Vegetable fats improve blood lipids and may extend lifespan
A common dietary recommendation is to replace saturated animal and tropical fats with unsaturated vegetable and fish fats. Which fats to include in standards diets is disputed, however. In a new dissertation, David Iggman has evaluated how different fats affect the body’s metabolization of fat and sugar during obesity, as well as the risk of death from cardiovascular and other major diseases.
The primary aim of the dissertation is to evaluate the health effects of vegetable fats, particularly those of the most common polyunsaturated fatty acid, linoleic acid from the family omega-6.
In a randomised study involving individuals with elevated blood lipids, a large proportion of saturated fatty acids were replaced with unsaturated fatty acids by providing all participants with specific diets. Butter, cheese and cream were replaced with an increased amount of rapeseed oil, which resulted in improved blood fats (upwards of 20 % improvement) after as little as three weeks, and with no weight loss. The effects on other risk factors for cardiovascular disease and diabetes were less pronounced in the short term.
Even with less than seven weeks of calorie-dense food intake and moderate weight gain (1, 5 kg), positive blood lipid effects were observed with a diet rich in polyunsaturated linoleic acid from sunflower oil, compared to saturated fatty acids from palm oil. However, despite the modest weight gain and despite the 39 people involved being healthy at the onset of the study, negative effects on insulin levels and markers of vascular functions were seen, regardless of group assignment.
As self-reported surveys of fat intake can be unreliable, directly measuring the levels of fats in the body can provide objective information about how different fats in diets affect health. Your subcutaneous fats reflect what types of fats you’ve eaten over the last years, especially for polyunsaturated fatty acids like linoleic acid. The amount of subcutaneous linoleic acid was found to be associated with improved insulin sensitivity, as well as lower mortality risk among 853 men in their 70’s.
In all, the findings of the dissertation strengthen the current recommendations to partially replace saturated fatty acids (hard fats such as butter) with unsaturated (vegetable oils, such as rapeseed oil, olive oil and sunflower oil) to reduce the risk of cardiovascular and obesity-related diseases.