What Happens If I Only Eat in the Afternoon?

November 27, 2025 •

4 min read

According to a 2022 study, lean and healthy adults who ate one meal per day in the afternoon saw greater body fat loss compared to those eating three meals daily. But what happens if I only eat in the afternoon over the long term, and are the potential risks worth the rewards? This extreme form of intermittent fasting, known as One Meal A Day (OMAD), can trigger significant metabolic changes, nutrient deficiencies, and other health issues that should be carefully considered.

Quick Summary

Limiting food intake to one afternoon meal, a form of intermittent fasting, can lead to weight loss but also introduces significant risks. Long-term practice may cause nutrient deficiencies, blood sugar fluctuations, metabolic disruptions, and hormonal imbalances, with sustainability issues for many.

Key Points

Weight Loss vs. Sustainability: Eating only in the afternoon can cause weight loss by creating a calorie deficit, but the extreme restriction is difficult to sustain and poses long-term health risks.
Metabolic Impact: Prolonged fasting can disrupt your metabolism, with some studies showing increased blood pressure and cholesterol levels, especially in the long run.
Nutrient Deficiency: Meeting all your daily nutrient requirements in a single meal is challenging and can lead to deficiencies that affect overall health, including bone density and immune function.
Circadian Alignment: Aligning your single meal with the afternoon aligns with your body's natural rhythm for digestion, but this does not negate the risks of extreme fasting.
Less Restrictive Alternatives: Less extreme versions of intermittent fasting, like the 16:8 method, are more sustainable and have fewer associated health risks for most people.
Consult a Professional: Always consult a healthcare provider or dietitian before beginning a restrictive diet like OMAD to ensure it is appropriate for your individual health needs.

Understanding the OMAD Diet and Afternoon Eating

Eating only one meal a day (OMAD) in the afternoon is an extreme variant of intermittent fasting (IF). It confines your daily caloric intake to a very short window, typically one to two hours, around midday. While this approach can simplify your schedule and initially create a substantial calorie deficit for weight loss, it forces your body into a prolonged fasting state every day. Your body must adapt to using stored fat for energy instead of relying on a consistent supply of glucose from meals, leading to significant metabolic shifts. The timing of this single meal—the afternoon—is also a crucial factor, as it aligns with the body's natural circadian rhythm, which research suggests is more efficient at metabolizing food earlier in the day.

Potential Benefits of Eating Only in the Afternoon

For those who adhere strictly to a balanced and nutritious single meal, potential short-term benefits can arise from the extended fasting period.

Weight and Fat Loss: The primary draw of OMAD is the potential for weight loss. By restricting eating to a single meal, many people find it easy to create a calorie deficit, which is the fundamental requirement for losing weight. Studies have shown that consuming one meal in the evening can increase fat oxidation during exercise.
Mental Clarity and Focus: Some individuals report feeling more alert and focused during their fasting window. This is sometimes attributed to the body releasing a chemical called orexin-A, which increases alertness when fasting.
Improved Insulin Sensitivity: Fasting can lead to lower insulin levels, potentially improving insulin sensitivity, which is beneficial for metabolic health.
Simplification of Routine: With only one meal to plan and prepare, this eating pattern can dramatically simplify a person's daily routine.

Significant Risks and Drawbacks

Despite the potential short-term upsides, the risks associated with consistently eating only one meal in the afternoon are considerable and cannot be ignored. The extreme restriction poses serious challenges for meeting nutritional requirements and maintaining long-term health.

Nutrient Deficiencies: It is extremely difficult to consume all the necessary vitamins, minerals, and macronutrients in a single meal, especially in the long run. This can lead to health problems ranging from fatigue to weakened immune function and decreased bone density.
Metabolic and Hormonal Disruption: For some, OMAD can cause significant metabolic and hormonal issues. Studies have shown potential increases in blood pressure and cholesterol levels in those following an OMAD pattern. For women, extended fasting can disrupt the endocrine system, potentially leading to irregular periods and stress on the body.
Extreme Hunger and Binge Eating: A 23-hour fast can lead to intense hunger and cravings, which may lead to binge eating or poor food choices during the short eating window. This can result in consuming high-calorie, low-nutrient, and heavily processed foods.
Muscle Mass Loss: While effective for fat loss, OMAD can also result in a loss of lean muscle mass. The body has a limit to how much protein it can effectively absorb at one time, making it difficult to get enough protein in a single meal to maintain muscle.
Blood Sugar Volatility: Especially for individuals with or at risk for diabetes, the significant fast followed by a large meal can cause a major blood sugar spike. Some studies even show higher fasting blood sugar levels and reduced insulin response with OMAD compared to more frequent meals.

OMAD vs. Less Restrictive Time-Restricted Eating

To better understand the implications of a single-meal approach, it's helpful to compare it with more moderate intermittent fasting methods, such as the 16:8 protocol. The comparison highlights why OMAD is considered a more extreme and potentially riskier choice.


Feature	Eating Only in the Afternoon (OMAD)	Time-Restricted Eating (e.g., 16:8)
Fasting Window	22–23 hours	16 hours
Eating Window	1–2 hours	8 hours
Nutrient Intake	Extremely challenging to get sufficient nutrients	Easier to meet daily nutritional needs
Sustainability	Very difficult for most people long-term	More manageable and sustainable
Metabolic Risks	Potential for elevated cholesterol, blood pressure, and cortisol	Generally fewer metabolic risks reported
Muscle Mass	Higher risk of muscle mass loss	Better capacity for muscle maintenance

The Importance of Chrononutrition

Chrononutrition is the study of how meal timing affects our metabolism and health. Research in this field shows that the body is more efficient at metabolizing food during the daytime, while late-night eating has been linked to negative metabolic outcomes. Choosing to eat your single meal in the afternoon, rather than late at night, aligns with your body's circadian rhythm and may help mitigate some of the negative effects associated with late-night eating, such as higher blood sugar levels. However, it does not erase the significant nutrient and metabolic challenges posed by an extreme fasting schedule like OMAD. The optimal eating pattern for most people involves eating earlier in the day and closing the eating window well before bedtime to allow for an overnight fast. For more detailed information on meal timing research, a good source is the National Institutes of Health.

Conclusion

While eating only in the afternoon, as a form of OMAD intermittent fasting, can lead to short-term weight loss and increased mental alertness for some, it comes with a multitude of potential risks that should not be taken lightly. The difficulty of obtaining sufficient nutrients, the potential for metabolic and hormonal disturbances, and the high rate of non-adherence make this an unsustainable and potentially dangerous long-term strategy for most. Anyone considering this diet should consult with a healthcare professional to determine if it is appropriate and to create a safe plan for managing nutritional intake. For a majority of individuals, a less restrictive form of time-restricted eating, combined with a balanced diet, is a safer and more effective path to achieving health and wellness goals.

Frequently Asked Questions

Yes, for most people, eating only once a day in the afternoon can be unhealthy, particularly as a long-term practice. It increases the risk of nutrient deficiencies, metabolic issues, muscle loss, and binge eating.

You may lose weight due to the severe calorie restriction associated with eating only one meal a day. However, this is often unsustainable and can lead to negative side effects, and it's not necessarily more effective than other forms of calorie reduction.

Common side effects include fatigue, dizziness, irritability, headaches, constipation, and intense hunger pangs. It can also cause metabolic issues like blood sugar spikes and elevated cholesterol.

Yes, eating only once a day can slow down your metabolism, as your body may enter a "starvation mode" and conserve energy. Over time, this can make it more difficult to lose weight and maintain a healthy weight.

People with a history of eating disorders, pregnant or breastfeeding individuals, children, and those with diabetes or other chronic conditions should avoid this diet. It can exacerbate underlying health issues.

From a circadian rhythm perspective, eating earlier in the day is generally more beneficial, as your body is more efficient at processing food. Therefore, an afternoon meal is often metabolically preferable to a late-night one.

Ensuring adequate nutrition in a single meal is challenging but requires careful planning. Focus on a nutrient-dense meal rich in protein, healthy fats, fiber, and a wide variety of whole foods. Consulting a dietitian is recommended to create a balanced plan.