For the past few years, a new trend in the world of weight loss has been gaining momentum. So-called intermittent fasting is a strategy that involves restricting calorie intake for certain hours of the day, or on specific days of the week or month. But why do this? Is it really effective for losing weight or improving our health?
What does intermittent fasting involve?
As mentioned, intermittent fasting essentially consists of abstaining from food during specific time periods, which may last for hours or even days.
There are different approaches to intermittent fasting. For example, it can be practised by restricting the hours during which eating is allowed to only part of the day: 12 hours of fasting and 12 hours for eating, 14 hours of fasting and 10 hours for eating, or the most common 16:8 approach, and even extending to ratios such as 18:6 or 20:4. Alternatively, some protocols involve fasting on one or two non-consecutive days per week, or for two or three consecutive days each month.
What happens when we fast?
When we eat, the nutrients that enter our body are broken down into smaller molecules that enter the bloodstream, such as glucose from carbohydrates or fatty acids from fats. With the help of the hormone insulin, glucose is taken up by the body’s cells, and any excess is stored as fat in adipose tissue.
When we fast, insulin levels decrease, causing adipose tissue cells to release fatty acids. These can be used as an energy source or transported to the liver to be converted into ketone bodies, which some organs, such as the brain, can use for fuel. In short, our body begins to mobilise its energy reserves in order to continue functioning.
Benefits and risks of intermittent fasting
Intermittent fasting has been shown to help reduce body weight and improve metabolic profiles, as well as enhance glucose regulation and reduce inflammation. It also activates cellular defences against oxidative stress and mechanisms that remove or repair damaged molecules through a process known as autophagy. Autophagy occurs continuously in all our cells; however, the energy scarcity produced during fasting appears to increase its activity, accelerating cellular renewal and potentially delaying ageing.
Many studies support that this strategy, when supervised by a healthcare professional, applied prudently and in individuals who can tolerate it, may provide health benefits. However, as the saying goes, “all that glitters is not gold”, and intermittent fasting can also entail certain risks, especially when not supervised by a professional. These include loss of muscle mass, a slowing of metabolism, excessively low blood sugar levels, bad breath, headaches, irritability and low mood. In addition, the practice of “skipping meals” may encourage the development of eating disorders.
Given the growing popularity of intermittent fasting, several studies have also compared its effectiveness with traditional calorie restriction, which is commonly used in individuals with overweight or obesity. The results indicate that while intermittent fasting is effective for weight loss and improving metabolic parameters, it does not generally offer significant advantages over conventional calorie restriction.
In summary, based on the available scientific evidence, most researchers agree that intermittent fasting may offer promising health benefits, but further studies in humans are still needed before this strategy can be widely recommended to the general population.
A healthy balance
Scientific evidence suggests that even a simple overnight fasting interval can provide health benefits. For this reason, a sensible approach to intermittent fasting may be as straightforward as having dinner earlier, thereby extending the fasting period until breakfast. In addition to reducing some of the risks associated with intermittent fasting, since our activity levels are much lower while we sleep, eating earlier in the evening also aligns better with our circadian rhythms, as eating late at night has been associated with an increased risk of obesity.We recommend that before starting any form of intermittent fasting or other dietary strategies, you should consult your GP or a registered dietitian-nutritionist. Each person has individual needs, and it is important to assess each case on an individual basis to determine whether there are any contraindications that could negatively affect your health.
