Can Eating One Meal a Day Make You Tired? Understanding OMAD Fatigue

January 1, 2026 •

4 min read

According to a study published in The Journal of Nutrition, extreme eating patterns like consuming one meal a day (OMAD) can lead to potential nutrient deficiencies and metabolic shifts. For many people, these changes manifest as fatigue and low energy, raising the critical question: can eating one meal a day make you tired?

Quick Summary

This article explores the primary reasons behind fatigue when practicing OMAD, including nutritional gaps, blood sugar instability, and metabolic adjustments. It offers actionable strategies to mitigate tiredness and optimize energy levels on a single-meal diet.

Key Points

Nutrient Deficiencies: It is challenging to get all essential nutrients in one meal, which can lead to deficiencies in vitamins like B12 and minerals like iron, causing fatigue.
Blood Sugar Swings: A large meal after a long fast can cause a blood sugar spike, followed by a crash, leading to a feeling of tiredness or a 'food coma'.
Electrolyte Imbalance: Fasting can deplete key electrolytes like sodium and potassium, resulting in symptoms such as fatigue and dizziness.
Metabolic Adjustment: Your body requires time to transition from burning glucose to fat for fuel, and this adaptation period often includes temporary fatigue and brain fog.
Inadequate Hydration: Many get their hydration from food, and reducing meal frequency can lead to dehydration, a primary cause of low energy and headaches.
Meal Composition Matters: Eating a balanced meal rich in protein, healthy fats, and fiber is crucial for sustained energy and preventing blood sugar fluctuations.

Why One Meal a Day (OMAD) Can Lead to Fatigue

While OMAD offers benefits like improved insulin sensitivity for some individuals, it can also cause significant challenges, especially concerning energy levels. Feeling tired on an OMAD diet is a common complaint, rooted in several physiological and nutritional factors. The body, accustomed to a steady supply of energy from food, must adapt to long fasting periods and a single, large energy intake.

Nutrient Deficiencies and Imbalances

Eating all your day's calories within a narrow window makes it difficult to consume a sufficient quantity and variety of essential nutrients. A single meal, however large, often fails to provide the full spectrum of vitamins and minerals required for sustained energy production. For example, deficiencies in key nutrients like B vitamins (crucial for energy metabolism) and iron (essential for red blood cell production) can directly cause fatigue. Similarly, a lack of electrolytes such as sodium, potassium, and magnesium can lead to symptoms like muscle weakness and general tiredness.

Blood Sugar Rollercoaster

One of the most significant causes of OMAD fatigue is the fluctuation of blood sugar levels. After an extended fasting period, consuming a large meal can cause a substantial spike in blood glucose. The body releases a large amount of insulin to manage this, which can then lead to a subsequent crash, resulting in feelings of drowsiness, lethargy, and an energy 'slump'. This is often called 'post-meal fatigue' or the 'food coma' effect, and it is exacerbated when the single meal is high in refined carbohydrates and sugar.

Dehydration and Electrolyte Imbalance

Staying hydrated is vital, especially on a fasting diet. When you consume fewer meals, you naturally miss out on the water content present in many foods. Furthermore, fasting and associated metabolic changes can cause the body to excrete more water and electrolytes. Inadequate intake of water and electrolytes, such as potassium, can lead to dehydration, which is a major contributor to fatigue, headaches, and dizziness.

The Metabolic Adjustment Phase

For those new to OMAD, the transition period can be particularly draining. The body is used to relying on glucose for immediate energy. During fasting, it must switch to burning stored fat for fuel, a process known as fat adaptation. This shift can take time and often comes with a temporary dip in energy levels, commonly referred to as the 'keto flu' or 'fasting fatigue'. Symptoms like tiredness, brain fog, and irritability are part of the body's metabolic adjustment.

Comparison Table: Causes of OMAD Fatigue


Cause	Mechanism	Fatigue Symptom	Mitigation Strategy
Nutrient Deficiency	Inadequate intake of essential vitamins and minerals in one meal.	Weakness, constant tiredness, brain fog.	Focus on nutrient-dense foods; consider supplements.
Blood Sugar Crash	Insulin spike after a large meal leads to a subsequent energy drop.	Post-meal drowsiness, lethargy, irritability.	Balance the meal with proteins, fats, and fiber; reduce refined carbs.
Dehydration/Electrolytes	Reduced fluid intake and mineral loss during fasting.	Headaches, dizziness, muscle cramps, low energy.	Drink plenty of water and use electrolyte supplements.
Metabolic Transition	Body adapts from using glucose to burning fat for energy.	Temporary low energy, mental fog, irritability.	Ease into OMAD gradually; be patient with the process.

Strategies to Mitigate Fatigue on OMAD

Experiencing tiredness on OMAD is not inevitable. By making mindful adjustments, you can help your body adapt more smoothly and maintain consistent energy levels throughout the day.

Here are some actionable strategies:

Prioritize Nutrient-Dense Foods: Make your single meal count. Focus on incorporating a wide variety of whole foods, including lean proteins, healthy fats, and a large portion of fibrous vegetables. This approach helps maximize your intake of essential vitamins and minerals.
Balance Your Macronutrients: Build your meal around high-quality protein and healthy fats. These macronutrients promote satiety and help stabilize blood sugar, preventing the dramatic spikes and crashes associated with high-carb meals.
Electrolyte Management: Consider supplementing with electrolytes, especially during the initial adaptation phase. A simple solution of water with a pinch of sea salt, potassium, and magnesium can make a significant difference.
Stay Hydrated: Drink plenty of water throughout your fasting window. Herbal teas and black coffee are also options that won't break your fast and can help with hydration and focus.
Consider Meal Timing: The timing of your meal can impact your energy. Some people find that eating in the late afternoon or early evening prevents a post-meal slump from affecting their workday. Others prefer an earlier meal. Listen to your body and adjust accordingly.
Ease into It: Don't jump straight into OMAD. Begin with less restrictive intermittent fasting methods, such as 16:8, to allow your body to gradually adapt to the longer fasting periods.
Incorporate Gentle Exercise: Light to moderate exercise, like walking, can improve insulin sensitivity and boost energy. Avoid intense workouts during the initial transition, which can exacerbate fatigue.

Conclusion: Navigating OMAD for Sustainable Energy

While the answer to "Can eating one meal a day make you tired?" is often 'yes', particularly during the initial phase, it's not a permanent state for everyone. Fatigue is a common side effect rooted in identifiable causes, such as nutrient deficits, electrolyte imbalances, and blood sugar fluctuations. By being strategic with your meal's nutritional composition, managing hydration and electrolytes, and allowing your body a gradual transition, it is possible to minimize tiredness and maintain consistent energy levels. For those considering OMAD, approaching it mindfully and listening to your body's signals is paramount. Consulting a healthcare professional is always recommended, especially if persistent fatigue or other concerns arise. This can help ensure your diet is both sustainable and safe for your individual health needs.

Authoritative Link: The effect of consuming one meal a day (OMAD) on insulin sensitivity.

Frequently Asked Questions

Yes, feeling tired is a common and normal side effect, especially during the initial adaptation phase. It can be caused by your body adjusting to different fuel sources (switching from glucose to fat) or imbalances in nutrients and electrolytes.

OMAD fatigue is often temporary. For most, the initial tiredness subsides as the body becomes more efficient at burning fat for energy. This adaptation period can take anywhere from a few days to a couple of weeks.

To prevent a post-meal energy crash, focus on a balanced meal rich in high-quality protein, healthy fats, and a large portion of fibrous vegetables. Minimize refined carbohydrates and sugars, which cause sharp blood sugar spikes and subsequent crashes.

Absolutely. During fasting, you lose the fluid intake typically provided by food. Inadequate water and electrolyte intake can lead to dehydration, which is a major contributor to fatigue, headaches, and brain fog.

Prioritize nutrient density in your one meal. Include a variety of whole foods such as lean meats, eggs, avocados, nuts, seeds, and leafy greens. You can also consider a quality multivitamin and mineral supplement to fill any potential gaps.

For some, eating earlier in the day helps maintain energy, while for others, a later meal works better with their body clock and sleep patterns. Experiment to find the timing that aligns best with your energy needs and personal schedule.

Gradually transition by starting with a less restrictive fasting schedule, like 16:8 or 18:6, before moving to a single meal. This allows your body to adapt more smoothly to longer fasting periods and metabolic shifts.