People who replace saturated fat (mainly found in meats and dairy foods) in their diets with refined carbohydrates do not lower their risk of heart disease, according to a new study led by researchers at Harvard T.H. Chan School of Public Health. On the other hand, those who replace saturated fats with unsaturated fats (found in vegetable oils and nuts) or whole grains lower their heart disease risk.
Many people fall back on carbs, especially refined carbs like white bread, when they reduce saturated fat in their diet. This may in part explain findings from a controversial 2014 paper that called into question recommendations for limiting saturated fat for heart health, and led to headlines promoting the return of butter.
This is the first prospective analysis to directly compare saturated fat with other types of fats and different types of carbohydrates in relation to heart disease risk.
Previous research looked at the association between consumption of saturated fatty acid and the risk of coronary heart disease, but did not specify what replaced saturated fat -- such as unsaturated fats or the type of dietary carbohydrate. This is one of the first studies to distinguish between polyunsaturated fatty acids, monounsaturated fatty acids, and carbohydrates from whole grains or refined starches and added sugars.
The researchers analyzed data from the Nurses' Health Study, a cohort of 121,701 female nurses enrolled in 1976, and the Health Professionals Follow-up Study, a cohort of 51,529 men enrolled in 1986. For this study, researchers followed 84,628 women and 42,908 men who were free of diabetes, cardiovascular disease and cancer and documented 7,667 incidents of coronary heart disease.
Participants provided information on diet, lifestyle, medical history, and newly diagnosed diseases through questionnaires at baseline and every two to four years for 24 to 30 years. The questionnaire asked how often and in what quantity specific foods had been consumed in the past year and to specify the types of fats or oil used for frying, baking and at the table.
Researchers noted that participants generally replaced calories from saturated fatty acids with calories from low-quality carbohydrates -- such as white bread or potatoes -- rather than calories from unsaturated fats found in vegetable oils, nuts and seeds or high-quality carbohydrates like those in whole grains.
They estimated that replacing 5% of energy intake from saturated fats with equivalent energy intake from either polyunsaturated fats, monounsaturated fats, or carbohydrates from whole grains was associated with 25%, 15%, and 9% lower risk of CHD, respectively.
On the other hand, swapping 5% of saturated fat calories for the same amount of refined carbohydrates and sugars was not associated with CHD risk. These analyses took into account cardiovascular risk factors such as age, body mass index, smoking, and physical activity.
Examples of the kinds of changes that could result in reduced risk of heart disease include:
- Cooking with healthy fats such as canola oil, olive oil or other vegetable oils instead of butter, lard, and hard margarine.
- Exchanging snacks like potato chips and cookies for peanuts, almonds and olives.
- Making sandwiches with a whole-wheat bun, avocados and chicken breast instead of large amounts of cheese and processed meats.
Study limitations included the observational nature that did not allow the study to prove causality. However, the authors stated that their results were broadly consistent with those from randomized clinical trials.
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