Palm oil is one of the most widely consumed vegetable oils in the world, valued for its versatility in food products, cosmetics, and industrial applications. It is present in approximately half of all packaged supermarket items. The controversy surrounding palm oil’s potential link to cancer does not stem from the raw oil, but rather from chemical compounds that are unintentionally created during industrial processing. This article will investigate the scientific evidence behind this concern, focusing on the specific chemical byproducts, their toxicology, and the regulatory response.
Byproducts of High-Heat Refining
The question of palm oil’s potential risk exists because of the high temperatures used in the refining process, specifically during the final stage called deodorization. This step is necessary to remove unwanted colors, tastes, and odors to produce a commercially viable fat. The heat, which can exceed 200°C, causes chemical reactions in the oil’s fat structure, creating process contaminants: Glycidyl Esters (GEs) and 3-monochloropropane-1,2-diol (3-MCPD) esters.
3-MCPD esters form when oil components react with chloride ions present in the crude oil or introduced during processing. Glycidyl esters are primarily formed from diacylglycerides (DAG) and monoacylglycerols (MAG) at temperatures above 230°C. Palm oil naturally contains a higher concentration of these DAG compounds compared to many other vegetable oils, which explains why it often contains the highest levels of these contaminants after refining.
Scientific Assessment of Potential Carcinogens
The concern for human health arises after consumption, as the body’s digestive system hydrolyzes these fatty acid esters, releasing their simpler, free forms: glycidol from GEs and 3-MCPD from its esters. These two released compounds have distinct toxicological profiles. Glycidol is classified by the International Agency for Research on Cancer (IARC) as a Group 2A substance, meaning it is “probably carcinogenic to humans.” This classification is based on sufficient evidence showing that glycidol acts as a genotoxic carcinogen, directly damaging the cell’s DNA.
In contrast, 3-MCPD is classified by the IARC as a Group 2B substance, or “possibly carcinogenic to humans.” It is considered a non-genotoxic carcinogen, suggesting it does not cause cancer by directly damaging DNA. Instead, 3-MCPD has been shown to cause adverse effects on the kidneys and male reproductive organs in rodents. Both released compounds are the focus of international risk assessments, which aim to determine safe exposure levels for consumers.
Official Safety Thresholds and Regulations
Global health authorities have differentiated their approach to regulating these two contaminants based on their toxicological mechanisms. For 3-MCPD, a Tolerable Daily Intake (TDI) has been established, representing the amount that can be consumed daily over a lifetime without posing an appreciable health risk. The Joint FAO/WHO Expert Committee on Food Additives (JECFA) set a Provisional Maximum Tolerable Daily Intake (PMTDI) of 4 micrograms per kilogram of body weight per day. The European Food Safety Authority (EFSA) later updated its TDI to 2.0 micrograms per kilogram of body weight per day in 2018.
The regulation of Glycidyl Esters is significantly stricter because glycidol is a genotoxic carcinogen for which no safe threshold can be determined. For substances that damage DNA, the guiding principle is ALARA—”As Low As Reasonably Achievable”—meaning that exposure should be minimized. The European Union (EU) enacted Commission Regulation 2017/2158, setting maximum levels (MLs) for GEs in refined oils. For instance, the maximum level for GEs (expressed as glycidol) in vegetable oils and fats for the final consumer is set at 1,000 micrograms per kilogram (1 ppm). These maximum levels are even lower for products intended for vulnerable populations, such as infant formula.
Consumer Strategies for Lowering Exposure
Since the health concern is tied to the contaminants formed during high-heat processing, consumers can take practical steps to reduce their intake from processed foods. The contaminants are found primarily in highly refined vegetable oils and fats, which are often used in pre-packaged snacks, pastries, and fried products.
A direct strategy involves limiting the consumption of processed foods that use refined palm oil, such as certain margarines, hazelnut spreads, and commercial baked goods. Choosing whole, unprocessed foods like fresh fruits and vegetables is another way to indirectly reduce exposure to these process-induced contaminants. Looking for ingredient labels that list “refined vegetable fat” or “vegetable oil” without specifying the source can be a general indicator of a highly processed ingredient.