It's not just your tongue that has taste receptors for sweet things - your gut contains them too, a new study suggests.
The remarkable discovery, announced this week by U.S. scientists, provides new insights into how we absorb nutrients from the foods we eat. And it could also explain why artificial sweeteners don't seem to help a lot of people to lose weight.
"Cells of the gut taste glucose through the same mechanisms used by taste cells of the tongue," said Robert Margolskee, who led the research team at Mount Sinai School of Medicine in New York.
"Sensing glucose in the gastrointestinal tract is the first step in regulating blood-sugar levels."
Dr. Margolskee explained that carbohydrates ingested from meals and beverages break down into glucose, which stimulates the "sweet-sensing" taste receptors in the gut. Once they are stimulated, the receptors trigger the release of hormones that make the intestines absorb sugar into the bloodstream.
The study was carried out on mice, but the researchers think the same biological processes are going on in the human body.
The disturbing thing about this research is that artificial sweeteners also appear to turn on the gut receptors, Dr. Margolskee said.
That means that even though a diet soft drink is sugar-free, the artificial sweetener leads to a greater uptake of sugars from other foods that might be in your belly at the same time.
"Under these conditions, even if people limit their food intake or limit the amount of carbohydrates in their diet, they will absorb as much sugar as possible," added Dr. Margolskee, whose study was published in the journal Proceedings of the National Academy of Sciences.
The new finding helps shed light on another recent study that found people who down diet beverages are just as likely to develop heart disease and diabetes as those who consume sugary drinks.
A diet pop is still "probably better than drinking too much sugar-sweetened soda," Dr. Margolskee said. But a diet drink isn't "neutral," he stressed. "Whatever hormones are released by sugars could also be released by artificial sweeteners."
Even so, this study could have a positive outcome by leading to the development of better artificial sweeteners, he said.
"One possibility is to have an artificial sweetener that is sweet in the mouth but breaks down in the stomach so it doesn't activate the gut taste cells."
DRUG TRIALS IN QUESTION
There's an old saying: "He who pays the piper calls the tune."
Well, the same principle seems to be at work in drug industry clinical trials.
A recent analysis of 192 trials of cholesterol-lowering medications revealed that study results tend to favour a drug company's own product. In other words, if a drug company paid for the trial, it was likely to produce favourable findings.
The studies were conducted between 1999 and 2005. They all involved so-called head-to-head trials in which one drug was pitted against another.
Researchers at the University of California, San Francisco, found that study results were 20 times more likely to back the drug made by the firm sponsoring the trial.
"I think ... patients, policy makers and physicians should be extremely critical of these head-to-head comparison trials," said Lisa Bero, who led the analysis published in the online journal PLoS Medicine.
There are numerous ways companies can skew results in favour of their own medications. They can select non-equivalent doses of drugs for testing. Or, they may simply decide not to report those findings that cast their product in an unfavourable light.
Many of the studies examined by the UCSF research team "were clearly designed for marketing purposes rather than to rigorously compare the effects of drugs within a class," Dr. Bero said in an e-mail interview.
There is certainly a lot at stake. Worldwide sales for a class of cholesterol drugs known as statins amount to $35-billion (U.S.) a year. And, unfortunately, doctors could be making prescription choices based on dubious studies.