The popularity of intermittent fasting has grown in recent years, but this trendy dietary lifestyle is hardly new. History shows that this age-old eating practice has been embraced by everyone from ancient Greek civilizations to monks to Native Americans. Below, we take a deep dive into intermittent fasting, including different ways to make it work for you.
What Is Intermittent Fasting?
“Intermittent fasting is a term used to describe various eating patterns that cycle between scheduled periods of eating and not eating,” says Mopelola Adeyemo, MD, MPH, a clinical instructor in the division of clinical nutrition at UCLA Health in Los Angeles. “It’s a form of caloric restriction, so during the fasting periods you eat either very little or nothing at all.”
Previous generations adopted this eating pattern to improve their spiritual, mental, and physical health. But today, the main focus is on weight loss.
Does Intermittent Fasting Work for Weight Loss?
Any time you’re in a calorie deficit, you’re more likely to lose weight. By restricting when you eat, you often eat less simply by skipping meals. However, a recent study conducted at the University of Illinois Chicago concluded that when 90 adults categorized with obese BMIs were divided into three groups — one control group, one group that reduced calories by 25 percent, and one group that only ate during an eight-hour window — there was virtually no difference between the group that reduced calories and the one that followed an intermittent fasting pattern.
How Does Intermittent Fasting Impact Hunger?
If you’re worried that restricted eating windows may make you even hungrier, rest assured this isn’t typically the case, at least not for the long term. “When you’re first starting, it’s common to experience increased hunger or cravings as your body adjusts,” says New York City–based Amy Shapiro, RD, founder of Real Nutrition NYC. “The adjustment period typically lasts for a few days and may affect hormone levels involved in hunger and satiety. Some research suggests that fasting may potentially reduce hunger and increase feelings of fullness over time.”
How Much Weight Can You Lose on Intermittent Fasting?
The amount of weight you will lose while intermittent fasting largely depends on several factors, including your average calorie intake, age, sex, activity level, and, of course, your genetics.
“A recent review of 27 clinical trials on intermittent fasting found that individuals lost between 0.8 and 13 percent of their body weight with intermittent fasting,” says Dr. Adeyemo. “Study durations ranged from two weeks to 26 weeks. Still, it is important to remember that every individual is unique, so responses will vary. To achieve the best results, pair intermittent fasting with adequate exercise and healthy food choices.”
How Does Intermittent Fasting Compare to Other Strategies for Weight Loss?
The truth is that intermittent fasting may work wonders for your weight loss goals or not do anything at all. “The best diet for weight loss is one that aligns with the individual and their preferences and health goals,” says Shapiro. “You should also make sure that you’re promoting sustainable eating habits and getting a balanced intake of nutrients. It’s most important to choose a dietary approach that you can maintain long term.”
Types of Intermittent Fasting
There are several different variations of intermittent fasting, so it’s important to find the method that works best for you. Adeyemo breaks down the basics below.
Time-Restricted Eating
This is the most popular method, according to Adeyemo. “It involves eating during an 8-hour window, then fasting for 16 hours,” she says. “Another method is 12:12, which involves a 12-hour fasting period followed by a 12-hour eating window.”
Alternate-Day Fasting
Alternate-day fasting, says Adeyemo, requires you to fast for 24 hours followed by an eating period. “For example, you don’t eat from lunch one day until lunch the next day,” she explains. “This can be done a few times per week on nonconsecutive days and involves eating normally on your non-fasting days.”
Modified Fasting
“Also known as the 5:2 method, modified fasting involves eating 20 to 25 percent of your estimated caloric needs on fasting days, then 125 percent of your caloric needs on non-fasting days,” says Adeyemo.
Pros and Cons of Intermittent Fasting, According to a Lose It! Dietitian
The simplicity of intermittent fasting may sound appealing, especially if you’ve struggled with fad diets in the past, but the truth is that there are still plenty of factors to consider before you adopt this dietary lifestyle. We recently chatted with Anna Smith, a registered dietitian for Lose It!, about the pros and cons of intermittent fasting. Here’s what she had to say.
Pros of Intermittent Fasting
It’s flexible. “There’s not as much emphasis on what to eat. This freedom feels nice if you’re used to diets that restrict food groups or if you need a break from counting calories.”
It’s simple. “If you’re a habitual breakfast skipper, waiting to eat until later is usually not a huge adjustment.”
It forms good habits. “It sets a firm boundary in the evening to help you break any mindless nighttime munching.”
It’s good for your health. “It can be a good plan for weight loss, but many also see improvements in their lipids and blood pressure, according to research.”
Cons of Intermittent Fasting
It can be tough if you have an erratic schedule. “It can be a really difficult diet to adhere to for those who work 12-hour shifts like nurses or find themselves up late like Uber drivers and students. You may need a snack to fuel your energy levels.”
It may stifle your social life. “Social gatherings can be tricky if they are outside your eating window.”
You might not lose weight. “While the emphasis is technically on when to eat, it is possible to go over your calorie goal in your eating window. If you suddenly have to restrict when you eat and what you eat, it can feel overly restrictive.”
There can be side effects. “Research shows that headaches, mood swings, and constipation are some of the most common side effects.”
Is Intermittent Fasting Right for Everyone?
Like any big lifestyle change, intermittent fasting isn’t right for everyone. Certain members of the population — including people who are pregnant or breastfeeding, individuals with diabetes, anyone who’s had an eating disorder, children, and adolescents,according to Johns Hopkins Medicine — should assess their health status before adopting this eating plan because the risks can outweigh the benefits in some cases.
“Fasting periods can serve as a trigger for disordered eating,” says Adeyemo. “For people with diabetes, alternating between fasting and feeding periods may require adjustments in medications to prevent varying blood sugars. And if you’re pregnant or breastfeeding, the body requires more calories to maintain breast milk supply or provide adequate nourishment to a growing fetus. So it’s important to talk to your healthcare provider before starting any new diet.”
Tips to Get Started on Intermittent Fasting
If you’ve decided intermittent fasting is the perfect way to meet your weight loss goals, you’re definitely in good company. A 2022 survey of 901 Americans ages 19 to 81 concluded that 80 percent of them had dieted at some point in their lives, and 44 percent of them were currently on a diet. The most popular way to lose? You guessed it! Intermittent fasting.
Not sure how to get started? Rest assured it’s easier than it sounds, so don’t be intimidated. Shapiro shares her top five tips for beginners here.
- Start slowly, and gradually increase your fasting window over time.
- Stay hydrated to reduce feelings of hunger. Consider consuming herbal tea, black coffee, and sparkling water during your fasting periods to curb your appetite.
- Focus on nutrient-dense foods during periods of eating and avoid highly processed or sugary foods.
- Listen to your body and remain aware of how it feels during periods of fasting and eating.
- Be patient and remind yourself of the initial adjustment period and the importance of consistency if you want to experience any potential health benefits.
The Bottom Line
Intermittent fasting has been around for thousands of years, but it’s recently had a huge surge in popularity among celebrities and many others looking to drop unwanted pounds. Although the plan is incredibly flexible with several different eating methods, it isn’t a one-size-fits-all solution for weight loss woes. Always consult your doctor first and carefully weigh the risks and benefits before changing your current eating plan.
“The most important thing to consider when choosing a diet is to choose one that best aligns with your lifestyle and is sustainable,” says Adeyemo. “Intermittent fasting is not superior to other diets, but it has been shown to have numerous benefits. However, any significant changes in your diet should always be discussed with your healthcare provider to ensure that the changes match with your health needs and goals.”
Editorial Sources and Fact-Checking
- Ravussin E et al. Early Time-Restricted Feeding Reduces Appetite and Increases Fat Oxidation but Does Not Affect Energy Expenditure in Humans. Obesity (Silver Spring). August 2019.
- Lin S et al. Time Restricted Eating Without Calorie Counting for Weight Loss in a Racially Diverse Population. Annals of Internal Medicine. June 27, 2023.
- Welton S et al. Intermittent Fasting and Weight Loss: Systematic Review. Canadian Family Physician. February 2020.
- Naous E et al. Intermittent Fasting and Its Effects on Weight, Glycemia, Lipids and Blood Pressure: A Narrative Review. Nutrients. August 2023.
- Shalabi H et al. Intermittent Fasting: Benefits, Side Effects, Quality of Life, and Knowledge of the Saudi Population. Cureus. February 2023.
- Intermittent Fasting: What Is It, and How Does It Work? Johns Hopkins Medicine.
- 2022 & 2023 Intermittent Fasting Statistics and Trends. VitalityPro. 2022.
