Is one big meal a day unhealthy? An expert look at the OMAD diet

November 10, 2025 •

4 min read

While proponents of the One Meal a Day (OMAD) diet praise its potential for weight loss and simplified eating, many health experts advise caution. This extreme form of intermittent fasting has both touted benefits and significant risks that must be carefully considered. Before adopting this restrictive eating pattern, it's essential to understand if is one big meal a day unhealthy for your specific health needs.

Quick Summary

This article examines the science behind the OMAD diet to determine if it is a healthy eating pattern. It explores the potential benefits like weight loss and fat burning, alongside serious risks such as nutrient deficiencies, metabolic disruptions, and heightened cardiovascular risk factors.

Key Points

The OMAD diet restricts eating to one meal per day, forcing a 23-hour fasting period.
Risks include potential nutrient deficiencies and metabolic issues, such as increased cholesterol and blood pressure.
It can cause significant blood sugar fluctuations, which is particularly dangerous for individuals with diabetes.
OMAD carries a risk of muscle mass loss because of the long periods without protein intake.
The diet can lead to extreme hunger and binge-eating tendencies, negatively affecting one's relationship with food.
Most healthcare professionals recommend less restrictive and more sustainable eating patterns, like 16:8 intermittent fasting or simply focusing on balanced, nutritious meals.
Certain individuals, including those with diabetes and eating disorders, should avoid OMAD.

What Happens to Your Body on the OMAD Diet?

Eating one meal a day, or OMAD, means you fast for approximately 23 hours and consume all your daily calories within a single, short eating window. During the fasting period, your body shifts from using glucose for energy to burning stored fat in a process known as ketosis. While this may lead to weight loss due to reduced calorie intake, the physiological effects are complex and not all are beneficial.

Potential Benefits

Some research suggests potential short-term benefits from consuming all calories in one meal:

Weight Loss and Fat Reduction: By restricting calories to a single meal, many people create a calorie deficit naturally, which can lead to weight loss. A 2022 study showed that restricting calories to a two-hour evening window resulted in greater body fat loss than eating three meals a day for a small group of healthy, lean adults.
Improved Insulin Sensitivity: Prolonged fasting can help improve insulin sensitivity, which is beneficial for metabolic health. A longer fasting period allows insulin levels to drop, preventing constant insulin spikes.
Enhanced Autophagy: Fasting periods can trigger autophagy, a cellular repair process where the body cleans out damaged cells. Some proponents believe this promotes longevity.
Simplified Eating: The routine of eating just one meal simplifies meal planning and preparation, freeing up time and mental energy.

Significant Health Risks

For many, the risks of long-term OMAD use outweigh the potential benefits, making the question "is one big meal a day unhealthy?" a valid concern. The extreme restriction poses several health challenges:

Nutrient Deficiencies: It is extremely difficult to consume all the necessary macronutrients, vitamins, and minerals in a single meal, regardless of how nutritionally dense it is. This can lead to serious deficiencies over time.
Cardiovascular Issues: Some studies have shown that eating one meal a day can increase total and "bad" LDL cholesterol levels, as well as blood pressure, raising the risk for cardiovascular disease.
Blood Sugar Problems: For some individuals, particularly those with or at risk for diabetes, OMAD can cause significant fluctuations in blood sugar. Studies have shown that a single, large meal can lead to higher morning fasting blood sugar levels and a delayed insulin response.
Loss of Muscle Mass: When the body is in a prolonged fasted state, it may begin breaking down muscle tissue for energy, especially if protein intake is insufficient. Spreading protein intake throughout the day is generally recommended for optimal muscle maintenance and growth.
Metabolic Slowdown: While initially boosting fat-burning, prolonged extreme fasting could potentially slow down a person's metabolic rate over time as the body adapts to consuming fewer calories.
Increased Hunger and Binge Eating: Extended fasting can increase levels of the hunger hormone ghrelin, leading to intense cravings and a higher risk of overeating or bingeing during the single meal. This can create an unhealthy relationship with food.

Comparison: OMAD vs. Spreading Meals


Feature	One Meal a Day (OMAD)	Spreading Meals Throughout the Day
Weight Management	Effective for creating a calorie deficit and rapid initial weight loss.	Sustainable, steady weight loss can be achieved by managing overall calorie intake.
Satiety & Hunger	Extreme hunger and cravings are common, potentially leading to overeating.	Helps regulate blood sugar and hormone levels, preventing extreme hunger pangs.
Nutrient Intake	Challenging to meet all daily nutritional requirements in a single sitting, risking deficiencies.	Easier to distribute nutrient intake across several meals, ensuring a balanced diet.
Metabolic Health	Can improve insulin sensitivity and increase fat oxidation, but may negatively impact blood sugar and cholesterol long-term.	Stable blood sugar and nutrient supply throughout the day support a steady metabolic rate.
Muscle Preservation	Higher risk of muscle loss, especially with insufficient protein intake.	Better for maintaining or building muscle mass by distributing protein intake.
Sustainability	Very high dropout rate due to the restrictive and challenging nature.	Generally considered a more manageable and sustainable eating pattern for most people.

Is the OMAD Diet Right for You?

For most healthy adults, OMAD is not recommended as a sustainable or ideal long-term eating strategy. The health risks associated with potential nutrient deficiencies, blood sugar instability, and cardiovascular strain are significant. Most healthcare professionals advise exploring less extreme intermittent fasting methods, such as the 16:8 or 18:6 eating windows, which are more sustainable and less likely to cause adverse side effects.

Furthermore, certain populations should strictly avoid the OMAD diet, including pregnant or breastfeeding women, children, older adults, and individuals with a history of eating disorders or blood sugar regulation issues, such as type 1 or type 2 diabetes.

Ultimately, the optimal eating pattern depends on individual health goals, lifestyle, and how your body responds. If weight management is your goal, many studies suggest that the overall quality and quantity of your diet matter more than meal frequency. Consistent, healthy eating patterns and regular physical activity are more sustainable and safer paths to long-term health than extreme restriction.

Conclusion: The Balanced Approach

While the concept of eating just one big meal a day may seem appealing for its simplicity, the overwhelming evidence suggests that for most people, is one big meal a day unhealthy. The potential for nutrient deficiencies, metabolic disruptions, and other negative health effects makes it a risky approach, particularly over the long term. Safer and more sustainable strategies focus on balanced, nutrient-dense meals within a less restrictive timeframe. Before embarking on any extreme diet, a consultation with a healthcare provider or registered dietitian is crucial to ensure your eating plan aligns with your individual health needs and goals.

Frequently Asked Questions

Research suggests that both methods can lead to weight loss if they result in a calorie deficit. However, eating smaller, more frequent meals often results in less hunger and a more stable metabolism, making it a more sustainable and potentially healthier long-term option for many.

The risks include nutrient deficiencies, increased cholesterol and blood pressure, blood sugar imbalances, fatigue, irritability, and potential muscle mass loss. It can also increase hunger and lead to binge-eating behaviors.

Yes, there is a risk that prolonged extreme fasting could potentially slow down your metabolic rate as your body adapts to a significantly lower, and inconsistent, calorie intake. This can make long-term weight management more difficult.

The OMAD diet is not suitable for everyone. It should be avoided by pregnant or breastfeeding women, children, older adults, and people with diabetes, blood sugar issues, or a history of eating disorders.

Yes, OMAD is considered an extreme form of intermittent fasting, often referred to as the 23:1 method, which involves a 23-hour fasting window and a one-hour eating window.

It is extremely challenging, if not impossible, to obtain all essential nutrients, vitamins, and minerals from a single meal, even if carefully planned. Consistently following OMAD risks developing significant nutritional deficiencies over time.

Yes, less extreme forms of intermittent fasting, like the 16:8 or 18:6 methods, are often recommended as more sustainable and less likely to cause adverse effects. Additionally, focusing on a consistently balanced, nutritious diet across multiple meals is a safer long-term strategy.