Can High Fat Make You Tired? The Link Between Diet and Fatigue

December 22, 2025 •

5 min read

According to a 2016 study published in the journal Nutrients, men who consumed the highest amounts of fat were significantly more likely to experience excessive daytime sleepiness compared to those who ate less fat. This suggests a clear connection between fat consumption and fatigue, but the exact mechanisms are complex and involve more than just heavy digestion.

Quick Summary

This article explores the connection between high-fat diets and fatigue, examining how heavy meals, inflammation, and gut hormones contribute to sleepiness. It also addresses the misconception that fat is the sole culprit and offers actionable advice for maintaining energy while on a high-fat eating plan.

Key Points

High-Fat Digestion: High-fat meals slow gastric emptying and digestion, requiring more bodily energy and potentially causing a sluggish feeling.
Inflammatory Response: Long-term high-fat consumption, especially of unhealthy fats, can promote systemic inflammation linked to chronic fatigue.
Hormonal Impact: High-fat foods can trigger the release of gut hormones like cholecystokinin (CCK), which have somnogenic (sleep-inducing) effects.
Sleep Cycle: Fatigue from high-fat consumption can lead to cravings for more high-fat foods, creating a vicious cycle of poor diet and sleep.
Quality Matters: The type of fat is critical; healthy fats from whole foods support energy, while unhealthy, processed fats are more likely to cause tiredness.
Balanced Approach: Combining healthy fats with complex carbs and protein can help stabilize energy levels and prevent post-meal crashes.
Not Always Tired: A well-formulated ketogenic diet can lead to stable energy for some people, but others may experience temporary fatigue during adaptation.

The Biological Mechanisms Behind High-Fat Fatigue

Consuming large amounts of dietary fat, especially unhealthy saturated and trans fats, can trigger several biological responses that lead to feelings of sluggishness and fatigue. It's not simply the weight of the food, but the way our body processes it that causes the problem.

Impact on Digestion

One of the most immediate effects of a high-fat meal is the slowing of the digestive process.

Slower Gastric Emptying: Fat-rich foods remain in the stomach longer, which requires more energy for digestion. This can divert blood flow and metabolic resources toward the gut, away from the brain and muscles.
Digestive Distress: An overload of fat can be difficult for the body to break down, leading to bloating, gas, and an overworked digestive system that drains your energy.
Overproduction of Hormones: The digestive system releases gut hormones like cholecystokinin (CCK) in response to a fatty meal. These hormones have been shown to have somnogenic (sleep-inducing) effects, contributing to a post-meal energy crash.

The Role of Inflammation

Long-term, high-fat diets, particularly those high in saturated fats, can lead to systemic inflammation. This low-grade inflammatory state has been consistently linked to chronic fatigue and other health issues.

Cytokine Release: Chronic consumption of high fat can lead to the overproduction of pro-inflammatory cytokines, which are signaling molecules that help mediate the body's immune response. Elevated levels of these cytokines have been associated with fatigue.
Leptin Resistance: High-fat diets can disrupt the signaling of leptin, a hormone that regulates hunger and energy balance. Increased leptin levels, often a result of high fat intake, have also been reported to contribute to fatigue.
Altered Metabolism: Inflammation and hormonal imbalances can interfere with cellular energy production, causing a feeling of constant fatigue and low energy.

The Sleep-Diet Vicious Cycle

The relationship between a high-fat diet and feeling tired can become a self-perpetuating cycle. Poor sleep and daytime fatigue can increase cravings for high-fat, high-carbohydrate foods, which in turn leads to poorer sleep quality. This creates a difficult pattern to break, as fatigue from poor diet perpetuates the craving for the very foods that cause the exhaustion.

Comparison: High-Fat vs. Balanced Diet Effects on Energy

To better understand the issue, it's helpful to compare the effects of a high-fat diet versus a balanced diet on the body's energy levels.


Feature	High-Fat Diet (especially high in saturated fats)	Balanced Diet (includes lean protein, complex carbs, and healthy fats)
Digestion Speed	Slows down digestion significantly, potentially causing sluggishness after meals.	Supports steady and efficient digestion, providing a consistent release of energy.
Hormonal Response	Can trigger the release of sleep-inducing gut hormones like CCK.	Maintains balanced hormonal responses, supporting stable energy levels throughout the day.
Inflammation	Can promote systemic, low-grade inflammation, which is linked to chronic fatigue.	Contains anti-inflammatory nutrients from fruits, vegetables, and healthy fats, supporting overall health.
Energy Source	Rely heavily on fat for energy, which can cause metabolic fluctuations and energy crashes, especially if not fully adapted.	Utilizes a mix of macronutrients for sustained energy, preventing crashes and spikes.
Sleep Quality	Linked to excessive daytime sleepiness and a higher risk of sleep disorders like sleep apnea.	Supports better sleep quality due to stable blood sugar and balanced hormones.

Is All High-Fat Eating Bad for Energy?

It's crucial to differentiate between unhealthy high-fat eating and a structured, healthy high-fat diet, such as a well-formulated ketogenic diet. While excess fat can cause tiredness, the type and quality of the fat, along with the overall diet composition, are key determinants.

The Keto Difference: In a state of ketosis, the body becomes highly efficient at burning fat for fuel, including for the brain. For some, this can lead to sustained energy and mental clarity, not fatigue. However, others experience a temporary 'keto flu' during the initial transition, which can include fatigue.
The Importance of Quality Fats: The type of fat matters. Healthy fats from sources like avocados, nuts, seeds, and olive oil provide essential fatty acids and can be part of an energizing diet. In contrast, trans fats and excessive saturated fats are inflammatory and more likely to cause adverse effects.
Adequate Fiber and Nutrients: A balanced diet, even a high-fat one, must include adequate fiber and essential nutrients. Neglecting fruits, vegetables, and whole grains for processed, high-fat foods can lead to nutrient deficiencies that cause fatigue.

Practical Strategies to Combat High-Fat Fatigue

If you believe your high-fat diet is making you tired, here are some actionable steps you can take:

Assess Your Fat Sources: Swap out unhealthy saturated and trans fats found in fried foods and processed snacks for healthier options like monounsaturated and polyunsaturated fats. Prioritize whole food sources.
Ensure Hydration: Sometimes, fatigue is a symptom of dehydration. Ensure you are drinking enough water, especially if your dietary fat is high, as it can affect fluid balance.
Mind Your Meal Timing: Avoid very large, heavy, and high-fat meals right before demanding tasks or exercise. Schedule these meals for when you have time to rest afterward, such as dinner.
Balance Macronutrients: For non-keto diets, pair healthy fats with complex carbohydrates and lean protein to stabilize blood sugar and prevent energy crashes. Avoid pairing high fat with simple sugars.
Listen to Your Body: Track your energy levels throughout the day relative to your meals. This can help you identify specific trigger foods or timing issues that are making you tired.

Conclusion

The answer to "can high fat make you tired?" is a complex 'yes,' but with important caveats. The fatigue associated with high-fat diets is not an inevitable outcome but rather a result of specific factors, including the type of fat consumed, the overall quality of the diet, and individual bodily responses. The sluggishness can be a result of slower digestion, systemic inflammation, and a hormonal cascade that promotes sleepiness. By understanding the underlying biological mechanisms and making conscious choices about fat sources and meal timing, individuals can manage their energy levels effectively. A balanced approach, focusing on nutrient-dense, healthy fats and listening to your body's signals, is key to avoiding the fatigue trap and maintaining vibrant energy.

For more information on the link between diet, sleep, and fatigue, you can visit the National Institutes of Health website at: https://pmc.ncbi.nlm.nih.gov/articles/PMC7071235/.

Frequently Asked Questions

You feel sleepy because high-fat meals require more energy and time to digest, redirecting blood flow and resources to your stomach. The release of sleep-inducing gut hormones, like cholecystokinin (CCK), is also triggered by fatty foods.

Yes, some people experience temporary fatigue, often called the 'keto flu,' when transitioning to a ketogenic diet as their body adapts to burning fat for fuel instead of carbohydrates. Once adapted, many people report more stable energy.

Yes, the type of fat is crucial. Healthy monounsaturated and polyunsaturated fats from sources like avocados and nuts provide stable energy. Unhealthy trans and saturated fats, especially in excess, can promote inflammation and sluggishness.

To prevent fatigue, choose healthy, unsaturated fats over saturated and trans fats, stay properly hydrated, time your meals wisely, and ensure you're also consuming adequate fiber and micronutrients from whole foods.

Fatigue from high-fat meals is typically not caused by blood sugar spikes, unlike the crash experienced after a high-sugar meal. Instead, it's often due to slower digestion, hormonal responses, and inflammation.

Yes, high-fat diets have been linked to poor sleep quality and an increased risk of sleep disorders like sleep apnea, which can lead to excessive daytime sleepiness and fatigue.

No, fatigue from food can be caused by many factors, including high sugar intake, dehydration, and nutrient deficiencies. However, high fat is a notable contributor, especially when paired with an unhealthy, inflammatory diet.