El intermittent fasting It has crept into conversations about health and weight loss to the point of becoming one of the most talked-about weight-loss strategies. More and more people in Spain and Europe are considering reducing the number of hours they eat each day, but many doubts remain about whether it really works, who it's suitable for, and how to implement it without harming one's health.
Far from offering magic solutions, experts insist that Intermittent fasting is a time management tool, not a miracle dietIts effectiveness depends on how you eat within the eating window, whether your energy needs are met, and whether it's adapted to your individual lifestyle. Used sensibly, it can help with fat loss; poorly planned, it offers little benefit and can even cause problems.
What is intermittent fasting really and how is it structured?
When someone says they do intermittent fasting, what they really mean is that Divide the day into a period of time for eating and another without eating.In other words, it establishes an "intake window" in which it concentrates all its meals and leaves the rest of the time for fasting.
Pharmacist and trainer María Casas, from Fit Generation, reminds us that This is not a rigid diet, but rather a different way of distributing meals.It is possible to do intermittent fasting and still eat poorly: an abundance of ultra-processed foods, excess calories, or very high-calorie products that end up ruining any attempt to lose weight.
One of the simplest formats is the 12/12 fastingIn this scheme, twelve hours are spent without eating, and the other twelve are dedicated to meals. Given that much of the fasting time coincides with sleep hours, Many people would simply need to have dinner a little earlier and breakfast a little later. to accomplish it without great effort.
From there, you can try longer windows, such as the 16/8 (sixteen hours of fasting and eight hours of eating) or protocols with fewer meals per day. However, experts emphasize that Before committing to more demanding schedules, it's advisable to check if the chosen format It suits him at least for several monthsBecause the key is adherence, not enduring a few days through willpower alone.
Why fasting helps with weight loss (and why it's not magic)
Fasting has developed an almost legendary aura, but its workings are less mysterious than they seem. According to Casas, The main effect of intermittent fasting is that it reduces opportunities to snack between meals., one of the most common mistakes when trying to lose weight.
By limiting the number of hours in which one can eat, it also becomes more difficult to consistently exceed the limit. the calories that the body needs. It's not the same to fit in four 500 kcal meals as it is to try to make two 1.000 kcal meals.The second option is more burdensome and difficult to fulfill, while the first fits better with the usual appetite of most people.
From a physiological point of view, during the first few hours without food intake the body consumes the available glucose; subsequently, Insulin levels decrease and the use of fat as an energy source increasesThis transition is associated with a slight weight loss, improved insulin sensitivity already some reduction in oxidative and inflammatory stress.
Cardiologists and nutritionists who have reviewed recent scientific literature agree that, in overweight or obese individuals, Fasting can achieve weight loss and metabolic improvements similar to a classic low-calorie dietHowever, when comparing well-designed studies in which total calories are equal, intermittent fasting is not found to be clearly superior to a traditional meal plan.
In other words, the "magic" of fasting usually lies in the greater control over when you eat and in the involuntary reduction of caloriesIt's not so much about going hours without eating. If, during those allowed hours, you overindulge in fried foods, pastries, alcohol, or enormous portions, the slimming effect is completely negated.
Intermittent fasting versus low-calorie diet
Several research teams have compared intermittent fasting with traditional low-calorie diets. [The following appears to be a separate, unrelated section:] [The following appears to be a separate, unrelated section:] selected clinical trials that analyzed Weight loss with different fasting methods versus a classic calorie reduction.
In some of these studies, people who practiced intermittent fasting They lost slightly more weight than those who followed a low-calorie dietHowever, the authors themselves point out that the results are limited by methodological constraints and by the fact that what the participants ate was not always precisely controlled.
When calories are equalized and protocols are strictly compared, nutritionists like José Francisco López Gil point out that It cannot be said that intermittent fasting is superior to other approaches.In some specific markers, small improvements are observed, but it is not clear whether these are due to the fasting itself or to the weight loss.
Therefore, scientific societies and specialists agree on a cautious message: Fasting is a valid tool for those who feel comfortable with it, but it is not universally better or worse.It may work particularly well for certain people; for others, a more classic scheme of several meals a day is more viable and effective.
When might intermittent fasting fit into your life?
Beyond the numbers on the scale, professionals focus on something very practical: whether intermittent fasting fits with your schedule, your family, and your lifestyleChoosing this strategy just because it's trendy is usually a bad starting point.
Casas insists that the decision has to be personal and well thought out. Some people prefer to eat every few hours. They feel unwell when they go too long without eating; for them, prolonged fasting can become a source of stress and anxiety. In contrast, those who naturally tend to space out their meals can better cope with limiting their eating window.
A common example is that of those who They skip breakfast Because they leave home in a hurry and don't feel hungry first thing in the morning. For these cases, starting a twelve-hour fast is usually simple: the person has dinner a little earlier and delays their first meal of the day until they finish their morning's work or training.
In other situations, it may be beneficial to concentrate meals between 9 a.m. and 9 p.m., including a substantial breakfast and a relatively early dinner. This structure It allows you to maintain some social or family life around the table without completely giving up fasting.
The common denominator in all cases where experts recommend this strategy is that It will help to better coordinate meal times with the daily rhythm.From there, some people can gradually extend the fasting time, and even reach protocols of only one meal a day, as long as it is feasible to meet energy needs without discomfort.
Who shouldn't do intermittent fasting (or at least not without supervision)
Although it's often touted as suitable for everyone, intermittent fasting isn't recommended for all population groups. Nutritionists and cardiologists point out that There are groups in which this strategy may be directly inadvisable or require very close monitoring..
Among the cases in which it is not usually recommended are: children, adolescents, pregnant or breastfeeding women, and frail elderly peopleIn these groups, nutritional needs are especially delicate, and a prolonged period without food can aggravate existing deficiencies or health problems.
Experts also point out that It is not a safe option for those with eating disorders or a history of a troubled relationship with food. The very logic of restricting mealtimes can trigger binge eating, compensatory behaviors, and unhealthy control dynamics.
In people with metabolic or cardiovascular diseases, such as diabetes treated with certain drugs or uncontrolled heart diseaseThe risks include hypoglycemia, decompensation, and dizziness. That's why it's so important to consult a healthcare professional before drastically changing your eating habits.
Nutritionists like Edna Orellana emphasize that intermittent fasting It should only be considered in healthy adults, without glucose problems or diseases that affect metabolismAnd always on the condition of maintaining a balanced diet within the intake range. Their message is clear: nutrition should be designed in a personalized way and based on evidence, not on viral trends.
Potential benefits beyond body weight
In addition to fat loss, intermittent fasting has been discussed in recent years as a strategy for improve certain parameters of metabolic healthSome studies have observed small reductions in blood pressure, LDL cholesterol, and triglycerides in overweight or obese people who have followed fasting regimens for a period of time.
Effects related to improved insulin sensitivity and increased lipolysis (the use of body fat as an energy source). In parallel, some studies point to a slight decrease in oxidative stress and some inflammatory markers, although the results are not uniform nor always applicable to the entire population.
It is often said that by limiting eating hours, the body can dedicate more resources to internal repair processes and balance. However, scientific bodies point out that many of these hypotheses come from studies in animal models or in highly controlled contexts, so there is still room to confirm their clinical relevance in humans.
In any case, experts agree that There's no point in practicing intermittent fasting if the diet is then high in ultra-processed foods, added sugars, and unhealthy fats.Without a solid foundation of healthy eating, any potential metabolic benefits are severely limited.
Risks and side effects to keep in mind
Like any nutritional tool, intermittent fasting can have adverse effects if applied without proper guidance or in people for whom it is not suitable. Among the problems described, cardiologists warn of the possibility of hypoglycemia in people with diabetes treated with drugs that lower blood sugarespecially if meals are skipped without adjusting medication.
Another risk is the appearance of binge eating or disordered eating When the eating window is treated like an "all-you-can-eat" after many hours without food, this dynamic can lead to indigestion, discomfort, and, in the medium term, frustration at not seeing the expected results.
In people with uncontrolled cardiovascular disease or cardiovascular disease with complex treatmentsSudden changes in food intake and glucose or electrolyte levels can lead to imbalances. Therefore, cardiology societies emphasize the importance of any drastic changes in eating habits being done under medical supervision.
Beyond clinical cases, it is common to notice during the first few weeks anticipatory hunger, irritability, or difficulty concentratingEspecially if the body is used to eating at very specific times. In many cases, these sensations lessen over time, but it's important to interpret them as signals to be taken seriously, not as something to be ignored at all costs.
Experts remind us that a strategy that works on paper but is incompatible with daily life (meetings, shifts, family, rest) ends up being abandoned or only partially followed, which reduces its potential advantages and increases the feeling of failure.
How to get started with intermittent fasting without going crazy
For those who want to try it, professionals recommend doing so gradually. The first step is to accept that The brain is accustomed to certain schedules and will "ask" for food during those times.That feeling of hunger does not always respond to an urgent physiological need, but to a mixture of routine, emotions, and learned signals.
During the first few days, it's common to feel hungry before the fasting window ends. Casas suggests interpreting that hunger as a sign that It can be handled calmly, without dramatizing.and observe how it evolves over the weeks. Over time, the body usually adapts to the new schedule.
A practical recommendation is Start with short fasts of about 12 hours And, if the experience is positive, gradually extend it to 14 or 16 hours. From there, those who wish can organize themselves to have two main meals a day, and those looking for more demanding protocols can consider even narrower windows, always with professional supervision.
What experts advise against is jumping straight into very aggressive schemes, such as entire days without eating or a single very large meal. especially in people with high physical activity or high energy needsIn these cases, concentrating all the calories in a single moment can be inconvenient, difficult to digest, and unsustainable.
In all scenarios, the message that is repeated is the same: The priority is that the dietary pattern be compatible with real life.It's not about overcoming a specific challenge, but about finding a way of eating that, if it works, can be maintained for months or years without causing anxiety.
Intermittent fasting and physical exercise: how to combine them
A common question is whether it's a good idea train during the fasting periodTrainers and dieticians agree that it is possible to do it, but it is advisable to organize it so as not to make it more difficult for the body than necessary.
Personal trainer Ángel Gardachal suggests trying to The end of training coincides with the end of fasting.This way, you can have your first meal of the day right after the session, which facilitates muscle recovery and replenishes energy at a crucial time.
You can also train at the beginning or middle of the fasting period, but it's usually less comfortable, especially if the session is demanding. In any case, experts insist that The priority is to adapt schedules to each person's reality.: work shifts, family responsibilities, type of exercise and level of experience.
From a physiological point of view, training in a fasted state implies that Glycogen stores will be lower and the body will rely more heavily on fat for fuelHowever, the available evidence does not show that this automatically translates into greater fat loss if there is no calorie deficit throughout the day.
What does seem to have more influence is the type of trainingIn high-intensity exercise, research indicates similar fat oxidation whether training is fasted or after eating. However, in strength training, speed work, or very long sessions, some people experience poorer performance when they arrive on an empty stomach, while experienced athletes show a greater capacity for adaptation; in some cases, BCAA supplementation can influence.
Intermittent fasting, parties, and guilt: what makes no sense to do
Times like Christmas, with their string of special meals, often trigger the temptation to using intermittent fasting as punishment after excessesDietitians like Maria de Lluc recommend avoiding this approach, because in addition to not being particularly effective, it can damage your relationship with food.
Consider a long fast the day after a large dinner It usually only results in arriving at the next meal much hungrier and more anxious.increasing the risk of uncontrolled eating. The body responds better to regularity than to extremes, and a single day of celebration is not what determines long-term weight.
The idea of training extremely "to burn off" what was eaten the day beforeExperts remind us that the body doesn't work with such simple arithmetic: subjecting it to overexertion out of guilt can increase stress and fatigue, but it doesn't directly compensate for a single higher-calorie meal.
Instead of skipping meals, obsessively weighing oneself, or stringing together very intense exercise sessions, the recommendations involve return calmly to normal habits: resume normal schedules, prioritize fresh foods, stay well hydrated and move reasonably.
The weight that appears the day after a celebration usually reflects fluid retention, food volume, and transient inflammationIt's not an immediate increase in body fat. Understanding this helps reduce anxiety and avoids making drastic decisions that end up being counterproductive.
The importance of global nutrition and lifestyle
One idea that is repeated among nutrition professionals is that, To date, science has not identified a single perfect diet pattern.What does exist is a broad consensus on some characteristics shared by the most beneficial health guidelines.
Among them, one stands out low presence of ultra-processed foods high in sodium, sugars and poor quality fatsand a high consumption of fruits, vegetables, legumes, nuts, and whole grains. The classic Mediterranean diet The DASH diet and other similar diets remain solid references when it comes to reducing cardiovascular risk.
Furthermore, current recommendations go beyond isolated nutrients and include factors such as culinary techniques, a preference for seasonal and locally sourced foods and lifestyle aspects such as rest, physical activity, social environment or respect for the environment.
From this perspective, intermittent fasting is understood as one more cog in a much larger systemOn its own, it does not compensate for a poor diet or lack of exercise, just as a good distribution of meals does not replace adequate rest or stress management.
Scientific organizations insist on three basic principles for any diet plan: safety, sustainability over time and adaptation to the individual clinical situationThe best protocol is the one that the person can maintain without constantly pushing themselves and that fits with their medical and social context.
Intermittent fasting can be a An interesting option for those who are comfortable eating within a narrower time frame.Provided it's accompanied by a balanced diet and healthy lifestyle habits, it's not a magic bullet or an obligation: it's simply another tool that, used judiciously and with professional guidance, can help some people better manage their diet and improve their health without resorting to extremes.
