- How It Works
- 7 Methods
- Who Should Avoid It
While most diets focus on what to eat, intermittent fasting focuses on when you eat. It’s a popular health and fitness trend that alternates between fasting eating, where you fast for a set amount of time before eating again.
There are different fasting schedules you can try, but the principle is roughly the same: you eat only during a specific period of time, and avoid consuming anything other than water and other noncaloric beverages during the fasting period.
How does intermittent fasting work?
The food we eat is broken down into macro and micronutrients. Carbohydrates, such as rice and starchy vegetables, get broken down into glucose and used for energy. Unused glucose gets stored in the liver and muscles as glycogen and fat in the fat cells.
7 ways to do intermittent fasting
There are several methods of intermittent fasting, varying in the fasting period and the calorie allowances. Since different methods may suit different people, you may want to experiment to see what works best for your lifestyle and preferences.
Before embarking on an intermittent fast or deciding how often to fast, it is important to talk to a medical professional about potential benefits and risks, especially if you have a medical condition.
Below are 7 popular methods of intermittent fasting:
- 16/8 method: Involves fasting for 16 hours and restricting the eating window to 8 hours. Within the eating window, you can fit in 2-3 or more meals.
- 12-hour fast: Involves a 12-hour fasting window every day. The easiest way to do the 12-hour fast is to include sleep in the fasting window.
- The 5:2 diet: Involves eating normally for 5 days of the week and restricting calorie intake to 500-600 calories for 2 days of the week.
- Alternate-day fasting: Involves fasting every other day either by not eating anything or eating about 500 calories on fasting days.
- Eat stop eat: Involves 1-2 complete 24-hour fasts per week. Fasting from dinner one day to dinner the next day amounts to a full 24-hour fast. This is an extreme form of fasting and is not recommended.
- The warrior diet: The warrior diet involves eating small amounts of raw fruits and vegetables during the day (a 20-hour fasting window) and eating 1 huge meal at night within a 4-hour eating window.
- Meal skipping: Another way to do intermittent fasting is to occasionally skip 1-2 meals according to your hunger levels or time constraints. This flexible approach may be good for beginners, since you don’t need to follow a structured plan to reap benefits.
What are the benefits of intermittent fasting?
Studies show that intermittent fasting may have health benefits, including:
- Weight loss: Calorie deficit, increased metabolic rate, and enhanced hormone function can contribute to weight loss.
- Reduces risk of diabetes: Reduced insulin resistance can lower blood glucose and insulin levels if you are at risk of diabetes. It may also help those who suffer from polycystic ovarian disease by reducing insulin levels.
- Lowers cholesterol: Improved lipid profiles, including lower overall cholesterol, low-density lipoprotein (LDL), and triglyceride levels, have been linked to intermittent fasting.
- Improves heart health: Intermittent can help prevent heart disease, as well as recovery after a heart attack, by:
- Improves brain health: Emerging evidence shows that intermittent fasting may play a role in the suppression of inflammation in the brain, thus reducing the risk of neurological disorders, such as Alzheimer's disease, Parkinson's disease, and stroke.
- Reduces oxidative stress: Studies show that intermittent fasting may reduce oxidative stress, which causes aging and many chronic diseases.
- Reduces inflammation: Intermittent fasting has been shown to reduce concentrations of pro-inflammatory markers, such as homocysteine, interleukin 6, and C-reactive protein, which play a role in the development of these chronic diseases (such as atherosclerosis, osteoporosis, heart disease, and diabetes).
- May help prevent cancer: Research indicates that intermittent fasting may delay the growth of tumors and reduce the risk of cancer, although further research is needed.
- Induces cellular repair: Evidence suggests that intermittent fasting increases the frequency of autophagy, removing unwanted and dysfunctional cells. Increased autophagy prevents several diseases, including cancer, inflammatory diseases, neurodegenerative diseases, and cardiovascular diseases.
- May extend lifespan: Intermittent fasting may increase overall quality of life and reduce the risk of developing chronic diseases. Weight loss, decreased blood pressure, and other benefits may contribute positively to extending lifespan.
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What are possible drawbacks of intermittent fasting?
Potential risk factors associated with intermittent fasting include:
- Weight gain: Some people indulge in binge eating behavior during non-fasting periods. Eating more calories than you burn will lead to weight gain.
- Feelings of being sick: Long periods of fasting can lower blood sugar levels and may cause headaches, lethargy, crankiness, constipation, dizziness, or nausea.
- Dehydration: Intermittent fasting is sometimes associated with dehydration because when people don’t eat, they sometimes forget to drink.
- Nutrient deficiencies: Not getting enough calories or not eating healthy food to meet basic needs can lead to nutrient deficiencies, decreased immunity, and lower energy levels.
- Sleep disturbances: Intermittent fasting may cause decreased rapid-eye movement (REM) sleep, leading to sleep disturbances. This can affect memory, cognitive processing, and concentration.
- Fatigue: Fasting can increase stress levels, leading to tiredness, fatigue, or brain fog.
- Mood changes: The biochemical that regulates appetite also regulates mood. Dysregulating appetite may cause mood changes or irritability.
- Hair loss: Sudden weight loss or nutrient deficiency, especially protein and B vitamins, can lead to hair loss.
- Menstrual cycle changes: Insufficient calorie intake, sudden weight loss, or being underweight can disrupt the hormone cycle and cause missed periods.
- Eating disorders: Skipping meals or restrictive eating may lead to eating disorders in some cases.
- Dangerous if taking certain medications: Intermittent fasting can be dangerous for people who take medications for blood pressure or heart disease, as they may be prone to imbalances of sodium, potassium, and other minerals during intermittent fasting.
How to reduce side effects of intermittent fasting:
- Consider a simpler method of intermittent fasting.
- Slowly reduce the time window for eating over a period of several months to help your body adjust.
- Avoid binge eating during non-fasting periods.
- Be active throughout the day so that your body can burn fat.
- Drink plenty of water or calorie-free beverages to stay hydrated.
Who should avoid intermittent fasting?
Individuals with the following health conditions should avoid intermittent fasting:
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Patterson RE, Laughlin GA, LaCroix AZ, et al. Intermittent Fasting and Human Metabolic Health. J Acad Nutr Diet. 2015;115(8):1203-1212. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516560/
de Cabo R, Mattson MP. Effects of Intermittent Fasting on Health, Aging, and Disease. N Engl J Med. 2019 Dec 26;381(26):2541-2551. https://www.nejm.org/doi/full/10.1056/nejmra1905136
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