What happens to your body if you eat one meal per day?

As an extreme form of intermittent fasting, the One-Meal-a-Day (OMAD) diet has gained considerable attention, with a 2017 study showing that eating one or two meals daily was linked to a lower Body Mass Index over time compared to three. This raises the question: what happens to your body if you eat one meal per day? The effects are complex and span from metabolic changes to potential health risks, making it a practice that requires careful consideration.

Quick Summary

This article explores the physiological effects of eating one meal a day (OMAD). It covers how this eating pattern influences weight loss, metabolic health, and potential issues like nutrient deficiencies and digestive problems. It also details the benefits, risks, and compares OMAD to less restrictive fasting methods for overall health.

Key Points

• Weight Loss: Eating one meal a day often creates a calorie deficit, which can lead to significant weight and fat loss.

• Metabolic Shift: After prolonged fasting, the body switches to burning fat for energy, a process known as metabolic switching.

• Nutrient Deficiency: Consuming all daily nutrients in one meal is extremely challenging and carries a high risk of vitamin and mineral deficiencies.

• Muscle Loss: Inadequate protein intake combined with prolonged fasting can lead to the breakdown and loss of lean muscle mass.

• Blood Sugar and Heart Health: OMAD can cause unstable blood sugar levels and may increase LDL ('bad') cholesterol and blood pressure in some individuals.

• Not for Everyone: People with diabetes, pregnant women, and those with a history of eating disorders should avoid the OMAD diet.

The 'One Meal a Day' (OMAD) Concept

The One Meal a Day (OMAD) diet is an intense form of intermittent fasting (IF), also known as the 23:1 eating pattern. It involves fasting for approximately 23 hours and consuming all of your daily calories within a single, designated one-hour eating window. The premise is that by dramatically restricting the eating period, you naturally reduce your overall calorie intake and promote metabolic changes that aid in fat burning. During the fasting period, supporters typically consume only zero-calorie beverages such as water, black coffee, or herbal tea to stay hydrated.

The appeal of OMAD lies in its simplicity. With only one meal to prepare, proponents enjoy saved time and less mental energy spent on food decisions. However, this extreme restriction can also lead to significant drawbacks, as it is challenging to meet all nutritional needs in one sitting and can trigger intense hunger and cravings.

Potential Benefits of the OMAD Diet

For some individuals, adopting a one-meal-a-day schedule may lead to certain physiological benefits. It's important to note that much of the supporting evidence comes from broader intermittent fasting studies, not specifically OMAD.

• Weight Loss and Fat Burning: By limiting calorie intake to a single meal, many people easily create a calorie deficit, which is a key component of weight loss. Extended fasting also triggers a state known as metabolic switching, where the body, after exhausting its sugar stores, begins to burn fat for energy.
• Improved Insulin Sensitivity: Intermittent fasting can help lower blood sugar and insulin levels, potentially improving the body's sensitivity to insulin. This can be beneficial for those at risk of or managing Type 2 diabetes, though specific caution is advised.
• Cellular Repair (Autophagy): Some research suggests that longer fasting periods trigger autophagy, a natural process where the body cleans out damaged cells to generate new, healthier ones.
• Mental Clarity and Focus: Anecdotal reports suggest that after the initial adjustment period, some individuals experience improved concentration and mental focus during the fasting window. This is potentially due to stable blood sugar levels without the spikes and crashes associated with multiple meals.

Significant Risks and Side Effects

Despite the potential upsides, the risks of eating just one meal a day are considerable, particularly when practiced long-term or without proper nutritional guidance.

List of Potential Risks:

• Nutrient Deficiencies: It is extremely difficult to consume the full spectrum of essential vitamins, minerals, and macronutrients in a single meal. This can lead to weakened immunity, poor bone density, and fatigue over time.
• Loss of Muscle Mass: Without a consistent intake of protein, the body may break down muscle tissue for energy during prolonged fasting, especially without resistance training.
• Blood Sugar Fluctuations: For those with insulin sensitivity or diabetes, OMAD can cause dangerous spikes after the large meal and severe drops (hypoglycemia) during the extended fast.
• Digestive Issues: Consuming a large volume of food in one sitting can strain the digestive system, leading to bloating, nausea, and discomfort.
• Metabolic Slowdown: The body may perceive prolonged fasting as a state of famine and slow down its metabolism to conserve energy, potentially hindering future weight loss.
• Unhealthy Eating Patterns: Intense hunger can lead to binge eating or an unhealthy obsession with food, which is a potential precursor to eating disorders.
• Elevated Cholesterol and Blood Pressure: Some studies have linked eating only one meal per day to an increase in LDL ('bad') cholesterol and higher blood pressure levels.

Comparison: OMAD vs. 16/8 Intermittent Fasting

Feature	One Meal a Day (OMAD)	16:8 Intermittent Fasting
Fasting Window	~23 hours	16 hours
Eating Window	1 hour	8 hours
Flexibility	Very limited; all calories in one sitting.	Moderate; allows for multiple meals within the window.
Sustainability	Low for many due to social and physical challenges.	Higher for most, as it's less restrictive.
Calorie Deficit	Can be very significant and hard to control.	Easier to manage and maintain over time.
Nutrient Deficiency Risk	High; requires very careful planning.	Lower; more opportunity to consume a balanced diet.
Side Effects	Higher risk of fatigue, mood swings, and hunger pangs.	Generally milder side effects, less extreme hunger.

Who Should Not Practice the OMAD Diet?

Eating only one meal a day is not suitable for everyone, and certain groups should avoid it due to significant health risks.

• Individuals with Diabetes: The risk of both dangerously low (hypoglycemia) and high (hyperglycemia) blood sugar is heightened. Any diabetic considering IF must do so under strict medical supervision.
• Pregnant or Breastfeeding Women: Nutritional needs are high during these periods and cannot be met with one meal.
• Children and Adolescents: These groups require consistent nutrition for proper growth and development.
• People with a History of Eating Disorders: The restrictive nature of OMAD can exacerbate unhealthy eating behaviors and psychological distress.
• Endurance Athletes or Heavily Active Individuals: Higher caloric and nutritional demands require more frequent meals for fuel and recovery.
• Individuals Taking Food-Dependent Medication: Some medications must be taken with food, making OMAD an unsuitable regimen.

Making Your Single Meal Count

If you have consulted a healthcare professional and determined that OMAD is a safe option for you, maximizing the nutritional value of your one meal is critical to avoid deficiencies. The meal should be nutrient-dense and balanced to cover your daily requirements.

A well-planned OMAD meal should prioritize:

• High-Quality Protein: To preserve muscle mass, include sufficient lean protein sources like chicken, fish, tofu, or legumes.
• Healthy Fats: Avocados, nuts, seeds, and olive oil provide essential fatty acids.
• Complex Carbohydrates and Fiber: Whole grains, starchy vegetables, and a variety of colorful vegetables and fruits provide sustained energy and fiber for digestive health.
• Micronutrients: Focus on a diverse range of whole foods to ensure you get enough vitamins and minerals. For some, supplementation may be necessary to fill potential gaps.

Conclusion: Consider Your Body and Goals

While the prospect of effortless weight loss and improved focus makes eating one meal a day an appealing trend, the reality is far more complex. The OMAD diet is an extreme approach to intermittent fasting with significant risks, including nutrient deficiencies, muscle loss, and cardiovascular strain. For most people, less restrictive forms of IF or standard calorie restriction offer similar benefits with fewer potential dangers and higher sustainability. The decision to try any dietary pattern, especially one as restrictive as OMAD, should always be made in consultation with a healthcare professional to ensure it aligns with your specific health needs and goals. For a deeper scientific dive into metabolic changes during fasting, one can review studies like Meessen ECE, et al. (2022), which examined the differential effects of one meal per day on metabolic health and physical performance in lean individuals. Ultimately, listening to your body and prioritizing long-term, sustainable health over quick fixes is the safest and most effective strategy.

Frequently Asked Questions

Is it safe to eat only one meal per day?

For most healthy people, it is not recommended as a long-term strategy. The extreme restriction poses significant risks, including nutrient deficiencies, fatigue, and potential metabolic and cardiovascular issues. It should be undertaken only after consulting a healthcare professional.

What are the common side effects of eating one meal a day?

Common side effects include intense hunger, fatigue, low energy, dizziness, irritability, headaches, and digestive problems like bloating and constipation.

Can you lose weight by eating only one meal a day?

Yes, many people experience weight loss because eating one meal a day typically results in a significant calorie deficit. However, this is not necessarily more effective than other forms of calorie restriction and comes with greater risks.

Is it better to eat one big meal or multiple small ones?

For most people, consuming two or three balanced meals per day is a more sustainable and healthier option. It is easier to get adequate nutrients and maintain stable energy levels, and it does not carry the same risks as the OMAD diet.

What should be included in the one meal?

To mitigate risks, the single meal must be exceptionally nutrient-dense. It should include a balanced mix of lean protein, healthy fats, complex carbohydrates, and plenty of fruits and vegetables to provide essential vitamins and minerals.

Can I exercise while on the OMAD diet?

Gentle exercises like walking or yoga are generally safe. Strenuous exercise like heavy strength training is not recommended due to insufficient energy intake for muscle recovery. The timing of your meal relative to your workout can also affect your energy levels.

Is OMAD sustainable long-term?

For most individuals, OMAD is not a sustainable or practical long-term dietary strategy. The high potential for nutrient deficiencies, social challenges, and restrictive nature often lead to high dropout rates and a potential rebound weight gain.