Intermittent fasting is defined as ‘voluntary abstinence from food and drink’. It has received a lot of attention in recent years, one example being the popular 5:2 diet where people are instructed to eat a certain number of calories for two days of the week and for the other five days of the week, there is no restriction in caloric intake. The difference with intermittent fasting is instead of telling you what to eat, it tells you when to eat.
Research indicates that intermittent fasting has a number of positive metabolic effects such as reduced obesity associated body weight, reduced fasting insulin and glucose concentrations, reduced plasma cholesterol and triglyceride concentrations.
There are a few variations on intermittent fasting:
Alternate day IF: Alternate day intermittent fasting involves alternate fasting days where no calories are consumed and feeding days where foods and drinks are consumed with no restriction. This particular method has shown reduced levels of obesity, fasting insulin and glucose concentrations as well as reduced cholesterol and triglyceride concentrations. However, it has also been shown to be just as effective as simple calorie restriction for weight loss as well as less desirable effects such as extreme hunger and fatigue on fasting days.
Modified fasting regimes: This form of IF is slightly different. It has the similar ‘fasting days’ however, instead of fasting completely, food intake is restricted to 20-25%. This form of IF has shown similar benefits as the above as well as an increased feeling of fullness. Some negative side effects include feeling cold and irritable, hungry and low energy levels.
Time restricted feeding: This particular method is slightly different. Instead of having fasting days, it involves restricting food intake to particular times of the day. Take for example an eating window of 8 hours, and a 16 hour fast. Depending of preference, one might make their eating window between 11-7. This way they can skip breakfast but their eating window is slightly more social to allow time with friends.
The main bulk of research has been carried out in animals, which gives a good insight into IF’s benefits, however we cannot compare a human to a mouse. More research in humans is needed to identify the best form of intermittent fasting and its long-term implications for humans.
My opinion – intermittent fasting is another diet. It has its place and may allow people to better stick to a caloric deficit due to time restrictions on food consumption, however it does take quite lot of planning. I wouldn’t recommend it to the general population.
Yes, there is evidence that this form of eating can help reduce weight and various blood parameters which may benefit some populations such as high level athletes who need to make weight for competition, or obese patients who are working with a qualified professional to reduce weight and weight associated disease. For the general population however, fasting completely for two days and eating with no restriction for the other five is a recipe for binge-restrict cycles of feeding. If someone is unfamiliar with this type of eating, the night before their first fast will cause panic and a need to ‘stock up’ on food for the next day of fasting. Similarly, the day after the fast may cause a feeling of extreme hunger. This can lead to disordered eating patterns leading the person back to stage one, or even worse.
There is very little evidence coming from human studies to identify whether this is a long term option for the general population. I agree that it may suit some people however we are all different and what might suit you may be completely wrong for somebody else. Similarly, any studies available are done in a controlled environment where constant support is available. Time restricted feeding is the most sustainable option in my opinion. Giving a window of eating daily rather than fasting days is more sustainable and suited to our current working environment. My biggest concern with time restricted feeding is eating enough and meeting nutrient requirements. This can however negatively affect social life as it can be quite restrictive in regards to when you can consume food and drinks.
If you’re looking to give intermittent fasting a go, maybe start off with time restricted feeding as it’s the easiest form to fit in to a normal daily routine. The most important thing here is to increase the size of your meals to ensure you are eating enough and getting all the essential nutrients for your long-term health.
My personal advice would be to improve your health and reduce weight through a healthy balance diet and regular exercise. Its much more social and sustainable.. life’s too short to be living by strict rules around eating and diet!
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