Grapefruit has a long tradition of being helpful with weight control and while these studies were done on animals, and while I could not find equivalent studies done on humans, there may be something to be learned from these. 

Study 1  

Planta Med
2010; 75 (10), Pages 950-955
DOI: 10.1055/s-0029-1240870 

Grapefruit Oil Attenuates Adipogenesis in Cultured Subcutaneous Adipocytes

Shinichiro Haze1, Keiko Sakai1, Yoko Gozu1, Mio Moriyama

Abstract

We investigated the effects of different essential oils on adipogenesis in rat subcutaneous adipocytes.

Subcutaneous preadipocytes were cultured in Dulbecco’s Modified Eagle Medium (DMEM) containing insulin, transferrin, fibroblast growth factor, dexamethasone, indomethacin, fetal bovine serum, and an essential oil at 37 °C in 5 % CO2 to induce their differentiation. After 7 days, the number of viable cells, and the amount of triglycerides accumulated in the cells were determined.

Differentiation markers such as the enzymatic activity of glycerol-3-phosphate dehydrogenase (GPDH) and the expression of GPDH and peroxisome proliferator-activated receptor γ (PPARγ) genes were also measured, as well as the intracellular Ca2+ levels.

We found that grapefruit oil inhibited the accumulation of triglycerides in a dose-dependent manner at concentrations of 50 to 400 µg/mL.  Furthermore, it suppressed the expression of GPDH and caused a 70 % decrease in the enzymatic activity of GPDH at a concentration of 50 µg/mL.

Grapefruit oil also caused a nearly 2-fold increase in the intracellular concentration of Ca2+ and suppressed the expression of PPARγ genes.

Our results demonstrate that grapefruit oil efficiently inhibits adipogenesis in cultured subcutaneous preadipocytes and adipocytes.

Study 2 

Brain Research
Volume 1058, Issue 1 – 2 , October 2005, Pages 44-55
https://doi.org/10.1016/j.brainres.2005.07.048

Olfactory stimulation with scent of essential oil of grapefruit affects autonomic neurotransmission and blood pressure

Mamoru Tanida, Akira Niijima, Jiao Shen, Takuo Nakamura, Katsuya Nagai

Abstract

Previously, we observed that olfactory stimulation with scent of grapefruit oil (SGFO) enhances sympathetic nerve activities and suppresses gastric vagal (parasympathetic) nerve activity (GVNA), increases plasma glycerol concentration and body temperature, and decreases appetite in rats.

Here, we show that olfactory stimulation with SGFO for 10 min elevates renal sympathetic nerve activity (RSNA) and blood pressure (BP) and lowers GVNA in urethane-anesthetized rats.

Olfactory stimulation with limonene, a major component of grapefruit oil, also elicited increases in RSNA and BP in urethane-anesthetized rats. Anosmic treatment with ZnSO4 eliminated both the effects of SGFO and scent of limonene on RSNA and BP. Intracerebral administration of diphenhydramine, a histaminergic H1-antagonist, abolished SGFO- or scent of limonene-mediated increases in RSNA and BP as well as the decrease in GVNA. Moreover, bilateral lesions of the hypothalamic suprachiasmatic nucleus (SCN) eliminated the SGFO- and limonene-mediated increases in RSNA and BP and decrease in GVNA, but bilateral lesions of the cerebral cortex did not have any effect on these parameters.

These findings suggest that scent of grapefruit oil and its active component, limonene, affect autonomic neurotransmission and blood pressure through central histaminergic nerves and the suprachiasmatic nucleus.

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