This article has been Fact-Checked by Kendall Kennedy MS, RD, RYT
Everyone knows about eating less to lose weight but can you also eat nothing at all? If so, what are some things you need to keep in mind?
Not eating for extended periods of time, also known as fasting, is something that has been around for a long time. People have been not eating all throughout human history both for spiritual and health reasons.
Not eating can be a really helpful and healthy way to lose weight if you do it right for most people. Even though it sounds simple you can actually do a few things wrong.
How does weight loss work?
Your body uses energy all throughout the day. Exercising, walking, eating, sleeping, standing up,… all these things require energy which is measured in calories. You mainly get this energy from macronutrients: protein, fats and carbohydrates, in your food.
When you absorb more energy from your food than you burn you are left with extra energy. Your body doesn’t want this energy to go to waste so it stores it for later use. Fuel from carbohydrates gets stored as glycogen in your liver and muscles up to a point. Once those places are full excess fuel from carbs gets stored as body fat. Excess energy from fat gets stored as body fat too.
In prehistoric days this process was very useful. Humans didn’t always have calorie sources readily available. Every tiny amount of energy had to be stored to survive. These days calorie dense food is easily available. The problem is that excess body fat is bad for your health.
Luckily you can do this process in the other way too by absorbing fewer calories than you use. When this happens your body turns to stored energy, glycogen and body fat, for energy. If you keep this up long enough the stored body fat will get used up.
So to lose weight you have 2 options. Absorb fewer calories or increase the amount of energy you use. By not eating you can reduce the amount of calories you absorb from food for a while and lose weight.
Difference between not eating and not eating enough
At first, it might sound weird but there is a difference. Not eating at all puts your body in a fasted state. This can have all kinds of health and weight loss benefits.
Not eating enough, on the other hand, can cause weight gain. It can make you feel hungry and it can slow down your metabolism because of muscle loss and hormonal changes.
In general, a healthy calorie deficit is about 500 calories a day. If you start at a very high weight you can go more in the direction of 1000 calories. More than those numbers and you can get in the “not eating enough” zone. You can lose weight in the short term in this zone but sooner or later you will regain the weight.
Additional benefits of not eating
Not eating is not just good for weight loss because you consume less calories. There are also other health and weight loss benefits to it.
Can help manage blood glucose levels
Not eating can help you control blood glucose and insulin levels (1, 2). This is almost certainly great against diseases like diabetes. Lower insulin levels can potentially promote fat burning. This can lead to a better body fat to muscle mass ratio (3). In turn that would be beneficial for long term weight loss and health.
May increase metabolism
Besides avoiding a lot of calories by not eating, you can potentially improve your metabolism for a while (4, 5). This won’t come down to 100’s of calories but small bits add up.
Can benefit long term health
Fasting can also benefit your long term health by reducing inflammation, reducing risk on cancers, and reducing risk on diseases like Parkinson’s and Alzheimer’s (6, 7, 8, 9, 10).
It would be great to see more research regarding fasting but so far it looks like a promising habit for health and weight loss.
Different durations
How long you want to stop eating for weight loss depends on a few factors. There are different common durations with different advantages and disadvantages.
Longer durations will help you lose more weight if you do them right. The downside is that they are harder to stick to and involve more risks.
Time restricted eating
The first way of not eating for weight loss is something called time restricted eating. This involves only eating calories within a certain time period each day. Some common durations are 8 hours, 10 hours, and 12 hours a day but shorter is possible too. This also means not adding any creamers to your coffee or having any alcoholic drinks after dinner.
When you do it is your choice. In general, doing this earlier in the day would be better. Your body is better able to deal with food closer to waking up. However, for social reasons many people choose to skip breakfast and stop eating after dinner which is usually at 6 or 7 p.m.
Time restricted eating is great because it doesn’t require too much preparation or attention to detail. It’s fairly easy for most people to get enough nutrients and to stick with it. Initially, you might feel hungry at times you used to eat but this usually stops after a few days.
Not eating for 24-48 hours
The next duration of not eating is between 1 and 2 days.
Your body stores vitamins and minerals for later use. The thing is that these stores can run out. This doesn’t happen often within the first 24 hours but after that, you need to keep this in mind.
Some of the stores that often run out first are salt, potassium, and magnesium. Certainly when you sweat and exercise a lot. When you don’t eat for 24-48 hours and longer it can be necessary to supplement with certain micronutrients. For example by adding salt to the water you drink.
Depending on the rest of your diet, other stored micronutrients can run out too. If your diet has not been healthy up to this point you might want to stick to time restricted eating.
Once you start eating again, you want to start with something light in a small quantity. for example some yogurt with berries.
Extended periods of not eating
After that you have extended fasts which can last up to whatever duration, a few days, a week and even longer.
Extended periods of not eating are not recommended without expert guidance. Vitamin and mineral deficiencies are no joke. They can have serious side effects both in the short and long term. You would have to supplement with exactly the right things. Even then extended fasts can be something your body is not equipped to deal with right now.
Different ways to do not eating for weight loss
Besides different durations you have also different guidelines on what you can consume during the fast. Both have their advantages and disadvantages.
Water fast
A water fast is basically eating and drinking nothing besides water. The advantage is that you give your digestion some rest. The downside is that you risk micronutrient deficiencies when you do this for too long.
In general a water fast is mostly for durations up to 24 hours. After that, you might want to supplement with certain nutrients. Avoiding deficiencies is more important.
Calorie fast
A calorie fast means that you are still consuming things like vitamins, minerals, and calorie-free drinks like coffee and tea. This method can be both healthier and easy to stick to. It can be surprisingly hard to taste nothing but water if you’re not used to it.
You get most of the advantages for weight loss with both methods. In terms of health, it can be helpful to give your digestion some rest too. Avoiding vitamin and mineral deficiencies is a bigger priority.
Possible side effects of not eating
While not eating can certainly offer many benefits for losing weight, there are also some potential side effects. Sometimes doing a few small things can help you avoid these side effects.
- Hunger
- Weak
- Tired
- Dizzy
- Headache
Potential headaches are often because of low salt and water intake. This is easy to solve by adding some salt to a glass of water and drinking it. You can also supplement with other electrolytes like magnesium and potassium.
It’s possible that your body is not used to converting fat into usable energy. This can lead to you feeling tired, hungry, and weak. Over time these things should go away. One way to avoid this is by eating a lower-carb diet leading up to your time period of not eating.
Micronutrient deficiencies
This is a potential downside of not eating extended periods of time. You have to consume more food in a shorter amount of time to reach your daily requirements. Vitamins and minerals are important for both short and long term health and weight loss.
With lower durations like time-restricted eating, this shouldn’t be too much of a problem. On the other hand, doing multiple 24 hour periods of not eating a week could cause this if you don’t pay enough attention to your diet.
Potential for disordered eating
While it can definitely offer benefits, fasting can also become an unhealthy habit if done incorrectly and with the wrong mindset.
Besides the potential physical health consequences of disordered eating, it can also be a reason for unhealthy emotions about food. This in turn can lead to more negative physical health side effects.
If you notice you are developing some kind of disordered eating due to fasting you likely want to postpone doing it for now. Talking about this with friends, family, and mental health professionals may help you avoid disordered eating.
People who shouldn’t fast
It can be helpful to talk to your doctor before making any drastic lifestyle changes. Certainly, if you are one of the following people:
- Pregnant and breastfeeding women
- People who have (had) an eating disorder
- People under 18
- People with diabetes
- People who are recovering from surgery
- People who take medication
Tips for not eating for weight loss
There are some things you can do to make not eating more comfortable and better for weight loss.
Eat the right things before you start
By eating the right foods before your fast you reduce the risk of running out of certain nutrients. Consider eating these foods:
These foods are often high in important nutrients but also lower in refined carbohydrates. The nutrients will help you feel better and healthier. Avoiding refined carbohydrates will allow you to have more energy during your period of not eating.
Not eating and working out
You can still do most exercises in a fasted state. The only workout you might want to avoid is weight lifting. It’s likely that you won’t have the energy to do a good weight lifting workout. On top of that, your body doesn’t get the nutrients it needs to repair your muscles.
In terms of other workouts, you have to see how you feel. Some people can do their regular cardio and HIIT workouts. Others take it easy with just some walking.
Duration is again something that makes a big difference. With time restricted eating you should be able to do any workout. With longer fasts even a light cardio exercise might be too much.
Drink enough water
The food you would normally eat contains water. Staying hydrated is important for both short term and long term health. This means that you should drink a little more water than usual to make up for not eating any food.
On top of the health benefits, drinking water can also help you with losing weight by reducing appetite and increasing the amount of calories you burn.
Don’t overeat after
Not eating can backfire for weight loss if you can’t control your portions after the fast. Certainly the first few times you try fasting you might feel hungry after. This can lead to overeating if you don’t control yourself.
You can overeat both on healthy food and unhealthy food. That being said, it’s harder to overeat on whole foods like vegetables, meat, and complex carbohydrates. If you stick to these foods after your period of not eating you should be alright.
Should you use not eating for weight loss?
Not eating for a period of time can be very helpful for weight loss. For most people, there are mostly potential advantages once you get over the initial hunger and adaptation period. If you pay attention to what you eat and drink you can avoid most problems.
Do keep in mind that permanent weight loss is about permanent changes. The only way fasting helps you lose weight in the long term is if you do it regularly. Not too often, of course, if you choose the longer time periods. That would lead to problems.
