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Calorie restriction is the first advice you will hear when it comes to losing weight. Since overeating is considered a culprit when it comes to gaining excessive weight, limiting the total calories you eat in a day can lead to weight loss in the long term.
Experts recommend limiting calories between 20% and 50% based on the amount of weight you want to lose as well as the total calories you consume, to begin with. (1)
But weight loss is not the only benefit of calorie restriction. Studies have found calorie restriction to: (1)
- Increase lifespan by two- to threefold
- Reduce the risk of type 2 diabetes
- Prevent the occurrence of chronic illnesses such as heart disease
- Reduce the risk of cancer
- Improve the function of the nerves, brain, and immune system
While limiting the total amount of food you consume throughout the day or choosing low-calorie options is one way to restrict calories, another effective way is to fast. (2)
The good news is there are various fasting methods you can choose to obtain health benefits.
How to Fast for Weight Loss
Fasting is simply abstaining from food for a set period. When you fast, you end up limiting the total calories consumed throughout the day.
There are different patterns you can follow so you can stick to fasting long term or until you achieve your desired results.
1. Time-restricted fasting
Also known as intermittent fasting, time-restricted fasting employs avoiding solid foods and drinks that contain many calories (such as fruit juice or milk) for a few hours each day. The usual split is avoiding food for 16 hours and eating during the remaining 8 hours. (3)
The idea behind time-restricted fasting is that during the period of fasting, the body switches over to fat stores to burn for energy which when combined with limited caloric consumption helps in losing weight faster. (4)
You can follow this pattern of fasting by eating your dinner by 8 pm and breaking your fast at noon the next day. Until 8 pm that day, you can eat and drink normally.
2. Alternate-day fasting
As the name suggests, alternate-day fasting means fasting every other day. However, in such a fasting method, you don’t completely abstain from food.
On the fast day, you can consume about 25% of calories, which usually amounts to 500 calories. The next day, you can eat a healthy amount of calories for your weight. (5)
These diets are well-tolerated for short periods (8–12 weeks) and produce the same amount of results as those of a 3%–7% daily calorie restriction (300–500 calories per day). (5)
Other benefits users have reported include: (5)
- Improved insulin sensitivity
- A reduction in blood pressure
- Some improvement in the levels of LDL, total cholesterol, and triglycerides
Studies have reported alternate-day fasting to also bring about similar weight loss results as daily calorie restriction. (6)
3. 24-hour fasting
Another way of fasting is fasting for 24 hours once or twice a week and eating normally the remaining days of the week. (6)
During the 24-hour fasting period, the body empties its glycogen reserves from the liver and switches over to the stored fat in the body to burn for energy. This process kick-starts the weight loss process. (7)
How to Eat on a Fast: Expert Recommendations
While fasting is an effective technique to lose weight, and though most fasts don’t place restrictions on the type of food being consumed during the eating windows, you need to choose your meals with care.
1. Choose high-protein foods
Foods that are high in protein, such as chicken, turkey, fish, eggs, and yogurt, are all valuable contributors to a healthy diet.
Not only does a high protein diet prevent the loss of muscles when you fast, but it has also been found to bring about weight loss while preventing weight regain. Protein-rich foods are able to modulate hormones to increase satiety and feeling of fullness, which is very useful in preventing the feeling of hunger during the fasting period. (8)
2. Eat lots of fruits and vegetables
Fruits and vegetables are rich sources of dietary fiber and water, which can help increase the feeling of fullness and prevent hunger. (9)
Studies have found green leafy vegetables, berries, and citrus fruits to bring about the most weight loss. (9)
3. Hydrate well
While you can consume water during the fasting windows of the different types of fasts mentioned in this article, increasing the amount of water you drink can also be a useful way to add to the weight loss progress.
Studies have reported drinking enough water (3–3.5 liters) each day can contribute to weight loss by: (10)
- Increasing the feeling of fullness
- Influencing the body’s hormones to increase fat burning
4. Avoid high-sugar, high-fat foods and alcohol
High-sugar foods such as cookies, biscuits, pastries, cakes, and packaged fruit juices are the biggest contributors to obesity. These foods also often contain high amounts of fat, which further increase the risk of obesity. (11)(12)
Moreover, alcohol contains empty calories and does not contribute any nutrients to the diet. Instead, it can be a risk factor for obesity. (13)
When you consume such high-calorie foods in your eating window, you are not likely to see any weight loss despite fasting.
Precautions to Consider
While fasting is beneficial and safe for most people, you need to be careful with it and assess its suitability for you. Fasting is not recommended for: (14)
- People with type 1 diabetes who are dependent on external insulin
- Pregnant or breastfeeding mothers
- Those at risk of or are recovering from an eating disorder
- People with hormonal imbalances specifically hypothyroidism
Does fasting cause anemia?
Fasting doesn’t prohibit you from eating foods rich in nutrients that contribute to healthy hemoglobin levels. So, it does not cause anemia. However, if you are already anemic, it is better to avoid fasting.
How long should I fast to achieve weight loss?
It can take 8–12 weeks to see beneficial results from fasting, but the fasting duration also depends on your weight loss goal and health condition. (5)
- Fasting is a way to restrict calories and bring about weight loss.
- Based on the duration of fasting and how you split your eating and fasting window, you can follow three main types of fasting.
- In time-restricted fasting, you eat during a few hours of the day and fast for the remaining.
- In alternate-day fasting, you consume very minimal calories (500 calories) on one day and eat normally on the other day.
- In 24-hour fasting, you often fast for 24 hours once or twice a week and eat normally on the other days.
- All types of fasts bring about similar weight loss results as those from daily calorie restriction.