August 2022 Is Intermittent Fasting Evidence-Based?
By Eliza Venetis & KRNC staff
Intermittent Fasting (IF) is trending, but what is the hype all about and what are its impacts? This approach to eating has been popularized as an effective way to lose weight and improve health, but actually the research isn’t so clear. Keep reading to learn more about IF and what the current research says (and doesn’t say).
What is Intermittent Fasting?
IF is a method of eating that focuses on when to eat rather than what to eat. It requires shortening the window of eating or limiting eating to certain days. There are three main types of IF: 5:2, 16:8 and Eat Stop Eat. All of these methods involve fasting or calorie restriction during a certain period of time with the intention to create a caloric deficit throughout the day/week.
- 5:2 Eating “normally” for five days a week and lowering calories to 500-600 per day for two days during the week.
- 16:8 Eating during an eight-hour window during the day and fasting the remaining 16 hours of the day. Research focuses on this time ratio, though some individuals opt for different eating and fasting window lengths.
- Eat Stop Eat Eating “normally” for five to six days a week and fasting for one to two days a week.
What does the research say about IF?
There are currently no evidence-based IF diet recommendations because the research is not definitive. Because there is no one standardized IF diet (see variations above), it has been difficult to achieve any consensus among the available studies. While some IF studies suggest that the dietary approach may improve biomarkers of disease, slow aging, reduce oxidative stress, and improve insulin sensitivity, many of these studies are using mice subjects and aren’t looking at long-term effects. It’s not to say that IF is definitely ineffective, it’s just too soon to tell how effective it might be given the current body of research. Especially the research surrounding IF and weight loss—these studies have been relatively short and IF doesn’t seem to have an edge over other weight loss diets. Of note, there is typically a high dropout rate in weight loss studies using IF, which demonstrates how hard it is to stick to IF in the long run.
While the benefits of long-term IF aren’t clear at this point, the risks also remain somewhat unknown. That being said, reviewing what is known about dietary restriction in research, there are some concerns that need to be considered before restricting eating in any way. IF has especially been scrutinized for its long-term sustainability. Like with any “diet”, restriction is hard to sustain long-term for psychological and physiological reasons. Namely, appetite hormones increase in the face of food deprivation. As such, weight cycling—fluctuating between weight loss and weight gain—is a common occurrence among dieters, and this can actually have detrimental physiological and psychological effects.
Here are some other things to consider about IF:
- IF may lead to inadequate eating, which can lead to decreased energy levels, mood changes, loss of muscle mass, nutrient deficiencies and malnutrition.
- IF is a form of dieting, and therefore may promote disordered eating. Dieting is often a gateway to an eating disorder and could lead to restrict-binge behaviors.
- Restriction and irregular eating patterns can worsen digestive symptoms.
- Food deprivation can compromise sleep quality.
- IF can affect blood sugar regulation and increase risk for hypoglycemia.
- IF may decrease performance during exercise due to low energy levels.
What’s the Bottom Line?
IF research is still in its infancy and there isn’t enough evidence to suggest its efficacy for long-term weight management or disease prevention/management. While some studies have demonstrated some promising results, its important to consider the limitations of the current body of research (mainly short term studies, inconsistent IF definition, and studies in mice). Also, there are important risks to consider before ever practicing dietary restriction. IF is not recommended for children, pregnant and lactating women, older adults, individuals with immunodeficiency, people with diabetes, or people with a history of an eating disorder. If you are considering practicing IF, we recommend first consulting with a registered dietitian nutritionist to understand the pros/cons as they relate to you and your unique health and nutrition needs!
About the Author:
Eliza Venetis is a graduate student at Colorado State University working towards her Master’s degree in Food Science and Human Nutrition. She is originally from the suburbs of Chicago and moved to Nashville to complete her Bachelor of Science in Exercise Science at Belmont University. Eliza is a certified personal trainer who is passionate about gastrointestinal health and eating disorders. She hopes to become a Registered Dietitian, working as a nutrition counselor with those population groups!
More Information
For additional resources for healthy eating, check out these programs from our registered dietitian nutritionists. Find delicious and healthy recipes on our Recipes page! More health tips are also available at the College of Health and Human Sciences Pinterest board. Lastly, don’t forget to sign up for the KRNC monthly newsletter!