With every new year (and newfound zest for improving our health) inevitably comes a new popular diet or fitness trend. This year, you may have heard of something called “intermittent fasting”, or IF. Unlike traditional diets, IF doesn’t restrict what foods a person should eat. Rather, it tells us when to eat and cycles periods of fasting with normal eating.
Fast. Feast. Repeat.
It may sound like a new concept, but let’s not forget our ancient ancestors who would often go hours to days between meals as food was relatively scarce. Despite their food-deprived state, they would still be able to maintain high physical and cognitive function. This practice has since been adapted into various traditions, cultures, and religions worldwide, and recent research has brought new light to this age-old topic.
What are the health benefits?
Let’s be honest, most of us (including myself) find intermittent fasting compelling for one main reason: weight loss. So, does it work? Research has shown that intermittent fasting is not only safe but also effective for burning fat and achieving weight loss. Nearly all intermittent fasting studies have resulted in some degree of weight loss (ranging between 2.5-9.9%).
A recent New England Journal of Medicine (NEJM) review article identified several other health benefits linked to intermittent fasting, including:
- Life Expectancy. Although definitive research in humans is lacking, intermittent fasting has been shown to be effective for slowing aging and prolonging life in mice and rats (increasing life expectancy by 4-27%), though the results are conflicting in our fellow primates, monkeys.
- Memory. Intermittent fasting has been shown to improve brain health and memory in older adults. Furthermore, there is strong preclinical evidence that this way of eating may delay the onset and progression of Alzheimer’s disease.
- Heart health. Intermittent fasting improves multiple indicators of cardiovascular health, including blood pressure, heart rate, cholesterol, triglycerides, glucose, and insulin.
- Cancer. Ongoing studies are looking at the effect of intermittent fasting on patients with cancer. It is thought to impair energy metabolism in cancer cells, and numerous animal studies have shown it inhibits tumor growth and makes it more susceptible to chemotherapy and radiation.
- Physical function. Some human research shows intermittent fasting can help your body retain muscle mass more effectively. Animal studies have shown better running endurance, balance, and coordination.
- Inflammation. Several studies have found that this eating pattern may reduce specific blood markers of inflammation which may have impacts for chronic diseases including asthma, multiple sclerosis, and rheumatoid arthritis.
Although the current research is encouraging, more human studies on intermittent fasting are still needed to investigate it’s sustainability, long-term outcomes, and effect on chronic diseases.
How is it done?
There are two main approaches to intermittent fasting, but it all comes down to personal preference. Select the approach that works best for you and your schedule.
Daily time-restricted feeding. In this option, you restrict your eating to a limited time each day. Benefits have been shown with as little as 12 hours of fasting, although the most effective method is the 16/8 method, or fasting 16 straight hours and consuming food during the remaining 8 hours each day. Start simply by cutting out nighttime snacking and limiting your “eating window” to 12 hours each day (for example, 8 a.m. to 8 p.m.) 5 days a week. Gradually, over a period of several months, reduce the time window during which you consume each day, with the goal of fasting for 16-18 hours a day.
Here is one approach to the 16/8 method of time-restricted feeding:
- Month 1: 12 hour eating period for 5 days a week
- Month 2: 10 hour eating period for 5 days a week
- Month 3: 8 hour eating period for 5 days a week
- Month 4 (goal): 8 hour eating period for 7 days a week
5:2 fasting. This approach focuses on reducing your caloric intake to 500 calories a day for 2 days a week and maintaining a normal, healthy diet for the other 5 days. On fasting days, it is important to focus on high-fiber and high-protein foods to help you fill up. You can decide which days are your fasting days (i.e. Mondays and Thursdays) as long as there is at least one non-fasting day between them.
Here is an example of a 5:2 eating plan:
- Month 1: 900-1000 calories 1 day per week
- Month 2: 900-1000 calories 2 days per week
- Month 3: 750 calories 2 days per week
- Month 4 (goal): 500 calories 2 days per week
But what about my morning cup of joe, you may ask? There is a great debate as to what foods and drinks will break a fast. Generally speaking, water, herbal teas, black coffee (without cream or sweeteners), and most medications are considered fine to consume during the fasting period.
What can I eat or drink?
Ok, you get through the fasting period and you finally get to eat. So, what can you eat? Technically, anything! Remember, intermittent fasting isn’t about what you eat, it’s about when. That being said, you’ll still overall want to focus on healthier food options and moderating other foods, otherwise, you may find intermittent fasting won’t be as effective.
What are the side effects?
Coming from personal experience, I will caution you that intermittent fasting can initially come with some unpleasant side effects, which I can best describe as “hangry”-ness (or, as Urbandictionary.com defines it, “When you are so hungry that your lack of food causes you to become angry, frustrated or both”).
When starting intermittent fasting and while your body adjusts to this new way of eating, you may experience hunger, irritability, difficulty concentrating, or low energy during the fasting periods. There’s good news, however! These effects are short-lived and usually resolve within a few weeks. Bottom line: keep calm and stick with it.
Who should avoid intermittent fasting?
Intermittent fasting is considered safe for most people, however, restricting calories for an extended period of time may not be best for everyone. You should talk to your provider before starting an intermittent fasting regimen if you fall into any of these categories:
- Pregnant women
- Breastfeeding women
- History of low blood pressure
- Difficulties regulating blood sugar
- History of an eating disorder
- Take medications that require taking them with food
Where do I start?
Here are some tips that can help you get started and be successful:
- Select a plan. Pick an approach best suited for you and your schedule. Start a journal if you feel that will be helpful in keeping you on track.
- Start simple. This can be challenging at first and is best used as a gradual process adopted over time.
- Eat healthy. Focus on healthy, high-fiber, vegetable-rich foods during the feeding periods and moderate other less-healthy options.
- Move your body. Engage in regular physical exercise for 30 minutes a day most days out of the week.
- Hydrate, hydrate, hydrate. Drink plenty of water.
- Relax. Practicing mindfulness and deep breathing can help cope with the “hangry”-ness.
- Be patient. Don’t expect immediate results. It can take a few weeks before your body adapts to the point where you’ll start losing weight and experiencing improved health indicators.
The One Medical blog is published by One Medical, an innovative primary care practice with offices in Boston, Chicago, Los Angeles, New York, Phoenix, Portland, the San Francisco Bay Area, Seattle, and Washington, DC.
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