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Is The 'One Meal A Day' Diet Safe? Here's What You Need to Know
Diet & Exercise

Is The 'One Meal A Day' Diet Safe? Here's What You Need to Know

How much fasting is too much fasting?

It’s a major trend that’s known by a lot of names. Time-restricted eating. Intermittent fasting. Eating windows. The Warrior Diet. The list goes on.

In case you haven’t heard of it, here’s another term to add to your vocabulary: OMAD, or the ‘one meal a day’ diet.

RELATED: How to Properly Meal Prep and Why You Really Should Be Doing It

As the name implies, the OMAD diet consists of restricting your meals to once a day with no snacking in between. It’s essentially a more extreme version of intermittent fasting, or IF, which involves restricted ‘feeding times’ along with longer periods of fasting. 

Is this style of eating restriction a good idea? Read on to learn the pros and cons of the OMAD diet. 

The OMAD Diet Defined

woman sitting on couch

As mentioned, the OMAD diet is an extreme form of intermittent fasting. For instance, one of the most common ratios for IF involves 16 hours of restriction with 8 hours of feeding time, also known as the 16:8 diet.

The OMAD diet lengthens the restriction time to essentially 23 hours, shrinking the feeding period to about an hour for a 23:1 ratio. Part of the gimmick of the OMAD diet is that you can theoretically eat whatever you want for that one hour window and still maintain or even lose weight. The diet has some high profile followers, including athletes like pro wrestler Ronda Rousey and former pro football player Herschel Walker

RELATED: Hunger Vs. Appetite: Knowing the Difference Will Help Your Fitness Goals

Of course, these top-level athletes aren’t using their single meal to binge on candy and junk food. For instance, Walker’s diet mostly consists of vegetables and bread, which affords him a lot of energy in the form of carbohydrates. 

The Benefits of Intermittent Fasting

eating salad

What does the research say about the OMAD diet? Honestly, not a lot. However, there has been plenty of research on intermittent fasting in general.

For instance, a 2021 study found that meal reduction to a single meal per day lowered total body mass and glucose levels, and didn’t negatively impact physical performance during exercise. 

A 2016 study of mice found that extended fasting with water was linked to a lower rate of diseases, including cancer and diabetes.  Additionally, a small 2017 study of 10 people with type 2 diabetes illustrated that an 18 to 20 hour window of fasting each day led to better-controlled blood glucose levels. The reason for this may lie in the process of autophagy, which literally means ‘self-eating’ in Latin. Autophagy is the process by which unused components within the cells are reused for cellular repair.

RELATED: Alternate Day Fasting (ADF): Is It Right for You

In other words, it’s kind of like your body recycling itself. It’s a natural waste removal mechanism that breaks down and digests damaged, abnormal, or unused cells. As far as IF is concerned, as soon as you start consuming calories, the body stops digesting itself and instead focuses on digesting what you’re putting in it, stopping the autophagy process.

However, there is a certain level of autophagy that happens naturally without deliberate IF practices. For instance, autophagy can be stimulated by:
- exercise
- sleep
- dietary restriction, including the ketogenic diet
- genetics

According to a 2021 review, “autophagy is a crucial determinant of cellular health and organismal longevity, and impairment or imbalance in autophagy promotes pathological aging and disease.”

The Downside of the OMAD Diet

woman lying on bed feeling ill

On the other hand, not all the research on intermittent fasting and OMAD-like diets is favorable. For instance, a 2007 controlled trial showed that eating once a day was linked to an increase in blood pressure and cholesterol in middle-aged adults who were considered healthy and of ‘normal’ weight.

However, the study also showed that body weight and body fat decreased in the subjects, likely due to changes in metabolic activity.

Other downsides of fasting may include:
- fatigue
- dizziness
- binge-eating
- difficulty focusing
- constipation
- headaches
- diarrhea
- nausea
- bloating
- malnutrition

When restricting your eating, it’s possible to get hangry (hungry-angry) as well as experiencing fatigue and even dizziness. It’s also possible to engage in binge-eating if you’re missing food for the remaining 23 hours of the day. 

RELATED: 9 Foods to Improve Your Mood and Cognitive Functioning

On top of that, fasting diets like OMAD can result in digestive issues, including bloating, gas, constipation, and diarrhea, especially if you aren’t getting a wide variety of foods and plenty of fiber.

When you’re not eating for most of the day, you may also forget to drink. This is especially dangerous, as the human body can go an average of one to two months without food, but only three days without water. For children, those timelines are even shorter.

In rare cases, food restriction can result in malnutrition. If you adhere to a fasting diet like OMAD for an extended period of time and your diet doesn’t contain enough micronutrients, it’s possible that you won’t get enough nutrition. 

This can be prevented by eating lots of whole foods like vegetables, fruits, grains, and health proteins and fats. However, you should never embark on an extended fast without approval and supervision from a doctor. 

Who Shouldn’t Do the OMAD Diet?

pregnant woman

Experts agree that there are several categories of people who shouldn’t participate in extended fasts like the OMAD diet.

These include people who are:
- pregnant 
- breastfeeding
- kids and teens
- older adults who have compromised health, strength, or energy
- immunocompromised
- experiencing an eating disorder
- diabetic
- experiencing dementia
- have a history of traumatic brain injury

This list isn’t exhaustive, and it’s always essential to talk to a doctor or healthcare professional about the kind of diet that’s uniquely suited for your needs—especially when it comes to fasting. 

To OMAD or Not?

woman eating sandwich

The general consensus in the scientific community is that intermittent fasting and its cousins can offer health benefits. However, it’s always a good choice to consider your unique situation and needs before you start a diet like OMAD. Certain groups of people are better off avoiding fasting diets like OMAD, and speaking to a healthcare professional about what’s right for you is a great first step. 

In the meantime, you can start out with a less extreme form of intermittent fasting, like a 16:8 eating window, if you don’t have any medical conditions that might be worsened by IF. 


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