This study investigates how the consumption of interesterified palm oil (IPO) affects the metabolic and morphological features of brown adipose tissue (BAT) in C57BL/6 mice fed a high-fat diet (HFD). Mice were divided into four groups: control, HFD (lard), HFD with palm oil (PO; HFP), and HFD with IPO (HFI). The HFP and HFI groups exhibited significant body weight gain, increased fat mass, and impaired glucose metabolism. Histological analyses revealed lipid infiltration in BAT, leading to structural remodeling from multilocular to unilocular adipocytes, hallmark features of the whitening process. This morphological shift was accompanied by reduced nuclear density and impaired vascularization. Gene expression analysis indicated downregulation of key thermogenic markers, including Ucp1, Pparγ, and Prdm16, especially in the HFI group. Increased expression of endoplasmic reticulum (ER) stress markers such as Chop and Atf4, and inflammatory cytokines (Tnfα and Il6), highlighted the pro-inflammatory and pro-apoptotic microenvironment induced by PO and IPO. These changes culminated in a loss of BAT thermogenic capacity, as evidenced by decreased UCP1 protein levels and impaired adaptive thermogenesis. Our findings underscore the detrimental effects of palm oil, mainly IPO, on BAT functionality, exacerbating obesity-related metabolic dysfunctions such as insulin resistance and glucose intolerance. The results emphasize the need for caution in the dietary use of these fats, particularly in ultra-processed food formulations, given their potential role in promoting adipose tissue remodeling and metabolic imbalances.

The position of fatty acids in the TAG molecule (sn-1, sn-2 and sn-3) determines the physical properties of the fat, which affects its absorption, metabolism and distribution into tissues, which may have implications for the risk of CHD. The TAG structure of fats can be manipulated by the process of interesterification, which is of increasing commercial importance, as it can be used to change the physical characteristics of a fat without the generation of trans-fatty acids. Interesterified fats rich in long-chain SFA are commercially important, but few studies have investigated their health effects. Evidence from animal and human infant studies suggests that TAG structure and interesterification affect digestibility, atherogenicity and fasting lipid levels, with fats containing palmitic and stearic acid in the sn-2 position being better digested and considered to be more atherogenic. However, chronic studies in human adults suggest that TAG structure has no effect on digestibility or fasting lipids. The postprandial effects of fats with differing TAG structure are better characterised but the evidence is inconclusive; it is probable that differences in the physical characteristics of fats resulting from interesterification and changes in TAG structure are key determinants of the level of postprandial lipaemia, rather than the position of fatty acids in the TAG. The present review gives an overview of TAG structure and interesterified palmitic and stearic acid-rich fats, their physical properties and their acute and chronic effects in human adults in relation to CHD.