16:8 intermittent fasting, which people sometimes call the 16:8 diet or 16:8 plan, is a popular type of fasting. People who follow this eating plan will fast for 16 hours a day and consume all of their calories during the remaining 8 hours.
Suggested benefits of the 16:8 plan include weight loss and fat loss, as well as the prevention of type 2 diabetes and other obesity-associated conditions.
Read on to learn more about the 16:8 intermittent fasting plan, including how to do it and the health benefits and side effects.
16:8 intermittent fasting is a form of time-restricted fasting. It involves consuming foods during an 8-hour window and avoiding food, or fasting, for the remaining 16 hours each day.
Some people believe that this method works by supporting the body's circadian rhythm, which is its internal clock.
Most people who follow the 16:8 plan abstain from food at night and for part of the morning and evening. They tend to consume their daily calories during the middle of the day.
There are no restrictions on the types or amounts of food that a person can eat during the 8-hour window. This flexibility makes the plan relatively easy to follow.
The easiest way to follow the 16:8 diet is to choose a 16-hour fasting window that includes the time that a person spends sleeping.
Some experts advise finishing food consumption in the early evening, as metabolism slows down after this time. However, this is not feasible for everyone.
Some people may not be able to consume their evening meal until 7 p.m. or later. Even so, it is best to avoid food for 2–3 hours before bed.
People may choose one of the following 8-hour eating windows:
- 9 a.m. to 5 p.m.
- 10 a.m. to 6 p.m.
- noon to 8 p.m.
Within this timeframe, people can eat their meals and snacks at convenient times. Eating regularly is important to prevent blood sugar peaks and dips and to avoid excessive hunger.
Some people may need to experiment to find the best eating window and mealtimes for their lifestyle.
While the 16:8 intermittent fasting plan does not specify which foods to eat and avoid, it is beneficial to focus on healthful eating and to limit or avoid junk foods. The consumption of too much unhealthful food may cause weight gain and contribute to disease.
A balanced diet focuses primarily on:
- fruits and vegetables, which can be fresh, frozen, or canned (in water)
- whole grains, including quinoa, brown rice, oats, and barley
- lean protein sources, such as poultry, fish, beans, lentils, tofu, nuts, seeds, low fat cottage cheese, and eggs
- healthful fats from fatty fish, olives, olive oil, coconuts, avocados, nuts, and seeds
Fruits, vegetables, and whole grains are high in fiber, so they can help keep a person feeling full and satisfied. Healthful fats and proteins can also contribute to satiety.
Beverages can play a role in satiety for those following the 16:8 intermittent fasting diet. Drinking water regularly throughout the day can help reduce calorie intake because people often mistake thirst for hunger.
The 16:8 diet plan permits the consumption of calorie-free drinks — such as water and unsweetened tea and coffee — during the 16-hour fasting window. It is important to consume fluids regularly to avoid dehydration.
People may find it easier to stick to the 16:8 diet when they follow these tips:
- drinking cinnamon herbal tea during the fasting period, as it may suppress the appetite
- consuming water regularly throughout the day
- watching less television to reduce exposure to images of food, which may stimulate a sense of hunger
- exercising just before or during the eating window, as exercise can trigger hunger
- practicing mindful eating when consuming meals
- trying meditation during the fasting period to allow hunger pangs to pass
Researchers have been studying intermittent fasting for decades.
Study findings are sometimes contradictory and inconclusive. However, the research on intermittent fasting, including 16:8 fasting, indicates that it may provide the following benefits:
Weight loss and fat loss
Eating during a set period can help people reduce the number of calories that they consume. It may also help boost metabolism.
A 2017 study suggests that intermittent fasting leads to greater weight loss and fat loss in men with obesity than regular calorie restriction.
Research from 2016 reports that men who followed a 16:8 approach for 8 weeks while resistance training showed a decrease in fat mass. The participants maintained their muscle mass throughout.
In contrast, a 2017 study found very little difference in weight loss between participants who practiced intermittent fasting — in the form of alternate-day fasting rather than 16:8 fasting — and those who reduced their overall calorie intake. The dropout rate was also high among those in the intermittent fasting group.
Supporters of intermittent fasting suggest that it can prevent several conditions and diseases, including:
- type 2 diabetes
- heart conditions
- some cancers
- neurodegenerative diseases
However, the research in this area remains limited.
A 2014 review reports that intermittent fasting shows promise as an alternative to traditional calorie restriction for type 2 diabetes risk reduction and weight loss in people who have overweight or obesity.
The researchers caution, however, that more research is necessary before they can reach reliable conclusions.
A 2018 study indicates that in addition to weight loss, an 8-hour eating window may help reduce blood pressure in adults with obesity.
Other studies report that intermittent fasting reduces fasting glucose by 3–6% in those with prediabetes, although it has no effect on healthy individuals. It may also decrease fasting insulin by 11–57% after 3 to 24 weeks of intermittent fasting.
Time-restricted fasting, such as the 16:8 method, may also protect learning and memory and slow down diseases that affect the brain.
A 2017 annual review notes that animal research has indicated that this form of fasting reduces the risk of nonalcoholic fatty liver disease and cancer.
Extended life span
Animal studies suggest that intermittent fasting may help animals live longer. For example, one study found that short-term repeated fasting increased the life span of female mice.
The National Institute on Aging point out that, even after decades of research, scientists still cannot explain why fasting may lengthen life span. As a result, they cannot confirm the long-term safety of this practice.
Human studies in the area are limited, and the potential benefits of intermittent fasting for human longevity are not yet known.
16:8 intermittent fasting has some associated risks and side effects. As a result, the plan is not right for everyone.
Potential side effects and risks include:
- hunger, weakness, and tiredness in the beginning stages of the plan
- overeating or eating unhealthful foods during the 8-hour eating window due to excessive hunger
- heartburn or reflux as a result of overeating
Intermittent fasting may be less beneficial for women than men. Some research on animals suggests that intermittent fasting could negatively affect female fertility.
Individuals with a history of disordered eating may wish to avoid intermittent fasting. The National Eating Disorders Association warn that fasting is a risk factor for eating disorders.
The 16:8 plan may also not be suitable for those with a history of depression and anxiety. Some research indicates that short-term calorie restriction might relieve depression but that chronic calorie restriction can have the opposite effect. More research is necessary to understand the implications of these findings.
16:8 intermittent fasting is unsuitable for those who are pregnant, breastfeeding, or trying to conceive.
The National Institute on Aging conclude that there is insufficient evidence to recommend any fasting diet, especially for older adults.
People who wish to try the 16:8 method or other types of intermittent fasting should talk to their doctor first, especially if they are taking medications or have:
- an underlying health condition, such as diabetes or low blood pressure
- a history of disordered eating
- a history of mental health disorders
Anyone who has any concerns or experiences any adverse effects of the diet should see a doctor.
While evidence indicates that the 16:8 method may be helpful for diabetes prevention, it may not be suitable for those who already have the condition.
The 16:8 intermittent fasting diet is not suitable for people with type 1 diabetes. However, some people with prediabetes or type 2 diabetes may be able to try the diet under a doctor's supervision.
People with diabetes who wish to try the 16:8 intermittent fasting plan should see their doctor before making changes to their eating habits.
16:8 intermittent fasting is a popular form of intermittent fasting. Potential benefits include weight loss, fat loss, and a reduction in the risk of some diseases.
This diet plan may also be easier to follow than other types of fasting. People doing 16:8 intermittent fasting should focus on eating high fiber whole foods, and they should stay hydrated throughout the day.
The plan is not right for everyone. Individuals who wish to follow the 16:8 intermittent fasting diet should speak to a doctor or dietitian if they have any concerns or underlying health conditions.