Written by: Marissa Dankosky, MS, RDN
Published November 20th, 2023
Intermittent fasting (IF) is increasing in popularity as a method for weight loss. By participating in IF you may have a reduction in your daily caloric intake that could lead to weight loss. Other theorized perks of IF are that it may aid in blood sugar control, burn fat, improve thinking and memory, and increase lifespan (1). Is there data to support these claims? First, it is important to know the different methods of intermittent fasting
You will need to keep an eye on the clock if you participate in the time-restricted eating method of Intermittent Fasting.
The most common IF method is time-restricted eating (TRE). This is when there is a predetermined time to fast, or, abstain from eating followed by a window of time to consume food. Calories are not restricted in the time period of eating. It is highly encouraged to eat an overall healthful diet during the period of eating versus foods high in sugar, fat, salt. Otherwise, you may not experience all the potential benefits of IF. Many participants choose a 16 to 8 hour time restriction. An example of this is eating from 11AM to 7PM then fasting from 7PM to the 11AM the next morning.
Another method of IF is alternate day fasting (ADF). There is a 5 to 2 method where participants eat for five days a week with no caloric restrictions, then fast for two non consecutive or consecutive days. Some ADF methods allow for up to 500-600 calories per day during the fasting days. You are allowed 0 calorie drinks during the fast such as water, tea, or black coffee. TRE is usually better adhered to than ADF.
So, what do the studies show? One systematic review analyzed studies published between January 2000 and June 2021 that looked at the effects of TRE and ADF on weight loss, glucose metabolism, blood pressure, and lipid labs. Most of the studies showed those who participated in IF had significant benefits on body composition, including weight loss and fat mass reduction. There was also a decrease in fasting glucose, insulin levels, and improved lipid profiles (2).
A 2023 randomized control trial found that TRE and a traditional calorie restriction (25% reduction in daily calories) found no significant difference in the participants weight loss. Both methods produced similar results, around a 5% reduction in weight over a 12 month period (3). A systematic review and meta analysis of randomized controlled trials also showed no superior improvements in anthropometrics and cardio-metabolic risk markers compared to continuous energy restriction diets (4).
It is important to note that IF is contraindicated for certain populations such as those with history of eating disorders, pregnant or lactating women, or those with diabetes. The long fasting periods could cause hypoglycemia in diabetics that are on insulin medication, that is potentially fatal if not treated in a timely manner. Restrictions in eating or dieting in general can remerge disordered eating patterns for those with history of bulimia, anorexia, or binge eating disorder.
Bottom line: IF does has data supporting its efficacy as a method for weight loss. The traditional low calorie, low fat diet for weight loss produces the same results as someone who is intermittent fasting. So, it’s really up to you. Think about your unique needs. Which diet are you most likely to stick to? Are you included in the populations where IF is contraindicated? Discuss with a trusted healthcare provider before starting IF to see if it’s right for you.