out during this period of under eating. Then, you would eat the majority of your daily intake within a 4 hour over feeding window. After that 4 hour over feeding period, you would repeat the under eating/fasting for the next 20 hours. Generally, most people place their 4-hour over feeding window at the end of the day, as it’s more convenient for family dinners and after-work training sessions. However, modifications can be made based on individual and scheduling differences.
Fasting is nothing new, humans have fasted for most of our history for religious reason or during times of food scarcity. We all fast every night between dinner and breakfast, unless you’re a fridge raider in the night we hopefully get about 10-12 hour fast per day. What is new is that clinical research on the benefits of intermittent fasting for health and longevity is slowly beginning to catch up.
The list of proposed benefits of fasting is very impressive, it’s said that fasting can improve insulin sensitivity, lower cholesterol, reduce oxidative stress, reduce inflammation, improve appetite control, increase fat burning, and a whole host of other cool things. A lot of these benefits come from giving our digestive system a complete break from having to deal with food and allowing our body to reset, as well as the benefit of simple calorie reduction from reduced food intake.
Research in favour of fasting looks compelling, however most the research to date has been done on animals. Which obviously aren’t perfect models for predicting human responses. Human studies on intermittent fasting are limited, lets face it what companies are going to pay big money for research which ultimately supports not eating. However some studies have been done and support intermittent fasting for fat loss, improving insulin sensitivity and reducing cholesterol. Most of the studies are carried out on overweight or obese individuals which leave questions over whether its applicable for athletes and people with lower body fats as a start point.
As fast as intermittent fasting’ popularity has grown so too has its critics, questions have been raised over how intermittent fasting effects our stress response, ability to sleep, satiety hormones and reproductive hormone and there are reports in women having problems including binge eating, metabolic disruption, lost menstrual periods and early onset menopause. Sadly there is a lack of research done on humans for the effects of intermittent fasting on our hormones, however studies into women who fast during Ramadan show that some women experience alterations in their menstrual cycle from fasting. What is well recognised is that men and women respond differently to fasting. Which doesn’t mean woman shouldn’t fast, just there are some things to understand before trying.
For women, if you generally eat quite a healthy diet, especially if follow a calorie restricted diet anyway then intermittent fasting probably isn’t for you. Its not worth finding out the hard way if intermittent fasting may have an effect your menstrual cycle.
Women usually respond better with a 1 x 500kcal meal during the fast to start with
Trial a prolonged fasted period first, start with 14 hour fast and build up to 24 hours in stages and start with just one day per week before moving on to a second day. This is true for both men and women that want to try fasting
For issues fasting may have on sleep, make sure you start the fast after dinner so you are not woken in the night with low blood sugar. Sleep is too important to allow anything to disrupt it.
It could take another 10 years of research before we find out exactly what the real benefits and issues with intermittent fasting are. What we have seen from using IF protocols with people over the past 5 years as the diet has become more popular is that its not a one size fits all method.
One of the biggest take aways I got from fasting is understanding that what we think is hunger is more a response to the habit of eating. Its amazing how easy fasting 24 hours really is after you have done it a few times
I generally see intermittent fasting as a tool rather than a diet. It hasn’t got to be something you do weekly, it can just be something in your arsenal of fat loss methods that you pull out when you fancy a boost to your weight loss or if you have just had a period of gluttony and fancy giving your digestive organs a rest. Having food available all the hours we are awake is not in-keeping with how we evolved and taking a break from eating for a period every now and then isn’t a bad idea.
Intermittent fasting can work but it’s not for everyone, nor does it need to be. In the end, intermittent fasting is just one approach, among many effective ones, for improving health, performance, and body composition.
Here’s the thing, I live in a social media bubble where I surround myself with women lifting weights, getting strong and generally being freaking badass human beings. Yet when I walk into most gyms, this isn’t exactly what I’m seeing.
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