There has been a lot of buzz in the media around intermittent fasting (IF), but what exactly is it?
While fasting for religious or cultural reasons is not new, the idea of intermittent fasting for weight loss or improved health is a relatively new practice.
What is intermittent fasting?
Intermittent fasting is an eating plan that alternates between periods of fasting and periods of unrestricted food intake. The 3 most common forms of intermittent fasting are time-restricted eating, alternate day fasting, and 5:2 intermittent fasting:
- Time-restricted eating is a daily eating window followed by a period of fasting. You may hear people say they are on a 16:8 plan which is referring to 16 hours of fasting followed by an 8 hour eating window. For example, a person would eat from 11am to 7pm and fast from 7pm to 11am the following day.
- Alternate day fasting (ADF) is where a person would alternate every other day between fasting or reduced calorie intake (typically ~25-40% of energy requirements or 500-700 calories) and unrestricted intake on other days of the week.
- 5:2 intermittent fasting is a plan in which a person has 2 days of fasting or reduced caloric intake (typically 500-700 calories) and 5 days of unrestricted intake.
Does intermittent fasting promote weight loss?
You may have heard that intermittent fasting can help you lose weight, but what does the research actually tell us?
A recent review article in the Journal of American Medical Association (JAMA) looked at the results of many studies to evaluate the effectiveness of different forms of fasting including alternate day fasting, 5:2 intermittent fasting, and time-restricted eating. They found the only fasting regimens that promoted weight loss were the ADF and the 5:2 regimen. While weight loss was statistically significant for the study, it was fairly modest ranging from 2-10% of body weight. They also found that IF was only beneficial as a weight loss approach for the first 1-6 months after which many participants would hit a weight loss plateau, likely due to their metabolism becoming adapted to this style of eating and to less adherence to the plan.
Another study also found that when subjects skipped the breakfast meals, there was an increase in the hunger hormone (ghrelin) and a decrease in their fullness or satiety hormone (leptin) after the lunch meal, which may lead to greater energy intake later on in the day.
Who should avoid intermittent fasting?
Intermittent fasting is not recommended for those with a history of eating disorders, people with diabetes on insulin, adolescents or anyone in an active growth stage or while pregnant or breastfeeding.
In general, it is recommended to check with your clinician before starting a special diet or eating pattern.
What about intermittent fasting while on GLP-1 agonist or other weight loss medications?
We don’t recommend intermittent fasting for most people on these medications, as the appetite suppression component of these medications can already make it more challenging to meet nutrient needs.
By shortening our eating window or severely restricting calorie intake, it becomes more difficult to consume enough energy, protein, fiber, healthy fats and vitamins and minerals which may put put you at risk for:
- Nutrient deficiencies
- Muscle loss and wasting
- Hair thinning, fatigue, and difficulty with concentration
- Reducing your metabolism which will make it difficult to continue to lose weight
While intermittent fasting focuses on when you eat, it doesn’t provide any guidance on what to eat which we know to be the most important factor in both weight loss and overall health and wellness. At the end of the day, a calorie deficit still remains the most reliable and studied method for weight loss, and a calorie deficit is not guaranteed simply by limiting your eating window.
While IF may work for some people, it doesn’t work for all people. For more guidance on a specific nutrition plan that is best for you, visit with one of our Sequence dietitians!
