Is Intermittent Fasting Healthy? What Dietitians Want You to Know
Before you skip breakfast... read this.
Intermittent fasting is everywhere, but is it actually supporting your health, or is it just another form of restriction? As dietitians, we look at the data—and the humans behind the data. For some, it might help with blood sugar; for others, it’s a fast track to hormone disruption and food noise.
What is Intermittent Fasting?
In short, Intermittent Fasting (IF) is an approach to eating that restricts when you can eat without necessarily restricting what you can eat. Folx who intermittently fast essentially restrict their eating to a certain amount of allotted hours during the day or limit their eating to certain days of the week and fasting the other days.
There is no standardized version of IF. Instead, there are several variations; some of the most common are listed below:
Time-Restricted Eating: Eating during a certain window of time and then fasting at a designated time. Can include the 16:8 approach (i.e., eating during an 8-hour window, fasting for 16 hours) or 12:12 (i.e., eating for 12 hours, fasting for 12 hours). .
Alternate Day Fasting: Rotating days of eating and days of fasting
Modified Fasting (5:2): 1-2 days of limited caloric intake with no restriction other days of the week.
OMAD: One meal a day
Note: There are fasting practices that are used in religious or spiritual practices, including those observed during Ramadan, Lent, Yom Kippur, and more. Please note that fasting for religious and spiritual purposes is not the topic of this blog post.
The Science vs. The Hype: Does IF Actually Work?
Many of us naturally fast while we are asleep, but IF involves extending the amount of time in a fasted state while condensing the amount of time in a day in which you can try to eat what you need to meet your nutrition needs.
People may use IF for various reasons (e.g, weight loss, disease management, health promotion), but none have sufficient evidence to support their use. Based on the current literature, IF does not lead to any clinically significant differences in weight, body composition, energy expenditure, fasting glucose, A1c, or energy intake.
The current evidence base is limited because many studies were only carried out over the short-term, there are very few human studies (most carried out with mice), and inconsistent definitions of IF in the research. We have very limited evidence to support any potential long-term effects on IF. That being said, IF is comparable to any other restrictive diet and we do have evidence for how restrictive diets impact our health and well-being.
Potential Risks: Fasting, Hormones, and Disordered Eating
At Side by Side Nutrition, we prioritize your relationship with food and your body. Intermittent fasting often acts as a "wolf in sheep’s clothing"—disguised as health, but frequently causing physiological and psychological stress.
Here are the potential risks from a weight-neutral, pro-nourishment perspective:
Hormonal Disruption: Prolonged fasting can spike cortisol (the stress hormone), which may lead to irregular cycles, hair loss, and sleep disturbances—especially for those with ovaries.
The Binge-Restrict Cycle: Ignoring hunger cues for long periods often leads to intense "food noise" and overeating once the fasting window ends, creating a cycle of guilt and physical discomfort.
Metabolic Slowdown: When the body senses a lack of consistent energy, it may lower your basal metabolic rate to "save" energy, leaving you feeling cold, tired, and sluggish.
Loss of Intuitive Signals: Fasting teaches you to trust a clock rather than your body. Over time, this numbs your natural hunger and fullness cues.
Increased Anxiety and Irritability: Low blood sugar (hypoglycemia) from fasting can lead to "hanger," brain fog, and increased anxiety.
Social Isolation: Restrictive eating windows often clash with social connections—like dinners with friends or family brunches—leading to feelings of deprivation or "missing out."
Masking Disordered Eating: For many, the rigid rules of fasting can serve as a socially acceptable way to hide or fuel disordered eating or an active eating disorder.
Weight Cycling: Fluctuations in weight loss and gain in response to unsustainable dieting behaviors like food restriction and IF. Weight cycling can have detrimental physiological and psychological effects.
Low Energy Availability: IF often leads to undereating, which can then lead to lower energy availability and, for active folx and athletes (at all levels), can negatively impact performance during activity and recovery.
A Weight-Neutral Perspective on Time-Restricted Eating ~ What Do Dietitians Recommend?
Beyond these risk factors, it is important to note that IF is NOT recommended or appropriate for children and adolescents, pregnant or lactating individuals, older adults, individuals with diabetes or blood sugar issues, individuals with an immunodeficiency, or anyone with an eating disorder or disordered eating.
Ultimately, a weight-neutral approach to time-restricted eating shifts the focus back toward your body’s internal wisdom. Instead of using a clock to dictate your hunger, we look at how the timing of your meals impacts your actual well-being—things like your sleep quality, digestive comfort, and sustained energy levels.
True health isn't found in a rigid window of restriction; it’s found in a flexible, compassionate relationship with food that honors your hunger and supports your metabolic needs without the stress of "doing it perfectly."
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