Intermittent Fasting: Does It Really Help You Lose Weight?
Intermittent fasting promises weight loss, better health and even a younger body. We review what human trials have found and who shouldn't try it on their own.
What intermittent fasting is
It isn't a diet about foods but about timing. What changes is when you eat, not what you eat.
There are several approaches. With 16:8, you fast for sixteen hours and eat within an eight-hour window. With 5:2, you drop to around 500 to 600 kilocalories two days a week. With alternate-day fasting, normal days alternate with days of eating almost nothing.
Its real advantages
The first is that it makes things simpler. Closing the kitchen at a set time cuts out late-night snacking. That helps you eat less without having to count calories.
The second doesn't depend on losing weight. In a 2018 study, eight men with prediabetes ate only between the morning and 3 p.m. They consumed the same calories and didn't lose weight. Even so, within five weeks their insulin sensitivity and blood pressure improved.
The result is promising. But eight people aren't enough to draw general conclusions.
Does it lead to more weight loss than other ways of eating?
In a 2020 trial with 116 adults, those who ate only between noon and 8 p.m. lost less than a kilo in three months. Those who ate three meals a day lost almost the same amount.
In 2022, another trial followed 139 people with obesity for a year. All of them ate fewer calories. Half of them also ate only between 8 a.m. and 4 p.m. The eating schedule made no significant difference.
In a 2017 trial with one hundred adults, alternate-day fasting didn't lead to more weight loss either. It also had more dropouts.
There are other drawbacks. Hunger, irritability and headaches are common at the start. And in the 16:8 trial, some of the little weight that was lost appeared to be muscle.
The conclusion is clear: according to these trials, fasting helps you lose weight when it makes you eat less, not because of the clock.
Autophagy and the promise of rejuvenation
Autophagy is fasting's headline promise. The 2016 Nobel Prize awarded to Yoshinori Ohsumi recognized the discovery of how this cellular recycling works. It was studied in yeast. The prize was not for the effects of fasting in people.
The idea of rejuvenation comes from studies in mice, worms and flies. In humans, no trial has demonstrated it.
Who shouldn't try it on their own
People with diabetes treated with insulin or sulfonylureas. If they don't eat and keep the same dose, their blood glucose can plummet. A doctor must adjust the treatment first.
Pregnant women, breastfeeding women and minors. They need more energy and nutrients to build tissue and grow.
Anyone who has or has had an eating disorder. This is the most delicate case, because skipping meals can reactivate the cycle of restriction and bingeing.
If you are an older, frail person or take medication, check first with a doctor or a registered dietitian-nutritionist.
Verdict and how to get started
Intermittent fasting works like any other way of eating less, no better and no worse. The clock doesn't burn fat: it just closes the kitchen.
If you decide to try it, start with a twelve-hour fast. Include protein at every meal. And do strength training two days a week to protect your muscle.
Frequently asked questions
Does intermittent fasting lead to more weight loss than a regular diet?
According to human trials, no. It leads to weight loss when it makes you eat less, just like any other way of reducing intake.
Can a person with diabetes do intermittent fasting?
If their diabetes is treated with insulin or sulfonylureas, they shouldn't do it on their own, because their blood glucose can plummet. A doctor must adjust the treatment first.
Has fasting been proven to make you younger?
No. That idea comes from studies in mice, worms and flies, and no human trial has demonstrated it.
How do you get started with intermittent fasting?
With a twelve-hour fast, protein at every meal and strength training two days a week to protect your muscle.
Informative article written with the help of AI tools from the verified script of the video. The video is in Spanish.