Do you still absorb calories if you throw up your food?

December 22, 2025 •

3 min read

Research shows that vomiting cannot get rid of all ingested calories, even when done immediately after eating. This is because your body begins to absorb calories if you throw up your food, making purging an ineffective method for weight control.

Quick Summary

Your body starts absorbing calories the moment food enters your mouth, so throwing up doesn't remove all of them and is a dangerous and ineffective practice.

Key Points

Immediate Absorption: Digestion and calorie absorption begin as soon as food is chewed and mixed with saliva in the mouth.
Limited Removal: Vomiting, even immediately after eating, typically removes less than 50% of the calories consumed, not all of them.
Ineffective Strategy: Purging is an ineffective weight loss method, and many individuals who practice it actually gain weight over time.
Health Risks: Frequent purging can cause severe and irreversible health problems, including dental erosion, esophageal tears, and potentially fatal electrolyte imbalances.
Small Intestine's Role: The small intestine is where the majority of nutrient absorption happens, a stage of digestion that purging cannot stop once food has passed the stomach.
Misunderstanding the Body: The belief that purging 'undoes' caloric intake is a dangerous myth stemming from a misunderstanding of the body's robust digestive efficiency.

The Flawed Logic of Purging

Many misconceptions exist around how the body processes food and calories, including the dangerous belief that throwing up food eliminates all calories consumed. This idea misunderstands the digestive system, as calorie absorption is a continuous process that starts almost immediately after eating.

The Science Behind Calorie Absorption

The human body efficiently converts food into energy through digestion, a series of mechanical and chemical reactions beginning in the mouth and continuing through the stomach and small intestine.

Digestion Starts in the Mouth

Calorie absorption begins in the mouth. Chewing and saliva, which contains enzymes, start breaking down carbohydrates. Food then moves to the stomach, where acids and enzymes break down proteins, and the stomach lining can absorb simple sugars and alcohol. Therefore, some calories are absorbed before vomiting can occur.

The Small Intestine: Where Most Absorption Occurs

The majority of nutrient and calorie absorption happens in the small intestine. The stomach empties its contents into the small intestine within a few hours. The small intestine's villi increase surface area for absorption, breaking down food further into absorbable components like amino acids, fatty acids, and simple sugars. Once food is in the small intestine, purging cannot remove it, meaning a percentage of calories will be absorbed even if vomiting happens soon after eating.

Comparison of Calorie Retention


Action	Expected Calorie Retention	Reasons for Retention
Normal Digestion	Approximately 90-100% of available calories	Full digestive process, from mouth to small intestine, completes absorption.
Vomiting (Purging)	At least 50% of calories, often more	Absorption begins in the mouth and stomach; some contents may already be in the small intestine.
Laxative Abuse	Over 90% of calories	Laxatives affect the large intestine, primarily leading to water loss, not preventing calorie absorption in the small intestine.
Diuretic Abuse	100% of calories	Diuretics cause water loss and have no impact on calorie absorption.

The Dangerous Reality of Purging

Purging is ineffective for calorie elimination and has severe health risks, often associated with bulimia nervosa. It is not a safe way to control weight, and many people with bulimia gain weight.

Health Consequences of Purging

Frequent purging can lead to serious health issues:

Dental problems: Stomach acid erodes enamel, causing decay.
Esophageal damage: Acid irritates and damages the esophagus, potentially leading to tears or rupture.
Electrolyte imbalance: Loss of electrolytes can cause dangerous heart arrhythmias.
Gastrointestinal issues: Chronic strain can cause acid reflux and impaired gut function.
Nutrient deficiencies: Despite some calorie retention, purging causes malnutrition and dehydration.
Psychological impact: The cycle of binging and purging impacts mental health.

For more information on digestion, consult resources like the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Conclusion

The idea that throwing up removes all calories is a myth. Due to the rapid digestive process starting in the mouth, a significant portion of calories is absorbed before purging can occur. Purging is ineffective for weight management and carries severe, potentially fatal health risks, including heart problems and damage to the digestive system. Seeking professional help is crucial for those struggling with purging behaviors.

Frequently Asked Questions

Yes, you do. Calorie absorption begins in your mouth with saliva and continues in the stomach. Even if you vomit right away, some simple sugars and other nutrients will have already started to be absorbed.

Vomiting is not an effective method for long-term weight loss. Any initial weight change is likely due to water loss and not true fat loss. In fact, many individuals with bulimia nervosa gain weight over time.

Studies have shown that vomiting can only remove up to about half of the calories eaten, and often much less. The percentage absorbed depends on the type of food and the time elapsed.

Health risks are severe and include dental erosion from stomach acid, esophageal damage or rupture, heart problems due to electrolyte imbalance, malnutrition, and chronic dehydration.

Food can begin moving from the stomach into the small intestine within 1.5 to 3 hours. Once it reaches the small intestine, it is no longer possible to purge it through vomiting.

No, laxatives are highly ineffective at preventing calorie absorption. They primarily cause water loss and affect the large intestine, not the small intestine where most calories are absorbed.

If you or someone you know is struggling with purging behaviors, it is vital to seek professional help. Resources are available from medical professionals, therapists, and organizations specializing in eating disorders.