What Happens if I Eat Once Everyday? Benefits and Risks of OMAD

October 23, 2025 •

4 min read

While intermittent fasting has grown in popularity, the extreme version of eating just once a day, known as OMAD, is gaining traction. This restrictive diet, consisting of a 23-hour fast and a 1-hour eating window, has proponents who praise its simplicity and fat-burning potential. However, health professionals caution that significant risks often outweigh the benefits of eating once everyday.

Quick Summary

This article explores the bodily effects of eating one meal a day, detailing potential short-term weight loss and metabolic changes, alongside considerable risks like nutrient deficiencies, muscle loss, and metabolic slowdown. It examines the impacts on energy, cognitive function, and cardiovascular health, contrasting OMAD with safer eating patterns.

Key Points

Weight Loss vs. Calorie Restriction: Short-term weight loss on OMAD is primarily due to reduced calorie intake, not necessarily a superior metabolic effect compared to other diets.
Significant Health Risks: Long-term OMAD use is associated with a high risk of nutrient deficiencies, slowed metabolism, and increased LDL cholesterol and blood pressure.
Mental and Social Impact: The extreme restriction can lead to intense hunger, food obsession, disordered eating, and social isolation.
Metabolic Strain: Fasting for 23 hours can disrupt blood sugar levels, especially for diabetics, and increase stress hormones like cortisol.
Not for Everyone: OMAD is not recommended for pregnant women, diabetics, or individuals with a history of eating disorders without strict medical supervision.
Better Alternatives Exist: Less extreme and more sustainable intermittent fasting methods, such as the 16:8 approach, offer similar benefits with fewer risks.
Prioritize Nutrient Density: If attempting OMAD, the single meal must be extremely nutrient-dense to mitigate the risk of deficiencies, a challenge for most people.

The practice of eating only one meal a day, widely known as OMAD (One Meal A Day), is the most extreme form of time-restricted eating. It involves fasting for approximately 23 hours and consuming all daily calories and nutrients within a single, concentrated eating window. While some anecdotal accounts praise its simplicity and effects on weight loss, a deeper look at the science reveals a complex picture of potential benefits and serious health risks.

Short-Term Effects of Eating Once Everyday

Immediately after starting an OMAD diet, your body undergoes several changes as it adapts to the new eating pattern. The most immediate effect is the transition from using glucose for energy to burning stored fat.

Initial Weight Loss: Many people experience rapid weight loss in the early stages, primarily due to a natural reduction in overall calorie intake. It is significantly harder to consume a full day's worth of calories in one sitting than across multiple meals.
Metabolic Shift: After about 12-17 hours without food, the body exhausts its primary glucose stores and begins to burn fat for fuel, a metabolic process called ketosis. This fat oxidation is a core mechanism behind the diet's appeal.
Energy and Mental Clarity: Some individuals report improved focus and mental clarity during the fasting period, which proponents attribute to increased levels of the chemical orexin-A. However, this experience is not universal and can be overshadowed by fatigue.
Hunger and Cravings: Most people will experience intense hunger and cravings, especially during the initial adaptation period. The hormone ghrelin, which stimulates appetite, increases significantly when meals are restricted to one per day.

Long-Term Effects and Health Risks

While short-term results can seem promising, health experts raise significant concerns about the long-term sustainability and safety of OMAD. The restrictive nature makes it difficult to maintain, and the extreme stress on the body can have serious consequences.

Nutrient Deficiencies

Consuming a complete and balanced nutritional profile in a single meal is extremely challenging. Over time, this can lead to serious deficiencies in essential vitamins and minerals.

Key nutrients often missed: Calcium, iron, vitamin D, and B vitamins are commonly lacking, which can lead to fatigue, bone density loss, and a compromised immune system.
Specific issues: Insufficient fiber can cause constipation, while inadequate protein intake can lead to muscle mass loss.

Metabolic and Cardiovascular Health Concerns

Prolonged fasting can put a strain on metabolic function, with a potential impact on long-term health markers.

Slower Metabolism: The body can adapt to long fasting periods by slowing down its metabolic rate to conserve energy. This can make it harder to lose weight over time and increases the risk of weight regain.
Increased Cholesterol: Studies have linked eating once a day to elevated levels of LDL (bad) cholesterol and blood pressure, which increases the risk of cardiovascular disease.
Blood Sugar Fluctuation: The massive insulin spike followed by a drop can be dangerous, especially for individuals with diabetes or prediabetes, potentially leading to hypoglycemia.

Mental and Social Impact

The psychological toll of such a restrictive diet should not be underestimated.

Disordered Eating: The cycle of intense restriction followed by a large meal can trigger disordered eating habits, such as binge eating, and lead to an unhealthy relationship with food.
Social Isolation: Mealtime is a cornerstone of social interaction, and adhering to OMAD can lead to feelings of isolation and make social gatherings difficult to navigate.

OMAD vs. Other Intermittent Fasting Methods

To understand why OMAD is considered extreme, it's helpful to compare it with more moderate intermittent fasting (IF) methods.


Feature	OMAD (One Meal A Day)	16:8 Method	5:2 Diet
Fasting Window	23 hours	16 hours	5 days of normal eating
Eating Window	1 hour	8 hours	2 days of calorie restriction
Calorie Intake	All daily calories in one large meal.	Normal calorie intake within the window.	Severely restricted calories (500-600) on 2 days.
Difficulty	High. Intense hunger and risk of nutritional deficiency.	Moderate. Easier to sustain and get nutrients.	Varies by individual, may experience fatigue on fasting days.
Expert Consensus	Cautious. Not recommended for most people, especially long-term.	Generally positive. Considered safer and more sustainable.	Generally positive. Offers a different approach to calorie restriction.
Primary Risks	Nutrient deficiency, muscle loss, metabolic slowdown.	Overeating during the eating window, dehydration.	Hunger on fasting days, requires careful planning.

Who Should Avoid OMAD

For a variety of health and lifestyle reasons, some groups should not attempt the OMAD diet without strict medical supervision.

Pregnant or breastfeeding women: Nutritional needs are critical and cannot be met in a single meal.
Individuals with diabetes: Blood sugar management becomes extremely difficult and dangerous.
Those with a history of disordered eating: OMAD can trigger or worsen restrictive and binge-eating behaviors.
Growing children and teens: Their development requires a steady supply of nutrients.
People with physically demanding jobs or intense exercise routines: OMAD can lead to fatigue and hinder performance and recovery.

A Safer Path to Intermittent Fasting

For those interested in exploring time-restricted eating, starting with a less extreme method is a safer and more sustainable approach. The 16:8 method, where you fast for 16 hours and eat within an 8-hour window, is often recommended as a manageable starting point. It provides many of the potential benefits of fasting without the intense risks of OMAD.

Conclusion

While the concept of eating once everyday may be appealing for its simplicity and initial weight loss potential, it carries significant risks that outweigh the benefits for most individuals. The danger of nutrient deficiencies, metabolic disruptions, and developing disordered eating patterns is high. Unlike more moderate intermittent fasting methods, OMAD is not a sustainable or healthy long-term strategy and is not advised by most health professionals. For those seeking sustainable weight management and health improvements, a balanced, nutrient-dense diet combined with regular meals is a safer and more effective path. Consulting a healthcare provider or registered dietitian before making drastic dietary changes is always the most responsible course of action.

Frequently Asked Questions

Most health professionals and recent research suggest that eating only once a day is not safe or sustainable for the long term for most individuals. It can lead to serious risks such as nutrient deficiencies, muscle mass loss, and metabolic slowdown.

It is difficult to consume enough essential nutrients in a single meal. Common deficiencies include vitamins D, B12, and C, as well as minerals like iron, calcium, and magnesium. This can lead to fatigue, bone density loss, and poor immune function.

Yes, prolonged and severe calorie restriction can cause your body to enter a 'preservation mode' where it slows down your metabolic rate to conserve energy. This can make future weight loss more difficult and increase the likelihood of regaining weight.

Some studies, including older ones, have linked eating once a day to increased levels of LDL ('bad') cholesterol and blood pressure, especially if the single meal is high in processed foods or unhealthy fats. This raises the risk of cardiovascular disease.

While OMAD can cause short-term weight loss due to a large calorie deficit, it is not necessarily more effective than less restrictive forms of calorie reduction. The weight loss is often unsustainable due to side effects, and some studies suggest it is no more effective long-term.

A safer and more sustainable alternative is the 16:8 method, where you fast for 16 hours and eat within an 8-hour window. This approach allows for adequate nutrient intake while still providing many benefits of time-restricted eating.

To make your single meal as nutritious as possible, focus on whole, unprocessed foods. Include sufficient lean protein, healthy fats (like avocados or olive oil), complex carbohydrates (such as quinoa or sweet potatoes), and a wide variety of vegetables to maximize nutrient intake.