Harvard Study: Swapping Butter for Plant-Based Oils Could Help You Live Longer

Replacing less than a tablespoon of butter with plant-based oils can lower the risk of premature death from cancer and other causes by 17%, shows a new study.

Even small dietary changes towards plant-based food can render big health benefits, according to a new study by researchers at the Harvard TH Chan School of Public Health, Mass General Brigham, and the Broad Institute.

Published in the Jama Internal Medicine journal, their analysis found that swapping a small amount of butter – 10g per day – with plant-based fats like soybean, canola or olive oil could lower the risk of premature death from all causes by 17%.

“That is a pretty huge effect on health,” noted lead author Yu Zhang. “Higher butter intake was associated with increased deaths from all causes and cancer, while higher intake of plant-based oils was associated with lower deaths from all causes, cancer and cardiovascular disease.”

The results were presented at the American Heart Association’s (AHA) EPI/Lifestyle Scientific Session (March 6-9), with the authors stating that while there has been a lot of research on the links of saturated fat to mortality, few studies have homed in on their primary food sources.

Plant-based oils can reduce death risks

The researchers analysed 33 years of dietary data of over 220,000 American adults, sourced from three national studies. Every four years, the participants, a majority of whom were women, answered questions about how often they ate certain types of food.

Their consumption of these fats included margarine blends, spreadable butter added to foods, or butter used in baking and frying, as well as plant-based oils in frying, baking, sautéing, and salad dressings.

The study authors used statistics to compare death rates across different dietary intake levels, and found that the participants who ate the most butter had a 15% higher risk of death from all causes compared to those with the lowest butter consumption. Each additional 10g of butter per day was linked to a 12% increased risk of death from cancer.

At the same time, those who ate the highest amount of plant-based oils had a 16% lower risk of premature death, with an extra 10g of intake per day associated with an 11% reduction in death risk from cancer and 6% from cardiovascular disease (the leading cause of death in the US).

“From a public health perspective, this is a substantial number of deaths from cancer or from other chronic diseases that could be prevented,” said corresponding author Daniel Wang.

The study ascribed to the high concentration of saturated fatty acids in butter, which can trigger adipose tissue inflammation, a key pathogenic pathway in the development of various cancers. “Moreover, studies have shown that dietary saturated fats can alter hormonal activity, influencing hormone-sensitive cancers such as breast and prostate cancer,” it stated.

“Higher saturated fat intake, particularly when it replaces unsaturated fat intake or makes that ratio imbalanced, promotes the synthesis of less healthy cholesterol profiles, which can lead to atherosclerosis [the thickening of arteries due to fat and cholesterol buildup],” said Maya Vadiveloo, chair of the AHA’s Lifestyle Nutrition Committee, who was not involved in the study.

Scientists slam ‘butter bros’ and ‘anti-seed-oil brigade’

“Sometimes when we talk about saturated fat, like butter, we forget that people don’t eat saturated fat, they eat food that contains saturated fat,” said Vadiveloo. “So, in addition to making substitutions for plant-based oils, one way to reduce saturated fat intake is by building a dietary pattern focused on eating vegetables, fruits, whole grains, nuts and legumes, and only occasionally including sources of saturated fats like processed red meats.”

The AHA’s dietary recommendations suggest limiting saturated fat intake to less than 6% of daily calories, in line with the draft proposals for the upcoming national dietary guidelines in the US. Due to be published later this year, the latter emphasise a shift to a plant-rich diet, with an emphasis on vegetables, fruits, legumes, whole grains, nuts, fish and seafood, low- and non-fat dairy, and unsaturated fats.

“These results support current dietary recommendations to replace animal fats like butter with nonhydrogenated vegetable oils that are high in unsaturated fats, especially olive, soy, and canola oil,” the study suggests.

Saturated fats are present in many foods, and mostly come from animal sources, including red meat, beef tallow, butter, and cheese, plus tropical fruits like coconut or palm.

In the US, there has been a resurgence of fats like tallow amid a growing backlash against seed oils, whose critics argue that the high consumption of omega-6 fatty acids can lead to inflammation and decreased metabolism (although the AHA has pushed back on this claim). The ultra-processed food debate has heightened these concerns, thanks to comments by the new health secretary, Robert F Kennedy Jr.

“Social media is currently awash with influencers promoting butter as a health food and claiming that seed oils are deadly. This large-scale, long-term study finds the reverse,” said Sarah Berry, nutritional sciences professor at King’s College London, who was not involved in the study. “In a sane world, this study would give the butter bros and anti-seed-oil brigade pause for thought, but I’m confident that their brand of nutri-nonsense will continue unabated.”

Parveen Yaqoob, professor of nutritional science at the University of Reading, highlighted that “not all vegetable oils are equal”, with monounsaturated oils more beneficial than polyunsaturated fats, according to the research. “Given that there are some plant-based oils that are high in saturates – such as palm oil and coconut oil – it is important to consider them separately,” she said.

“Recent dietary fads have suggested a re-examination of evidence on dietary fat.  People who are confused about these conflicting messages about their diet should focus on broader, well-established advice, which can be summarised as: eat more fresh vegetables.”