Fasting days can cause tiredness and a lack of concentration, which can impact on your daily life. Photo / 123RF
If you haven't heard about fasting yet then you must have been living in a dark cave somewhere.
This diet trend gained momentum with the introduction of the 5:2 diet that has helped many people to lose weight, said the Daily Mail.
Since then the idea of fasting has evolved into several other methods including the eight-hour fast and the more extreme concept of abstaining from food completely for one day each week.
But one size doesn't fit all when it comes to intermittent fasting, explains Rob Hobson, head of nutrition at Healthspan.
While more and more people are turning to this eating method to lose weight, Hobson warns you need to choose the right numbers to fit in with your day-to-day life.
So which one should you choose?
Here, Hobson explains the benefits of the various approaches, and how you can match the numbers to meet your lifestyle.
What's the evidence?
Despite the hype surrounding intermittent fasting, a lot of the research is still in its early stages.
Although good quality clinical research is lacking and most of the research is on rats, some of the findings are really interesting.
There are no studies testing the specific fasting methods such as the 5:2 diet.
A lot of the health benefits associated with intermittent fasting are centered around the changes that occur in the body when it's deprived of food.
These include low levels of blood insulin (promotes fat burning), increase in human growth hormone (increases fat burning and muscle gain), cellular repair (removing waste from cells) and gene expression (changes are thought to be linked to longevity and protection against disease).
Many people choose to fast as a way of losing weight rather than a long-term lifestyle change and are successful in meeting their health goals.
The weight loss is essentially a result of eating fewer calories given the smaller window for eating or the reduced amount of food on fasting days.
But the increase in hormones and reduction in insulin also promote the breakdown of body fat and potentially increase your metabolic rate.
Some of the strongest research for fasting is around the potential to reduce insulin resistance and lower the risk of type 2 diabetes.
There are down-sides.
It's not clear whether one method of fasting is better. It's also not fully clear where the numbers have come from for methods such as the 5:2. And there is no evidence to show where the 500-600 calories were derived from.
There is also a misconception with fasting that you can eat what you like on non-fasting days (especially the 5:2) but you still need to eat within the realm of a healthy diet.
These diets are often based on calories and as we know not all calories are created equally so what are the effects of eating very few calories if these are obtained from unhealthy sources such as quickly digested carbohydrates that can increase hunger and cause blood sugar imbalances? This will make sticking to fasting methods like the 5:2 tricky.
However, many observational studies have cited benefits to fasting, such as reducing oxidative stress and inflammation in the body (both of which increase ageing and disease risk).
The diet is also believed to help lower heart disease risk factors such as cholesterol levels, triglycerides and blood pressure.
And it protects brain health and maybe even lowering the risk of developing Alzheimer's disease.
Eating good quality, nourishing calories will help with satiety and ensure you get an adequate intake of micronutrients that are essential to good health.
SOCIABLE TYPES
You should go for... 6:1
Burning the candle at both ends can mean working hard and playing hard.
Maintaining energy levels throughout the day is essential and the last thing you want to do is leave the office for drinks on an empty stomach, which is always a recipe for disaster.
Fasting can also interfere with dining out. The best type of fasting may be eat-stop-eat during a quite weekend every one or two weeks.
HOME-BODIES
You should go for... 5:2
Those who prefer a more relaxed week, and a cozy weekend in, may have more time to prepare some nourishing low-calorie meals.
MOMS AND DADS ON THE SCHOOL RUN
You should go for... 16:8
Busy mornings can often mean skipping breakfast as you dash around getting the kids ready for school. Before you know it, its mid-morning and you're ready to eat.
You like to sit down as a family to eat with the children so your evening meal is served early. Without realizing it you are already conforming to the 16:8 method of fasting.
AMBITIOUS TYPES
You should go for... 16:8
Busy work focused individuals require a steady source of micronutrients and energy to deal with the demands of their hectic schedules.
A lack of food can make it difficult to concentrate and deal with the job in hand and there may also be an increased demand for nutrients such as the B vitamins as the body must cope with excess stress levels. Eating within an eight-hour window leaves plenty of time throughout the day to nourish the body.
RETIRED
You should go for... 5:2
Older people may find it easier to follow methods such as the 5:2. Appetites diminish as you age so fasting days may feel like less of a burden.
Many people as they get older become slightly less active and not working makes fasting days a little easier to commit to. Being at home gives more scope to prepare nourishing, low calorie meals that may be more difficult for working people that buy lunch on the high street.
TRAINING FOR A RACE OR EVENT
You should go for... 16:8
You need fuel to train so full days of fasting and intermittent days of very low calories can leave your muscles depleted of glycogen, which is required to give you the energy you need to get through workouts.
Post training also means eating protein and replacing carbohydrates, which can be tricky if you're limiting your food intake or fasting all day.
The 16:8 method means you can reload muscles with energy the night before ready for your training session in the morning. If you eat at 7pm you will be ready for breakfast between 9am and 11am depending on whether you fast for 14 or 16 hours.
Intermittent fasting can work and has a lot of potential health benefits but it's not for everyone, nor does it need to be.
If it ain't broke then don't fix it' is a good motto if you already have a healthy diet and an active lifestyle that works for you.
Intermittent fasting is just one approach, among many effective ones, for improving health, performance and body composition. If you do fancy giving it a try then use the SMART guidance to decide on the best method for you.
EXPLAINED: THE TYPES OF INTERMITTENT FASTING YOU CAN TRY
The 5:2
This fasting method involves eating normally (and this means healthily!) for five days of the week and limiting your food intake to 500 or 600 calories (depending on your sex) for the remaining two days.
This is not for everyone as the fasting days can be tricky to fit around busy lifestyles, especially if you like to train a lot or have a hectic work schedule.
Fasting days can cause tiredness and a lack of concentration, which can impact on your daily life.
The 16:8
This involves fasting for 14-16 hours each day, which restricts your eating window to between eight and ten hours.
Eating this way usually means limiting your intake to three daily meals given the short window although you could try eating more, smaller sized meals if this is how you prefer to eat.
This is the simplest of fasting methods and normally means eating your evening meal a little earlier and breakfast late.
This can get tricky if you're a big breakfast lover but for people who often skip breakfast they're usually instinctively eating this way regardless.
Water, coffee and herbal teas can help to stave off hunger in the mornings.
The 6:1 (eat-stop-eat)
This involves a full 24-hour fast every one or two weeks. This is not for the faint-hearted.
The start of your fast may be fine but for most people they become ravenously hungry towards the end of the day and this can lead to mood swings, dizziness and an inability to concentrate.
Definitely not something you want to do during work or on a training day.
New York Times: The best ways to foster healthy eating are also the simplest.