This is the last of the series of blogs on intermittent fasting and I do hope that you have found them interesting! Alternate days fasting is the ‘hard-core’ cousin of 5 2 and 16 8! It is another form of intermittent fasting (a dietary pattern which focuses on extending the length of time between meals), which alternates a whole day of fasting followed by a whole day of feasting……!
It’s more extreme than other forms of intermittent fasting as you fast every other day, not just 2 days a week or 16 hours a day. The benefits? Weight loss, as well as a potential edge in terms of maintaining muscle mass and metabolic rate. But this needs to be offset against hunger and fatigue on the fasting days…..
What can you eat on the fasting days?
In theory, nothing except liquids – black tea and coffee and water in all its glory. It is possible to do a modified version of alternate day fasting, where you consume 500-600 calories during the day (so like the 5 2 diet but with an extra couple of days!).
What should you eat on the feast days?
Anything you want! There are no limitations (a ‘feast’ in the real sense of the word!). In terms of calories, the small human studies performed to date, highlight that while people might eat slightly more than normal on their feast days, they are not eating 2 days’ worth of food on the feast days. Therefore, they consume less calories over a weekly period.
In terms of health though, it makes sense to follow a Mediterranean style diet on the feast days and moderate consumption of junk food and added sugar.
What are the benefits of alternate day fasting?
The obvious benefit is weight loss. A 4-week *randomised controlled study on a small sample of healthy adults following a strict alternate day fasting diet, found that the fasting group consumed 37% less calories and lost more weight compared to the control group.
The fasting group lost fat, as opposed to muscle, particularly visceral fat (the most dangerous kind of fat around are abdomens) while metabolic markers such as blood pressure improved.
While metabolic markers tend to improve with weight loss, the study was able to study certain genetic markers linked to lifespan across a longer alternate fasting period, and identified that the positive changes in these markers were specifically due to fasting.
As a further bonus, bone mass was maintained and the metabolic rate (the rate at which we burn energy) did not drop significantly. Note that most diets result in a slightly lower metabolic rate which is the body’s protective response to conserving energy when food intake is reduced.
So a win, win, win!
*What is a randomised control trial?
This is a type of study that splits participants randomly into groups to study the outcome of a particular variable (such as a medication, or dietary changes) known as an intervention. One group called the ‘control group’ will carry on as the normal while the other group(s) will receive intervention. The only difference between the groups is the variable being studied, everything else remains the same. This means that any significant differences between the control group and other groups (s) will be a result of the intervention being studied. These types of studies provide the strongest evidence regarding whether an intervention is effective.
What are risks of alternate day fasting?
Provided you are in good health, the limited studies to date do not indicate any health risks with alternate day fasting.
The issues are more practical – such as hunger. Strict fasting can cause extreme fatigue, a lack of concentration and disturbed sleep. However, a modified alternate day fasting, consuming 20-25% of your normal calorie intake is possibly more realistic and easier to follow.
Who should avoid alternate day fasting?
As with any form of intermittent fasting, anyone with a history of eating disorders, or a requirement to eat regular meals should avoid alternate day fasting. I am going to underline again that alternate day fasting is for healthy adults, so please do check with your doctor if necessary.
I am a fan of intermittent fasting – the emerging research is really interesting although more human studies are definitely needed. I find alternate day fasting a little too hardcore for me and this is even when following the modified version and eating small amounts on the fast days! I found myself counting the hours until I could eat, and I also slept really badly. This is not how I want to spend 3-4 days a week!
All forms of intermittent fasting seem to show similar potential benefits, my advice would be to try a form of intermittent fasting which works for you. My preference is for a 16 8 approach or a relaxed 5 2 (consuming 800 ish calories during a light day). If these seem too difficult, you can start by aiming to eat your supper slightly earlier in the evening while pushing back your breakfast by a couple of hours. For example, eating breakfast at 10 am instead of 8 am. This gives you a fasting window of 12-14 hours. It also gets you into a healthy habit of not snacking late at night!
Flexibilty and adherence
One of the clear benefits of intermittent fasting is its flexibility. You do not have to ‘diet’ every day and this, I believe makes it easier to follow. I would also add that while the ‘non fasting’ days or ‘meals’ are meant to be unlimited in terms of your food choices, I think it is important to consume nutrient rich meals on these days. This helps to ensure you get all the nutrients you need across a typical week, an important point which is not always highlighted. While you can and should enjoy a nice dessert, or a few drinks (!), the majority of your meals should be balanced and based around nutrient rich foods.