Have you heard that you can literally sniff your way to weight loss? Don't get too excited, because the new "aromatherapy diet" is totally unproven. One renegade aromatherapist, Eugeny Couture, has received some press attention for her intriguing claim that sniffing grapefruit oil (several deep breaths, up to six times per day) will help to regulate one's appetite — presumably leading to less overeating and more weight loss. But there simply isn't any even semi-scientific evidence to suggest that this is true.
Grapefruit oil is a real product, but it is used mostly for non-weight loss purposes, like flavoring water without adding sugar and freshening up around the home. Seasoned dieters may associate grapefruit with weight loss because of the horrible fad "grapefruit diet," which has stubbornly refused to die and has been regaining popularity from time to time for over 80 years now. Grapefruit itself doesn't burn fat, but it's a reasonably healthy addition to your usual diet (and eating grapefruit before meals may keep you from overeating, thereby promoting weight loss).
Grapefruit has also made it into the famous Atkins Diet, whose proponents claim that grapefruit helps to prevent insulin resistance. But, again, that's when the grapefruit is ingested, not sniffed. If any people are actually losing weight from sniffing tubes of grapefruit oil as recommended by some aromatherapists, it must be because the ritual helps them to avoid stress eating, by calming down and refocusing on whether they're actually hungry — not due to any magical properties of the grapefruit oil.
Our sense of smell is closely related to our sense of taste, but it's not enough to point that out and then recommend a totally unrelated smelling ritual as an appetite solution. As usual, people are looking for a quick fix to their weight loss problems and willing to suspend disbelief in hopeful ignorance of their scientific knowledge. You've heard it a million times, but if you want to manage your weight healthfully and effectively in the long run, you really need to eat right and get moving – not stick your nose into voodoo oils and cross your fingers for the best.