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What is intermittent fasting?
Fasting for religious or cultural reasons has been practised for a long time, but using fasting for weight loss or to improve health is relatively new. Intermittent fasting is a popular way to try to reduce overall calorie intake. The method involves alternating periods of fasting with periods of eating, known as “eating windows”. There are several different types of intermittent fasting, the most common being 16:8, 5:2 and Eat-Stop-Eat.
How does intermittent fasting work?
When you follow intermittent fasting, you alternate between periods of eating and periods of fasting. During the fasting phase – which can range from 16 consecutive hours to two full days per week, depending on the method – the body has the opportunity to use its energy stores in a different way.
There are several forms of intermittent fasting, including the popular 16:8 method, where you fast for 16 hours and eat within an 8-hour window, and the 5:2 diet, where you eat as usual five days a week and restrict calorie intake to 500–600 calories on two days. Regardless of the method, intermittent fasting means giving the body longer periods without food, which encourages the use of stored energy. This can lead to weight loss and, in people with overweight, potentially positive effects on health.
Different types of fasting – 16:8, 5:2 and Eat-Stop-Eat
The 16:8 method involves fasting for 16 hours and eating within an 8-hour window. Many people skip breakfast and eat later in the day. The popular 5:2 method means eating “as usual” five days a week and consuming only 500 calories for women and 600 calories for men on the remaining two days. Eat-Stop-Eat involves a 24-hour fast once or twice a week, with normal eating on the other days. By giving the digestive system longer breaks between meals, some people may experience fewer digestive issues such as gas, bloating and stomach discomfort.
Intermittent fasting therefore focuses on when you eat. It does not provide guidance on what or how to eat – factors we know are important for weight loss, weight maintenance, health and overall wellbeing.
Health benefits of intermittent fasting – what does the research say?
Intermittent fasting can be a way to reduce calorie intake and, as a result, lose weight. Weight loss in turn has positive effects on metabolic health, including improved blood glucose control and lower blood pressure.
Some also claim that fasting has specific effects on cellular repair, known as autophagy. However, this has not been clearly demonstrated in humans. Certain effects may be possible but have not yet been confirmed in human studies. To achieve some health benefits, intermittent fasting may need to be followed for a long time, and some effects may only appear after prolonged fasting. More research is therefore needed to fully understand the long-term effects of fasting.
Disadvantages of intermittent fasting
Intermittent fasting is generally safe for healthy individuals who feel well doing it. However, certain groups should avoid it, including pregnant or breastfeeding women, people with diabetes treated with insulin, and individuals with current or previous eating disorders.
Some people experience fatigue and headaches while fasting, and others find it socially restrictive. Many people also tend to eat more healthily earlier in the day compared with evening meals and snacks. For some, eating breakfast and avoiding late-night eating may therefore be more helpful for weight loss and for establishing healthier habits.
As with any form of calorie restriction, it can be challenging to get enough protein, fibre, healthy fats, vitamins and minerals. Fluid intake may also be lower, as some of our daily fluid comes from food.
Intermittent fasting for weight loss
As with all weight loss, a calorie deficit is what ultimately matters. Intermittent fasting can be one way to reduce calorie intake during certain hours or days, but it does not guarantee a calorie deficit. Studies show that it does not appear to matter for weight loss whether calories are reduced during certain hours of the day, on certain days of the week, or evenly every day. What matters is achieving a calorie deficit through a way of eating that suits you and that you can maintain long term.
Intermittent fasting and Yazen
Intermittent fasting can generally be combined with Yazen and medical weight-loss treatment. If you have any health conditions, or if you are pregnant or breastfeeding, you should consult a doctor before starting intermittent fasting. Results may vary between individuals, and it is important to follow recommendations to ensure fasting is safe and effective.
At Yazen, we do not promote any specific diet. Instead, we focus on a healthy way of eating and living based on current nutritional guidelines. We also value personal choice and encourage eating in a way that feels manageable and sustainable in everyday life. Always consult your Yazen team before making changes to your diet, so they can help tailor adjustments to your individual needs.
Summary
- Intermittent fasting focuses on when you eat, not what or how you eat
- There are several forms of intermittent fasting, the most common being 16:8, 5:2 and Eat-Stop-Eat. Some methods involve complete fasting during the fasting period
- For weight loss, it does not appear to matter whether calorie reduction occurs at certain times of day, on certain days of the week, or daily
- With the 16:8 method, for example, you fast for 16 hours and eat within an 8-hour window
- Intermittent fasting can generally be combined with Yazen and medical weight-loss treatment
Read our article series on diets.
References
Patikorn C, Roubal K, Veettil SK, et al (2021). Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. JAMA Netw Open.
Patterson, Ruth E, and Dorothy D Sears (2017). “Metabolic Effects of Intermittent Fasting.” Annual review of nutrition vol. 37: 371-393.
Links to references:
https://jamanetwork.com/journals/jamanetworkopen/fullarticle/2787246
https://www.annualreviews.org/content/journals/10.1146/annurev-nutr-071816-064634
June 27, 2024
January 9, 2026
