DEAR MAYO CLINIC: A friend told me that she was fasting to lose weight. I’ve tried many diets over the years with little success, so I’m thinking of trying fasting as well. Is intermittent fasting a healthy way to lose weight? Is it just skipping a meal once in a while or is there more to it?
ANSWER: One dietary trend that shows no signs of going away anytime soon is intermittent fasting. This is when you voluntarily refrain from eating or drinking anything other than water for a period of time. Some fast for religious reasons, while others fast to lose weight.
The three most popular approaches to intermittent fasting are:
- Two day fast
Eat a normal, healthy diet one day, then fast completely or eat a small meal the next day. Usually the small meal contains less than 500 calories.
- 5-2 fasting
Eat a normal diet five days a week and fast two days a week.
- Time-limited daily fasting
Eat normally but only within an eight hour window each day.
Recent research has shown that using intermittent fasting for weight loss may have some short-term benefits.
It appears that fasting for a short period of time can produce ketosis, which is a process that occurs when the body doesn’t have enough glucose for energy, so it breaks down stored fat instead. This causes an increase in substances called ketones. This, coupled with fewer calories consumed overall, can lead to weight loss. Research suggests that alternate-day fasting is about as effective as a typical low-calorie diet for weight loss.
Fasting also affects metabolic processes in the body that can help reduce inflammation, as well as improve blood sugar regulation and response to physical stress. Some research shows that it can improve conditions associated with inflammation like arthritis, asthma, and multiple sclerosis.
Little long-term research has been done on intermittent fasting to examine how it affects people over time. Therefore, the long-term health benefits or risks are unknown.
Intermittent fasting can have unpleasant side effects, such as hunger, fatigue, insomnia, irritability, decreased concentration, nausea, constipation, and headaches. Most side effects disappear within a month.
Sticking to an intermittent fasting routine may be easier for some people than trying to track calories every day. Other people, especially those with busy or fluctuating schedules, have a harder time maintaining an intermittent fasting routine.
Intermittent fasting is safe for many people, but not everyone. Skipping meals is not recommended for people under the age of 18, people with a history of eating disorders, pregnant or breastfeeding women. Athletes may struggle to refuel and refuel appropriately for an active lifestyle. If you have diabetes or other medical conditions, it is important that you speak with your health care team before beginning any type of fasting regimen.
Also note that the key to losing weight with intermittent fasting is not to overeat during your meal times. As with any weight loss plan, eating fewer calories than you expend is the foundation for weight loss.
Also, keep in mind that shortening your food window can make it difficult to get the vitamins and minerals your body needs. While on an intermittent fasting diet, it’s important to eat nutritious meals made with healthy, quality ingredients, such as fruits, vegetables, whole grains, low-fat dairy products, and lean proteins.
Intermittent fasting can be dangerous if taken too far. A technique called dry fasting restricts food and water intake. This can lead to severe dehydration and pose serious health problems. Malnutrition can occur if calorie restriction is too severe, such as a long-term average of less than 1,200 calories per day.
I always recommend that patients speak to their primary healthcare team before beginning any fasting routine to ensure there are no concerns related to other medical conditions or overall nutrition. — Romi London, RDN
clinical dietetics, mayo clinic health system,
La Crosse, Wis.
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