Is it harmful to only eat once a day?

November 22, 2025 •

4 min read

According to a 2023 study published in The Journal of the Academy of Nutrition and Dietetics, regularly skipping meals can lead to an increased risk of poor dietary quality and nutrient deficiencies. This raises important questions about the one-meal-a-day (OMAD) diet and whether it is harmful to only eat once a day, despite its popularity for weight loss.

Quick Summary

The practice of eating only one meal a day, known as OMAD, is an extreme form of intermittent fasting that may cause nutritional deficiencies, fatigue, and other health issues. While sometimes used for rapid weight loss, medical experts caution against its long-term sustainability due to potential metabolic and cardiovascular risks. It is not suitable for everyone, particularly those with pre-existing conditions.

Key Points

Nutritional Risks: Eating only one meal a day can easily lead to nutritional deficiencies in essential vitamins, minerals, and macronutrients, impacting overall health.
Blood Sugar and Energy: The long fasting period can cause significant fluctuations in blood sugar, resulting in fatigue, dizziness, irritability, and low energy levels.
Unsustainable Practice: OMAD is difficult for most people to sustain long-term due to extreme hunger and the potential for triggering disordered eating patterns.
Cardiovascular and Metabolic Concerns: Some studies link eating once daily to increased blood pressure and cholesterol, while for diabetics, it poses a high risk of dangerous blood sugar spikes and crashes.
Not for Everyone: High-risk groups who should strictly avoid OMAD include individuals with diabetes, pregnant or breastfeeding women, children, and those with a history of eating disorders.

Understanding the One-Meal-a-Day (OMAD) Approach

The one-meal-a-day (OMAD) diet is a highly restrictive version of intermittent fasting, a dietary pattern that cycles between periods of eating and fasting. Specifically, OMAD involves a 23-hour daily fast, with all caloric intake consumed within a single one-hour window. Proponents of the diet often point to its potential for rapid weight loss and simplified meal planning as major benefits. However, this extreme restriction is not without significant health concerns that warrant careful consideration.

Potential Benefits of OMAD

While the science on OMAD specifically is limited, some observed benefits are often associated with intermittent fasting in general.

Weight Loss: By restricting food intake to a small window, many individuals naturally consume fewer calories, leading to a calorie deficit and subsequent weight loss. Some studies suggest that time-restricted feeding may help with fat loss.
Metabolic Flexibility: Prolonged fasting can push the body to burn fat for fuel after exhausting its glucose stores, potentially improving metabolic flexibility.
Increased Productivity: Some OMAD followers report feeling more focused and less sluggish during their fasting period, possibly due to a lack of a post-meal energy crash.
Autophagy: Fasting is believed to induce autophagy, a process where the body recycles damaged cellular components. While more research is needed, this is associated with cellular health and longevity in some studies.

Significant Risks and Drawbacks of OMAD

For most people, the potential harms of OMAD far outweigh the theoretical benefits, especially in the long term.

Nutritional Deficiencies: Cramming all of your daily nutritional needs into one meal makes it extremely difficult to consume adequate vitamins, minerals, fiber, and protein. This can lead to serious deficiencies and health problems over time.
Energy and Mood Swings: Extended fasting can lead to significant drops in blood sugar, causing irritability, fatigue, and difficulty concentrating. This state is often colloquially known as being "hangry."
Disordered Eating Patterns: The extreme restriction required by OMAD can trigger or worsen disordered eating behaviors, such as binge eating during the designated eating window. This can foster an unhealthy and unsustainable relationship with food.
Metabolic and Cardiovascular Stress: Some studies have shown that eating only once a day can increase blood pressure and LDL ("bad") cholesterol levels. It can also disrupt insulin sensitivity and blood sugar control, which is especially dangerous for individuals with diabetes.
Muscle Mass Loss: Rapid and extreme weight loss can lead to the breakdown of lean body mass in addition to fat stores. This can have negative long-term health consequences.
Digestive Issues: Consuming a very large volume of food in a short period can overwhelm the digestive system, leading to bloating, acid reflux, and general discomfort.

Who Should Avoid OMAD?

Eating one meal a day is not suitable for everyone and is generally not recommended as a long-term eating strategy. It is particularly dangerous for certain groups, including:

Individuals with Diabetes: The risk of blood sugar crashes (hypoglycemia) or spikes (hyperglycemia) is too high for those with diabetes.
Pregnant or Breastfeeding Women: These individuals have significantly higher nutritional needs that cannot be met through a single meal.
Children and Adolescents: Their growing bodies require consistent and balanced nutrition.
People with Eating Disorders: The restrictive nature of OMAD can be very detrimental and should be avoided.
Highly Active Individuals or Athletes: These individuals have elevated energy and protein requirements for performance and recovery that are challenging to fulfill in one sitting.

Comparison: OMAD vs. Sustainable Eating Patterns


Feature	OMAD (One Meal a Day)	Sustainable Eating Patterns
Meal Frequency	All daily calories and nutrients are consumed in one, typically 1-hour, window.	Calorie and nutrient needs are distributed across multiple meals and snacks.
Nutrient Intake	High risk of nutrient deficiencies due to difficulty packing all necessary vitamins, minerals, and fiber into one meal.	Allows for balanced and varied food intake throughout the day, minimizing deficiency risk.
Weight Loss	Often leads to rapid weight loss by creating a calorie deficit, but this is often unsustainable and accompanied by side effects.	Promotes gradual, steady, and more sustainable weight loss by fostering healthy habits.
Energy Levels	Significant fluctuations in blood sugar can cause fatigue, dizziness, and irritability during the long fasting period.	Consistent energy supply throughout the day, preventing drastic peaks and crashes in blood sugar.
Sustainability	Very difficult to maintain long-term due to extreme hunger, restrictive nature, and negative side effects.	Focuses on lifestyle changes that are easier to integrate and sustain over a lifetime.
Impact on Mental Health	Can lead to a poor relationship with food, cravings, and increased risk of disordered eating.	Encourages mindful eating and a healthy, balanced mindset around food.

Conclusion: A High-Risk, Unsustainable Approach for Most

While some short-term weight loss has been observed in studies involving OMAD, the overall consensus from health professionals is that eating only one meal a day is an extreme, potentially harmful, and unsustainable practice for the vast majority of people. The risks of nutritional deficiencies, metabolic disruptions, and developing unhealthy eating habits are significant. Instead of seeking a "quick fix" like OMAD, safer and more sustainable alternatives exist. For most people, adopting a balanced, nutrient-dense diet with regular, less extreme meal patterns (such as 16:8 intermittent fasting or simply reduced overall calorie intake) is a much healthier and more effective path to achieving long-term health and weight goals. Before considering any restrictive diet, especially one as extreme as OMAD, it is crucial to consult with a healthcare provider or a registered dietitian to determine the best and safest approach for your individual needs.

Frequently Asked Questions

While eating one meal a day (OMAD) can cause weight loss by creating a calorie deficit, experts advise against it as a sustainable method. Less extreme forms of intermittent fasting or standard calorie reduction are generally safer and more effective for long-term weight management.

Common side effects include intense hunger, low energy, fatigue, irritability, headaches, dizziness, and constipation. These are often caused by blood sugar fluctuations due to the long fasting period.

It is extremely challenging to consume enough calories and get all the necessary vitamins, minerals, and fiber from a single meal. This puts individuals at high risk for nutritional deficiencies over time.

Yes, OMAD is dangerous for individuals with diabetes, as the extended fasting can lead to dangerously low blood sugar (hypoglycemia), while the large meal can cause significant blood sugar spikes (hyperglycemia).

Research does not show that OMAD is superior to eating multiple smaller, balanced meals for overall health or sustainable weight loss. The risks of OMAD, such as nutritional deficiencies and metabolic stress, often outweigh the perceived benefits.

Yes, following a restrictive diet like OMAD can lead to a loss of lean muscle mass in addition to fat, especially if adequate protein is not consumed in that single meal. This is a common risk with extreme fasting methods.

Healthier alternatives include balanced, regular eating patterns or less extreme intermittent fasting methods like 16:8 (16-hour fast, 8-hour eating window), which are more sustainable and less prone to side effects.