What is intermittent fasting?
It's an eating pattern that alternates periods of fasting with windows for eating. It doesn't dictate what foods you should eat, but rather when you should eat them.
What happens in your body during fasting?
When you stop eating for several hours, your body goes through a series of completely normal physiological changes. Far from "entering survival mode," the body gradually begins to use the energy reserves it already has available.
During the first few hours, the main source of energy is still glucose from previous meals and glycogen stored in the liver. As time passes and these reserves diminish, the use of body fat as fuel gradually increases.
This metabolic shift doesn't happen instantly, nor does it mean you're burning exclusively fat, but it does explain why many people find fasting an effective strategy for weight control when combined with a balanced diet.
Hormones and metabolism: do they really change?
One of the most commonly used arguments in favor of intermittent fasting is its effect on certain hormones related to metabolism. Although these effects are often exaggerated, scientific evidence does confirm that some interesting changes occur.
During fasting, insulin levels decrease, which makes it easier to mobilize fat reserves. Growth hormone also increases slightly, whose main function is to help preserve tissue and support repair processes. However, these changes alone don't cause significant weight loss if overall diet doesn't support it.
For this reason, researchers agree that the greatest benefit of intermittent fasting doesn't come from a supposed "metabolic reset," but from the fact that many people find it easier to maintain sustainable eating habits.
Is it better to eat breakfast or skip it?
For years it was claimed that breakfast was the most important meal of the day and that skipping it would slow down metabolism. Today we know the reality is much more complex.
Studies published through 2026 show that, in healthy individuals, there is no clear difference between eating early or delaying the first meal when total calories and diet quality are similar.
Some people perform better after eating breakfast, while others find it much easier to control hunger by waiting a few hours before their first meal. Both strategies can be perfectly valid.
Most commonly used protocols
| Method | Description |
|---|---|
| 16:8 | 16 hours of fasting and 8 hours to eat. |
| 18:6 | 18 hours of fasting. |
| 5:2 | Two days of calorie restriction. |
| OMAD | One meal a day. |
Does it work?
Yes, it can help many people because it makes it easier to eat fewer calories, although when calories are equal, results are similar to other diets.
What does the scientific evidence say in 2026?
In recent years, numerous clinical trials and systematic reviews have been published comparing intermittent fasting with traditional calorie-restriction diets. The current scientific consensus is quite clear: intermittent fasting works, but not because it "activates a special fat-burning mode," but because it helps many people maintain a calorie deficit more easily.
In other words, if two people consume exactly the same calories and the same amount of protein, one following a 16:8 protocol and the other spreading meals throughout the day, fat loss tends to be very similar.
However, a restricted eating schedule can offer practical advantages. Many people report feeling less hungry, snacking less between meals, and finding it easier to stick to their diet. That greater adherence is precisely one of the reasons fasting can be an effective long-term strategy.
Benefits that are backed by studies
Although intermittent fasting isn't a miracle solution, there are several benefits that consistently appear in scientific literature when combined with a healthy diet.
- Easier fat loss by spontaneously reducing energy intake.
- Better glucose control and improved insulin sensitivity in many overweight individuals.
- Reduction in certain inflammatory markers, although their long-term effects are still being researched.
- Greater metabolic flexibility, meaning a better ability of the body to use both glucose and fat as an energy source.
- Simplification of daily eating, reducing the number of food-related decisions.
Do you lose muscle while fasting?
One of the biggest myths is that a few hours without eating causes significant muscle loss. Available evidence shows this doesn't happen in healthy people who consume enough protein and regularly engage in strength training.
What really matters is reaching your recommended daily protein intake and maintaining muscle stimulus through resistance exercise. As long as these two conditions are met, meal timing has a much smaller impact than has traditionally been assumed.
For this reason, many athletes use protocols like 16:8 without experiencing performance or muscle mass losses, as long as they properly adapt their nutrition during the eating window.
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Most common mistakes when intermittent fasting
Intermittent fasting can be a very useful tool, but many people get poor results because they make mistakes that have nothing to do with fasting itself. Here are the most frequent ones:
1. Overcompensating by overeating
One of the most common mistakes is going many hours without eating only to then consume an excessive amount of food during the eating window. Fasting doesn't automatically eliminate a calorie surplus. If by the end of the day you consume more energy than you burn, you won't lose fat.
2. Neglecting food quality
Fasting doesn't mean any food is fine. A diet based on ultra-processed products, sugary drinks, and low-nutrient foods will still have negative consequences even if you only eat during an eight-hour window.
The best options remain minimally processed foods: vegetables, fruits, legumes, lean meats, fish, eggs, nuts, and whole grains.
3. Consuming too little protein
Reducing the number of meals causes some people to fall short of their daily protein needs. This can make it harder to maintain muscle mass, especially during a fat loss phase.
4. Not drinking enough water
During fasting hours it's common to forget about hydration. Maintaining good water intake helps reduce feelings of hunger and supports physical and cognitive performance.
Black coffee, herbal teas, and unsweetened tea can also be consumed during fasting without adding practically any calories.
Who shouldn't do intermittent fasting?
Although fasting is safe for most healthy adults, there are situations where it's not recommended without medical supervision.
- Pregnant or breastfeeding women.
- People with a history of eating disorders.
- Children and adolescents who are still growing.
- People who are underweight or malnourished.
- Patients with certain metabolic conditions or those taking medication for diabetes.
In all these cases, it's advisable to consult a healthcare professional before starting any fasting protocol.
Tips for getting started as a beginner
If you've never practiced intermittent fasting, there's no need to start with very demanding protocols. In fact, easing into it gradually usually makes adaptation much easier.
- Start by delaying breakfast by 30 to 60 minutes for a few days.
- Once you're comfortable, try a 14:10 protocol before moving to 16:8.
- Maintain good hydration throughout the day.
- Don't cut back on protein or vegetables.
- Train with weights several times a week to preserve muscle mass.
- Sleep at least seven hours each night.
Conclusion
Intermittent fasting isn't magic, but it is a useful tool if it fits your lifestyle. The priority remains maintaining good nutritional habits over the long term.
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