Intermittent Fasting
Intermittent fasting is a pattern of eating based on time limits. For a set time of hours or days, you eat a typical diet. At the end of the set time, you switch to very few or no calories, called fasting.
Alternate-day fasting means eating a typical diet one day and no meals the next day. One example is 5:2 fasting, also called twice-a-week fasting. This means you eat very little or nothing two days a week. The other five days you eat a typical amount of calories.
Alternate-day modified fasting is eating a typical diet one day and only about 25% of your typical calories the next day.
The idea is that intermittent fasting causes the body’s cells to change how they work. Timed eating may push cells to focus on repair, energy use and balancing body-wide functions.
Research shows that intermittent fasting may improve some signs of health in the short term. These include:
- Blood sugar.
- Weight.
- Blood cholesterol.
- Blood pressure.
- Chronic inflammation.
But the long-term health effects of intermittent fasting aren’t clear. And some studies find just limiting calories in general may have the same benefit as intermittent fasting.
Also, researchers don’t know if different fasting cycles have the same benefits. Some evidence suggests that a 16-hour fasting, 8-hour eating cycle may raise heart disease risk compared with other time-restricted eating cycles.
Intermittent fasting also may cause people to feel very tired and dizzy. It can affect diabetes management and cause headaches or mood swings. Intermittent fasting also may cause constipation and affect the menstrual cycle.
Although it may appear to be a new trend, intermittent fasting has been popular for over 1,500 years. While we know that it works for some people to lose weight, the reality is that whether or not it helps organs such as the heart is still to be determined. Early research presented at a recent scientific meeting suggested that intermittent fasting might be harmful or risky in general. It showed that people practicing intermittent fasting are twice as likely to die from heart disease or die in general than those who don’t practice.
The main problem is that intermittent fasting is not standardized. There are many ways to do intermittent fasting. Over the past few decades, it has been popularized in the UK as “eat whatever you want for five days, then don’t eat for two full days other than fluids and soups.” People were losing weight, and from that point on, people started adapting to fasting in very different ways. Some people will restrict their time for eating to 10 a.m. to 3 p.m., for example. The most common form of intermittent fasting I have seen is that people just skip breakfast.
Whether breakfast is “the most important meal of the day” is still under debate. Skipping breakfast historically hasn’t been something necessarily healthy. It is not fully understood why, but there are numerous studies showing that people who skip breakfast have an increased risk for heart disease and other ailments. Early morning is the time when people have the most heart attacks. Part of the reason for that is the high-adrenaline state that occurs early in the morning. If you match that with no food, no calories at all, that might be the reason why studies show that people practicing intermittent fasting are not necessarily healthier or safer. I think that’s important to keep in mind.
People who lose weight through intermittent fasting can benefit their overall health, but that doesn’t necessarily mean that they have to continue forever. We have to consider many other factors when people don’t have breakfast or other meals. Stress hormones go up, which may increase blood pressure and adrenaline, causing many changes in our system that might actually be more harmful than beneficial.
When patients ask if intermittent fasting is healthy, the response should be, “It all depends.” If they start skipping dinner, having very light dinners or just trying not to have dinner too late, that’s an excellent way to practice. Or perhaps having a very light lunch or skipping lunch altogether — just not necessarily going for too long with no food.
Studies show that having multiple small meals throughout the day versus just two big meals results in better cholesterol and many other positive changes in the metabolism. So, this idea of not having any food or calories for long periods of time is still under debate. Based on recent evidence, intermittent fasting is particularly unsafe for patients with heart disease or with a history of heart disease. Practicing intermittent fasting can be safer with supervision from your healthcare team.
Limiting what you eat to a small part of each day is called time-restricted eating. This can mean fasting for up to 16 hours a day. But fasts of 6 to 8 hours also are common.
Some people eat earlier in the day and fast in the afternoon and evening. Others fast in the morning, eat around midafternoon then fast again in the evening.
Only eating during a short window often means skipping breakfast or dinner. If those meals are important parts of your social life, then intermittent fasting may not work for you.
While intermittent fasting is safe for many people, it may not be a healthy pattern for people who:
- Have an eating disorder.
- Are pregnant or breastfeeding.
- Are at high risk of bone loss and falls.
If you’re thinking about intermittent fasting, talk to a healthcare professional about the pluses and minuses. Other eating patterns might work as well or better depending on your health goals.
One diet trend that shows no sign of going away soon is intermittent fasting. That’s when you voluntarily abstain from food or beverages other than water for a certain amount of time. Some fasting is for religious reasons, while others fast for weight loss.
The three most popular approaches to intermittent fasting are:
- Alternate-day fasting
Eat a normal, healthy diet one day and then completely fast or have one small meal the next day. Usually, the small meal is fewer than 500 calories. - 5-2 fasting
Eat a normal diet five days per week and fast for two days per week. - Daily time-restricted fasting
Eat normally but only within an eight-hour window each day.
Recent research has found that using intermittent fasting for weight loss may have some benefits in the short term.
It appears that fasting for a short 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 may work to decrease inflammation, as well as improve blood sugar regulation and physical stress response. Some research shows this may improve conditions associated with inflammation like arthritis, asthma and multiple sclerosis.
Little long-term research has been conducted on intermittent fasting to examine how it affects people over time. As a result, long-term health benefits or risks are unknown.
Intermittent fasting can have unpleasant side effects, like hunger, fatigue, insomnia, irritability, decreased concentration, nausea, constipation and headaches. Most side effects go away within a month.
Sticking with an intermittent fasting routine can be easier for some people rather than trying to watch calories every day. Other people, especially those with busy or variable schedules, have more difficulty maintaining an intermittent fasting routine.
Intermittent fasting is safe for many people, but it’s not for everyone. Skipping meals is not recommended for people under 18, those with a history of disordered eating, or those who are pregnant or breastfeeding. Athletes may find it difficult to fuel and refuel appropriately for an active lifestyle. If you have diabetes or other medical issues, it is important that you talk with your health care team before starting any type of fasting regimen.
Also, note that the key to achieving weight loss with intermittent fasting is not to overeat during your eating windows. As with any weight loss plan, eating fewer calories than you expend remains the basis for losing weight.
Also, keep in mind that shortening your eating window may make it difficult to get the necessary vitamins and minerals your body needs. While on an intermittent fasting diet, it is important to eat nutritional meals made from quality, healthy ingredients, such as fruits, vegetables, whole grains, low-fat dairy and lean protein.
Intermittent fasting can be dangerous if taken too far. A technique called dry fasting restricts food and fluid intake. This can result in severe dehydration and pose serious health concerns. Malnutrition can occur if the caloric restriction is too severe, such as averaging fewer than 1,200 calories per day long term.
I always recommend patients speak to their primary health care team prior to beginning any fasting routine to ensure there are no concerns related to other medical conditions or overall nutrition.
References
intermittent fasting (mayoclinic) (https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/expert-answers/intermittent-fasting/faq-20441303)
Is intermittent fasting a helpful practice or health risk? (mayoclinic) (https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-is-intermittent-fasting-a-helpful-practice-or-health-risk/)
Is intermittent fasting good for weight loss? (mayoclinic) (https://newsnetwork.mayoclinic.org/discussion/mayo-clinic-q-and-a-is-intermittent-fasting-good-for-weight-loss/)
Related Topics
Other Specialities
Fasting
Fasting refers to abstaining from food and drink for a certain period of time, usually in line with religious beliefs. Fasting, practiced by Muslims during Ramadan, covers a period from sunrise to sunset. Some of the benefits of fasting can include resting the digestive system, weight control and regulating metabolism.
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