The one-meal-a-day diet is an eating plan that claims to help people lose weight through intermittent fasting.
When following this diet, a person will eat only one meal a day. This is usually dinner. They do not consume any other calories during the day.
Although this diet plan may offer a fast weight loss solution for some people, the risks may outweigh the benefits.
In this article, learn more about what it means to eat one meal per day, and find out more about the possible benefits and risks.
The one-meal-a-day diet is a weight loss plan in which a person eats only one meal per day. On this plan, they will not eat or drink anything containing calories for most of the day.
It is a type of intermittent fasting. It alternates long periods without eating or drinking anything containing calories with short time windows for eating.
The diet utilizes a type of intermittent fasting called 23:1. This means that a person spends 23 hours of the day fasting, leaving just 1 hour per day to consume calories.
Most people who follow this diet eat their meal at dinner time, then fast again until the following evening. However, some research suggests that eating breakfast may aid glucose control later in the day and reduce the risk of type 2 diabetes.
Other research contradicts these conclusions, suggesting that skipping breakfast may actually be a beneficial strategy for some people in managing overall calorie consumption.
For those who intend to eat breakfast and lose weight, learn which breakfast foods are best in this article.
What should a person eat on this diet?
There are several versions of the one-meal-a-day diet. Some suggest eating healthful, nutrient-rich foods, but most allow people to eat anything they want during their single meal.
People who follow the one-meal-a-day diet believe that it offers numerous benefits, such as the fact that:
- People can lose weight rapidly.
- The diet is easy to follow because there is no need to count calories.
- No food is off-limits.
Learn more about the possible benefits of intermittent fasting here.
However, there is little evidence to support the notion that the one-meal-a-day can aid weight loss.
One study in a review suggests that intermittent fasting may help people lose weight, though the authors also warn of multiple risks, such as rebound body fat increases.
Only one of the included studies focused on the one-meal-a-day pattern. Participants in this study ate their daily calories during a 4-hour window in the evening. Many saw improvements in fat mass and body weight, while others had increased cholesterol and blood pressure.
Other research, meanwhile, has concluded that alternate-day fasting was no more effective than a calorie-restriction diet in terms of weight loss, keeping weight off, cardiovascular risk, or being able to stick with the diet.
Other studies of intermittent fasting have found the following:
- Short-term fasting, in which people eat during a 4–8 hour window, may lower blood sugar levels and reduce weight in people with type 2 diabetes.
- Fasting 15 hours per day for a month may benefit a person’s overall health and, in people with obesity, boost the body cells’ ability to resist disease.
- Time-restricted feeding, or eating within an 8-hour or shorter window, turns on autophagy, which is a process that the body uses to clean up damaged material, according to a 2017 study. This may prove to be a valuable strategy in preventing and treating many age-related chronic conditions.
Many of these studies did not specifically address the one-meal-a-day option, however.
Intermittent fasting has become increasingly popular with people looking to lose weight or improve their overall health. Learn more about it here.
There has been little research into the effects of fasting for 23 hours per day. As an extreme diet plan, however, there may be risks.
For example, on a daily basis, a person may:
- feel very hungry
- experience fatigue, due to an uneven supply of energy
- feel shaky, weak, and irritable as their blood sugar levels fall
- have difficulty concentrating
For some people, eating only one meal per day may increase the risk of binge eating during the single mealtime. In some cases, following a restrictive diet can even increase the risk of developing a long-term eating disorder, according to some research.
Other problems that may arise include the following:
- The person may find it hard to eat at the single mealtime because they feel full quickly.
- Over time, their desire to eat may increase during the fasting period, rather than decrease, compared with other forms of fasting.
- Body fat may increase, rather than decrease.
- Nutrient deficiencies may occur if a person follows this diet plan long-term.
- The body may start to lose muscle mass as a person enter a state of semi-starvation.
How many calories per day does a person need? Find out here.
Effect on diabetes and cholesterol levels
People with underlying medical conditions may face additional risks. For example, those with type 1 diabetes or low blood sugar need to eat meals regularly throughout each day to maintain a steady blood sugar level.
A 2007 study compared the effect of eating the same number of calories in one or three meals per day for 6 months in a group of healthy adults.
None of the participants experienced a significant weight change, but those who ate only one meal per day experienced a reduction in body fat.
However, their levels of both low-density lipoprotein (LDL) and high-density lipoprotein cholesterol increased, and there was a negative effect on their morning glucose tolerance levels.
Metabolism and body clock genes
A 2012 mouse study suggested that eating only one meal per day may have worsen health, compared with eating two meals. In mice that consumed just one meal per day, there was an increase in body weight, insulin, and fat in the blood. There was also a higher risk of oxidative damage in fatty tissue and the liver.
The researchers concluded that eating one meal per day could negatively impact the genes that help regulate the body clock, sleep-wake cycles, and metabolism.
In another study, this time from 2017, 100 people consumed 25% of their energy needs in food on one day and 125% on the next, alternating days for a year. However, they did not restrict their intake to one meal per day.
Those who practiced this form of intermittent fasting experienced an increase in LDL, or “bad,” cholesterol. High levels of LDL cholesterol may increase the risk of high blood pressure, heart disease, and stroke.
Also, those who fasted in this way did not lose any more weight than those who reduced the number of calories they ate each day.
The one-meal-a-day diet may appeal to those looking for quick weight loss solutions, but there are safer and more healthful ways to lose weight.
Eating a healthful diet, such as the Mediterranean or DASH diet, is a good place to start.
As well as adopting a healthful diet, a person may also wish to consider:
- Regulating portion size: Eating less over several meals may be a more effective and sustainable way to lose weight.
- Reducing evening snacking: Snacking and eating large meals before bedtime may result in weight gain and increases in body fat, according to one 2012 study.
- Exercising: Guidelines recommend that adults do at least 150 minutes of moderate exercise, such as walking, each week.
- Keeping a food diary: Keeping a journal that shows what a person ate and when can help them understand how their dietary patterns affect their weight. Food journals are available for purchase online.
- Getting support: Talking to a dietitian or counselor, sharing diet plans with friends or loved ones, or joining a weight loss club may help.
- Eating a balanced diet: Adopting a healthful diet that focuses on fresh fruits and vegetables and limits processed foods may help a person lose weight and improve their overall health.
- Talking to a doctor: A doctor can check for any underlying medical conditions, such as thyroid problems, that can increase the chance of carrying excess weight.
- The best way to manage weight is by making healthful, sustainable, and long-term dietary and lifestyle choices.
Get some tips for losing weight here.
The one-meal-a-day diet is a weight loss plan in which a person eats only one meal per day and fasts for the rest of the time. This diet may help some people lose weight, but it may also carry some risks.
There is growing evidence to suggest that intermittent fasting can help some people, but little evidence supports eating only one meal per day. Scientists need to conduct more research to determine if this diet is safe and effective for weight loss.
People who want to lose weight should start by making small, sustainable changes to their diet and lifestyle.
Those interested in fasting should consider less restrictive forms of fasting. It is also best to consult a doctor or dietitian on how to lose weight safely, particularly if a person has an underlying medical condition.
Learn how to get started with intermittent fasting here.
How long is it safe to eat just one meal per day, and might there be long-term bad effects if a person carries on with it for too long?
Although fasting can be a powerful tool in a person’s health toolbox, most health professionals do not support the one-meal-a-day diet as a long-term strategy. There is not yet enough research to confirm how long it is “safe” for, or any of the possible negative effects, though rebound weight gain, increased hunger, and nutritional inadequacy are some top concerns.
Natalie Butler, R.D., L.D. Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.