An ancient and time-honoured practice, long embraced for spiritual purposes, fasting has in recent years gained recognition for its potential health benefits. But is fasting actually good for you? Could a 24-hour fast help you feel better — or even lose weight?
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What is a 24-hour fast?
A 24-hour fast is a water fast, meaning its principle is based on the complete absence of food intake but the freedom to drink, as long as the beverages contain no calories. So for 24 hours, you eat nothing, but you can drink as much as you like — water and herbal teas and optionally a lemon juice diluted in water in the morning, along with a clear vegetable broth with no salt or fat. It also means avoiding all stimulants, such as tea, coffee or tobacco.
It’s also worth noting that during the fasting period, it is advisable to avoid stressful situations while staying physically active — that is, continuing to stretch and even walk to keep your metabolism going.
This form of intermittent fasting, much like sequential fasting or the 5:2 diet, is growing increasingly popular. It is credited with a wide range of benefits. But what exactly are they?
Benefit no1 of the 24-hour fast: giving your digestive system a rest
During a 24-hour fast, the digestive organs are given a complete break. The stomach no longer needs to digest any food, since none is consumed. Even more interesting: the pancreas no longer needs to secrete insulin, the hormone responsible for converting dietary glucose into energy reserves. The same applies to the liver and gallbladder, which are no longer called upon by the digestive process. The feeling of lightness experienced during a 24-hour fast is therefore not only due to the absence of food in your stomach, but also to the absence of digestion itself — a process that, as we know, demands a great deal of energy from the body!
Benefit no2: stimulating the emunctory organs
A 24-hour fast is a water fast: it encourages you to hydrate generously. And we all know that more often than not, we simply don’t drink enough. Yet we cannot survive without water — and beyond survival, water plays a key role in keeping the body functioning well. This is one of the real advantages of fasting: it encourages proper hydration and, in doing so, helps detoxify the emunctory organs. The kidneys, skin, lungs and intestines will naturally eliminate the water absorbed, carrying toxins along with it — a kind of detox on fast-forward! There’s another reason to drink more: during fasting, the body produces nitrogenous waste as it enters a state of ketosis. Staying well hydrated helps flush these out effectively.
Benefit no3: reducing oxidative stress
Fasting triggers a paradoxical phenomenon: it causes a slight increase in oxidative stress (an excess of free radicals in the body, which attack cells and in particular DNA), but also a greater resistance to it. In reality, the rise in free radicals is only temporary: the body responds by ramping up its production of antioxidant enzymes. By inducing mild oxidative stress, a 24-hour fast essentially prompts the body to adapt and grow stronger.
Benefit no4: improving insulin sensitivity
Could a 24-hour fast be a tool in the fight against diabetes? When practised regularly (for example, one day per week), it allows the body to secrete less insulin and, in turn, to help prevent insulin resistance. Over the course of a full day, the body no longer needs to metabolise any carbohydrates:
- the pancreas stops secreting insulin;
- blood sugar levels drop;
- the body eventually draws on its fat reserves to find energy sources;
- when normal eating resumes, the body becomes far more sensitive to insulin, meaning it is no longer produced “in excess.”
Benefit no5: reconnecting with the feeling of hunger
What happens when you stop eating? You get hungry — of course! And that’s actually a good thing, because eating is all too often driven by the clock (“it’s time to eat”) rather than by genuine hunger signals. The 24-hour fast has the distinct advantage of helping you reconnect with your body’s physiological hunger cues: a rumbling stomach, a dry mouth, a passing wave of fatigue (low blood sugar), sometimes a headache or a shift in mood. When you return to your normal eating routine, you’re better equipped to recognise when you’re truly hungry and when to stop eating (the much-talked-about satiety), because you’ve become more attuned to your body’s signals.
Common questions about the 24-hour fast
How do you start a 24-hour fast?
Whenever you feel ready — ideally choosing a quiet day with no particular social commitments: no family gatherings, no work, no plans with friends. It’s also advisable to begin your fast after dinner and break it at dinner the following day.
Is fasting for 24 hours dangerous?
Not really, provided you are in good health. One important note: a 24-hour fast is not recommended for pregnant women or those who are breastfeeding, nor for people with eating disorders or chronic conditions (including diabetes). Seeking medical advice beforehand is always a good idea!
Does this type of fast help with weight loss?
Opinions are divided. A single 24-hour fast, done once in a lifetime, will have virtually no impact on weight. If it becomes a regular habit (for example, once a week), it could potentially lead to weight loss. That said, fasting appears to have a greater effect on the weight of people who are obese than on those who are already at a healthy weight.
What are the side effects of a 24-hour fast?
They can be a little unpleasant: headaches, low energy, as well as effects on mood — including heightened emotionality and irritability — and on concentration (the brain needs glucose to function properly). That said, a 24-hour fast is short-lived, and everything returns to normal as soon as it’s broken.