Weight Loss

Intermittent Fasting for Weight Loss

Jacqueline Kaminski
Jacqueline Kaminski
| Stay Updated with NASM!

Intermittent Fasting… something that everyone wants to try when it comes to losing weight fast. But does it work? Are there any real health benefits to doing it? If so, what’s the best way to navigate it?

If you are wanting to learn even more strategies for weight loss, check out the free NASM mini-course on The Science of Effective Weight Loss

What is Intermittent Fasting?

First, what is intermittent fasting? Intermittent fasting is described as an eating pattern that includes hours or days of no or minimal food consumption without deprivation of essential nutrients.

Types of Intermittent Fasting

Common types of intermittent fasting include:

• Complete alternate day fasting - this method involves alternating days of fasting, where no energy/calorie-containing foods or beverages are consumed with eating days (ad libitum).

• Modified fasting or 5:2 diet - this method involves consuming 20-25% of energy needs on non-consecutive fasting days and eating ad-libitum the other five days.

• Time-restricted feeding - this method allows ad-libitum food consumption during specific feeding windows of the day. Fasting windows can range from 12-20 hours, with people most commonly fasting for 16 hours/day.

• Religious Fasting - A wide variety of fasting regimes undertaken for spiritual or religious purposes.

Is Intermittent Fasting Effective? 

Most individuals adopt intermittent fasting as a means to lose weight. But is it effective? According to several studies, subjects participating in intermittent fasting lost a significant amount of weight. However, when compared to simple calorie restriction, weight loss results were comparable.

So, if losing weight is the only reason you want to try intermittent fasting, be aware that a simple, daily calorie restriction should yield similar results.

BUT… there are some additional health benefits to fasting if choosing to adopt this eating pattern.

Inflmmatory Health Benefits of Intermittent Fasting

Studies on alternate day fasting and modified fasting (5:2) have shown improvements:

  • Inflammatory markers, including c-reactive protein (CRP), tumor necrosis factor (TNF-a) and brain-derived neurotrophic factor (BDNF)
  • Improved fasting insulin levels.
  • These fasting models showed reductions in fat cell size, cell proliferation, and levels of insulin-like growth factor in rat models.

In summary, intermittent fasting may help reduce systemic inflammation.

Fasting and Digestion Health

As of lately, there is also interest in how time-restricted feeding can help improve digestion, the gut microbiome, and sleep via our circadian rhythm. The circadian rhythm represents all the physiological processes in our body that run on a 24/hr cycle, such as sleep, hormone secretion, cognitive performance, and mood regulation.

This cycle is also highly affected by food intake, light exposure, and physical activity. Disruptions in this cycle, especially extension of eating periods, can lead to metabolic pathologies such as obesity. Therefore, research suggests that food intake's specific timing can help regulate this process, which has been shown to enhance sleep, energy levels and improve metabolic markers.

How long will it take intermittent fasting to work?

While the research is varied, some studies have shown improvements in metabolic markers and weight within two weeks of following an IF diet.

Does working out while fasting help with fat loss? Or is it better to exercise during eating windows?

When partaking in exercise fasted, a greater amount of fat is broken down and used for energy. This process is commonly known as lipolysis. However, this does not equate to more fat burning. It just means more fat is being utilized to provide the body with energy for exercise.

During fasted workouts, the body will break down stored energy in the body (from fat or stored carbs) to supply muscles with energy to perform the activity. If optimizing performance is your primary goal, fasted workouts may not be advisable since you are further depleting your body and not providing your muscles with ample energy to perform.

Additionally, eating within an hour after exercise becomes more crucial to promote recovery and stimulate muscle protein synthesis. The best recommendation would to always perform exercise close to or during feeding periods to promote optimal muscle recovery.


Overall, intermittent fasting is an eating pattern that can incur some health benefits such as decreased inflammation, improved fasting insulin levels, and moderate weight reduction or weight maintenance if feasible for your daily routine.

However, following a regular eating pattern (consuming food every 3-4 hours) with a slight calorie reduction will also lead to similar weight loss results. Before deciding to adopt intermittent fasting, you should always consult a health professional. Intermittent fasting is not always for everyone.

If you are someone who is severely malnourished or underweight, suffer from disordered eating patterns, are pregnant or breastfeeding, diabetic, or have any other chronic health conditions or metabolic disorders. Intermittent fasting may not be for you.

Additional Fasting TIps

Some additional tips if choosing to adopt an intermittent fasting eating pattern:
• Make sure you’re consuming a wide range of nutrients to avoid vitamin & mineral deficiencies.
• Include protein-rich options for all meals
• Ensure you are meeting daily calorie requirements during eating periods or days where fasting is not occurring.

The Author

Jacqueline Kaminski

Jacqueline Kaminski

Jackie Kaminski is a registered dietitian/ nutritionist with a Master's degree in Exercise Physiology & Sports Nutrition from Florida State University. Her first introduction to working with professional athletes was back in 2017 when she worked at the UFC performance institute in Las Vegas, Nevada. Since then, Jackie has worked with various professional fighters and other clientele and now operates under her company she started back in March, The Fight Nutritionist LLC. The Fight Nutritionist is dedicated to providing the most effective nutrition plans to ensure her athletes are performance at their absolute best. All of her plans are individualized to the athlete and are backed by the latest research to ensure complete safety and efficacy. Jackie is also a member of the international society of sports nutrition, where she often participates in different research projects and data collection with other ISSN members from Nova University. When Jackie isn’t working, you can find her at Combat Club where she trains kickboxing and Muy Thai. As a sports dietitian, Jackie’s aim is to provide her athletes with the necessary fuel to excel in training and provide the proper education to ensure her athletes are engaging in the safest health practices (as they relate to combat sports). You can find her on LinkedIn here.


Start Your Fitness Career Today

Become A Top-Notch Certified Personal Trainer

A NASM advisor will contact you to help you get started.

Get Started