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Here are the individuals who a registered dietitian would advise against trying intermittent fasting.
Intermittent fasting (IF) has gained popularity as a strategy for shedding pounds, aiming to enhance metabolic health and reduce inflammation through cycling between periods of eating and not eating. Common IF practices include a 16-hour fast followed by an eight-hour eating period or maintaining a typical diet for five days a week, then limiting caloric intake to around 500 to 600 calories on the remaining two days.
Although IF can offer benefits, it also carries potential risks. Pregnant individuals and those with specific chronic conditions should steer clear of this approach. To gain further insight into IF, we consulted with Ana Reisdorf, MS, RD, a Registered Dietitian and the Founder of GLP-1 Hub, who explains why she advises some clients against adopting this regimen.
For individuals in their 40s, 50s, and older, IF may hinder the ability to consume enough protein daily, potentially accelerating muscle loss, which is already a concern as muscle mass diminishes with age. Furthermore, IF might lower metabolic rates and gradually increase levels of cortisol, the hormone associated with stress.
For those in their 40s, 50s, and beyond, IF can make it challenging to meet daily protein needs, which can lead to increased muscle loss. This is concerning, as muscle mass already naturally decreases with age. In addition, it can decrease metabolic rate and increase cortisol (the stress hormone) over time.
Who Shouldn’t Intermittent Fast
While IF can be a successful method for some—and there’s a ton of supporting research behind its benefits—it’s not the right path for everyone.
“In those with hormonal changes (menopause/perimenopause), high stress, or on GLP-1s, fasting can cause calorie/protein intake to drop too low, increasing fatigue, muscle loss, or hormonal dysregulation,” says Reisdorf.
Who’s More Likely To Experience Negative Effects
According to Reisdorf, women in menopause and perimenopause, those who have diabetes (especially type-1), those with greater nutritional requirements (i.e. athletes), and individuals taking GLP-1 medication are most likely to experience negative side effects of IF.
“These groups have higher protein needs, hormonal imbalances, and can’t really afford to underfuel,” Reisdorf explains.
How Common It Is To Experience Setbacks With IF
Experiencing setbacks with IF is quite common, particularly in women who aren’t already consuming sufficient calories or those under significant stress.
“Many don’t realize they’re not eating enough because of IF until they feel exhausted, their hair starts falling out, they lose muscle, or weight loss completely stalls,” Reisdorf points out.
Mental and Behavioral Challenges You May Face When Fasting
IF typically increases obsessive thoughts about food, rebound overeating, and “black and white thinking” around eating habits.
“For some, IF makes an all-or-nothing mindset worse,” Reisdorf says.
If you’re curious about what else GLP-1s can do, check out 5 Surprising Health Benefits of GLP-1 Drugs That Have Nothing to Do With Weight Loss.