6 Scientifically Backed Reasons You Feel Sleepy After Fast Food
21 Jul 2025
1 min read
Have you ever ordered your favorite burger and fries through online delivery services, devoured every bite, and then felt an irresistible urge to nap? You’re not imagining it. Feeling sleepy after eating fast food is a real phenomenon, and there’s plenty of science to explain why.
In reality, more than 65% of people become tired or lethargic within an hour of eating heavy-fast food, according to studies. But why does this happen in the first place? Let’s unpack the six scientifically backed reasons fast food leaves you drowsy.
- Blood Sugar Spike/Crash
Fast food meals are overloaded with refined carbs — think burger buns, fries, and sugary drinks that bring your blood sugar up very quickly, and then your body releases a surge of insulin to try to knock it back down. The only problem is that once it spikes, it crashes, leaving you feeling run down.
This is one reason why most people relying on online delivery services for quick meals end up experiencing sudden energy crashes.
According to a study in the American Journal of Clinical Nutrition, people who eat high-glycemic foods have 20% higher levels of fatigue within two hours of consumption than those who eat balanced meals. So, if you feel the urge to yawn after eating that pizza, blame it on the carbs.
- The Tryptophan Effect
Some meat and cheese or beef, for example, which abound in tryptophan, are amino acids your brain uses to manufacture serotonin and melatonin, the house regulators of sleep in your body. He adds that if you combine the tryptophan with the high carbohydrate meal, it will be absorbed even more quickly, and that’s when you again feel calm and sleepy.
Fun fact: It’s actually the same amino acid in turkey that makes everyone go zonked-out sleepy during Thanksgiving!
- High Fat Content Slows Digestion
Many people rely on online delivery services for quick fast-food meals, but these high-fat options can leave you feeling sluggish and heavy. Fast food contains ridiculous amounts of fat to help you enjoy your meal. But the more fats in it, the harder it becomes to digest, and when that happens, your body will redirect blood away from your brain to your stomach, making you feel heavy and drowsy.
Research published in the Nutrients Journal shows that individuals who consume high-saturated-fat meals experience post-meal fatigue that is 30% more than individuals who consume low-fat meals.
- Sodium Overload and Dehydration
No wonder you feel like you could drink an ocean after eating fast food. A regular serving of burger and fries can give 1,200–1,800 mg of sodium—it’s almost the total amount that is safe to consume every day. Sodium makes your body hold on to water, which can then bring on symptoms of dehydration like tiredness and fuzziness.
Throw in a sweet soda with that salty meal, and the perfect cocktail for a drowsy afternoon begins to take shape.
- Lack of Fiber
Fast food is by no means like a balanced diet from home or Food for Offices in Lahore since it is low in fiber. Fiber helps to moderately slow down sugar absorption and keep energy levels stable. In its absence, sugar is absorbed very fast, resulting in sharp highs and lows in blood sugar, which then causes energy slumps. Unlike balanced meals such as Food For Offices in Lahore, fast food lacks the fiber needed to keep your energy stable.
The Harvard School of Public Health suggests an intake of 25-30 grams of fiber per day; however, a typical fast food meal provides less than 5 grams.
- Going Further with Portion Sizes and Overeating
Portions of fast food are huge, and who stops at just half a burger when it’s that tasty? Overeating overpowers your digestive system, making it work too much, hence causing that terrible food coma.
A review in Sleep Medicine Reviews found that overeating subjects reported 45% more daytime sleepiness than those eating moderate portions.
Bonus Tip: How to Avoid the Post-Fast-Food Slump
If you love fast food but hate the sleepy aftermath, here’s what you can do:
- Pair your meal with water instead of soda to stay hydrated.
- Add veggies or a salad on the side for fiber.
- Go for grilled options over fried.
- Order smaller portions or share your meal.
Better yet, swap that greasy fast food for a healthier option. If you’re managing a team lunch, opt for freshly cooked, balanced meals. Instead of depending on generic online delivery services that bring you greasy meals, opt for balanced, homemade alternatives for sustained energy. Services like FOODO provide Food for Offices in Lahore that’s tasty, wholesome, and keeps your team energized—without the food coma.
The Bottom Line
Feeling sleepy after fast food isn’t a personal flaw—it’s biology. From sugar crashes to fat-heavy digestion, your body responds naturally to what you eat. The next time you plan to order through online delivery services, think about whether you want that 3 PM energy crash—or a meal that keeps you alert and productive.
With smart choices, you can enjoy convenience without sacrificing energy.
Getting sleepy after fast food is not a personal flaw but biology. Your body naturally responds to the stuff in a healthy way, from sugar crashes to fat-heavy digestion. Next time you order through online delivery services, consider whether you want a post-meal slump or a wholesome alternative. Choosing Food For Offices in Lahore means productivity, health, and taste—all in one meal.
Services like FOODO provide Food For Offices in Lahore that’s tasty, wholesome, and keeps your team energized—without the food coma.
Learn more about 10 Signs Your Body Needs a Clean Eating Reset
