Intermittent fasting (IF) has become one of the most discussed diets in the United States and across the globe, with self-identified advocates of this approach touting weight loss and possibly longevity benefits. Recent science offers complexity to the benefit and risk potential of IF and emphasizes that it is not for everyone.
This article will summarize key components of intermittent fasting, based on peer-reviewed literature, comparing the health effects to traditional eating patterns, and discussing potential harms and individuals who should avoid this growing approach to eating.
Understanding Intermittent Fasting
In its simplest form, intermittent fasting describes eating and fasting at different time intervals. Common options include time-restricted eating, where individuals eat food only during a specific timeframe, such as the 16/8 or 5/2 methods, or alternate day fasting. Unlike traditional diet plans, intermittent fasting shifts the focus of the eating approach, from what you eat to when you are eating food, making it easier for those who are tired of keeping track of what foods they are eating or restricting foods. The rise in popularity of intermittent fasting is possibly linked to recommendations by celebrities, health influencers, and technology leaders that tout its weight management and prevention of disease benefits.
Promoted Benefits: Evidence from Science
Weight Management and Metabolic Health
Recently, systematic reviews and clinical trials from multiple countries indicate that intermittent fasting may be as effective as low-calorie diets for weight loss, with the alternate-day fasting pattern showing the greatest improvement in studies. Not only did individuals lose weight in these studies, but also reductions in waist circumference, cholesterol and triglyceride levels, and biomarkers of chronic inflammation were documented. Improvement in blood pressure (BP) and insulin sensitivity were also reported, suggesting that intermittent fasting has potential to help individuals at risk for metabolic disease.
Cellular Repair Mechanisms and Longevity
In animals and some human studies, metabolic switching and cellular stress response pathways are observed when organisms are fasting. These studies suggest that fasting triggers cellular repair ability and may induce longevity. If cellular repair can be enhanced with intermittent fasting, and oxidative stress reduced, then risks for many chronic diseases, such as cancer and neurodegenerative diseases, could also reduce, even though an overwhelming amount of evidence on humans is pre-clinical with more permission being warranted.
Potential Risks and Emerging Concerns
Cardiovascular Risks
Fresh evidence from major observational studies is altering the narrative of intermittent fasting as safely effective for most people. For example, a study following over 19,000 adults showed people who took eating to an eight-hour window had a 135% increased risk of dying from cardiovascular issues compared to those who had eating opportunities over a 12 to 14-hour window. Certainly, those with known heart disease or cardiovascular risk factors should exercise caution since fasting can increase physiological vulnerabilities to the heart and cause life-threatening complications like strokes and heart attacks.
Nutritional Deficiency and Side Effects
Limiting eating times can make it more difficult to consume enough calories or obtain adequate nutrients – especially, if one has higher caloric needs like children, teens, and very active adults. The most reported side effects when beginning intermittent fasting include fatigue, irritability, dizziness, constipation, headaches, and altered menstrual cycle/irregularities. In at-risk populations, fasting may worsen current illness, predispose people to loss of lean mass, impair bone health, as well as other poor eating behaviors.
Who Should Avoid Intermittent Fasting?
Current expert recommendations and recent studies are in agreement that intermittent fasting is not for everyone, and many people should avoid addressing intermittent fasting on their own or without medical or allied health professional advice. General groups of people for whom is intermittent fasting is not advisable include the following:
- Individuals with cardiovascular disease or cancer: New data shows the potential to increase risk of death from cardiovascular disease or stroke in populations.
- Pregnant and lactating individuals: Increased nutrient needs would lead to the fear of diminishing maternal and infant health.
- Children and adolescents: Children and adolescents need consistent nutrient intake to support growth; therefore, intermittent fasting may eliminate nutrient intake and compromise development and health in the long term.
- Elders: Older and elder individuals are at increased risk of muscle wasting and frailty or dietary risks for nutritional deficiency.
- Individuals with or past of disordered eating behavior: Intermittent fasting, by nature and to suitable for all, run the risk of triggering existing or adopting future unhealthy eating behavior.
- Individuals with diabetes and/or other blood sugar altering medications and insulin: Fasting can precipitate hypoglycemia or destabilize blood sugar levels, and a medical provider should be consulted about any fasting plan prior to implementing it.
- Individuals with a health condition or chronic illness: Any metabolic condition should be overseen by a physician before considering a dietary change, including thyroid.
Is Intermittent Fasting for You?
Recent studies suggest that intermittent fasting may provide metabolic and weight loss advantages comparable to conventional calorie restriction, at least in the short term. But there is still a lot of disagreement about how safe it is in the long term, especially for heart health. If you’re interested in IF, the general agreement is that you should talk to a doctor first, especially if you’re in a group that is at risk, have a long-term health problem, or take medications that are affected by your eating habits.
Health experts still emphasize that a healthy body weight, balanced diet, regular exercise, and abstaining from ultra-processed types of food are still the keys for disease prevention and health good – no matter when you eat.