Intermittent fasting goes extreme with the "One Meal a Day" diet. Here's why one registered dietitian says it's a dangerous approach.

By By Carolyn Brown, MS, RD
Credit: Photo: d3sign / Getty Images

At the start of every year, a new diet usually spikes on the ol' Google search, and inevitably some of my clients come in asking about it. Last year, intermittent fasting was all the rage. While I don't think it's for everyone (particularly current or former disordered eaters), I am a fan of intermittent fasting. Limiting your eating hours a bit can let your body stop focusing on digesting and instead spend some time on de-stressing, anti-inflammation, memory, immunity, and so much more.

But it's never a surprise to me when a good thing goes extreme. And then goes bad. That's the case of OMAD-the new diet that's seen a surge in popularity.

What Is the OMAD or "One Meal a Day" Diet?

The One Meal a Day (OMAD) diet, essentially takes intermittent fasting (IF) to the highest level. The type of IF I support and find beneficial is generally called 14:10 or 16:8 (14 to 16 hours without food, 8 to 10 hours of eating three regular meals). OMAD recommends 23:1-that's 23 hours of fasting, and one hour of eating per day. (Related: Everything You Need to Know About Intermittent Fasting)

Essentially, you can eat whatever you want during your one hour of eating. This diet is far more focused on when you're eating than what you're eating (which, as a dietitian, is one of my 100 concerns with OMAD).

There are 4 rules of OMAD:

  • Eat one meal per day.
  • Eat around the same time daily (within a one-hour window).
  • Eat off one single plate, no going back for seconds or thirds.
  • Your meal should only be 3 inches high (which I guess means you have to bring a ruler to lunch?).

This may sound outrageous-I hope it does-but the OMAD diet is gaining popularity because some celebrities and athletes (MMA fighter Ronda Rousey, for example) have talked about following it recently. And well, you know how these things catch Insta-wildfire!

There are claims that one meal a day means "deeper" benefits than are seen with standard intermittent fasting, including decreased inflammation and disease risk, and increased cellular turnover. However, there is no research yet to validate these statements. And in fact, the risks are much greater than any potential benefits.

The Risks of OMAD

When you go longer than 14 to 16 hours food-free, you run the risk of many biological issues. The first of these biological issues is, of course, being absolutely ravenous. You've probably joked about being "hangry," but the reality is that this type of restrictive eating doesn't just make you cranky. When you haven't eaten in almost a day, your body enters starvation mode. This can wreak havoc on your energy and on your metabolism (the opposite effect for anyone with a weight loss or maintenance goal in mind.)

It's also pretty much impossible to get all the nutrients you need from one meal a day, even if it's a super-healthy meal. A truly nutritious diet is about full body nourishment. It's meant to get you through your workout or work day with power and focus. I'd say this is close to impossible with OMAD.

OMAD-style dieting can also lead to serious binge eating in that one hour a day and can easily turn into "cheat day" style eating-one hour of eating whatever you want because you've deprived yourself for 23 hours. While there's a psychological component to this, it's also physiological: If you're entering a meal with low blood sugar, your body craves fast-absorbing calories, like sugar or white carbs. Eating all your food for the day in one hour can also cause serious digestive distress. (Related: How to Tell When Binge Eating Gets Out of Control)

Even more importantly, for women, hormones are extremely sensitive to blood sugar. When blood sugar dips, cortisol and other stress hormones are impacted. And when your hormones go haywire, your mood, period cycle, metabolism, and weight can all be impacted. Following OMAD will result in blood sugar fluctuations and leave you more likely to binge, followed by long-term metabolic and hormonal disruption.

All women's bodies are different-and I don't even recommend 16:8 intermittent fasting for everyone because of it. (Related: What Fit Women Need to Know About Intermittent Fasting) For example, some are much more sensitive to these longer food-free mini fasts than others. Some women need to eat first thing in the morning, while some women can wait until after a workout. Rather than listening to what you need as an individual, this diet means totally ignoring your body's individual nutritional needs, hunger cues, and daily life fluctuations (like hello, going to brunch or dinner with friends!), and blindly eating at the same time every day.

The Bottom Line

While I am generally in favor of a little self-experimentation, OMAD is just an OMG no for me. Thank u, next!

Comments (7)

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February 2, 2019
Hmmm, I've been eating OMAD (one meal a day) for more than 16 years. I've never experienced any of the supposed "biological issues" (lack of focus, digestive distress) mentioned here in this piece. Meanwhile, it's remarkably common for the mainstream several-meals-per-day population to be routinely chasing down the causes of their persistent GERD, IBS, IBD, etc., isn't it? I'm also super curious to know where these supposed "rules" listed here came from. I've never heard of them. "Eat off one single plate, no going back for seconds or thirds.", and, "Your meal should only be 3 inches high"? Who created those "rules"? Where did this author find them? Did she make them up? Not mentioned here: throughout the bulk of human history eating one meal per day has actually been more the norm than the exception. It's only recently that humans have suddenly been sold this idea that we're supposed to eat so much. Shouldn't we mention of all the "lack of focus" and digestive distress - plus serious diseases such as diabetes, heart disease, etc - that are rampant in adults and even our children now - as a result of all that overeating? I wonder how much healthier and wealthier we could be (and how much extra free time we'd all have) if one meal per day was brought back as a basic, balanced, way of life.
January 31, 2019
January 31, 2019
Fake News. Media providing false and laughably inaccurate information. It’s sad to see people trying to stop others from losing weight and being at their very best.
January 30, 2019
This article is crazy and so factually incorrect. Anyone who's lived OMAD and eats a quality healthful meal once per day knows that it doesn't make you "absolutely ravenous" or even cranky. Quite the opposite, in fact, it often balances out a person's cravings, energy and mood. And your body doesn't enter "starvation mode" - unless you're underweight and you're severely restricting your food intake. If you're a healthy weight (and especially if you're overweight, which is the case for the majority of Americans) eating a solid meal once per day is HARDLY starving oneself! OMAD also encourages us to listen to our bodies and individual needs. Eat what fuels YOUR body best. Eat a the time of day that works FOR YOU. Listen to your body, instead of blindly eating 3 times a day and mindlessly snacking. Who needs all that constant food? All that eating is, itself, is rather "extreme" and is making people fat and sick. Just look around at what it's done to the majority of people in our culture eating that way. Most of us are not out in the fields or on the farm - engaging in grueling physical labor from sun up until sun down. We eat far too much, low quality food, and far too often. And people struggle and suffer because of it. The writer of this article is just so majorly misinformed and doesn't understand OMAD, what's it actually like or all about - nor any of the science behind it.
January 30, 2019
Absolutely everything in this article is pure [filtered]. If you want the truth, read “Delay, Don’t Deny by Gin Stephens. The pseudoscience in this article is too much to refute here.