Is It Unhealthy to Eat One Meal? The Truth About the OMAD Diet

December 17, 2025 •

4 min read

While intermittent fasting has gained popularity, with some variants suggesting eating only once a day, the health community is divided on its safety. This raises a critical question for many: is it unhealthy to eat one meal regularly, and what are the actual risks and benefits of the OMAD diet?

Quick Summary

The one-meal-a-day (OMAD) diet, an extreme form of intermittent fasting, can lead to weight loss by restricting calories but is difficult for most people to sustain. It carries significant risks, including nutrient deficiencies, metabolic changes, and disordered eating patterns, and is often not more effective than less restrictive methods.

Key Points

Nutrient Deficiencies Are a High Risk: It is extremely difficult to consume all essential vitamins, minerals, and macronutrients in a single daily meal, which can lead to fatigue, weakness, and long-term health issues.
Metabolic and Hormonal Disruption is Common: OMAD can negatively impact blood sugar regulation, increase LDL cholesterol, and disrupt hormones, particularly affecting blood sugar stability and potentially increasing heart disease risk.
Sustainability is Challenging for Most: The intense 23-hour fasting period often leads to extreme hunger and irritability, making the diet hard to maintain long-term and increasing the risk of disordered eating behaviors like bingeing.
Weight Loss Can Come at a Cost: While weight loss can occur due to extreme calorie restriction, there is a risk of losing valuable lean muscle mass and slowing down metabolism, which is counterproductive for long-term health.
Safer Alternatives Exist: The benefits attributed to OMAD, like improved insulin sensitivity, can often be achieved through less extreme forms of intermittent fasting or a simple, balanced diet, without the associated risks.
Consult a Professional Before Starting: Due to the potential for serious health complications, especially for those with pre-existing conditions like diabetes, it is crucial to consult a healthcare provider before attempting OMAD.

What is the OMAD Diet?

The One Meal A Day (OMAD) diet is a highly restrictive form of time-restricted eating, an intermittent fasting protocol. Participants fast for approximately 23 hours, consuming all their daily calories within a single one-hour window. This differs from less extreme forms of intermittent fasting, such as the 16:8 method, which allows for a more forgiving eight-hour eating window. Proponents claim it simplifies eating, aids weight loss, and offers other metabolic benefits. However, health experts frequently caution against it due to its extreme nature and potential for adverse effects.

The Potential Benefits of OMAD (with Caveats)

Some research associated with intermittent fasting has been cited to support OMAD, but it is important to note these benefits are often linked to fasting in general, not necessarily the extreme 23-hour fast of OMAD.

Weight Loss: By compressing all eating into a single hour, it's difficult for most people to consume enough calories to maintain weight, naturally creating a calorie deficit. This is the primary driver of weight loss on the OMAD diet.
Improved Insulin Sensitivity: Some studies on intermittent fasting have shown improvements in insulin sensitivity and blood sugar control. The long fasting window can lead to lower insulin levels, which can be beneficial, particularly for those with pre-diabetes. However, this is not exclusive to OMAD and can be achieved with less extreme methods.
Autophagy: Extended fasting periods can trigger autophagy, a cellular process that recycles old, damaged cell components. While potentially beneficial for cellular health, OMAD is not the only way to induce this process, and the long-term impact on overall health is still being researched.

The Significant Risks of Eating One Meal a Day

While some anecdotal and limited research suggests benefits, the risks are widely documented and concern many health professionals. The extreme nature of OMAD makes it challenging for most people to maintain without negative consequences.

Nutritional Deficiencies

It is incredibly difficult to consume all the essential macronutrients and micronutrients in a single meal, no matter how balanced it seems. This can lead to a host of problems, including:

Inadequate protein intake: Necessary for muscle maintenance, especially as we age. Long-term OMAD may contribute to lean muscle mass loss.
Vitamin and mineral shortfalls: Deficiencies in essential nutrients like calcium, iron, and various vitamins can lead to weakened bones, fatigue, and other health issues.
Insufficient fiber: A single large meal may not contain enough fiber, which is crucial for gut health and regular bowel movements.

Metabolic and Hormonal Disruptions

The body is not designed for such long periods without fuel, which can trigger adverse metabolic responses.

Elevated Blood Sugar: Studies have shown that a single large meal can lead to higher spikes in fasting blood sugar and can impair glucose tolerance. This is particularly risky for individuals with or at risk of type 2 diabetes.
Increased "Bad" Cholesterol: Some research indicates that long-term OMAD can increase total and LDL ("bad") cholesterol levels.
Hormonal Imbalance: For women especially, extended fasting can disrupt hormones and affect the menstrual cycle. It can also increase the appetite-stimulating hormone ghrelin, leading to intense hunger.

Potential for Disordered Eating and Poor Choices

The restrictive nature of OMAD can promote an unhealthy relationship with food.

Binge Eating: The extreme hunger that builds up over 23 hours can lead to a tendency to overeat or binge during the one-hour window.
Poor Food Choices: When extremely hungry, people are more likely to crave and choose calorie-dense, processed foods over nutrient-rich options, negating any potential health benefits.

Comparison: OMAD vs. Standard Eating Patterns


Feature	OMAD (One Meal a Day)	Standard Eating (2-3 Meals)
Sustainability	Very low for most people; difficult to maintain long-term.	High; more flexible and easier to integrate into social life.
Nutrient Intake	Challenging to meet daily nutritional needs in one sitting, high risk of deficiencies.	Easier to distribute nutrient intake, promoting balanced consumption of vitamins and minerals.
Blood Sugar Control	Can cause significant blood sugar spikes and drops, especially for those with insulin issues.	Helps maintain more stable blood sugar levels throughout the day with regular fuel intake.
Weight Loss	Achieved through extreme calorie restriction, but potential for muscle loss is high.	Sustainable weight loss through moderate calorie control and healthier eating habits.
Energy Levels	Often results in fatigue, irritability, and low energy due to prolonged fasting periods.	Promotes steady energy levels by providing regular fuel to the body.

Who Should Avoid OMAD?

Certain individuals should never attempt the OMAD diet due to significant health risks. This includes:

Pregnant or breastfeeding women
Children and teenagers still in a growth period
People with a history of eating disorders
Individuals with diabetes or blood sugar regulation issues
The elderly, due to risk of muscle and bone mass loss
Those with kidney disease or other medical conditions

Conclusion: A High-Risk Strategy for Limited Reward

While the concept of eating one meal a day might seem appealing for its simplicity and potential for rapid weight loss, the science suggests it is a high-risk strategy. For most people, the potential for nutrient deficiencies, metabolic disruption, and unsustainable eating patterns far outweighs the claimed benefits. Health experts widely recommend that if you are interested in fasting, milder and more sustainable forms of intermittent fasting (like 16:8) are a much safer starting point. For long-term health and weight management, a balanced diet with nutrient-dense foods remains the most reliable and sustainable approach. For personalized advice, it is always best to consult a healthcare professional or registered dietitian. A great resource for general dietary guidelines is the USDA's MyPlate program, which provides a balanced approach to eating.

MyPlate official website

Frequently Asked Questions

Yes, it is very difficult. A single meal, no matter how large, may not provide the necessary balance and variety of vitamins, minerals, fiber, and protein required for optimal bodily function, increasing the risk of deficiencies.

Yes, it can. While initial weight loss is often rapid due to calorie restriction, prolonged, extreme fasting can cause the body to enter a conservation mode, slowing down your metabolism and making future weight management more difficult.

The OMAD diet is not suitable for children and adolescents, pregnant or breastfeeding women, individuals with diabetes or hypoglycemia, those with a history of eating disorders, and the elderly.

Yes. Eating all your calories in one large sitting can cause a significant spike in blood sugar, followed by a potential crash during the long fasting period. This can be dangerous for people with blood sugar regulation issues.

OMAD can lead to short-term weight loss due to calorie restriction, but it is not necessarily a more effective or sustainable method than traditional calorie control. The extreme nature often leads to weight regain when the diet is stopped.

Common side effects include extreme hunger, fatigue, low energy levels, irritability, headaches, dizziness, and difficulty concentrating due to inconsistent energy supply.

Safer and more sustainable alternatives include less restrictive intermittent fasting methods like the 16:8 schedule, where you fast for 16 hours and eat within an 8-hour window. Simply adopting a healthier, balanced diet is also a more effective and reliable long-term strategy.