Intermittent fasting (IF) is a nutrition strategy that has been around for a few years, it has recently started to get attention from the world of science, with increasing evidence that this is more than just another fad diet. IF, as the name suggests, involves extended periods of not eating and shortened eating ‘windows’. There are several types of IF that can be within the same day such as 16:8, where there is an 8 hour eating window between 16 hour fasts, alternate day fasting and variations on fasting where food intake is kept normal for a few days, with one or two restricted days eating thrown in, with the most popular version of this been the 5:2 diet.
An increasing amount of people are getting on board with this type of diet, some of the reasons are very well supported, other claims, well let’s just say it remains to be seen! However, there is some solid evidence that supports the use of IF and here we’ll discuss the top three.
1. Weight loss.
There are proponents of the IF diet that state that there is some kind of hormonal wizardry at play which means that IF is better for fat loss than other diets. Although IF appears to have some effects on hormonal levels, the main benefit of IF for weight loss is that by simply restricting the amount of time people have to eat, they will naturally reduce the amount of calories they consume and this will cause fat loss. The main advantage appears to be that for some people, this is an effective way to control intake because it does not directly limit the foods they can eat and makes the approach to fat loss much simpler and for both these reasons easier to stick to.
However, a word of warning, consume more calories in your eating periods than you expend over the course of the day (or week if you are using other fasting protocols) then weight loss will not occur, it’s a good strategy but it’s not that good that you can’t beat the laws of energy conservation!
2. Improved insulin sensitivity.
Insulin sensitivity is how well the cells of the body respond to insulin binding with them. This is important as the better our insulin sensitivity, the less insulin we need to produce to get the right effect, which is helps to open the cells ‘door’ and allow nutrients to enter and the lower insulin levels are the better for things like fat loss.
What we do know is that weight loss in overweight people will improve insulin sensitivity, this is a driving factor as to why IF will improve insulin sensitivity. However, some research suggests there is more to it than just fat loss, as IF improves insulin sensitivity and fat loss greater than other diet strategies, although the exact mechanisms behind this are not fully understood.
3. Reduced oxidative stress and inflammation.
Free radicals are produced in the body as part of normal metabolism. Under normal circumstances these can be dealt with by the body, but unfortunately when levels are elevated by physical or environmental stress, this can cause oxidative damage to our DNA and cause a whole host of problems, including chronic illnesses and cancer.
Acute short term inflammation is an important response to illness and injury, but if this develops into chronic, extended periods of inflammation, this is another important factor that can cause many diseases. Inflammation is also prevalent in those that are obese and it is suggested that being overweight causes dysfunction in our inflammatory response, leading to many of the health problems associated with being overweight such as heart disease and type-2 diabetes.
IF has been shown to improve markers of both oxidative stress and inflammation, suggesting it might have a benefit for improving health outcomes and preventing many chronic illnesses. However, it is not certain how much extra benefit that IF offers to conventional weight loss which would also improve these markers.
In summary, IF is a great nutritional tool for those looking to lose or maintain body weight whilst not having to worry excessively about counting calories, it is also an effective way to improve several markers of health in those who are overweight. For those who take part in sport, regular exercise and resistance training, it appears IF does not impact on performance as long as adequate energy and protein is contained in the diet. It’s efficacy in terms of muscle growth is still debated, however it is not optimal, as being fasted is not ideal to support muscle growth and during fasted periods the body is not primed for muscle building without a sustained supply of amino acids or fuel. However, that’s not to say you can’t grow muscle tissue whilst using IF, it just might not be at maximum rates!
Paul Rimmer (BSc, MSc, PhD).
