As with any food that is essentially pure fat, there are still health problems associated with margarine, especially if it is eaten in large quantities. One of the biggest potential problems is the increased risk of heart disease. Many kinds contain high levels of saturated fats and dangerous trans fats, which are known to lower the levels of beneficial high-density lipoprotein (HDL) cholesterol and increase levels of the harmful type known as low-density lipoprotein (LDL).
Once butter became associated with health risks such as heart disease due to its high levels of saturated fat and cholesterol, many people were looking for an alternative. Often individuals would switch to margarine, which often has no cholesterol and at least lower levels of saturated fat than butter and frequently fewer calories. The reason there is no cholesterol is because margarine is made from solidified vegetable fat instead of animal sources. As time passed, health professionals began to note health issues such as increased risk of developing heart disease for individuals who consumed margarine as well.
Researchers have found that the risk of heart disease associated with margarine is due to the presence of trans fatty acids, also known as trans fats. These substances are formed in the process of solidifying the vegetable oil and have been linked to several health issues. Solid sticks have much higher levels of trans fats than softer spreads. Trans fats have been shown to have an adverse effect on cholesterol levels, a major heart disease indicator, even though margarine does not actually contain cholesterol. The trans fats lower the levels of good HDL cholesterol and raise the amount of harmful LDL cholesterol found in the body.
Another contributing factor to the heart disease risk associated with margarine is the amount of saturated fat found in many brands. Even though there is less saturated fat than butter, high levels can be present in some margarine products. The amounts of these unhealthy substances can vary widely depending on the manufacturer. As a rule, it's a good idea for consumers to look for products with low levels of saturated fat and remember to use them in moderation.
Many manufacturers have removed as much trans fat as possible from their products, and many margarine types are also now made with unsaturated fats such as olive or canola oil. Products with reduced saturated fat and no trans fat are less harmful than others, but should still only be consumed in moderation. Consuming large amounts of any fatty food is likely to increase the chances of developing heart disease, but limiting consumption to small amounts of unsaturated fat reduces this risk.