Intermittent Fasting: Your 2025 Guide

Intermittent fasting is a strategy that establishes eating periods to regulate caloric intake. Typically used in conjunction with exercise and healthy eating habits, they are often part of a weight loss program. Designed to help people lose weight and achieve other health and fitness goals, intermittent fasting plans are complex systems supported by wide-reaching scientific research. While some may see a weight loss benefit from skipping breakfast because they take in fewer calories on a given day, intermittent fasting offers a long-term solution to shedding unwelcome pounds and body fat.

Science Supports Intermittent Fasting

The science behind intermittent fasting demonstrates that the practice of cycling between a well-defined healthy diet based on body weight maintenance-level calories and intermittent energy restriction can positively affect metabolic risk factors. One of the health benefits that researchers and nutritionists frequently cite involves energy resourcing.

While cycling through a program that calls for modified alternate-day fasting, the body shifts from using blood glucose for energy to utilizing fat. Known as ketosis, this naturally occurring state is triggered when muscles and systems cannot retrieve enough glucose from readily available carbohydrates. The body automatically starts processing the energy stored in fat cells to make up the difference. Triggering ketosis and intermittent fasting may result in improved insulin sensitivity.

Major Intermittent Fasting Regimens

It’s essential to speak with a medical professional about making significant dietary changes, particularly if you are managing an eating disorder. The type of fasting you employ for health and weight loss purposes has a direct and discernible effect on energy levels and blood sugar consistency. These are common approaches to fasting designed to help you lose weight.

Time-Restricted Eating (TRE)

Sometimes referred to as time-restricted feeding, TRE programs create food opportunity windows. People tend to favor time-restricted eating weight loss regimens because they can follow a normal, healthy diet for much of the day. When their 6- to 12-hour eating window closes, they get a hunger reprieve by sleeping through the night. The concept runs along the lines of alternate day fasting, but focuses on zero food intake for specific times instead of scheduling extremely low-calorie 24-hour periods.

Alternate Day Fasting (ADF)

The alternate-day fasting label can be a bit misleading. It doesn’t mean not eating right one day and going without food the next. Instead, alternate day fasting focuses on following a normal diet on scheduled days and establishing a substantial calorie restriction on others. Sometimes called “feast or famine,” alternate day fasting followers can reduce their intake down to zero or institute a daily calorie restriction of 500 or higher, depending on their unique health, fitness, body composition, and needs.

It’s not uncommon for people trying to lose weight and improve their health and wellness by tweaking their intermittent fasting schedule in a variety of ways. One of the more popular tactics is to simply eat one meal during the fasting period without counting calories. In this way, the weight loss method tends to help lower the stress and anxiety that sometimes accompany fasting periods.

5:2 Diet (Periodic Fasting)

The 5:2 periodic fasting diet does not necessarily involve abstaining from food intake. This weekly weight loss program revolves around taking in a set number of calories for five days per week to promote moderate weight loss. On two of the days, periodic fasting programs call for significantly low-calorie food intake. Men typically undergo a significant decrease in calories to approximately 600, while women lower theirs to 500 to lose weight more quickly.

What many view as the big perk to periodic fasting stems from the fact that the weight management program allows you to choose a pair of low-calorie days. This flexibility helps dieters boost their food-driven energy levels to negotiate work, physical activity, and other items. That’s important because low-calorie diets tend to make people feel less energetic at first.

Eat-Stop-Eat and Extended Fasts

Popularized by Canadian author and intermittent fasting advocate Brad Pilon, the Eat Stop Eat diet regimen has been touted as a common-sense approach to weight loss. Pilon’s Eat Stop Eat intermittent fasting book series generally calls for a calorie restriction of zero for up to 24 hours, twice weekly. During the non-fasting days, people can eat relatively freely.

The Eat Stop Eat program can be a good option for people who struggle with counting calories or whose cravings for certain foods throw off their weight loss diets. This type of intermittent fasting is said to help lose weight while building muscle and deliver wide-reaching health benefits. Exercise enthusiasts can also schedule their restricted eating periods on specific days so they won’t be tasked with exercising hungry.

Religious and Cultural Fasting Patterns

People of religious faith practice intermittent fasting to draw themselves closer to a higher being and increase their spiritual awareness. While these practices are not necessarily designed to promote weight loss or benefits such as heart health, religious and cultural fasting may inadvertently support modest weight loss, even if it’s only temporary. Abstaining from specific foods, such as Catholics not eating meat on Fridays, can support heart health if this branch of Christianity replaces fatty beef with healthy fish and lower-calorie vegetarian options.

Muslims practice intermittent Islamic fasting during Ramadan, which runs from mid-February through mid-March. In many ways, Ramadan mirrors time restricted fasting because Islam fasting calls for no food or water from dawn until sunset. Coupled with other moral and ethical obligations, cultural and religious fasting practices enjoy the health and wellness benefits of secular programs. However, they are in place as ways to show devotion and gain enhanced spiritual connections.

Intermittent Fasting and Weight Loss

The human trials, research, hard data, and metrics all point to intermittent fasting delivering the weight loss benefits that everyday people desire. Aside from looking at these healthy diet programs through a scientific lens, intermittent fasting programs are supported by common sense. The underlying premise is that people who leverage an eating pattern that involves taking in fewer calories than they burn experience fat loss.

The inherent challenge of employing intermittent fasting weight loss diets is over-eating and binging after they are put to rest. It’s not uncommon for people who drop a quick 10 or 15 pounds to return to the high-calorie habits and unravel the body weight losses they enjoyed during the calorie restriction period. That’s why it’s essential to consider a long-term approach to weight loss that starts with a specific intermittent fasting option and integrates an ongoing body weight management diet. Once you’ve gotten back into smaller-sized clothes and feel good about your appearance, weight management can help buoy your confidence.

Health Benefits of Intermittent Fasting

It’s important to keep in mind that intermittent fasting programs are not another fashionable trend. We’ve all seen the kitschy diet schemes that come and go. Extensive research has been performed that indicates the effects of intermittent fasting deliver solid health and weight loss benefits.

A comprehensive review in The New England Journal of Medicine highlighted that intermittent fasting can lead to improvements in various health indicators, including insulin sensitivity, blood pressure, and inflammation markers.

Johns Hopkins neuroscientist Mark Mattson spent more than 25 years studying the effects of intermittent fasting.

“Many things happen during intermittent fasting that can protect organs against chronic diseases like type 2 diabetes, heart disease, age-related neurodegenerative disorders, even inflammatory bowel disease and many cancers,” Mattson reportedly said. Along with reductions in body fat and the intermittent fasting benefits noted by Mattson, you can anticipate the following.

• Better Insulin Stability
• Lower Blood Pressure
• Reduced Risk of Cardiovascular Disease.
• Improve Blood Sugar Control

The intermittent fasting periods someone chooses are not necessarily related to the specific benefits they gain. In other words, one program is not necessarily better in terms of weight loss than another. Rather, the macro effects of intermittent fasting go hand-in-hand with things like blood sugar regulation and body fat loss.

Potential Risks and Considerations

The adage that too much of a good thing can be a bad thing holds true when it comes to intermittent fasting. When strategically implemented with an eye toward healthy eating and smart daily calorie restriction regimens, they can prove helpful in terms of weight loss and heart health issues such as cardiovascular disease. Unfortunately, excessively low-calorie diets can have debilitating effects such as the following.

• Unsafe Blood Pressure
• Hypoglycemia (low blood sugar)
• Malnutrition
• Muscle Mass Loss
• Fatigue, Nausea, Headaches
• Trigger an Eating Disorder
• Lead to Chronic Disease
• Digestive Tract Ailments
• Sudden Post-Fasting Weight Gain

It’s important to consult with a physician or medical professional before adopting a significant weight loss program such as intermittent fasting. Understanding the potential side effects of intermittent fasting is critical to being able to make an informed decision about the eating pattern you follow. Fasting for weight loss delivers proven results only if it is conducted within clinical nutrition parameters.

Designing an Intermittent Fasting Plan

Before selecting an intermittent fasting plan, consider taking an inventory of your health, fitness and long-term weight loss goals. Ask yourself questions about why you would be fasting for weight loss? Would you be doing it to lower your blood pressure, navigate a health condition, feel more energetic, or improve your physical fitness?

Take the answers to those questions and weigh them against your lifestyle. The intermittent fasting schedule you ultimately work with must seamlessly fit into your lifestyle. These are examples of how a typical diet in this class syncs with daily routines.

• The 5:2 Program: This intermittent fasting plan allows practitioners to take in a higher number of calories five days per week. A significant daily calorie restriction is imposed on the other two. This option can prove effective for people who work full-time and need more immediate blood sugar energy during the week. They can reduce activities in conjunction with food consumption, if necessary, on the two-day weekend.
• Time Restricted Eating: This weight loss plan allows people to eat relatively freely for 6–12 hours per day. Once that window closes, food abstinence is required for the remainder of the 24-hour period. People who need quick energy from food consumption early in the day can make this work. Rather than skipping breakfast, they get an early boost and fast during the second half of the day. If you experience hunger pangs, this intermittent fasting plan allows you to sleep them off.

While these examples highlight how intermittent fasting options can be coordinated with work and lifestyles, it’s important to take a deep dive into daily nutrition and calories. A healthy weight loss approach normally reduces overall calories enough to bring about fat mass loss. By that same token, we generally need a diet that falls within clinical nutrition metrics. As you decide on intermittent fasting weight loss programs, review and assess how your food consumption measures in terms of protein, carbs, healthy fats, vitamins, and minerals. A well-crafted intermittent fasting program meets the daily nutritional values you need.

Review of Scientific Evidence

The scientific community largely agrees that an intermittent fasting approach to weight loss and fitness proves beneficial as long as nutritional metrics are met and the eating regimen accounts for health conditions. Organizations such as the National Institute of Health, Johns Hopkins, and others note the positive effects. Researchers routinely point to improved insulin sensitivity, heart health, and additional conditions that obese adults suffer from.

In healthy subjects, intermittent fasting research indicated that young males who alternated fasting and non-fasting days reduced body fat while maintaining muscle mass. Scientists point to the body’s metabolic switching from readily available blood sugar to ketones for energy as a primary driver. By that same token, people who take intermittent fasting to extremes -- not eating for upwards of 18 hours daily -- are at increased risk of gallstones and other conditions. To put it succinctly, a smartly designed and implemented intermittent fasting regimen is supported by science.

Intermittent Fasting Tools and Resources

If you are considering starting an intermittent fasting weight loss diet, it’s important to gather helpful resources. There are online intermittent fasting calculators available that can track your daily caloric intake and other nutritional factors. These tools assess your caloric burn rate based on age, height, weight, and activity level.

A foundational aspect of any intermittent fasting option involves taking in the daily recommended amounts of protein, healthy fats, carbs, and other forms of nutrition. It’s generally prudent to stick with the basic good groups and slim down calories in a judicious manner.

Exercise While Following an Intermittent Fasting Regimen at Chicago Athletic Clubs

A well-conceived intermittent fasting approach to weight loss that maintains appropriate nutritional health requirements offers statistically significant benefits. Notable fat loss, lower blood pressure, and overall body composition improvements, intermittent fasting, and smart exercise programs help further the quality of life goals that health and fitness enthusiasts pursue.

We encourage Chicago Athletic Club members to practice healthy dieting and nutritional regimens to maximize the benefits of joining our community. As a CAC member, you’ll also get access to weekly classes, yoga, Pilates, swimming pools, personal training, and more. Join today, and let’s get the process started.