Her research highlighted two important things. First, that dieting two days a week was easier and that more people stuck to it than dieting all the time. Harvie compared two groups of women. The first group fasted two days a week and the second group followed a standard calorie-restricted diet, sticking to 1500 calories a day. After three months of following the diets, the research showed that intermittent fasters were almost twice as likely to stick to their diet.
The second and most impressive finding of her research was the reduction in a breast-cancer-causing hormone called leptin, which was reduced on average by 40 per cent, and a drop in insulin levels of 25 per cent, cutting the diabetes risk in these women.
Alternate day fasting (ADF)
Alternate day fasting originated in the US before the fast diet became popular in the UK. The principles of this diet are very simple. A strict fast diet is followed every other day. It also restricts how many meals you eat in that one day. The 5:2 diet is a variation on this theme, allowing you to fast for fewer days in a week and also to take weekends off. They are similar in terms of weight loss and effects, although obviously you may lose weight faster on ADF. But the success rate (i.e. the number of people who stick to the diet in the long term) is lower.
There has been an interesting study in the US by Dr Varady into ADF. Varady’s research is fascinating. She took a group of both male and female overweight volunteers and started them on ADF for a year. This study is still progressing, but initial results in this case show a low dropout rate, gradual and continued weight loss and falls in both total and LDL (‘bad’) cholesterol.
Window or 8-hour fasting
Window fasting is a slightly different way of structuring your fast days. You fast for a part of your day, seven days a week. For example, a popular structure is that you fast from 8 p.m. on one day until 12 p.m. the following day. This means that your eating ‘window’ is 12 p.m. to 8 p.m. every day. Some people find that this kind of fasting fits more naturally into their lifestyle as they can eat a normal lunch and dinner every day, but it’s definitely not to everyone’s taste.
There has not been much research into this particular type of intermittent fasting, but the results are likely to be similar to that of 5:2 fasting or ADF.
Intermittent fasting (IF)
Intermittent fasting is a coverall term for any type of fasting diet. So the 5:2 diet, the fast diet, the 2-day diet and ADF all come under the umbrella of intermittent fasting.
The advantages of 5:2/fast diet over other forms of intermittent fasting
There is a reason why more people follow the 5:2 diet than any other form of IF – you are more likely to have success because it’s easier to stick to and simpler to fit into your lifestyle. The dropout rate is lower than other types of IF and, indeed, than other types of diet. Put simply, the 5:2 diet is the simplest and most sustainable fast diet.
Possible dangers and side effects of the 5:2 diet
Because this diet is a fairly radical approach to weight loss, it is wise to speak to your doctor first to see if it is safe to follow the diet.
Current medical opinion suggests that the benefits of fasting are unproven. This is because long-term studies take several years, or even decades, to complete and this is a relatively new field.
The good news is that no significant dangers or problems with the diet have been reported so far. We can also take note that certain religions have been fasting for hundreds of years. Fasting during Ramadan requires Muslims to fast during daylight hours for a month. Fasting is also common among most Hindus. They fast on certain days of the week based on their belief and to appease certain deities. Both Hindus and Muslims believe that fasting is important for the wellbeing of human beings as it nourishes both physical and spiritual needs.
What about side effects?
As with all big changes to your normal diet and routine, there can be side effects. Some people will not experience any side effects, but a few will find the side effects to be so uncomfortable that they will be unable to continue with the diet.
Some of the side effects seem to occur only when fasting is first attempted. These effects, such as headaches and dizziness, will diminish and hopefully disappear altogether over a period of several weeks.
Dehydration seems to be a common side effect of following the fasting diet that doesn’t fade in time. It is easily dealt with by sipping plenty of water or other low-calorie drinks regularly throughout the fasting day.
What about irritability? Yes, some of us do get grumpy when we are feeling hungry. This does seem to reduce as we get used to fasting. But I can get grumpy on fast days and normal days too!
Some people report difficulties sleeping due to hunger and daytime sleepiness. This is less common than other symptoms. Most people feel a buzz of energy during their fasting days. Difficulties sleeping can occur, particularly if you eat the majority of your calories during the early part of the day. Increasing the size of the evening meal and making sure it is rich in complex, filling carbohydrates helps the body feel sustained until after we go to sleep.
Finally, here’s one side effect that has affected me. I’ve been feeling the cold all through the winter, but particularly on fasting days. It has been a rather cold winter this year, but I have been suffering more than I would expect. The result has been an increased wearing of jumpers – perhaps two or three at a time and a higher heating bill. I take comfort in the fact that this is likely to mean that my body fat is reduced and the diet is working well.
Fasting and hypoglycaemia
If you suffer from, or might be suffering from, hypoglycaemia as a medical condition consult your doctor before beginning the diet.
The feeling of low blood sugar when you haven’t eaten for a few hours is a common problem and one which I have suffered from in the past. It may put someone off fasting, because they feel that they need to eat every couple of hours to keep their blood sugar stable. The basic problem is that if you don’t eat every three or four hours then you can become hypoglycaemic and therefore irritable, moody, light-headed and shaky.
This is an interesting phenomenon as only a small proportion of the population actually have a malfunction in their ability to regulate blood sugar levels. The rest of us, who do not have an underlying medical condition, do not have to worry about getting ‘low blood sugar’ while fasting. This is because the body is amazingly effective at regulating the sugar flowing around the blood.
A study in which young adults who have symptoms of hypoglycaemia went on a monitored 24-hour fast found that, while they reported ‘feeling hypoglycaemic, their blood sugar levels remained normal. What to do if you are worried about having a ‘blood sugar crash’ during a fast period? This is a very real problem that I myself suffered from when I started the diet. I now know that my blood sugar levels are fine; I am in fact just exceptionally hungry. Here are my tips that helped me get through it, which I hope will help you too.
• Eat regularly during your fast day – this means three small meals.
• If you feel a wave of light-headedness coming over you, know that it will in all likelihood pass and you will feel normal again in 15 minutes.
• Finally, if it affects your ability to function normally or gives you a headache then you should eat something – nothing that big, ideally 100 calories or so of something filling, a slice of toast or a small banana, for example. Allow yourself those extra calories for that day, but carry on with the fast day