In addition to Sensa, which has been available since last summer, there is SlimScents, aromatherapy diet pens filled with fruity or minty odors; a jar of peppermint-scented beads called Happy Scent; and the vanilla-doused Aroma Patch, which you wear on your hand, wrist or chest. 
 
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 Last month, Compellis Pharmaceuticals of Cambridge, Mass., began human trials on a nasal spray designed to do the opposite of what Sensa does: to curb the appetite by blocking rather than enhancing smell. 
 
 “Eighty percent of what you perceive as taste is actually smell,” said Christopher Adams, a molecular biologist and the company’s founder. “The hypothesis is that if we can alter your sense of smell we can make food less palatable, because the hedonic effect — that is, the pleasurable effect you get from eating chocolate — won’t be there.” 
 
 Using smell to manipulate appetite may be an appealing premise, but only a few studies have been conducted, and some experts have doubts. 
 
 “There’s been a theory around for a number of years that if you saturate your sensory system that you’ll not be as hungry,” said Dr. Richard L. Doty, the director of the Smell and Taste Center at the University of Pennsylvania Medical Center in Philadelphia. “There needs to be more research done.” 
 
 Mark I. Friedman, associate director of Monell Chemical Senses Center in Philadelphia, said that while the sight, taste or smell of food may result in the release of insulin and an increase in metabolism, “those kinds of effects are short-lived. If you constantly smelled something you would adapt to the odor, and you wouldn’t smell it anymore.” 
 
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 But Sensa’s maker, Dr. Alan Hirsch, is confident that his product — which contains malodextrin, tricalcium phosphate, silica and natural and artificial flavors — works. 
 
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 “A large part of the reason that you feel full is your brain interpreting that you’ve smelled it and tasted it,” said Dr. Hirsch, a neurologist, psychiatrist and the founder of the Smell and Taste Treatment and Research Foundation in Chicago. 
 
 Dr. Hirsch has conducted several studies on smell, taste and appetite. In the early 1990s, he gave 3,193 patients inhalers containing aromatic ingredients, which they inhaled whenever they were hungry. They were instructed to keep their normal diet and exercise routines, and each month for a period of six months they were given new inhalers. The participants lost an average of 5 pounds a month, he said. 
 
 Around that same time, Dr. Hirsch licensed this research to the company that created SlimScents. (Shortly thereafter, he revoked the license, because of business disagreements, he said, although the company has continued to market the product.) Later, Dr. Hirsch went a step further by focusing on both smell and taste. In 2005, he gave 1,436 patients granules called Tastant crystals. His theory was that these granules, later marketed as Sensa, would trick the brain into thinking it was full. According to the study, the average weight loss was 30.5 pounds over six months, with a 5-point drop in Body Mass Index. 
 
 Kimberly Tobman, a spokeswoman for Sensa, said that “hundreds of thousands” of customers have used it. It is available at TrySensa.com and on television shopping networks, and costs $59 for a one-month supply, $145 for three months and $235 for six months. There are also several blogs devoted to the product. 
 
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 But there are detractors. As a woman named Mikaela wrote on www.real -customer-comments.com, a site devoted to weight loss, on April 3: “It didn’t make me feel full and decided against continuing it.” 
 
 But other researchers have found a link between scent and weight loss. 
 
 About a year and a half ago, Bryan Raudenbush, an associate professor of psychology at Wheeling Jesuit University in Wheeling, W. Va., asked 40 people to sniff peppermint every two hours for five days. For another five days he gave them a placebo. During the week they sniffed peppermint, they consumed 1,800 fewer calories. 
 
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 LAST year, after hearing about Dr. Raudenbush’s and Dr. Hirsch’s work, Donna Schilder, a business and life coach in Long Beach, Calif., brought Peppermint Happy Scent to market. “Whenever clients feel an urge to eat something, they take it out, shake it and smell it,” said Ms. Schilder, who charges $5.50 for each jar of silicon beads, which have been dipped in scented oil. She stressed that she did not make any promises about her product. 
 
 Mark Cohen, the founder of SlimScents, an aromatherapy inhalant, guarantees that his product works; he is prepared to offer it free for six months (minus shipping and handling) or until a person loses 2.5 percent of his or her body weight. 
 
 “We’ve never found a person who used the product correctly and didn’t lose weight,” he said. 
 
 Still, Dr. Friedman and others point out the lack of research supporting the link between smell and weight loss. 
 
 “There’s no scientific evidence that smelling or tasting flavors is going to suppress your intake over a nutritionally significant interval,” he said. ||||| It sounds like a New Age spin on the timeworn promises of diet aids everywhere: Sprinkle crystals on your food and -- abracadabra! -- start shedding weight.The makers of Sensa , of course, claim that there's more science than hocus-pocus behind their product. Much of the rest of the scientific community, including U.K. neuropsychologist Dominic Dwyer, isn't so sure. Nevertheless, the magic-seeming crystals that two years ago promised dieters in America that they could lose weight without having to exercise or change what they eat are getting ready to take the world by storm.The theory behind Sensa seems plausible enough (but then again, so does most infomercial logic at first glance, especially if you're watching it at 3 a.m.): Because we mostly experience the taste of food through our sense of smell, if you enhance the scent of food, you'll feel fuller faster, and thus eat less. Sensa's crystals supposedly do just that. (And so says spokesmodel and 'Millionaire Matchmaker' Patti Stanger .)Sensa's makers claim that, taken together, American dieters have lost over a million pounds by sprinkling the tasteless, calorie-free crystals on everything they eat, and soon, dieters in Canada, Mexico, Britain and Germany will be getting the opportunity to try Sensa for themselves.Still, there remains significant debate over whether the somewhat pricey Sensa Weight-Loss System actually works ($59 for a one-month supply). As Dr. Mark I. Friedman, associate director of Monell Chemical Senses Center in Philadelphia, pointed out last year in an article about Sensa in The New York Times, "There's no scientific evidence that smelling or tasting flavors is going to suppress your intake over a nutritionally significant level."
– Scientists may be dubious about their actual benefits, but Sensa diet crystals are set to go global anyway, reports Slashfood. The products claims to make the scent of food—and therefore the flavor—more intense. The idea is that a more intense flavor will make dieters feel fuller after eating less. The supposedly appetite-suppressing crystals have been available in the US for two years now, but the product is set to debut in Canada, Mexico, Britain, and Germany. Dieters considering them may want to heed the words of Dr. Mark Friedman, an expert on taste and smell: "There's no scientific evidence that smelling or tasting flavors is going to suppress your intake over a nutritionally significant level." (The quote appears in Slashfood via this New York Times article.)