Why do I feel bad after drinking sugary drinks?

December 1, 2025 •

4 min read

According to the CDC, sugary drinks are the leading source of added sugars in the American diet, and overindulging can lead to unpleasant symptoms like fatigue, jitters, and upset stomach. This phenomenon, often called a "sugar crash," is the body's natural reaction to a rapid spike and subsequent drop in blood glucose levels after drinking sugary drinks.

Quick Summary

The unpleasant feelings after consuming sugary drinks are caused by the body's reaction to rapid blood sugar spikes and crashes. High sugar intake triggers an insulin response that overcorrects, resulting in a sudden energy slump and mood changes. Digestive issues and other short-term discomforts can also occur. Long-term risks include weight gain, diabetes, and heart disease.

Key Points

The Sugar Crash: A rapid spike in blood glucose from sugary drinks is followed by a sharp drop, causing fatigue, mood swings, and jitters.
Reactive Hypoglycemia: The pancreas over-releases insulin in response to excess sugar, leading to a blood sugar level that is too low.
Digestive Issues: Carbonation and high sugar can cause bloating, gas, and stomach upset, exacerbated for those with sucrose intolerance.
Fluid Dynamics: Sugary drinks can contribute to dehydration as the kidneys work to process and flush out excess sugar.
Long-term Risks: Chronic consumption is linked to a higher risk of weight gain, type 2 diabetes, heart disease, and fatty liver disease.
Inflammation and Mood: High sugar intake can increase systemic inflammation and lead to mood disturbances like anxiety and depression.
Healthier Swaps: Opting for water, unsweetened tea, or fruit-infused water can prevent the negative side effects of sugary drinks.

The Blood Sugar Rollercoaster: The Science Behind the 'Sugar Crash'

When you consume a sugary drink, the simple sugars—like fructose and glucose—are absorbed into your bloodstream very quickly. Unlike sugars from whole foods, which are buffered by fiber, protein, and fat, the liquid sugar from a soda or juice is rapidly absorbed and hits your system all at once. This causes your blood glucose levels to spike dramatically, sometimes called a "sugar rush."

In response to this rapid spike, your pancreas releases a large amount of insulin, a hormone that helps transport the glucose from your blood into your cells for energy. This is a crucial bodily function, but when it overcorrects, it can cause your blood sugar levels to fall too low, a state known as reactive hypoglycemia. This rapid drop is the notorious "sugar crash," leaving you feeling weak, tired, and irritable.

Other Physiological Reactions That Cause Discomfort

Beyond the blood sugar spike and crash, several other mechanisms contribute to why you feel bad after drinking sugary drinks.

Digestive Distress: The carbonation in many fizzy drinks and the high sugar content itself can cause stomach pain, bloating, and gas, especially in individuals with sensitive digestive systems. For some, an intolerance to sucrose (common table sugar) may cause these symptoms more severely.
Dehydration: Excessive sugar intake can actually lead to dehydration. Your kidneys use more water to flush out the excess sugar, which can leave you feeling thirsty and unwell.
Inflammation: A diet high in added sugars can increase systemic inflammation throughout the body, which has been linked to a variety of negative health outcomes, including fatigue and mood changes.
Hormonal Imbalance: The rapid insulin response and subsequent low blood sugar can trigger the release of stress hormones like adrenaline and cortisol. This can lead to anxiety, shakiness, and heart palpitations. Additionally, excess fructose consumption can lead to leptin resistance over time, an important hormone that regulates hunger, causing you to feel hungry even after consuming a high-calorie drink.

Comparison of Blood Sugar Response


Feature	Sugary Drink	Balanced Meal (e.g., grilled chicken, vegetables)
Sugar Type	Mostly simple sugars (fructose, glucose) with no fiber, fat, or protein.	Complex carbohydrates, natural sugars, fiber, fat, and protein.
Absorption Rate	Very rapid, leading to a dramatic blood sugar spike.	Slower and more gradual, thanks to fiber, fat, and protein.
Insulin Response	A large surge of insulin to manage the sudden sugar load.	A more moderate and sustained insulin release.
Post-Consumption Feeling	Prone to a "crash" or reactive hypoglycemia, causing fatigue, jitters, and irritability.	Sustained energy and feeling of fullness, with no dramatic crash.
Digestive Impact	Can cause gas, bloating, and other digestive discomforts due to carbonation and high sugar.	Fiber and other nutrients aid in digestion.

Long-Term Effects of Chronic Sugary Drink Consumption

While the immediate crash is a noticeable consequence, consistently consuming sugary drinks can lead to more severe, long-term health problems. Many of these issues are interconnected and can exacerbate one another over time.

Weight Gain and Obesity: Sugary drinks are a major source of empty calories. Studies have shown a strong link between regular consumption of these beverages and increased weight gain and a higher risk of obesity. This is partly because liquid calories do not trigger the same sense of fullness as solid food, making it easy to over-consume without feeling satiated.
Type 2 Diabetes: Prolonged, frequent spikes in blood sugar can desensitize your body's cells to insulin, a condition called insulin resistance. Over time, this increases the risk of developing type 2 diabetes.
Heart Disease: High sugar intake has been associated with elevated blood pressure, unhealthy cholesterol levels, and inflammation, all of which are major risk factors for heart disease. The added strain on the cardiovascular system can lead to serious complications over time.
Fatty Liver Disease: Unlike other sugars, fructose is primarily metabolized by the liver. When consumed in large amounts, as in many sugary beverages, it can overwhelm the liver and lead to a build-up of fat. This can result in non-alcoholic fatty liver disease (NAFLD).
Dental Issues: The combination of sugar and acids in sweetened drinks creates a perfect environment for mouth bacteria to thrive. These bacteria produce acids that erode tooth enamel, leading to cavities and decay.

Healthier Alternatives to Sugary Drinks

To avoid the negative effects of sugary drinks, consider these healthier alternatives:

Infused Water: Add sliced fruit (like lemon, berries, or cucumber) and herbs (mint, basil) to plain water for a refreshing and hydrating beverage.
Unsweetened Tea and Coffee: These can be great options, but be mindful of adding excessive sugar. Explore natural sweeteners like cinnamon or vanilla extract instead.
Sparkling Water: For those who enjoy carbonation, sparkling water with a splash of fruit juice or a squeeze of fresh citrus can be a satisfying alternative to soda.
Herbal Teas: Enjoy a wide range of herbal teas, which offer flavor and hydration without the added sugar.
DIY Lemonade or Ginger Ale: Homemade versions allow you to control the sweetener. You can use less sugar or natural alternatives like stevia to create a tasty drink.

Conclusion

Feeling bad after drinking sugary beverages is a complex physiological response involving blood sugar fluctuations, hormonal changes, and digestive reactions. The initial energy rush is quickly followed by a crash, leaving you fatigued and irritable. The long-term consequences of regular consumption, including increased risks for obesity, type 2 diabetes, heart disease, and fatty liver disease, are even more concerning. By understanding why your body reacts this way, you can make informed decisions to reduce your sugar intake and opt for healthier, more hydrating alternatives. This proactive approach can help stabilize your energy levels, improve your overall mood, and support long-term metabolic health.

Visit Harvard's The Nutrition Source for more information on the health effects of sugary drinks.

Frequently Asked Questions

A sugar crash is the fatigue, irritability, and low energy that follows a rapid spike in blood sugar. It's caused by the pancreas releasing a large amount of insulin in response to the sugar, which then causes blood glucose levels to drop sharply below normal levels.

Sugary drinks can lead to bloating, gas, and an upset stomach due to their carbonation and high sugar content. For some people with a sucrose intolerance, the inability to properly digest sugar can also cause significant abdominal discomfort.

Yes, a sudden drop in blood sugar can trigger the release of stress hormones like adrenaline, which can cause symptoms such as shakiness, anxiety, and a rapid heartbeat. This is a common part of the reactive hypoglycemia response.

To prevent a sugar crash, moderate your sugar intake and try to consume it alongside fiber, protein, or healthy fats. These nutrients slow down sugar absorption. Drinking plenty of water also helps, and choosing healthier alternatives like fruit-infused water or herbal tea can eliminate the problem entirely.

Unlike sugary drinks, whole fruits contain natural sugars packaged with fiber. This fiber slows the absorption of sugar into the bloodstream, preventing the dramatic spike and subsequent crash associated with processed sugary beverages.

While diet sodas don't contain sugar, studies suggest they may still have negative health effects, potentially contributing to metabolic issues and cravings. The best alternative remains water or unsweetened drinks.

Regular consumption of sugary drinks can lead to increased risks for obesity, type 2 diabetes, heart disease, and fatty liver disease. The constant burden on the body's systems can cause serious, chronic health problems over time.