The popularity of intermittent fasting has grown over the past few years, catapulted into fame by the Horizon program first aired in 2012. The revelation of what we eat, and when we eat it may determine life expectancy. Traditionally, fasting diets have thought to increase life expectancy and reduce age related diseases, but the impact of weight loss has meant these types of diets are becoming more popular. So what are the types of fasting diets?
Alternate Day Fasting
Exactly as it says on the tin, fasting on every other day with a caloric restriction of between 500 and 600 kcal per day, roughly equating to a 75% energy deficit, followed by what you would normally eat on the next day. Research shows that on feed days, where there are no calorie restrictions, people do not overcompensate for the reduced energy intake on the fast days.
This is a very popular diet, comprising of 5 ‘feed’ days and 2 ‘fast’ days. The fast days can be consecutive days, ie a 48 hour fast, or more popularly any 2 non-consecutive days. There is no evidence to show either way of fasting is better than the other.
Is intermittent fasting suitable for everyone?
No. People who are underweight, under the age of 18, have diabetes, are pregnant or breast feeding or have underlying medical conditions should not use fasting as a method of weight loss. Individuals who are at a healthy weight may still benefit from fasting, but there is less research into these benefits so far. If you are unsure speak with your GP first.
Will intermittent fasting help me lose weight?
Unsurprisingly, intermittent fasting, either twice a week or every other day, usually results in weight loss. With a calorie intake of around 25% on a fast day, it is unlikely that you will eat 175% of your calorie allowance on the feed day provided you do not binge. Therefore there is a negative intake of energy consumed, which should result in weight loss.
Are there any side effects?
Generally the most common side effect people feel is extreme hunger on fast days, particularly when you start this diet. Additionally, you may have side effects such as tiredness and lack of energy, headaches or constipation.
And eating out can be a tough problem considering the restriction on food intake, so here are some high street food chains which have fast day food options.
But are there any other health benefits?
Research shows that calorie restriction and intermittent fasting can be beneficial for healthy ageing of the brain. The theory behind this is that reduced caloric intake can prolong the lifespan of the nervous system through metabolic and cellular pathways. Strictly speaking, it can help to reduce cell stress and help protect against genetic and environmental factors, but most studies have been conducted in animal and insect models, rather than in humans.
A second report, which looked at several clinical trial outcomes identified a small number of studies which showed a reduced prevalence of coronary heart disease or diabetes diagnosis in humans. However, there are few human studies to date, and further research is needed to confirm any metabolic effects of fasting.
So, in summary, the 5:2 diet and alternate day fasting can both be used for weight loss, and is down to personal choice. There is no evidence to show how you split the calories over the day has any impact on weight loss – choose the way that works best for you. Individuals should eat healthily on non-fasting days, and not worry about exact calories, but try to aim for foods that are high in protein and fibre to help you feel full. As people tend not to compensate completely for calorie deficit on non-fast days, this results in a net loss of calories, which translates to weight loss.