Can Eating Certain Foods Cause Fatigue? The Surprising Science Behind Your Energy Dip

December 12, 2025 •

5 min read

According to research published in the journal Nutrients, poor dietary intake and the consumption of nutrient-poor foods is a recognized contributor to fatigue and mental weariness. This phenomenon raises the important question: Can eating certain foods cause fatigue, and if so, how can you optimize your diet to feel more energized throughout the day?

Quick Summary

This article explores the definitive link between diet and energy levels, examining how high-sugar foods, refined carbohydrates, and certain sensitivities can trigger fatigue. It covers the metabolic processes involved and provides actionable dietary strategies to support sustained energy and prevent the dreaded post-meal slump.

Key Points

Blood Sugar Swings: Refined carbs and sugars cause rapid blood sugar spikes followed by crashes, leading to a sudden and pronounced feeling of fatigue.
Fatty Foods Slow Digestion: High-fat and fried foods require more energy to digest, diverting resources away from the brain and causing sluggishness.
Food Intolerances Cause Inflammation: Undiagnosed sensitivities to foods like gluten or dairy can cause internal inflammation and impaired nutrient absorption, leading to persistent tiredness.
Nutrient Deficiencies Deplete Energy: A lack of key nutrients such as iron, B vitamins (especially B12), and magnesium can directly cause fatigue by disrupting cellular energy production.
Complex Carbs for Sustained Power: Whole grains, fruits, and vegetables provide complex carbohydrates and fiber, resulting in a slow, steady release of energy and preventing crashes.
Hydration is Critical: Staying properly hydrated is fundamental for maintaining alertness and avoiding the tiredness that can result from even mild dehydration.
Timing and Portions Matter: Eating smaller, balanced meals throughout the day provides a more consistent energy supply than large, heavy meals, which can overwhelm the digestive system.

The experience of feeling inexplicably tired or sluggish after eating is surprisingly common, a phenomenon known as 'postprandial somnolence' or, more casually, a 'food coma'. While many assume this is a normal part of digestion, the truth is that the types and combinations of foods you consume play a critical role in how your body’s energy levels are affected. Understanding the specific foods and physiological mechanisms at play is the first step toward regaining control over your daily energy.

The Sugar Rollercoaster: The Link Between Refined Carbs and Fatigue

One of the most direct pathways from food to fatigue is through the consumption of refined carbohydrates and high-sugar foods. Items like white bread, pastries, sugary cereals, and sweetened beverages are quickly digested and absorbed into the bloodstream. This rapid influx of glucose causes a spike in blood sugar, prompting the pancreas to release a large amount of insulin. Insulin helps transport glucose into your cells for energy, but the resulting drop in blood sugar can leave you feeling drained, tired, and unfocused—a classic 'sugar crash'. This cycle of spikes and crashes can be exhausting for your body and mind.

The Impact of Processed Foods and Saturated Fats

Processed and fast foods often contribute to fatigue for multiple reasons. They are typically high in saturated fats, added sugars, and sodium but low in essential nutrients like vitamins, minerals, and fiber. High-fat foods, especially fried options, take longer to digest, requiring the body to divert significant energy to the digestive process. This can cause a noticeable slowdown in your mental and physical alertness. Additionally, nutrient-poor, ultra-processed foods can lead to inflammation, which has been linked to chronic fatigue over time.

Food Intolerances and Sensitivities

Beyond the immediate impact of high-sugar or fatty foods, chronic fatigue can also be a symptom of an undiagnosed food intolerance or sensitivity. Unlike a full-blown allergy, which triggers an immediate immune response, an intolerance can cause a delayed and more subtle reaction. When the body struggles to digest a certain food, such as lactose in dairy or gluten in wheat, it can lead to gut inflammation and poor nutrient absorption, both of which can lead to persistent tiredness. Common culprits include:

Gluten: In individuals with celiac disease or non-celiac gluten sensitivity, gluten consumption can damage the gut lining, impairing nutrient absorption and causing significant fatigue.
Dairy: Lactose intolerance or a casein allergy can lead to digestive distress and inflammation, which can manifest as fatigue.
Other common intolerances: Ingredients like soy, eggs, and certain fruits and vegetables can also cause issues for sensitive individuals.

Nutrient Deficiencies That Can Lead to Fatigue

What you're lacking in your diet can be just as impactful as what you're consuming. Several nutrient deficiencies are directly linked to fatigue and low energy levels because they disrupt the body's energy production at a cellular level.

Iron: This mineral is vital for producing hemoglobin, which transports oxygen throughout the body. Iron deficiency anemia can cause extreme tiredness, weakness, and impaired cognitive function.
Vitamin B12 and Folate: These B vitamins are crucial for red blood cell production and energy metabolism. Low levels can lead to megaloblastic anemia, a type of vitamin deficiency anemia characterized by large, immature red blood cells and profound fatigue.
Magnesium: Involved in over 300 biochemical reactions in the body, magnesium is essential for cellular energy production. A deficiency can cause muscle cramps, weakness, and fatigue.
Vitamin D: This vitamin plays a role in energy production and muscle function, and low levels have been linked to fatigue and muscle weakness.

Comparison: Energy-Draining vs. Energy-Boosting Foods

Understanding the contrast between foods that sap your energy and those that provide sustained fuel can dramatically improve your daily vitality. The key is to prioritize nutrient-dense, whole foods that support stable blood sugar and efficient digestion.


Feature	Energy-Draining Foods	Energy-Boosting Foods
Carbohydrates	Refined carbs (white bread, pasta, pastries) cause rapid glucose spikes and crashes.	Complex carbs (whole grains, sweet potatoes, oats) provide a slow, steady release of energy.
Fats	Saturated and trans fats (fried foods, processed meats) divert energy to digestion and can cause sluggishness.	Healthy fats (avocado, nuts, seeds, olive oil) support sustained energy and brain function.
Protein	Heavy, fatty proteins can be slow to digest and tax the system.	Lean protein (chicken breast, fish, eggs, legumes) promotes satiety and provides steady energy.
Sugar	Added sugars in candy, soda, and baked goods lead to the classic energy crash.	Natural sugars in fruit, paired with fiber, offer a more stable energy source.
Nutrients	Processed foods are typically low in vital nutrients.	Whole foods are rich in vitamins and minerals essential for energy production.
Hydration	Sugary beverages and alcohol contribute to dehydration and fatigue.	Water and hydrating foods are crucial for maintaining alertness and energy.

Conclusion: Fueling Your Body for Lasting Vitality

Yes, eating certain foods can absolutely cause fatigue, and the reasons are rooted in several interconnected metabolic and physiological processes. From the blood sugar fluctuations triggered by refined carbohydrates to digestive issues caused by food intolerances and even simple nutrient deficiencies, diet is a powerful driver of your daily energy levels. By shifting away from processed, high-sugar foods toward a diet rich in whole grains, lean proteins, healthy fats, and a wide array of fruits and vegetables, you can provide your body with the clean, stable fuel it needs. Pairing these mindful food choices with adequate hydration, good sleep, and regular exercise will create a robust foundation for sustained energy and well-being. If persistent fatigue continues despite dietary changes, it is always recommended to consult a healthcare professional to rule out underlying medical conditions.

Tips for Sustained Energy

Balance Your Macronutrients: Combine lean protein, complex carbohydrates, and healthy fats in every meal and snack to stabilize blood sugar levels.
Prioritize Complex Carbs: Choose whole grains like quinoa, oats, and brown rice over refined options to avoid energy crashes.
Stay Hydrated: Drink plenty of water throughout the day, as even mild dehydration can trigger fatigue.
Listen to Your Body: Pay attention to how different foods affect you and keep a food diary to identify potential intolerances or sensitivities.
Don't Skimp on Nutrients: Ensure adequate intake of iron, B vitamins, magnesium, and vitamin D through diet or supplementation if necessary.
Time Your Meals: Eat smaller, more frequent meals to provide your body with a consistent supply of nutrients, rather than overwhelming it with large, heavy portions.
Limit Sugary Drinks: Opt for water or unsweetened tea instead of soda and energy drinks, which cause rapid energy spikes and crashes.

Frequently Asked Questions

Foods most likely to cause fatigue include those high in refined sugars and simple carbohydrates (like white bread, pastries, and candy), high-fat and fried foods, and large meals that overwhelm the digestive system. Excess alcohol and caffeine, when consumed in large quantities or at the wrong time, can also disrupt sleep and lead to next-day fatigue.

A sugar crash happens after you eat refined carbs or sugary foods, causing a rapid spike in blood sugar. Your body releases insulin to manage this sugar, which then causes your blood sugar to plummet below baseline. This dip leaves you feeling tired, sluggish, and unfocused.

Yes, chronic fatigue can be a symptom of an undiagnosed food intolerance or sensitivity, such as to gluten or dairy. When your body has trouble digesting certain foods, it can lead to gut inflammation and poor nutrient absorption, which over time can cause persistent tiredness.

For sustained energy, focus on a balanced diet rich in complex carbohydrates (whole grains, vegetables), lean proteins (fish, chicken, beans), and healthy fats (avocado, nuts). These foods provide a steady release of energy and prevent sharp blood sugar fluctuations.

The 'food coma,' or postprandial somnolence, is a real phenomenon often exaggerated for holiday meals. While the tryptophan in turkey is a factor, the crash is more likely caused by the high volume of food, a large proportion of carbohydrates and fats, and the natural afternoon dip in your circadian rhythm.

Yes, proper hydration is critical for energy. Even mild dehydration can negatively impact your mood, alertness, and cognitive function, making you feel tired and less focused.

To prevent post-meal fatigue, eat balanced meals with a combination of fiber, protein, and healthy fats to stabilize blood sugar. Eat smaller, more frequent meals, stay hydrated, and limit your intake of refined sugars, processed foods, and large, heavy portions.