What Will Happen to My Body if I Eat One Meal Per Day?

October 18, 2025 •

4 min read

According to a 2022 study involving healthy adults, eating a single meal in the evening can lead to greater body fat and total body weight loss compared to a standard eating pattern. So, what will happen to my body if I eat one meal per day, also known as OMAD (One Meal A Day)? The effects can be both positive and negative, ranging from metabolic changes to nutrient imbalances, and require careful consideration.

Quick Summary

This article explores the physiological effects of eating one meal per day, examining potential benefits like improved insulin sensitivity and weight loss, alongside significant risks such as nutrient deficiencies, muscle loss, and metabolic slowdown.

Key Points

Metabolic Switching: Your body shifts from burning glucose to burning stored fat during the extended fasting period, which can aid in weight loss.
Insulin Sensitivity: Reducing the frequency of insulin spikes by eating once daily may improve insulin sensitivity, benefiting blood sugar regulation.
Nutrient Deficiencies: It is extremely challenging to obtain all necessary daily vitamins, minerals, protein, and fiber in a single meal, posing a significant risk of deficiencies.
Loss of Muscle Mass: Extended periods of fasting can lead to the breakdown of lean muscle tissue, which negatively impacts overall body composition and metabolism.
Adverse Side Effects: OMAD is associated with potential side effects including fatigue, dizziness, irritability, blood sugar crashes, and digestive issues.
Not for Everyone: Due to its extreme nature, OMAD is not suitable for people with certain medical conditions, pregnant or breastfeeding women, or those with a history of eating disorders.

The practice of consuming all of your daily calories within a single, condensed eating window is an extreme form of intermittent fasting known as One Meal A Day, or OMAD. While it can lead to rapid weight loss by forcing a significant calorie deficit, it is not without complex and sometimes risky consequences for your body. For some, it may offer benefits related to metabolic health, but for many, it poses considerable challenges and potential harm, particularly when sustained over the long term without professional guidance.

Potential Benefits and Metabolic Changes

What happens inside your body?

When you go for an extended period without food, your body undergoes a process called metabolic switching. After exhausting its readily available glucose stores, it begins to burn stored fat for energy. This shift can offer several potential health advantages for some individuals:

Improved Insulin Sensitivity: Prolonged fasting can help regulate blood sugar levels by reducing the frequency of insulin spikes. This can be particularly beneficial for those with insulin resistance or pre-diabetes.
Autophagy and Cellular Repair: Extended fasting can trigger autophagy, a cellular "house-cleaning" process where the body removes damaged cells. This process is associated with promoting cellular health and longevity.
Weight Loss and Fat Oxidation: A major draw of OMAD is weight reduction. By restricting calorie intake to one sitting, a significant daily calorie deficit is often created. Studies have shown this can lead to greater body weight and fat mass loss in some healthy individuals, partly due to increased fat oxidation during exercise.
Mental Clarity: Some individuals report increased focus and mental clarity during fasting periods. This may be due to the body's adaptation and shift in energy sources, though individual experiences vary.

Short-Term Effects vs. Long-Term Sustainability

The initial weeks of OMAD may deliver rapid results in terms of weight loss. However, these benefits often come with significant side effects during the adaptation period. Long-term adherence is challenging and may not be sustainable or advisable for most people.

Significant Risks and Drawbacks

Why OMAD is not for everyone

Despite the purported benefits, the downsides of eating only one meal a day are numerous and should not be overlooked. Most health professionals advise caution or against the practice entirely, especially for prolonged use.

Nutrient Deficiencies: It is extremely difficult to consume all the necessary vitamins, minerals, and macronutrients in a single meal. This can lead to deficiencies that negatively impact immune function, bone density, and overall health.
Loss of Muscle Mass: In addition to fat loss, extended fasting can also result in the breakdown of lean muscle mass. This is counterproductive for maintaining a healthy metabolism and overall body composition. Regular strength training is particularly challenging on this regimen.
Metabolic Slowdown: Prolonged and severe calorie restriction can cause the body's metabolic rate to slow down as a survival mechanism. This can make weight loss more difficult over time and may contribute to rebound weight gain when returning to normal eating habits.
Blood Sugar Fluctuations and Related Symptoms: Many people experience low blood sugar (hypoglycemia) while on OMAD, which can cause dizziness, fatigue, headaches, and irritability. This is especially dangerous for individuals with diabetes.
Disordered Eating and Bingeing: The highly restrictive nature of OMAD can trigger or worsen disordered eating behaviors. The extreme hunger experienced during the 23-hour fasting window can lead to overeating or binge eating during the one-hour feeding window.
Increased Cholesterol Levels: Some studies have linked eating one large meal per day to an increase in LDL (“bad”) cholesterol levels.

Comparing OMAD to Less Restrictive Intermittent Fasting

For those interested in exploring time-restricted eating, less extreme versions may offer a safer and more sustainable path with fewer risks.

OMAD vs. 16:8 Intermittent Fasting


Feature	One Meal A Day (OMAD)	16:8 Intermittent Fasting
Eating Window	1-hour	8-hour
Fasting Period	23-hours	16-hours
Nutritional Adequacy	Difficult to meet daily needs in one meal	Easier to consume adequate nutrients across a few meals
Weight Loss Potential	Can be rapid, but may include muscle mass loss	Steady and sustainable
Sustainability	Very difficult long-term; high dropout rates	More sustainable and flexible for most people
Side Effects	Higher risk of fatigue, dizziness, nutrient deficiencies	Fewer and less intense side effects; easier adaptation

Conclusion

While eating one meal per day can lead to rapid weight loss for some, the potential health risks and sustainability issues are significant. OMAD can cause nutrient deficiencies, muscle mass loss, metabolic disruptions, and potentially increase cholesterol. While it may offer some benefits related to metabolic function and cellular repair, these are often better and more safely achieved through less extreme forms of intermittent fasting, such as the 16:8 method. Anyone considering a drastic dietary change like OMAD should first consult with a healthcare professional to ensure it is appropriate for their individual health needs and to mitigate potential risks.

Mayo Clinic offers a useful overview of intermittent fasting from a trusted medical source.

Frequently Asked Questions

No, eating one meal a day (OMAD) is not safe for everyone. It is particularly risky for individuals with diabetes, pregnant or breastfeeding women, children, teenagers, and people with a history of eating disorders.

Yes, many people experience weight loss on OMAD, primarily because restricting food intake to a single hour creates a significant calorie deficit. However, this is not always superior to other forms of calorie restriction and can be accompanied by muscle loss.

If you follow OMAD, your meal must be extremely nutrient-dense. It should include lean proteins, healthy fats, complex carbohydrates, and a wide variety of vegetables and fruits to maximize vitamin and mineral intake.

Yes, prolonged periods of calorie restriction, such as with OMAD, can cause the body to lower its metabolic rate to conserve energy. This can make weight loss more difficult over time.

Common side effects include extreme hunger, fatigue, low energy, irritability, headaches, dizziness, and difficulty concentrating, especially during the initial adjustment phase.

There is no definitive evidence that OMAD is more effective than less restrictive forms of intermittent fasting, such as the 16:8 method. While OMAD is more extreme, it also carries greater risks and is harder to sustain long-term.

Yes, the extreme hunger caused by prolonged fasting can increase the risk of binge eating during the short eating window. This can lead to an unhealthy relationship with food and weight cycling.