Harvard University T.H. Chan School of Public Health: “Diet Review: Intermittent Fasting for Weight Loss.”
Is Eating One Meal a Day Safe?
The “One Meal a Day” diet, or OMAD diet, claims to help you lose weight by forcing your body to burn fat. It’s a type of intermittent fasting, which alternates between periods throughout the day in which you can eat anything and periods in which you don’t eat at all.
OMAD is particularly strict because you don’t eat for 23 hours, then consume all of your calories in a single meal.
How It Works
Like other kinds of intermittent fasting, eating one meal a day is a way of manipulating how your body finds and uses fuel. When you eat in a more traditional pattern, your energy comes from the food that you eat.
When you take in carbohydrates, your body breaks them down into sugars. If you have more sugar in your blood than you need, a chemical called insulin will carry the extra into your fat cells.
When you don’t eat for extended periods of time, your body produces less insulin. Your cells still need energy for fuel, so your fat cells release energy to compensate. For this to happen, however, you have to avoid eating for long enough that your insulin levels drop.
The Pros
Research on intermittent fasting is promising. The OMAD diet isn’t a magic bullet, but it may help some people to achieve their weight loss goals.
It may help you to burn fat. Study participants who tried eating one meal a day ended up with less total body fat. This particular group of people didn’t experience significant weight loss.
That said, intermittent fasting in general has proven to be an effective weight-loss method. The typical weight loss is 7 to 11 pounds over 10 weeks.
It can improve your metabolism. In adult men with prediabetes and obesity, a 6-hour period of eating followed by 18 hours of fasting improved their blood sugar levels.
It’s worth noting that these men followed a more general time-restricted eating plan, and not a strict OMAD diet. More research would be necessary to know whether eating one meal a day has the same effect.
You could feel more alert. When you fast during daylight hours, your body releases more of a chemical called orexin-A, which makes you feel more alert. This also isn’t specific to OMAD, and it wouldn’t apply if you ate your single meal in the morning.
Eating in the morning and fasting overnight can help you lose weight. The OMAD diet doesn’t tell you which meal to eat. That said, people who fast overnight and eat a larger meal in the morning tend to lose more weight than people who eat more at dinnertime.
The Cons
This diet is strict, and there’s no conclusive evidence that eating one meal a day works for weight control. Whether it’s worth the discomfort depends on your tolerance and body chemistry.
It can be difficult to sustain. Intermittent fasting regimens like OMAD have a dropout rate of up to 65%. It’s no easier to follow than other calorie restriction plans.
It may make you hungrier. When you eat one meal a day rather than three, your body produces more of a hormone called ghrelin, which makes you feel hungry.
It’s no more effective than calorie reduction. Even if the OMAD diet makes you feel hungrier, it’s unlikely to lead to more weight loss than if you simply reduced the number of calories you took in during the day.
Safety Concerns
For most people, there are no serious dangers involved in eating one meal a day, other than the discomforts of feeling hungry. That said, there are some risks for people with cardiovascular disease or diabetes.
Eating one meal a day can increase your blood pressure and cholesterol. This occurred in a group of healthy adults who switched to one meal a day to participate in a study. If you already have concerns in either area, eating just once a day might not be safe.
Eating one meal late can cause your blood sugar to spike. Some OMAD studies have asked people to eat their single meal between 4 p.m. and 8 p.m. These participants had morning blood sugar levels that were higher than normal, and their bodies were less able to deal with this extra sugar.
Fasting can cause blood sugar crashes. Fasting of any type increases the risk of extremely low blood sugar, also known as hypoglycemia, in people who have Type 2 diabetes.
The safety and effectiveness of any weight-loss plan are unique to each person. It’s best to speak with a doctor one-on-one if you have questions or concerns about trying the “One Meal a Day” diet plan.
Show Sources
American Journal of Clinical Nutrition: “A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults.”
Cell Metabolism: “Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes.” Harvard Health Publishing: “Intermittent fasting: Surprising update.”
Harvard University T.H. Chan School of Public Health: “Diet Review: Intermittent Fasting for Weight Loss.”
JBI Database of Systematic Reviews and Implementation Reports: “Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis.”
The Journal of Nutrition: “Meal Frequency and Timing Are Associated with Changes in Body Mass Index in Adventist Health Study 2.”
Metabolism: “Impact of reduced meal frequency without caloric restriction on glucose regulation in healthy, normal-weight middle-aged men and women.”
I Tried Extreme Fasting by Eating Once a Day — Here’s What Happened
The one meal a day (OMAD) diet is a type of intermittent fasting. With OMAD you can eat what you want, but you go without food for longer than with other types of fasting.
You could eat pizza and burgers every day, drink beer, and still lose weight — but is it a good idea?
When I started researching the One Meal a Day Diet (sometimes referred to OMAD), it was the simplicity that drew me to the plan: You eat one meal per day, consisting of whatever you want, typically at your regular dinnertime.
Super unconventional, right?
However, the OMAD is really just an extreme variant of intermittent fasting or a more hardcore cousin of the Warrior Diet. The difference between OMAD and traditional fasting is instead of fasting for the typical window, like 16 hours, you fast for about 23 hours (including the time you spend sleeping).
While the premise sounds a little shady, like a dietary supplement being hawked by a “doctor” on a late-night infomercial, let’s explore the reasoning — and science — on both sides of the debate before we totally write it off.
Most people cringe at the thought of missing a single meal. Intentionally missing all but one meal, every day, seems excessive and unnecessary. But proponents of OMAD claim a multitude of benefits, including:
- Increased focus and productivity. Who hasn’t
hit that groggy 2:30 p.m. slump at the office? OMAD is said to eliminate the
sluggishness people feel while digesting their lunch — because there is no
lunch. - Weight loss. It’s extremely hard to be at a
caloric surplus when you’re eating one time per day. Even if your one meal is
not “healthy” by normal standards, you’re not taking in as many calories as you
would if were eating all day long. - Diet freedom. Forget logging calories or
eating out of Tupperware. You free up a lot of mental energy when you don’t
have to plan four to six meals per day.
Some follow this eating pattern for religious reasons. But others, including prominent pro athletes like Ronda Rousey and Herschel Walker, voluntarily eat once a day for the long term. Walker claims to have been eating one meal a day, typically a salad and some bread in the evening, for years.
There’s even some historical evidence that the ancient Romans only ate one large meal a day before breakfast began its rise in popularity during the Middle Ages.
During my time experimenting with OMAD, I ate once a day multiple times, but never for an extended period of time. My longest streak was five days. Several times, I lifted weights, played full-court basketball, or did other types of strenuous exercise in a fasted state.
Here are my three most important takeaways from trying the OMAD diet:
1. Just because you CAN eat anything, doesn’t mean you should.
Early in my OMAD eating, I got caught up in the childlike glee of being able to eat freely.
Then I realized I had consumed only nachos, wings, and whiskey in 48 hours. This certainly isn’t the optimal fuel for a healthy body.
Yes, part of OMAD’s appeal is the fun of eating what you want, but you should strive to make your one meal balanced and micronutrient rich for the sake of your overall health.
2. It’s probably not great for serious strength training.
I’m an avid lifter. While I didn’t notice any serious loss of strength on OMAD, I wasn’t exactly plowing through the iron either.
If you simply lift for general health and aren’t concerned with performance, restricting your meals probably won’t change anything for you.
But serious lifters who care about increasing their strength over time may want to adopt a less-extreme version of OMAD, like the Warrior Diet or a typical 16:8 eating window.
3. It’s a great way to improve discipline and willpower.
One of the reasons I tried OMAD was to see if I had the mental toughness to prevent myself from eating. It was challenging — hunger is a powerful feeling. On some days I gave in and ate lunch.
But most of the time, I was proud I’d stuck to the diet and felt free to reward myself with a hearty meal. If you believe that discipline is a muscle and yours needs to be strengthened, OMAD is one way to do so, an option that will actually get you in better shape.
Like lots of health trends, just because people do it doesn’t mean it’s good for you. The research is mixed when it comes to whether or not it’s safe to eat one meal a day.
One 2007 study connects eating once a day to an increase in blood pressure and cholesterol. So if your one meal a day consists of highly processed fried foods or too many simple carbs, you’ll feel pretty bad, even if you’re losing weight.
Other risks of fasting may include:
- feeling extremely hungry or binge eating
- shakiness or physical weakness
- fatigue, or low energy
- brain fog, or trouble focusing
But a small 2017 study of 10 people with type 2 diabetes showed that fasting for 18 to 20 hours a day can lead to more controlled levels of blood glucose .
That said, if you have diabetes, long-term OMAD probably isn’t right for you. And of course, you should consult your doctor before drastically changing your diet.
Research that dates to 2005 shows that fasting can improve the body’s resistance to disease by putting cells under a “positive stress,” in a similar way that lifting weights causes tears that make muscle fibers grow back stronger.
Extended fasts where only water ingested have also been linked to a lowered rate of diseases, such as cancer and diabetes, in one 2016 study with mice as subjects.
In a 2018 chart review of 768 medical-facility patients, it was found that limited, water-only fasts did not result in any long-term medical complications.
The general medical consensus is that it’s probably safe for most healthy adults to fast every once in a while. However, the studies noted here reference general intermittent fasting or days of water-only fasting. There are not many studies specifically on the risks or benefits of OMAD.
Does that mean you should?
The answer is different for everyone. Whether or not OMAD is the right fasting diet is something you should discuss with your primary care provider.
When I decided to try OMAD a few months ago I was already doing intermittent fasting, and the idea of losing weight while eating whatever I wanted was appealing. Plus, I liked the idea of challenging myself and pushing through uncomfortable hunger pangs.
Q:
Who should not try OMAD?
A:
This is not a diet that can be sustained for a long period of time, therefore, as a Registered Dietitian, I do not endorse this weight loss diet approach.
When it comes to dieting, as a rule of thumb, people should be wary of methods and fads that presents itself as an easy fix to a complicated problem.
The OMAD diet can be extremely dangerous for children or young adults, people with diabetes or hypoglycemia, obesity, or metabolic rate issues, and it may increase the risk for binge eating.
Katherine Marengo, LDN, RD Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
Was this helpful?
Eating once a day isn’t as crazy or dangerous as you might think, but it’s not for everyone. Personally, I would not recommend it as a long-term way of eating for weeks or months at a time.
However, one 2016 study links eating one or two meals a day to a reduction in BMI , and some people have great results turning OMAD into a lifelong commitment.
Besides Herschel Walker (mentioned above), another example is Blake Horton, the ripped YouTuber who regularly posts videos of massive meals like chicken taco pizza or a 7-lb burrito of Fruity Pebbles.
Like most people, OMAD was a little too difficult for me to do every day. If you want to try fasting but are intimidated by OMAD, you could consider something more manageable for your daily meal plan, like the 5:2 Diet or the Warrior Diet.
However, I still only eat once a day every now and then, especially when I’m extremely busy or after eating a large dinner the night before. It’s also a great way to practice discipline and challenge yourself.
The key to success with OMAD, like any other diet, is to listen to your body.
Change things up if you notice serious negative effects, noting that it’s okay to be hungry from time to time. You may find yourself reaching new levels of focus and productivity as the pounds melt away.
If not, at least you’ll have fewer dishes to clean up!
Raj is a consultant and freelance writer specializing in digital marketing, fitness, and sports. He helps businesses plan, create, and distribute content that generates leads. Raj lives in the Washington, D.C., area where he enjoys basketball and strength training in his free time. Follow him on Twitter.
How we reviewed this article:
Healthline has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references. You can learn more about how we ensure our content is accurate and current by reading our editorial policy.
- Aranson T, et al. (2017). Effects of intermittent fasting on health markers in those with type 2 diabetes: A pilot study.
ncbi.nlm.nih.gov/pmc/articles/PMC5394735/ - Blake_201. (n.d.). Home [YouTube Channel] https://www.youtube.com/channel/UCay8ax_pRTYy0LUhUsFPDwA/featured
- Fessenden M. (2015). Mostly the old and ill ate breakfast until the rise of the working man.
https://www.smithsonianmag.com/smart-news/mostly-old-and-ill-ate-breakfast-until-rise-working-man-180954041 - Mattson MP, et al. (2005). Beneficial effects of intermittent fasting and caloric restriction on the cardiovascular and cerebrovascular systems.
doi.org/10.1016/j.jnutbio.2004.12.007 - Stote KS, et al. (2007). A controlled trial of reduced meal frequency without caloric restriction in healthy, normal-weight, middle-aged adults. DOI: https://www.doi.org/
10.1093/ajcn/85.4.981 - Strengthening self-control. (n.d.)
apa.org/helpcenter/willpower-self-control.pdf
Our experts continually monitor the health and wellness space, and we update our articles when new information becomes available.
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