While there has been a general consensus that olive oil and other plant-based fats are healthier than butter, scientists have now comprehensively put it beyond doubt, combining a number of diet-intervention studies and previous cohort research that all show how this lifestyle choice impacts serious disease risk.
“Our study confirms with even more certainty the health benefits of a diet high in unsaturated plant fats such as the Mediterranean diet and could help provide targeted dietary advice to those who would benefit most from changing their eating habits”, says Clemens Wittenbecher, research leader at Chalmers University of Technology and the study’s senior author.
However, the Mediterranean diet is just one aspect of this study. Scientists from Sweden's Chalmers University of Technology, the German Institute of Human Nutrition and several other colleges have directly linked how quality plant oils and butter directly affect the levels of fat in blood, and in turn change the risk of developing cardiovascular disease and type 2 diabetes, independent of other lifestyle choices.
The international team set out to remove the limitations that had plagued individual studies and weakened the link between 'good' fats and good health. Using "lipidomics" to home in on lipid blood profiles taken from a randomized controled dietary intervention trial, the researchers boiled findings down to a multilipid score (MLS), which could be applied to a host of studies.
What they found was that high quality plant-based oils had a significant impact on participants' MLS, with high scores across the board. Low scores, which indicated problematic fat levels in blood, were seen in cohorts that ate animal-fat dairy, such as butter, instead.
Until now, guidelines such as those from the World Health Organization (WHO) and the American Heart Association have been 'moderate' recommendations of swapping saturated fatty acids (SFA) for plant-based unsaturated fatty acids (UFA), due to study limitations and outcomes, and confounding factors.
"Despite data from over 56,000 trial participants and approximately 3.7 million observational study participants, there is considerable heterogeneity in total fat and SFA intake levels, nutrients and food sources replacing dietary SFAs and duration in the underlying studies and limited data from trials on hard endpoints," the researchers noted. "Therefore, the certainty of evidence for these WHO recommendations ranges from very low to moderate, subjecting the guidance on dietary fat quality to ongoing controversies."
The comprehensive new study had several parts to it, with the researchers first focusing on a University of Reading dietary intervention (DIVAS) trial with 113 participants over 16 weeks. One group adhered to a diet high in saturated animal fats, while the other a diet high in unsaturated plant-based fats. At the end of the 16 weeks, blood samples got the lipidomics treatment to detail the prevalence of 45 class-specific fatty acid molecules.
"We summarized the effects on blood lipids with a multilipid score," explained first author of the study Fabian Eichelmann, from the German Institute of Human Nutrition Potsdam-Rehbruecke. "A high MLS indicates a healthy blood fat profile, and a high intake of unsaturated plant fat and low intake of saturated animal fat can help achieving such positive MLS levels."
The MLS was then applied to other large observational studies – the German EPIC-Potsdam study, which looked at the Nordic diet, Mediterranean diet, and the risk of chronic diseases in 27,548 participants, Harvard's Nurses’ Health Studies (NHS) that assessed the risk factors for major chronic diseases in 121,701 women and the PREDIMED trial that investigated the health benefits of a Mediterranean diet boosted with extra-virgin olive oil or nuts, with 7,447 participants. The outcome was unanimous, in that a high MLS "substantially" reduced the risk of developing cardiometabolic diseases.
“Diet is so complex that it is often difficult to draw conclusive evidence from a single study," said Wittenbecher. "Our approach of using lipidomics to combine intervention studies with highly controlled diets and prospective cohort studies with long-term health tracking can overcome current limitations in nutrition research."
What's more, using MLS as the key indicator for disease, the researchers were able to demonstrate that swapping out saturated fats had a significantly greater impact on scores than other dietary adjustments. In the EPIC-Potsdam study, the researchers found weak correlations between MLS and age, body mass index (BMI), waist circumference and blood pressure, but stronger ties with triglycerides and total cholesterol, with margarine boosting MLS and butter negatively effecting it. Margarine has around 80% fat, but 65% SFA, 28% monounsaturated fatty acids (MUFA) and some polyunsaturated fatty acids (PFA).
In this same study, applying the statistical analysis developed for the DIVAs trial, the researchers found that participants with a high UFA-influenced MLS had a mean 32% lower cardiovascular disease risk and a mean 26% lower type 2 diabetes incidence at the end of the testing period.
In the NHS study, they found similar results: mean 28% lower type 2 diabetes risk, and a 24% lower risk in a subset that was tested over a period of 10 years.
In the PREDIMED cohort, the scientists found a mean 42% reduction in diabetes risk in participants who began the trial with a poor MLS. The Mediterranean diet had little impact on those with healthier lipid scores prior to dietary intervention.
While the researchers noted that despite robust controls, there were still limitations – such as the European-centric nature of the studies – however, it nonetheless highlights how big a role quality plant-based oils play in mitigating disease risk.
"Lipidomics scores that reflect lower SFA intake and high plant-based UFA intake were consistently associated with reduced incidence of T2D (type 2 diabetes) and CVD (cardiovascular disease) in prospective cohort studies," the researches concluded. "The associations of lipidomics scores with diet and disease risk are stronger than established surrogate markers, yielding larger estimated cardiometabolic benefits of improved dietary fat quality.
"Our findings corroborate the cardiometabolic benefits of replacing dietary SFAs with plant-based UFAs by integrating data from RCTs and nutritional cohorts and suggest that lipidomics-based scores may provide sensitive metrics for the health-related metabolic adaptation to change in dietary fat quality," they added.
The research was published in the journal Nature Medicine.
