In many Asian populations, traditional diets often feature lower fat intake compared to typical Western diets. Previous cross-sectional and ecological studies suggested an inverse association between adherence to traditional Asian dietary patterns and lower rates of CVD, cancer, and mortality [24]. However, these studies were strongly confounded by socioeconomic factors. Over the past several decades, a wealth of data from RCTs and large cohort studies has provided compelling evidence that different types of fats have different effects on various health outcomes. In the NHS and HPFS, types of fat were far more important than total amount of fat in determining the long-term risk of mortality [25]. Specifically, higher intakes of unsaturated fats (found predominantly in plant-based foods and marine fish) were associated with lower mortality risk, with linoleic acid exhibiting the strongest inverse association with mortality. On the other hand, higher intakes of trans fat and saturated fat were associated with increased mortality with the adverse effects of trans fat substantially stronger than those of saturated fat (Fig. 2). These associations were consistent when cause-specific mortality (including CVD mortality, cancer mortality, and mortality due to respiratory diseases or neurogenerative conditions) were analyzed separately. The benefits of polyunsaturated fats (PUFAs), especially linoleic acid, on CVD and total mortality were confirmed in systematic reviews and meta-analysis of cohort studies using biomarkers of linoleic acid intake [26, 27].

Fig. 2

Change in total mortality risk associated with increments of calorie intake from specific types of fat in the Nurses’ Health Study and Health Professionals Follow-Up Study. Multivariable HRs are shown for total mortality associated with replacing the percentage of energy from total carbohydrates with the same energy from specific types of fat (p-trend < 0.001 for all), adjusted for age, race, marital status, body mass index (BMI), physical activity, smoking status, alcohol consumption, multivitamin use, vitamin E supplement use, current aspirin use, family history of myocardial infarction, family history of diabetes, family history of cancer, history of hypertension, history of hypercholesterolemia, intakes of total energy and dietary cholesterol, percentage of energy intake from dietary protein, menopausal status and hormone use in women, and percentage of energy from the remaining specific types of fat. Source: The figure originally published in Hemler C, Hu F, “Plant-Based Diets for Personal, Population, and Planetary Health” Advances in Nutrition, 2019 Nov; 10(Suppl 4): S275–S283. https://advances.nutrition.org/. Reproduced with permission (superficially modified).

When interpreting these observed associations, it is important to consider substitution effects derived from isocaloric statistical modeling as such analyses emulate a dietary intervention study, while factoring in real-world dietary choices [28]. In the aforementioned study, replacing 5% of energy from saturated fat with the same amount of energy from monounsaturated fats (MUFAs) and PUFAs was associated with a 27% and 15% reduced risk of mortality, respectively [25]. In another study [29], replacing 5% of calories from saturated fat with PUFAs, MUFAs, or whole grains was associated with a 25%, 15%, and 9% lower risk of coronary heart disease (CHD), respectively. However, based on the substitution modeling, replacing saturated fat with carbohydrates from refined starches and added sugars did not alter CHD risk. The food source of fat (plant or animal) may also affect health outcomes, even when considering the same type of fat. For example, replacing 5% of energy intake from saturated fat, trans fat, and refined carbohydrates with MUFA intake from plant sources (e.g., vegetable oils, nuts, seeds, and avocados) was associated with lower risk of CHD, whereas the same substitution with MUFA from animal sources did not confer the same beneficial effects [30].