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Celebrity diets continue to be a source of fascination — unfortunately. The latest attention-grabbing weight loss trend is the one meal a day, or OMAD, diet.
It’s also become a big trend on TikTok, and the hashtag #omad has accrued more than 500 million views. Videos of “omaders” boast about their significant weight loss on the diet and proudly share their one meal, which is often a staggering amount of food for a single meal, totaling 2,000 calories or more.
A search on Amazon reveals more than 300 books on the diet, with a significant number published in 2023. OMAD meal delivery subscriptions offering frozen meals to help you break your fast have popped up.
While you may be hearing more about this diet just recently, it’s actually been around for more than 10 years. It was popularized in Silicon Valley as a form of “biohacking” to increase productivity.
[READ: Can You Do Keto and Intermittent Fasting Together?]
What Is the OMAD Diet?
OMAD is an extreme form of intermittent fasting, somewhat similar to the warrior diet but even more restrictive. As the name implies, it involves eating just one big meal a day with a 23-hour fast in between. Proponents claim it is an effective way to lose weight quickly.
How does the OMAD diet work?
Like intermittent fasting, the OMAD diet doesn’t have specific macronutrient requirements or particular foods you can and can’t eat. The focus is on when you eat instead of what you eat. Here are the rules for the OMAD diet:
— Follow a 23:1 regimen. Twenty-three hours of the day are for fasting, and 1 hour is for eating.
— Keep a consistent eating schedule. Eat your one meal around the same time each day.
— Drink whenever, as long as it’s calorie-free. Water, black coffee, unsweetened tea and other calorie-free beverages are allowed during the 23-hour fast.
— Eat anything you want for one meal. There are no calorie limits or nutrition guidelines to follow for the single meal, though many OMAD dieters choose a high-fat, high-protein or keto-type diet.
Is Eating One Meal a Day Healthy: Benefits and Risks
All the social media testimonials might tempt you to try the OMAD diet, but the benefits are questionable.
“At best, it can serve as a jump-start to weight loss because it doesn’t require much thought and is relatively simple to follow,” says Lisa Drayer, a New York City-based registered dietitian. “But like other intermittent fasting programs, the OMAD diet has its limitations.”
Primarily, Drayer explains, eating one meal and fasting the rest of the day is not sustainable.
“Developing long-term healthy eating habits without severe restriction is the key to successful weight maintenance.”
[READ: Factors That Contribute to Weight Loss and Weight Gain]
Does the OMAD Diet Work?
Some research suggests intermittent fasting overall does work, although most of the studies have been small and of short duration. Seemingly only three studies have explored the OMAD diet, and two are rather alarming.
A recent European study published in Frontiers in Physiology found that a single meal per day in the evening lowered weight and fat mass more than the same amount of calories divided between three meals a day — breakfast, lunch and dinner.
However, this randomized crossover study was extremely small, involving only 11 healthy, lean adults following the OMAD diet for a mere 11 days.
An earlier study published in the American Journal of Clinical Nutrition used a similar crossover design with 15 healthy, normal-weight adults participating in two eight-week treatment periods. Calories for weight maintenance were consumed either in three meals or one meal a day.
While the OMAD diet did result in modest changes in body composition, including reductions in fat mass, it also led to increased total and LDL “bad” cholesterol and higher blood pressure levels.
A similar study funded by the National Institute of Aging published in Metabolism found that one large meal a day raised blood sugar levels and worsened morning glucose tolerance compared to three meals a day.
“We don’t have enough evidence to know if one meal a day is safe or effective,” says Krista Varady, a professor of nutrition and kinesiology at the University of Illinois, Chicago, who has been studying intermittent fasting for 20 years.
“When you squeeze in so much food in a small window of time you overwhelm your body. That’s when bad things can happen.”
[Read: Best Exercises to Burn Fat.]
Is the OMAD Diet Safe?
So, if OMAD can help people lose weight, is it bad for you? Possibly. The diet is not suitable for everyone and could do more harm than good. For instance, fasting for 23 hours can be unhealthy for people with diabetes and anyone taking medication for heart disease or high blood pressure. Children, pregnant or breastfeeding women and people with a history of eating disorders should also avoid this type of extreme intermittent fasting.
Here are the groups that researchers say should not try the OMAD diet:
— Pregnant and breastfeeding women.
— Children and teenagers.
— Older adults.
— People with a history of disordered eating.
— Underweight adults (body mass index, or BMI, of less than 18.5).
— Shift workers. Studies suggest shift workers may struggle with fasting regimens, especially during overnight shifts.
— People with medical conditions or who need medications with food at specific times.
OMAD Diet Benefits
The OMAD diet may have some benefits, including:
— Simplicity.
— Weight loss potential.
— Suggested longevity benefits.
Simplicity
The upside to this diet for many people is the simplicity — the minimal need for meal planning and complete absence of calorie tracking.
Varady says intermittent fasting may be an effective alternative for people who are burned out on traditional dieting.
“For many people trying to lose weight, counting time is easier than counting calories,” she says.
However, she was quick to point out that intermittent fasting is not a better diet. It’s just a different diet, or another option.
The OMAD diet may sound appealing to people who want to indulge and continue eating their favorite foods. The “anything goes” approach for your single meal may be freeing to dieters.
Weight loss potential
Another potential benefit of OMAD is that it may actually help you lose weight — at least in the short-term. That’s because, chances are, you’re consuming fewer calories than you would be if you were eating three meals per day.
Yet, there is no convincing evidence that the OMAD diet will lead to any more weight loss than a conventional calorie-cutting regimen. And there are also some serious downsides to the diet.
Suggested longevity benefits
Proponents of OMAD also tout the diet’s longevity benefits. It’s true that animal studies suggest that temporarily abstaining from food may increase life span.
For instance, research shows that mice who ate one meal a day with the longest fasting period had a longer lifespan and better health outcomes compared to mice who were allowed to eat around the clock. However, it’s not clear that this benefit applies to humans.
“Because human lifespan is so long, there have been no studies of the effects of intermittent fasting on lifespan in humans,” says Johns Hopkins neuroscientist Mark Mattson, author of “The Intermittent Fasting Revolution: The Science of Optimizing Health and Enhancing Performance.”
However, Mattson, who has studied time-restricted eating for 25 years, says intermittent fasting has been shown to improve biomarkers of aging and chronic diseases, such as lowering blood glucose, lipids and blood pressure. Many of these studies have looked at eating windows of six to eight hours, or two meals a day, he says.
While the evidence for longevity and intermittent fasting looks positive, Mattson says that no studies yet have compared OMAD with time-restricted eating.
OMAD Diet Risks
Following the OMAD diet may carry some risks:
— Nutrient deficiencies.
— Feelings of failure.
— Socially isolating.
— Negative health implications.
Nutrient deficiencies
It’s virtually impossible to cram in enough food to meet your full daily nutrient requirements in one meal. Can you imagine sitting down to eat 6 cups of fruits and vegetables and 4 cups of grains on your plate?
That’s why there’s a real concern that the OMAD diet could lead to nutrient deficiencies. Inadequate protein intake is especially troubling because it could lead to muscle wasting.
“Depending on one’s level of physical activity and BMI, it may be difficult to take in enough calories in one meal to maintain muscle mass,” says Mattson.
Plus, research shows that it’s better to spread your protein intake evenly throughout the day to optimize muscle growth.
While dieters may turn to supplements to help avoid nutrient deficiencies, you can’t really capture all of the complexities of real food in a pill. For instance, you’ll likely lack fiber, bioactive compounds and other healthy elements found in food.
Feelings of failure
Fasting for 23 hours straight takes willpower, and you may find yourself giving in to hunger and “cheating” during the day, then blaming yourself for not sticking to the diet. Then the cycle begins again the next day.
This can lead to an unhealthy relationship with food and further disrupt long-term weight loss goals, says registered dietitian Lisa Young, author of “Finally Full, Finally Slim” and a nutritionist in private practice in New York City.
No diet should make you feel like you failed because you didn’t adhere to the severe restrictions.
Socially isolating
“From a social standpoint, the OMAD diet can be challenging if your main meal is eaten at lunch — that would mean skipping dinners out with friends, and other celebratory gatherings that involve food — unless you are willing to simply watch others eat,” says Drayer.
Young agrees with the social disadvantages of the diet.
“You might be missing out socially due to your different eating schedule, making it difficult to involve yourself in dinners, lunches or social events — ultimately leading to feelings of isolation,” she says.
To me, it’s important to remember the other roles that food plays in our lives. Food is more than just calories and nutrients. It’s part of our culture, celebrations and joy of life.
Negative health implications
Not eating for long periods may lead to headaches, dizziness, fatigue, intense cravings and low blood sugar, also called hypoglycemia, in people with diabetes, says Drayer.
But the bigger concern is the potential long-term effects of the diet. Beyond the research mentioned earlier that found OMAD elevated cardiovascular risk factors and blood sugar levels, eating just one meal a day may lack sufficient nutrients that could result in poor immune function, decreased bone density, muscle loss (sarcopenia) and digestive issues.
Additionally, the 23-hour fasting increases the amount of ketones your body produces. These chemicals are an efficient energy source, and it’s why fasting helps burn stored fat. Yet, too many ketones can have harmful health effects, and there can be complications with calorie-restricted diets.
Alternatives to the OMAD Diet
While there may be some weight loss benefits of intermittent fasting, the OMAD diet is the most extreme form and carries multiple risks.
“You can get those same benefits in a safer way with a shorter fasting time,” says Varady.
For instance, Varady and colleagues conducted research on four-hour and six-hour time-restricted eating (such as eating between 3 p.m. and 7 p.m. or between 1 p.m. and 7 p.m.). That’s fasting for 20 or 18 hours instead of 23 hours on the OMAD diet.
They found that limiting eating during those windows of time resulted in mild reductions in body weight (about 3%) and improvements in some measures of cardiometabolic health, such as insulin resistance and oxidative stress, compared to the control group with no meal timing restrictions. It also helped avoid the gorging needed when eating is restricted to just one hour a day, which is required with OMAD.
It also may just come down to calories. The four-hour and six-hour groups consumed about 550 fewer calories a day without calorie counting. In the study, the longer fasting did not produce superior weight loss.
So, if you’re interesting in trying intermittent fasting, you may want to opt for an even shorter fasting version, such as the 16:8 method — fasting for 16 hours and eating for eight. But always seek the guidance of your physician or a registered dietitian before following any time-restricted eating plan.
Or better yet, stick with a Mediterranean-style diet that is nutritionally balanced, enjoyable and sustainable.
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What Is the OMAD Diet? originally appeared on usnews.com
Update 11/16/23: This story was previously published at an earlier date and has been updated with new information.
