Blue Dye 2 vs Partially Hydrogenated Oils: which is worse?

What is Blue Dye 2?

Blue Dye 2 (Indigotine/Indigo Carmine) is a synthetic disulfonated derivative of indigo. Unlike natural indigo from the indigo plant, the FD&C version is synthetically manufactured from petroleum. It produces a dark royal blue to indigo color and is used in food, pharmaceuticals, and medical diagnostics.

What is Partially Hydrogenated Oils?

Partially hydrogenated oils (PHOs) are vegetable oils that have been treated with hydrogen gas in the presence of a catalyst to make them semi-solid at room temperature. This process creates artificial trans fatty acids (trans fats) as a byproduct. They were developed in the early 20th century as a cheaper, longer-lasting alternative to lard and butter.

Documented risks

Blue Dye 2: Animal studies conducted in the 1980s found that high-dose Blue Dye 2 caused brain tumors in male rats. An NTP bioassay (1987) found statistically significant increases in brain gliomas (astrocytomas) in male rats given high doses. The FDA reviewed these findings and determined that the doses far exceeded typical human dietary exposure. Nonetheless, the tumor finding remains in the scientific record as a concerning data point. EFSA's 2010 safety evaluation of Indigo Carmine (E132) reached an unusual conclusion: it could not establish an ADI due to data limitations, including the brain tumor findings. This means EFSA adopted an implicit conservative position — it neither declared Blue 2 safe nor formally banned it, but the absence of an established ADI signals scientific uncertainty. In medical diagnostic use, high intravenous doses of Indigo Carmine can cause hypertension, bradycardia, and in rare cases anaphylaxis. These are dose-specific clinical pharmacological effects, not relevant to dietary consumption at food use levels. Blue 2 was not included in the 2007 Lancet hyperactivity study. Limited direct research links Blue 2 to behavioral effects. The FDA's April 2025 announcement includes Blue 2 in the class of petroleum-based synthetic dyes to be phased out of the US food supply, reflecting updated policy on the category rather than specific new Blue 2 toxicity data.

Partially Hydrogenated Oils: Artificial trans fats (from PHOs) have the most well-established cardiovascular harm of any food ingredient ever banned. Multiple large meta-analyses have confirmed that trans fat consumption increases LDL ('bad') cholesterol, decreases HDL ('good') cholesterol, increases inflammatory markers, and significantly raises cardiovascular disease risk. The Harvard Nurses' Health Study and other landmark prospective studies in the 1990s identified trans fat as uniquely harmful — worse than saturated fat in its cardiovascular effects. A 2006 NEJM meta-analysis by Mozaffarian et al. estimated that eliminating artificial trans fats from the US diet could prevent 72,000 to 228,000 heart attacks per year and 30,000 to 100,000 coronary heart disease deaths annually. The WHO estimates that industrially produced trans fats cause over 500,000 cardiovascular deaths per year globally. The FDA revoked PHOs' GRAS status in 2015 based on this evidence, with compliance by 2018. Denmark banned artificial trans fats in 2003, the first country to do so, and observed a dramatic reduction in cardiovascular mortality in subsequent years.