Intermittent fasting is growing in popularity for its purported benefits including improved insulin sensitivity, weight loss, managing hunger cues, and increased fat burning (and this is just the shortlist). But is it for everyone? Is it safe? Is it effective over the long term? Let’s look at some facts to share with our personal training clients who are looking to embrace fasting as a practice.
Intermittent fasting (IF) means something different to everyone. Think about other dietary approaches to weight loss such as low-carb, high-protein, Ketogenic, etc. Just because an approach has a title doesn’t mean its rules and guidelines are consistent between various schools of thought.
What is Intermittent Fasting?
IF, as defined by the Academy of Nutrition and Dietetics, is the practice of restricting food and any calorie-containing beverages for a period of time (usually 16 hours). That said, you will find IF defined differently between sources.
That’s important to keep in mind as it’s not as simple as “don’t eat or drink for 16 hours”. It gets a little messy when we consider all of the different types of IF approaches.
Some alternate approaches to IF include alternate day fasting (eating every other day), meal-skipping, selective fasting (24-hour fast a couple days a week), and lean gains (16-hour fast and consuming all food within an eight-hour window) (Precision Nutrition).
What does this all mean? Simply stated, IF is an approach that includes going without food or calorie-containing beverages for specified periods of time. What that time frame looks like hinges upon the ultimate goal.
What does the research say about IF?
If we think about it, we already practice fasting. Humans (throughout history) fast. Humans fasted during scarce food sources, failed crops, poor financial status, and – as well still do – overnight. Fasting is nothing new to the human body.
What we do see is an increase in the research efforts made to determine IF’s benefits in clinical cases such as diabetes, Alzheimer’s, cardiovascular disease, and many other areas. However, questions about IF’s utility and conclusive benefits remain somewhat unanswered.
More research in humans is necessary to continue to build the body of literature and a collection of results before drawing any “cause and effect” conclusions. Some of the most exciting areas of research include IF’s potential benefits for cognitive diseases and weight loss.
One study published recently found that IF appeared to protect against cognitive decline, metabolic decrease, and dyslipidemia. This study examined IF in estrogen-deficient rats, so how these results translate to humans is still being actively studied. However, the initial results are promising. Because this study used estrogen-deficient animals, the results are also positive potentially preventing metabolic issues related to menopause.
Another area of research is particularly salient to health and fitness professionals – decreasing obesity/enhancing weight loss. A study published in 2017 used every-other-day-fasting (EODF) to examine how fasting could impact browning of white adipose tissue and gut bacteria. Interestingly, the results indicated gut microbe composition may provide a treatment for metabolic diseases and adipose tissue browning.
This is significant because we know an accumulation of white adipose tissue carries enormous consequences for health – physically and metabolically. Whereas the brown adipose tissue is metabolically active and appears to be uniquely low in obese individuals and those with diabetes (Bartelt & Heeren, 2014).
Is IF something clients should do?
No. There simply isn’t enough research (especially in humans) to conclude if this is an approach that everyone needs to try (especially in athletes as we don’t know how IF will impact performance). As we know, dieting, much like exercise, is individualized and should remain so. Further, any change in diet should be monitored by a qualified nutrition professional.
While research does indicate IF may positively impact human health, the mechanisms of action aren’t fully understood. Further, prolonged or constant fasting has consequences of its own. When it comes to our clients, this approach may not be the best (nor should we be recommending any specific dietary practice). IF can cause dizziness, nausea, fatigue, and a sense of “fog” in the brain.
If you do have a client that is interested in learning more about IF (and you will), consult with the registered dietitian in your network and guide your client accordingly.
- Academy of Nutrition & Dietetics
- Bartelt, A., & Heeren, J. (2014). Adipose tissue browning and metabolic health. Nature Reviews Endocrinology, 10, 24-36. doi: 10.1038/nrendo.2013.204
- Li, G., Xie, C., Lu, S., Nicholas, R., Tian, Y., Li, L., Patel, D., May, Y., Brocker, Cn., Yan, T., Krausz, K., Xiang, R., Gavrilova, O., Patterson, A., & Gonzalez, F. (2017). Intermittent fasting promotes white adipose browning and decreases obesity by shaping the gut microbiota. Cell Metabolism, 26(5), 801. doi: 10.1016/j.cmet.2017.10.007.
- Precision Nutrition
- Shin, B., Kang, S., Kim, D., & Park, S. (2018). Intermittent fasting protects against the deterioration of cognitive function, energy metabolism and dyslipidemia in Alzheimer’s disease-induced estrogen deficient rats. Experimental Biology & Medicine. doi: 10.1177/1535370217751610.