What Happens To Your Body When You Eat Fast Food

We've all been there: starving, way past hangry, and convinced your stomach is starting to digest itself. And then you see it out of the corner of your eye, like a desert mirage: the unmistakable golden arches of a McDonald's. In a last ditch effort to save your sanity, you whip through the drive-thru and house a Big Mac and large fries faster than you can blink.

At the time, fast food seems like a true gift. It's freaking delicious, and it's cheap. But within a few hours, you may start to feel off. Your stomach may hurt, or you might notice your skin is a little greasier than usual. You immediately curse the meal you ravaged not too long ago. Here's what's actually going on in your body when you eat fast food.

If you've ever looked at the nutrition facts on any food or drink label, you've probably noticed that every measurement is based on a 2,000 calorie diet. While the amount of calories you should eat daily to maintain a healthy weight depends on a number of factors, including your sex and height, in general the more calories you eat, the more weight you gain.

Fast food is notorious for containing a ton of calories. For example, a crunchy taco from Taco Bell has 190 calories, a Big Mac has 540 calories, and a Wendy's Baconator has 950 calories. Now, if these were your only meals of the day, that'd be one thing. But that's probably not the case, considering fast food is full of empty calories, meaning they hold little to no nutrients — which is why you're hungry again so soon after eating it. A 2004 study found that those who eat fast food frequently generally have a higher body mass index and are more likely to be overweight than those who don't.

In 2015, a Daily Mail writer tested fast food's effect on the body by eating nothing but fast food for a full week. By the end of the week, she reported that her "concentration levels were much lower than usual and [her] fatigue was a real issue, even after a long night's sleep."

If you've ever had a food coma, you'll relate. It turns out the exhaustion you feel after eating a large meal is real. The sleepiness comes from a certain type of amino acid called tryptophan, which becomes more available to the brain via carbohydrates. Since fast foods are typically heavy in carbs, it makes sense that the more fast food you eat, the more tired you'll feel.

According to the American Heart Association, there are two types of trans fats: naturally-occurring, which comes from animals, and artificial, which are created industrially and are the types of trans fats most fast food companies use because they're inexpensive, last a long time, and — if we're honest — they make food taste damn good.

Trans fats are known to raise your cholesterol levels, which increases your risk of heart disease and stroke. In fact, they're so bad for you that some places have even restricted the use of them, the American Heart Association confirms.

If you're out of your teens and wondering why your stubborn skin just won't clear up, the fast food you're eating might be to blame. It may have to do with where fast food falls on the glycemic index, which measures how fast certain foods release glucose into the bloodstream. A 2010 study in the Journal of the American Academy of Dermatology found "that high glycemic load diets may exacerbate acne."

To find the glycemic load of any kind of food, you multiply "the grams of a carbohydrate in a serving by the glycemic index, then dividing by 100," as explained by Harvard Health Publications. Ideally, you want to keep the glycemic load under 10. As Amy Shapiro, MS, RD, CDN, and founder of Real Nutrition NYC, told Yahoo Beauty, "It's the simple sugars, white flour, and empty carbs like french fries that can be blamed" for your post-fast food breakout.

If you've ever wondered why your pants feel like they're bursting at the seams after you eat a fast food meal, it's because all those fries and burgers are chock full of sodium. Don't panic: sodium is a necessary part of a healthy diet. According to MedlinePlus, "the body uses sodium to control blood pressure and blood volume. Your body also needs sodium for your muscles and nerves to work properly."

However, too much sodium can lead to high blood pressure and water retention at best, and "serious buildup of fluid in people with congestive heart failure, cirrhosis of the liver, or kidney disease" at worst. For optimal health, the American Heart Association recommends limiting your sodium intake to 1,400 mg per day. Unfortunately, as Seth Santoro of LA Life Chef told Yahoo Beauty, one fast food meal can surpass 2,300 mg.

During an experiment in which she ate only fast food for a seven days, a Daily Mail writer reported mood swings throughout her week. "My mood was up and down and I was constantly exhausted no matter how long I slept," she said. "It was a real effort to stay switched on at work and I found myself getting irritable and impatient." Those mood swings are the real deal — a 2012 study found that people who eat fast food are 51% more likely to develop depression.

At this point, you're probably thinking, "Okay, but what doesn't cause cancer?" And you're right — over the years, we've been told you can get cancer from eating and drinking, well, pretty much everything. But fast food is a special kind of cancer-causing horror. A study published in Environmental Health Perspectives in 2016 found that fast food contains toxic chemicals known as phthalates, "a class of high production volume industrial chemicals." According to the National Toxicology Program at the U.S. Department of Health and Human Services, phthalates are known carcinogens (substances that can lead to cancer).

To someone who craves Taco Bell more than pretty much anything else, the addictive properties of fast food make total sense. A 2011 study found evidence that fast food has a number of addictive properties and is "most likely to create dependence in vulnerable populations," such as in poor neighborhoods and among obese people, who the study says "eat more fast food than those who are normal weight." It doesn't help that we're inundated with ads that serve as triggers, like a beer commercial might trigger an alcoholic.

Sometimes you just can't avoid eating a fast food meal. And they're delicious, so you should be able to indulge every once in a while! But if you ever have a craving for a greasy fast food meal, keep in mind exactly what it's doing to your body — like causing depression, bloating, and acne, for example — and decide whether that burger is worth the consequences. Oh, and don't try to even out that burger by following it with a kale salad. A 2015 study found that people who eat a "higher diversity" of food are actually at risk of gaining more weight, "thus potential benefits of increased intakes of fruits and vegetables may be outweighed by unfavorable effects of trans-fat, sodium, starch, and refined carbohydrates."