Intermittent Fasting

What is it?

Common forms include: time-restricted eating within a daily window such as 8 or 10 hours; the 5:2 diet, eating normally on five days and substantially restricting intake on two days; alternate-day fasting, alternating regular eating days with very low-calorie or fasting days; and periodic fasting, fasting for longer periods at occasional intervals. The popular 16:8 pattern involves fasting for about 16 hours and eating within an 8-hour window.

What the diet emphasizes and limits

There is no universal food list. During eating periods, a person may eat any type of food, although overall food quality still matters.

During a fasting period, people may avoid all caloric foods and drinks. Some plans allow water, plain tea, or black coffee. Other plans permit a small amount of food on fasting days.

A person following intermittent fasting could still eat large amounts of sugary drinks, fried food, processed meat and refined snacks during the eating window. Fasting does not automatically make an otherwise poor diet nutritious.

A balanced version should include vegetables, fruits, beans, whole grains, fish or other protein sources and enough fluids during the eating period.

Where it came from

Fasting has long been part of religious and cultural traditions around the world. Modern intermittent-fasting plans are newer adaptations that apply fasting schedules to weight management and metabolic research.

Researchers now study several distinct approaches rather than one single “fasting diet.” These include time-restricted eating, alternate-day fasting and the 5:2 pattern. Their effects may differ depending on the fasting duration, food quality, total calorie intake, sleep and physical activity.

What the evidence says

Intermittent fasting can help some people lose weight, especially when it reduces overall energy intake.

A 2022 systematic review and meta-analysis of 17 randomized trials involving 899 adults found that time-restricted eating produced modest reductions in body weight and fat mass. However, it did not consistently improve blood pressure, body mass index, or long-term glucose control compared with control diets.

A 2026 network meta-analysis of 167 trials involving nearly 12,000 adults found that most intermittent-fasting approaches produced weight loss comparable to continuous calorie restriction when the overall amount of energy restriction was similar. The researchers concluded that the amount of energy restriction appeared more important than the timing pattern itself.

Intermittent fasting may therefore be helpful because it gives some people a simple structure for eating, rather than because fasting has a unique metabolism-resetting effect.

Who may benefit and who should be careful

Some adults with overweight or obesity may find time-restricted eating easier to follow than daily calorie counting. It may be useful for people who prefer clear meal times and do not experience excessive hunger or overeating during the eating window.

People with diabetes need particular caution. Fasting may cause low blood sugar, high blood sugar, dehydration, or medication-related complications. Medicines may need adjustment by a healthcare professional.

Intermittent fasting should not be self-started by children, pregnant or breastfeeding people, people with a current or past eating disorder, frail older adults, underweight people, or those taking medicines that require regular meals.

Takeaway

Intermittent fasting may support weight loss for some adults, but current research does not show that it is consistently better than other sustainable eating patterns.

The best plan is one that provides adequate nutrition, does not worsen a medical condition and can be followed without creating fear or rigid anxiety around food.