Eating unhealthy foods can make you feel bad, lead to weight gain and cause many health problems.

Here are 7 unhealthy foods you should limit.

You're probably not surprised to see sugar at the top of the list.

In the last few decades, sugar has been considered unhealthy because it provides empty calories, and it's true.

Refined sugar has a lot of calories but no essential nutrients.

But that is just the tip of the iceberg. New data links excess sugar consumption to diseases that affect millions of people: obesity, diabetes, heart disease and even cancer (, 2, 3, , ).

A new study that came out recently reveals how sugar can make you fat. The calories in fructose (50% of sugar is fructose) do not fill you up and make you satiated (6).

And there's a reason sugar is so hard to get rid of. It is addictive, leading to vicious cycles of cravings and binges (7, ).

A stimulated appetite and addictive features leading to cravings and binge eating. That's a recipe for fat gain.

Bottom line: Avoid all fruit juices and sugar-sweetened beverages, sugary treats and dried fruit. Agave syrup is no better than sugar.

There is a fair amount of evidence to suggest that people, even those who don't have celiac disease, react poorly to foods that contain gluten.

Yes, that also applies to whole wheat, which actually isn't healthy at all. One study reveals that whole wheat can raise cholesterol ().

Whole wheat also happens to have a very high glycemic index, leading to the blood sugar "roller coaster" that makes you crave another high-carb snack soon after eating (10).

Evidence is mounting that gluten sensitivity is fairly common in the population. Gluten appears to cause harmful effects on digestion and other aspects of health, even in individuals without celiac disease (, , , ).

Studies on low-carb diets (which eliminate sugars and starches like grains) suggest that people who need to lose weight or have metabolic issues should avoid all grains, which are the largest source of carbohydrates in the diet (13, ).

For people who exercise and don't need to lose weight, there is no proven reason to eliminate healthier, non-gluten grains like rice and oats.

At the end of the day though, grains are a food group that contains no essential nutrients that we can't get in much greater amounts from animal foods or vegetables.

Bottom line: Everyone who cares about their health should limit refined grains. Healthy people who don't need to lose weight can eat some healthier whole grains like rice and oats.

Trans fats, also known as "hydrogenated" or "partially hydrogenated" fats, are unsaturated fats that have been chemically modified to increase shelf-life and make them solid at room temperature.

This process requires hydrogen gas and high pressure. It is strange that anyone ever thought these industrially produced fats would be suitable for human consumption.

Trans fats increase levels of small, dense LDL cholesterol, lower HDL (the good) cholesterol, increased abdominal fat and may lead to various serious health problems (15, 16, ).

Bottom line: Avoid artificial trans fats. They are very harmful and can increase the risk of heart disease and other health problems.

Often portrayed as health foods, seed and vegetable oils like soybean and corn oil are very unnatural for the human body as we didn't have access to them until very recently in evolutionary history.

These fats contain an abundance of omega-6 fatty acids, but we need to get omega-6 and omega-3 in a certain ratio to ensure optimal functioning of the body.

Eating too much omega-6 and too little omega-3 can lead to inflammation, a leading cause of many modern health problems Polyunsaturated fats are also very sensitive to oxidation due to their abundance of reactive double bonds.

Excess consumption of processed seed and vegetable oils may lead to systemic inflammation, cardiovascular disease and even cancer (, 19, , , 22).

Bottom line: Avoid excess omega-6 fats from seed and vegetable oils. Increase intake of omega-3 from fatty fish or cod liver oil instead.

Even ingredients that are calorie free can still harm you and this may be especially applicable to artificial sweeteners.

Consumption of artificial sweeteners shows consistent and strong associations with preterm delivery and various diseases like metabolic syndrome, obesity and type II diabetes (23, , ).

These epidemiological studies don't prove that the artificial sweeteners caused the diseases, but until there are controlled trials that prove their safety I recommend you limit artificial sweeteners.

If you must use a sweetener for something, choose stevia, which may improve glycemic control in diabetics and lower blood pressure (, 27).

Bottom line: If you must sweeten, use stevia. Artificial sweeteners have not been conclusively shown to be safe.

Some of the marketers working at the junk food companies are dishonest, and unfortunately they get away with it.

Even products marketed towards children as healthy, with labels like "diet," "low fat" or "whole grain" are often high-sugar in sugar and very unhealthy.

Bottom line: Be smart and read labels. Even foods disguised as health foods often turn out to be little more than unhealthy junk foods.

Foods that are highly processed are low in nutrients and high in unhealthy ingredients and artificial chemicals.

If the ingredients list contains more than five ingredients or something that you don't understand, it's probably bad for you.

Real food doesn't need an ingredients list. Real food is the ingredient.

Easy rule to remember: "If it looks like it was made in a factory, don't eat it!"