In a sea of fad diets and nutrition information-overload, it can be difficult—even downright frustrating—to sort out fact from fiction. We all know that nutrition is a key component to health and wellness, so how do we determine which nutrition approach or protocol is right for us?

Answering that question is challenging, as it must be informed by many individualized factors. As always, consulting with a licensed nutrition professional or a physician is often the best starting point, but this article discusses basic information on one specific approach to nutrient intake: intermittent fasting.

What is intermittent fasting?

Whether you’re looking to decrease body fat, increase energy levels, or build muscle, you’ve likely heard the term intermittent fasting (IF) before. But what is IF and how do you use it to work toward your health and fitness goals? It’s important to understand that IF is not a diet and does not specify what a person should be eating. In general, there are no rules or restrictions on the type or amount of food to ingest (though some approaches to IF might allow a limited caloric intake during periods of fasting). Rather, it’s an eating pattern that determines when someone should eat. Essentially, IF lays out a specified window of time in a given 24-hour period during which food should be eaten. Outside of that timeframe, a person abstains from eating, thus creating intermittent periods of fasting. There are many different approaches to IF that include protocols like set eating hours each day, or set fasting days each week.

How does intermittent fasting work?

The food we eat is broken down inside the gut by digestive enzymes, allowing the nutrient molecules to be moved into the bloodstream and utilized by the body for critical processes like energy metabolism and building or repairing tissues. One of the three macronutrients, carbohydrates (the other two being fat and protein), are broken down into sugar (glucose), which is ultimately used by our cells as energy. As carbohydrates are broken down and the resulting sugar molecules enter the bloodstream, blood sugar levels rise. This rise in glucose signals the pancreas to produce insulin, a hormone that allows cells to absorb the glucose from the bloodstream. As this process continues and our food digests, blood sugar levels begin to decrease. When this process is complete, glucose remaining in the bloodstream that was not used for immediate energy will be stored inside of fat cells as potential energy. Between meals when carbohydrates aren’t readily available for use as energy, insulin levels in the body drop, allowing fat cells to release that stored glucose for the body to use as an alternate energy source.

This is where intermittent fasting can produce fat loss: fasting provides longer periods of time between meals, allowing insulin levels to drop and the body to derive energy from fat cells, over time reducing the amount of fat in the body. In other words, the body begins to “burn” fat.

It’s important to note that the studies and research on intermittent fasting are still young, and much of the evidence that exists to support its use is anecdotal. With that, there have been studies showing that when consistently implemented, IF can result in weight loss, but not more significantly than any other calorie restricted protocol. The key is that some individuals may find IF easier to adhere to than other “diets” or eating protocols. The most effective way to lose body fat is a consistent calorie deficit, which can be achieved through IF.

When should you use intermittent fasting?

As mentioned previously, IF can be effective for fat loss if a calorie deficit is achieved. However, it is possible to consume any number of calories while using IF, so fat loss is not guaranteed, nor is everyone who uses IF trying to accomplish that goal. Besides fat loss, other reasons to use IF include developing healthy and sustainable eating habits, lowering insulin levels, improving insulin sensitivity, lowering blood pressure, and decreasing appetite.

When should you avoid intermittent fasting?

One largely under-studied factor of intermittent fasting is its effects on hormone levels in the body. There is evidence to support that it may have positive effects to a certain extent—such as on insulin levels—but the endocrine system is complex and sensitive, suggesting those with hormone-related conditions should be extremely cautious in using an IF protocol. It’s also important to note that IF has significantly different effects on men and women. In women, hormones regulate key processes, such as ovulation, that are highly sensitive to energy intake (how much food is eaten). Women’s bodies are finely tuned to protect reproductive processes and potential offspring, so if the body receives signals that a woman could be starving because too much time has passed since last eating, it has the potential to shift hormone production to a detrimental level. Women can successfully use IF, but should approach it with her specific hormonal needs in mind.

People who should likely avoid IF, except under physician supervision, include women who are pregnant or breastfeeding, those with medical conditions, children, those who are new to diet and exercise, and those who experience side effects from IF that get in the way of their lifestyle, such as headaches, sleeplessness, and mood swings.

To fast or not to fast?

Intermittent fasting has anecdotal and limited scientific evidence to support that it can be a successful eating pattern for some people. After physiological and health considerations, the most important thing to consider when exploring whether IF is right for you is, can you stick to it? There are endless variations of nutrition lifestyles, diets, and eating systems, but when it comes to hitting and maintaining your health and fitness goals, the greatest predictor of long-term success is adherence.

If you’re interested in trying intermittent fasting, it’s a good idea to first do your research, talk to your trainer, and seek advice from a nutrition professional or physician. A great place to start to get your feet wet with IF is to give your body a break from eating between dinner and breakfast the next morning—generally a 12-hour window. This natural break in nutrient intake is often disrupted by late night eating or snacking. You might notice some of the benefits of IF by implementing this small change. From there, it can be easier to determine if IF is something you are interested in exploring further.


Hyatt Training personal trainer intern Elana WittAuthor Elana Witt is a personal training intern at Hyatt Training. She believes all people possess the ability to get stronger and feel better, no matter where they’re starting from. Through learning correct, functional movements, she wants each of her clients to better understand their body and their capabilities while feeling empowered to achieve their goals. Elana is a NASM certified personal trainer. Learn more about Elana, or get in touch with her by emailing us at

Hyatt Training is a collective of certified, enthusiastic and innovative personal trainers in Portland, Oregon. To read more exercise-related posts like this one, follow this link.