What is the 5:2 fasting diet?
A history of fasting
The practice of fasting for health or spiritual reasons is as old as the hills. Pretty much every religion has a form of fasting. Typically, fasting is promoted as a means of discipline, or for focusing the mind, but more recently, fasting has been promoted as a means to weight loss.
But what we want to know is: does it work and is it safe?
Do we have ‘thrifty genes’?
There is no doubt our bodies are built to cope with periods of little or no food. In fact, one theory of why we struggle with our weight today is called the ‘thrifty gene hypothesis’. The theory goes that our ancestors wasted little energy and conserved it well by preserving body fat in times of famine and then survived to pass on their genes to us. Today, the ‘thrifty’ genes that kept our ancestors alive are doing less ‘conserving’ and more ‘weight gaining’ because we live in an environment of abundant energy-dense food.
So one way of looking at things is that integrating regular fasting into your life is just emanating the environment we evolved to survive in.
Can fasting help us lose weight and keep it off?
The truth is we don’t really know yet. What we certainly know from animal studies is that eating fewer kilojoules lengthens an animal’s lifespan and lowers their risk of many chronic diseases, including cancer and there is pretty good evidence that this also occurs in humans. It’s just more difficult to test, since getting people to survive on lower kilojoule intakes is not easy.
There is also some evidence that fasting has benefits from a health perspective. For example, studies of people at the end of Ramadan, an Islamic fasting holiday, have shown improvements in indicators of heart disease risk, such as blood cholesterol profiles and insulin sensitivity. Whether this translates into long-term reductions in risk is not yet known, but it certainly looks promising.
Studies into intermittent fasting are still in their infancy, but at least one study, over a six-month period, showed that fasting two days a week was just as effective as following a reduced-kilojoule diet in overweight or obese premenopausal women.
Previous studies have looked at longer-term fasting over several days, but most haven’t come to any good long-term results. It seems that after a few days the body really does kick into starvation mode, hanging on to make the stored energy last as long as possible, and then ramping up the appetite to restore the body’s weight once food becomes available. However, this is a small concern and the bottom line is that chronic dieting and regaining weight is likely to be much more harmful. This is very different to intermittent fasting. Most of us are able to cope with a single day of fasting at a time easily.
Is there any harm from fasting?
This 2-day fast diet works on a 2100kJ/500-calorie total daily intake for women, and a 2500kJ/600-calorie total daily intake for men.
What will certainly not work is if you fast for two days, and then on the other days you overeat. However, the research on fasting seems to show this doesn’t happen to most of us.
You may be more likely to eat a bigger breakfast on the day after your fast, but the evidence to date suggests that most of us only eat about 20 per cent more the next day, and do not therefore replace all the kilojoules omitted on the fast day. But do be mindful of this.
It’s also important that you don’t ‘eat whatever you like’ on the other days. Nutrient intake matters! We need micronutrients and phytochemicals such as antioxidants for optimal health. Our food choices affect more than just our weight, it also affects how we look and feel, and our risk for disease.
There are some concerns over the long term effects of fasting. With theories that it may well be that our bodies just learn to cope better with a fast, in other words, you’d have to keep up the fasting routine forever just to remain weight stable, but should you stop fasting you risk gaining extra fat ready for the next fast that never comes. We need to wait for further research to understand more about these effects.
Those who should certainly not undertake fasting include pregnant and breast-feeding women, those with diabetes or those who are prone to hypoglycaemia and with any pre-existing medical problems. Many medications must be taken with food, and so you must not fast unless under the guidance of your doctor.
Pros of fasting
~ You learn to feel properly hungry and be okay with that. This may sound funny, but so many people tell me they are rarely hungry, or they are scared of being hungry. Most of us can easily cope with one day of little food.
~ Anecdotally, many people say they feel full of energy post their fast day, and feel quite euphoric. That may be from a sense of pride at their restraint, or there may be physiological reasons. By giving your body a rest from digestion, you feel lighter and have more energy to direct into other things!
~ Provided you don’t go crazy and overeat on the other days, it can be a terrific means of lowering your weekly kilojoule intake and chipping away at your fat stores.
~ You only have to restrict your food intake on two days out of seven. For many people, this is much easier, and a whole lot more appealing, than having to think about a small restriction in food every day.
~ You can change the days you fast, so if you have a dinner or celebration on the day you normally fast, you can swap it for the next day.
Cons of fasting
~ We don’t know how the genes associated with fuel and energy preservation will be affected. The theory, however, is that by only fasting one day at a time, you are not entering a true famine, and so the effects on genes are likely to be negligible.
~ You may feel tired, cranky and dizzy on the fast day, particularly if you are prone to low blood glucose. Plan your fast days on relatively quiet days to help deal with any side effects while you get used to it.
~ Fasting interrupts normal routines such as family dinners or invitations out. Minimise this by planning fast days according to your diary. If you have a partner, persuading them to fast with you will make it easier to stick to your plan.
~ You may find yourself overeating on the day before or after the fast, thereby replenishing any lost kilojoules. Be mindful of this and try to avoid it.
Article originally by Dr Joanna McMillan, Nutritionist and Dietitian, published in The Australian Women’s Weekly 2-Day Fast Diet.
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