What Happens to Your Body If You Only Eat One Meal Per Day?

November 17, 2025 •

4 min read

According to a 2023 study published in the Journal of the Academy of Nutrition and Dietetics, regularly skipping meals, especially breakfast, is associated with a higher risk of all-cause and cardiovascular disease mortality among US adults. This raises serious questions about the safety of an extreme eating pattern like eating only one meal per day (OMAD) and what happens to your body if you only eat one meal per day.

Quick Summary

The OMAD diet, an extreme form of intermittent fasting, can lead to weight loss by creating a calorie deficit but presents significant risks. These include nutrient deficiencies, metabolic slowdown, hormonal disruptions, and cardiovascular concerns. The eating pattern can also cause side effects like fatigue, irritability, and social isolation. Long-term sustainability and safety are major drawbacks for most individuals.

Key Points

Metabolic slowdown: Prolonged caloric restriction from OMAD can trigger a metabolic slowdown, making sustained weight loss and long-term maintenance challenging.
Nutritional deficiencies: It is highly difficult to obtain adequate vitamins, minerals, and protein in a single meal, risking nutritional deficiencies over time.
Blood sugar fluctuations: Eating one large meal causes significant blood sugar spikes and drops, which can lead to fatigue, irritability, and health risks, especially for diabetics.
Increased cardiovascular risk: Some studies indicate that long-term OMAD may increase total and LDL cholesterol and blood pressure, raising the risk of heart disease.
Potential muscle loss: Consuming all daily protein in one sitting is inefficient for muscle maintenance and growth, potentially leading to a loss of lean body mass.
Psychological and social impact: The restrictive nature can cause psychological distress, increase hunger hormones, and lead to social isolation due to meal-time constraints.
Digestive distress: Consuming a large volume of food in one meal can overwhelm the digestive system, causing bloating, indigestion, and general discomfort.

Metabolic Effects of Eating One Meal a Day

Eating only one meal per day (OMAD) involves an extended fasting period that can lead to a metabolic shift, with the body initially depleting glucose stores and then potentially entering ketosis by burning fat for energy. While this is proposed as a benefit for fat loss and insulin sensitivity, the long-term metabolic impact is complex. Prolonged calorie restriction may cause the metabolism to slow down, making sustained weight loss and maintenance more challenging and increasing the risk of regaining weight.

Blood Sugar and Insulin Fluctuations

OMAD significantly impacts blood sugar and insulin levels. A large meal after a long fast can cause a notable blood sugar spike, followed by lower, less stable levels throughout the day. Some older research suggests this pattern might increase morning fasting blood sugar and impair insulin response over time, which is particularly risky for individuals with diabetes or prediabetes. These fluctuations can also cause symptoms such as shakiness and low energy.

Nutritional and Digestive Challenges

A major hurdle with OMAD is meeting daily nutritional needs in one sitting. Consuming adequate vitamins, minerals, fiber, and protein within a short window is difficult for most people, increasing the risk of deficiencies that can lead to fatigue, reduced immune function, and decreased bone density.

Protein intake: The body has limits on how much protein it can effectively absorb at once, meaning consuming a full day's worth in one meal might hinder muscle maintenance.
Digestive issues: A large single meal can strain the digestive system, potentially causing discomfort and bloating.
Food choices: Intense hunger may lead to opting for less nutritious, high-calorie foods.

Psychological and Social Side Effects

The restrictive nature of OMAD can impact mental and social well-being. The constant struggle with hunger and cravings may lead to psychological distress and potentially contribute to disordered eating patterns like bingeing. OMAD can also be socially isolating, as meals are often central to social activities. This eating pattern might also increase cortisol, a stress hormone linked to poor sleep and increased anxiety.

Cardiovascular and Long-Term Health Risks

Recent research suggests potential long-term cardiovascular risks associated with extreme fasting. A 2023 study found a higher risk of all-cause and cardiovascular disease mortality among those eating only one meal a day compared to those eating two to three meals. Other studies have indicated increases in total and LDL cholesterol and higher blood pressure in individuals following an OMAD-style regimen.


Aspect	OMAD Diet	Traditional Eating (2-3 meals)
Weight Management	May cause rapid initial weight loss due to calorie restriction; risk of metabolic slowdown and rebound weight gain is high.	Promotes sustainable weight loss when calories are controlled; less risk of severe metabolic changes and rebound weight gain.
Nutrient Intake	High risk of nutrient deficiencies as it's difficult to consume all daily needs in one meal.	Easier to meet daily nutritional requirements with balanced meals spread throughout the day.
Energy Levels	Significant fluctuations, with potential crashes during the long fasting window; can cause fatigue and irritability.	More stable energy levels throughout the day; reduces hunger pangs and cravings.
Metabolic Health	Potential for improved insulin sensitivity in the short term, but risks include increased cholesterol and blood pressure over time.	Promotes better glucose control and overall metabolic health without the extremes of OMAD.
Sustainability	Difficult to maintain long-term due to extreme restrictions and social challenges; high dropout rates.	Sustainable and adaptable to most lifestyles and social situations.

Conclusion

While eating one meal per day may seem appealing for rapid weight loss, the potential risks, including nutritional deficiencies, metabolic changes, mood impacts, and possible long-term cardiovascular issues, warrant caution. While short-term fasting under medical supervision can be beneficial, long-term OMAD's restrictive nature is not widely recommended. Consulting a healthcare professional before adopting such a drastic dietary change is essential to ensure it's appropriate for individual health needs. A balanced diet with nutrient-rich foods and regular physical activity remains the recommended approach for sustainable health.

For additional information on the risks associated with restrictive eating, the National Eating Disorders Association provides a guide on disordered eating patterns.

Risks vs. Rewards: The Bottom Line

Nutrient Deficiency: Meeting all daily nutritional needs in one meal is very difficult, leading to potential deficiencies.
Metabolic Slowdown: Extended fasting can slow down your metabolism, hindering weight loss and maintenance.
Hormonal Disruption: OMAD may increase stress hormones and disrupt others affecting mood and appetite.
Cardiovascular Strain: Studies suggest a link between long-term OMAD and increased cholesterol and blood pressure.
Psychological Distress: The restriction can cause irritability, increased hunger, and potentially lead to unhealthy eating patterns.
Social Isolation: Mealtime restrictions can make social activities difficult, potentially leading to isolation.
Muscle Mass Loss: Inconsistent protein intake can risk a loss of lean muscle mass.

Finding a Healthier Path

Consider less extreme fasting: Options like the 16:8 method may offer benefits with fewer risks.
Focus on balanced nutrition: Prioritize nutrient-dense foods during eating periods to help prevent deficiencies.
Listen to your body: Be aware of negative symptoms and consult a professional if they occur.
Consult a professional: Always speak with a doctor or dietitian before making significant dietary changes like OMAD.

A balanced, sustainable approach is generally considered the most reliable path to long-term health and weight management.

Frequently Asked Questions

Most healthcare professionals do not recommend the one meal a day (OMAD) diet as a sustainable, long-term strategy. The extreme restriction poses significant risks, including nutrient deficiencies, metabolic slowdown, and potential cardiovascular issues, which may outweigh the short-term benefits.

While OMAD can lead to rapid weight loss by creating a calorie deficit, it is not necessarily more effective for long-term weight management than traditional calorie restriction. The risk of metabolic slowdown and rebound weight gain is high, and sustainable weight loss often comes from more gradual, balanced changes.

Yes, it is very difficult to consume all the necessary vitamins, minerals, fiber, and protein in a single daily meal. This can lead to nutritional deficiencies over time, affecting immune function, energy levels, bone density, and muscle mass.

Individuals who are pregnant or breastfeeding, children and teens, older adults, those with a history of eating disorders, or people with existing medical conditions such as diabetes or heart issues should generally avoid the OMAD diet. It is important to consult with a doctor before starting.

Common side effects include intense hunger, fatigue, dizziness, irritability, and constipation. These are often caused by blood sugar fluctuations and the body's adaptation to an extreme eating pattern.

Initially, OMAD can trigger fat burning, but in the long run, the extreme caloric restriction can cause your metabolism to slow down. This makes it more difficult to burn calories and maintain weight loss over time.

Research suggests that eating earlier in the day may offer better metabolic benefits, including improved insulin sensitivity, compared to eating late in the evening. However, the choice often depends on lifestyle, and some studies show potential risks with both timing approaches.