A study published in the Journal of the American College of Cardiology has found that replacing saturated with unsaturated fats and high-quality carbohydrates has a positive impact on health, whereas replacing them with processed foods, white bread and potatoes does not lead to a healthier diet.
The American Heart Association (AHA) describe saturated fats as "fat molecules that have no double bonds between carbon molecules because they are saturated with hydrogen molecules." At room temperature, they are normally solid.
The AHA warn against saturated fats, as their consumption has been shown to raise cholesterol levels, increasing the risk of heart disease and stroke.
They suggest limiting calories from saturated fat to a maximum of 5-6%. For an individual consuming 2,000 calories a day, no more than 120 calories should derive from saturated fats, which means about 13 grams of saturated fats a day.
What are healthy alternatives to saturated fats?
Healthier alternatives are polyunsaturated fats, provided by vegetable oils such as olive, canola, peanut, safflower and sesame, or monounsaturated fats from soybean oil, corn or sunflower oil. Fatty fish such as salmon, mackerel, herring and trout, or nuts and seeds, soy beans and tofu are also healthier alternatives.
Saturated fats are mainly from animal sources, such as meats, including chicken with skin, animal-based cooking fats such as lard and butter, and dairy products, including those made with reduced-fat (2% fat) milk. Many processed foods, baked goods and fried foods contain high levels of saturated fats.
Some plant-based oils, such as palm oil, palm kernel oil and coconut oil, also contain primarily saturated fats but do not contain cholesterol, according to the AHA.
The AHA recommend replacing foods high in saturated fats with foods high in monounsaturated and/or polyunsaturated fats. This includes foods made with liquid vegetable oil, but not tropical oils, fish and nuts, and beans or legumes instead of meat.
The current study, carried out by Dr. Frank B. Hu, PhD, professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health in Boston, MA, suggests that people have been removing saturated fats, but not replacing them with healthier options.
The study distinguishes between the effects of polyunsaturated fatty acids, monounsaturated fatty acids and carbohydrates from whole grains or refined starches and added sugars.
A combined cohort of 173,230 nurses and health professionals were enrolled in two major studies, starting in 1976 and 1986. Of these, 84,624 women and 42,908 men were selected for this study. Among them, 7,667 incidents of coronary heart disease were reported.
The participants provided information through questionnaires about diet, lifestyle, medical history and newly diagnosed diseases at baseline and then every 2-4 years for 24-30 years.
The questionnaire surveyed the quantity and frequency with which specific foods had been consumed in the previous year, including types of fat or oil used for frying, baking and at the table.
Saturated fats replaced, but with unhealthy alternatives
It was found that when participants removed calories from saturated fats from their diet, they tended to replace them with calories from low-quality carbohydrates, such as white bread or potatoes, instead of whole grains, which would provide high-quality carbohydrates.
Those who replaced the saturated fats with carbohydrates from polyunsaturated fats benefitted from a 25% lower risk of coronary heart disease. Those who replaced them with monounsaturated fats had a 15% lower risk of coronary heart disease, while those who replaced them with whole grains reduced their risk by 9%.
Replacing 5% of energy intake from saturated fats with carbohydrates from refined starches or sugars made no difference in terms of coronary heart disease - it neither increased nor decrease the risk.
To reduce the risk of heart disease, Dr. Hu suggests:
Replacing butter, hard margarine and lard with canola oil, olive oil or other vegetable oils
Replacing potato chips and cookies with peanuts, almonds and olives
Replacing white bread cheese sandwiches with whole wheat bread, avocado and chicken breast.
Dr. Hu calls for all health care workers to advise patients more specifically about the benefits of unsaturated fats and carbohydrates from healthy sources. He says:
"Our findings suggest that when patients are making lifestyle changes to their diets, cardiologists should encourage the consumption of unsaturated fats like vegetable oils, nuts, and seeds, as well as healthy carbohydrates such as whole grains."
One limitation of the study was that self-reported dietary data is not always reliable. However, the results are broadly in line with those from clinical trials, and the large number of participants lend credence to the findings.