White flour

While white breads and pastas might taste better than whole wheat options, but that's because white flour is processed and stripped away of all the healthy benefits whole grains have to offer.

"White flour is processed wheat that has all of the wheat grains' best attributes, like fiber and antioxidants, stripped away. As a result, you're left with something that might have a better taste and texture, but is incredibly low in nutrient quality," says Lisa Moskovitz, RD, CDN, CPT, and CEO of New York nutrition Group in New York City.

"Foods that are high in fiber like whole wheat bread ramp up your metabolism due to the extra work required to try and break down the indigestible fiber," Moskovitz said.

Fruit juice

Did you know that some fruit juice has more sugar than some sodas? Most fruit juices are stuffed full of sugar, chemicals, food colorings and flavorings. Make sure you're reading the ingredient labels on any fruit juices you're buying; be wary of ingredients like corn syrup, dextrose, fructose, juice concentrate, maltodextrin, raw sugar and brown sugar. Instead, mix real lemon juice into your water or sip on Kombucha for a metabolism boost.

Conventional apples

You've heard about the dirty dozen, but did you know that a certain type of fungicide used on fruits and vegetables (apples included) caused weight gain in mice? Researchers hypothesize that the same is true for humans. Next time you're buying from the dirty dozen, try to buy organic. And don't forget to thoroughly wash your produce! 

Omega-6 fatty acids

Not to be confused with the heart-healthy and weight loss-friendly omega-3 fatty acids found in chia seeds, walnuts, salmon, etc., omega-6 fatty acids actually have a high correlation with obesity. The American diet used to be balanced with both omega-3 and omega-6 fatty acids, but today the overprocessed nature of our country's foods results in much higher amounts of vegetable oils and hydrogenated fats, which cause inflammation and obesity. 

In fact, a study in the journal Nutrients found that "a high omega-6 fatty acid intake and a high omega-6/omega-3 ratio are associated with weight gain in both animal and human studies, whereas a high omega-3 fatty acid intake decreases the risk for weight gain." Plus, that same study found that omega-6 fatty acids promote insulin resistance, a process in which our bodies turn too many of our consumed carbs into fat.

Avoid foods rich in omega-6 fatty acids, like butter, pork products, chicken thighs and cookies.

Farmed beef (not grass-fed)

Traditionally farmed beef is full of antioxidants, that can harm the "good" bacteria living in your gut, which can lead to digestive problems and — you guessed it — weight gain. One study found that the antibiotics harming your gut are also changing and affecting the way you process your food. Next time you're at the grocery, spring for the grass-fed beef. Not only will your waistline thank you, but your long-term health will, too.