You've probably heard the term "food is medicine," but here's a pill that's hard to swallow: that's not always the case. Not only are some foods far from beingmedicine, but eating certain foods may even cause health problems that require you to take medicine.

Some foods are so unhealthy that they can cause an array of ailments, from metabolic disorders to cardiovascular diseases to cancer. Weight gain, while definitely a negative side effect, pales in comparison. However, weight gain is the term that typically gets your ears to perk up, so we'll start there. We found that 7 foods that are scientifically proven to cause weight gain—and that's going to be the least of your worries. Count these among the 100 Unhealthiest Foods On the Planet.

Processed Meats

Eating deli meats, bacon, hot dogs, and sausage aren't just making you gain weight—they may also be putting your life at risk. According to a Harvard study published in The New England Journal of Medicine, processed meat consumption is associated with nearly an extra pound of weight gain over a 4-year period. Weight gain isn't the only reason you should cut back on your processed meat consumption. The food has also been associated with an increased risk of diabetes, cancer, and hypertension. That's why these are also on our list of 50 Foods That Can Cause Heart Disease.

Diet Soda

Multiple studies have linked artificial sweeteners to excessive long-term weight gain. Researchers believe that drinking these non-nutritive sweeteners trick your body into thinking there are calories there aren't. The result is what they call "metabolic arrangements." Examples include poor insulin response and elevated blood glucose levels, which can lead to fat storage and weight gain. You may also suffer from a host of related disorders such as metabolic syndrome, type 2 diabetes, and cardiovascular disease.

Potato Chips

While potato chips have never been confused as a health food, what's surprising is that out of all the foods that can cause you to gain weight—soda, junk food, ice cream—the greasy potato chip is the worst offender. According to that same Harvard study referenced earlier, potato chips are the food most strongly associated with weight gain over four years.

French Fries

The second food Harvard researchers found to cause the most weight gain? Potatoes. And more specifically, french fries, which were associated with an additional 3.35 pounds of weight gain over the course of four years. It's not just that french fries extremely caloric due to absorbing all that fat, but they're also made through a dangerous process that can also cause weight gain. French fries are deep-fried. This method has been shown to yield a dangerous, carcinogenic chemical compound called acrylamide, which is associated with belly fat.

Alcohol

Sure, an occasional glass or so of alcohol won't cause weight gain alone; however, overdoing it on the booze is what will cause you to pack on the pounds. It's not just that alcohol is full of empty calories. It's also that consuming alcohol has actually been shown to trick your body into eating more, too. A study published in Journal of the Academy of Nutrition and Dietetics found that drinking alcohol can cause people to eat an extra 384 calories a day. To drink in a healthy way, take sips of water in between alcoholic drinks and try to avoid sugary cocktails.

White Bread

Eating highly-refined, white bread should be avoided at all cost while you're working to lose belly fat. Studies show that eating refined grains can increase belly fat. Plus, bread is the food that contributes the most sodium to Americans' diets. All that sodium will cause you to gain water weight and will lead to permanent bloating.

Sugar-Sweetened Beverages Like Soda

Sugar-sweetened beverages (soda, sweet tea, flavored juice drinks, sports drinks, and coffee drinks) are the single largest source of added sugar and the top source of calories in the U.S. diet. There is sufficient evidence to support that these sweetened beverages are the food item most closely linked to obesity and weight gain. Swap soda for water, smoothies, tea, or coffee.

Eat This, Not That!