There is a litany of popular diets and approaches to eating. From the Mediterranean Diet to keto, the Dash Diet to vegan, most diets are defined by what you eat (or don’t eat). However, intermittent fasting is a dietary approach that has gained traction over the past few years that instead is characterized by when you eat (and when you don’t).
Intermittent fasting involves limiting the time period in which you eat during the day and deliberately extending the period of fasting. Proponents believe it can be an effective avenue for weight loss and improve other markers of health simultaneously. To learn more about the pros and cons of intermittent fasting and how to do it, we spoke with Kayla Girgen, RD, LD, a Registered Dietician and Founder of Nutrition Untapped. If you’re looking to overhaul your eating habits and try a different approach to dieting, keep reading to see if intermittent fasting may be a helpful strategy for you.
Intermittent fasting is an umbrella term used to describe a couple of different patterns or structures of timed eating intervals interspersed with timed fasting intervals. Some of the most common types of intermittent fasting include the following:
- Time-restricted eating (TRE) or time-restricted feeding (TRF): Girgen says that TRE and TRF are interchangeable terms and refer to a reduced “eating window,” but there are many different ways to actually practice this. “It is often represented as the number of fasting hours to non-fasting hours and totals 24 hours. For example, one of the most common methods is 16:8 which involves fasting for 16 hours with an 8-hour eating window,” she explains. “This method is as simple as skipping breakfast. A person might break a fast with their first meal at 12 p.m. and finish their last meal by 8 p.m.”
- 5:2 method: According to Girgen, the 5:2 method involves restricting dietary intake to no more than 600 calories per day for men (500 calories or less for women) for two days of the week. “The calorie-restricted days should not be consecutive,” she says. “On the remaining 5 days, you eat normally.”
- Alternate Day Fasting (ADF): ADF involves fasting for 24 consecutive hours as frequently as every other day.
“Scientific evidence shows that intermittent fasting can help with weight management, improve insulin sensitivity, and reduce blood pressure,” explains Girgen. “The newest research shows promise of intermittent fasting in preventing neurodegenerative diseases such as Alzheimer’s.” Research also shows that intermittent fasting can reduce oxidative stress and inflammation.
Additional benefits of intermittent fasting include the following:
Weight loss is often a primary goal when it comes to any sort of structured diet, and according to Girgen, intermittent fasting can certainly be a successful weight loss approach for some. “Intermittent fasting can facilitate weight loss with little to no adverse side effects. Best of all, it’s free, and it can help add structure to your eating routine without much variance in what you eat,” she notes.
Improved Insulin Sensitivity
One of the primary benefits of intermittent fasting as a dietary approach to improved health and weight loss is to improve blood sugar control by reducing insulin secretion from the pancreas. When carbohydrates are ingested and get released into the bloodstream as glucose (blood sugar), the pancreas is signaled to release insulin because insulin stimulates the cells to take up and absorb the circulating glucose. “When insulin is present in the bloodstream, we have a higher likelihood of storing fat versus using it for energy,” explains Girgen. “Chronic exposure to insulin can also result in insulin resistance which is the primary cause of type II diabetes.”
Studies show that intermittent fasting can be helpful for reducing the frequency of insulin secretion and thus the resistance to it because there are fewer times, or a more limited window of time, in which the body is in a “fed” state with surges of blood sugar.
Intermittent fasting helps activate what is referred to as autophagy, a term that refers to cellular clean-up in the body. Autophagy, which was discovered in 2016 by Yoshinori Ohsumi, a cell biologist, who was awarded the Nobel Prize in Medicine for his discoveries, has been shown to help with cellular renewal, inflammation, and longevity.
In terms of dietary approaches, one of the primary benefits of intermittent fasting is that it’s flexible. “A person might fast for 16 hours per day during the workweek, and on weekends, their eating window might be longer so they can enjoy brunch with family or accommodate social outings later in the evening,” shares Girgen. “There are no hard-and-fast rules for intermittent fasting, though some individuals are more strict (on when and what they eat) than others.”
Girgen says that hunger is a common fear when starting intermittent fasting. “It’s true that hunger may be experienced in the beginning, but your body adjusts to this over time. Hunger isn’t a bad thing. On the other hand, intermittent fasting should not be miserable,” says Girgen. “Many people find they have more energy when they fast,” who advises that you should listen to your body and progress into intermittent fasting gradually.
“Headaches can be another initial side effect of intermittent fasting,” says Girgen. “To prevent them, be sure to drink plenty of water. Herbal tea and black coffee are also allowed.” She also recommends drinking electrolyte water or adding a pinch of salt to your water depending on the length of your fast to help regulate your electrolytes.
In addition to these potential drawbacks, intermittent fasting may be contraindicated for certain people depending on their health status and history. Girgen recommends that anyone interested in experimenting with intermittent fasting should consult their physician, particularly those with the following conditions:
- Type I or II diabetes (especially if you take oral medications or insulin which put you at risk for hypoglycemia)
- Low blood pressure
- Electrolyte imbalances
- On prescription medications
She adds that intermittent fasting is not appropriate for individuals who:
- Are pregnant or breastfeeding
- Are adolescents and still growing (<20 years old)
- Are underweight (BMI <18.5 kg/m2)
- Have an active eating disorder
- Have advanced kidney or heart disease
Technically, we all fast to some degree daily. Every night when you sleep, you are fasting. In fact, the word “breakfast” literally means to “break the fast.” If you happen to be the type of person who skips breakfast, you’re already unknowingly doing a version of intermittent fasting, probably along the lines of the 16:8 method. So, if you want to delve more deeply into intermittent fasting as a dietary approach, you would simply begin by being more deliberate in your fasting and eating windows and gradually modifying those intervals.
“The best intermittent fasting regimen is one that you will stick to,” advises Girgen. “It can be done short- or long-term. It is a great weight management tool, and many clients I have worked with have voiced that it is something they will practice life-long.”
Intermittent Fasting Best Practices
It’s vital to remember that intermittent fasting is ultimately only a tool, and its success as a weight loss diet is contingent upon how you use the strategy and your food and lifestyle choices. “Gorging or overeating the second your eating window opens should be avoided,” cautions Girgen. “To reap the most benefits from intermittent fasting, you have to be mindful of diet quality. Focus on minimally processed whole foods such as high-quality meats and animal products, vegetables, and healthy fats like avocado, olive oil, nuts, etc.” Not sure what that looks like practically? Girgen has some advice: “I like to recommend my clients follow the 80/20 rule: Eighty percent of what goes in your mouth is healthy, mostly whole food, and the remaining 20% is ‘fun food.’ These proportions may be adjusted to 70/30 or 90/10, for example, depending on your metabolism and health goals, but the same principles apply.
As with any of the best diets, in order for intermittent fasting to be successful, you have to make it work for you in a sustainable way. It’s key to listen to your body to determine if you’re feeling better or worse as you play with your eating and fasting windows, and adjust accordingly. Remember, your metabolism, physiology, lifestyle, and preferences are unique, so what may work best for you may be different than what works best for someone else.
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