An international group of scientists have solved the mystery of a genetic flaw which greatly increases the risk of obesity in one in six people.
A version of an obesity gene, called FTO, had been linked to a bigger belly, but the reason why was uncertain.
A study, published in The Journal of Clinical Investigation, showed FTO gene made fatty foods more tempting and altered levels of the hunger hormone, ghrelin.
Obesity experts said drugs targeting ghrelin might reduce weight gain.
There is a strong family link with obesity, and a person’s genetic code is thought to play a major role in the risk of them becoming overweight.
People have two copies of the FTO gene – one from each parent – and each copy comes in a high and a low-risk form. Those with two-high risk copies of the FTO gene are thought to be 70% more likely to become obese than those with low-risk genes.
But no-one knew why.
FTO gene made fatty foods more tempting and altered levels of the hunger hormone, ghrelin
A team, led by researchers at University College London, tested two groups of men. All were a normal weight, but one group had the high-risk FTO genes and the other was low risk.
The first tests looked at levels of the hormone ghrelin either side of a meal in 10 men from each group.
Levels of the hormone, which makes people hungry, did not fall as far in the high-risk patients after the meal. Their ghrelin levels also began to climb more quickly.
In separate tests, a series of brain scans after a meal showed further differences between the two groups. Men with the high-risk genes found pictures of high-fat foods more appealing than the low-risk men.
Dr. Rachel Batterham, the head of the centre for obesity research at University College London, said: “Their brain is set up to be particularly interested in anything to do with high-calorie food.”
She said they were “biologically programmed to eat more”.
Dr. Rachel Batterham said understanding how FTO affected the odds of becoming overweight would help patients.
She said exercise such as cycling was an excellent way to lower ghrelin levels and there was a significant amount of research from pharmaceutical companies working on the hormone.
Dr. Rachel Batterham added: “Also protein meals do lower ghrelin more, so anything that suppresses ghrelin is more likely to be effective in FTO patients.”
The FTO mutations were probably life-saving at one point in human history when piling on the pounds in the summer would help people survive the winter.
Few weeks ago U.S. researchers finally discovered why we like to combine sharp, acrid tastes with fatty flavors: a fry-up with a pot of tea; steak with red wine; and cheese with pickle.
Researchers at Rutgers University in New York asked volunteers to drink tea or water in between bites of a fatty meat such as salami.
Results showed the tea helped counter the fatty feeling left in the mouth by the meat.
“The way foods make our mouths feel has a great effect on what we choose to eat,” says Professor Paul Breslin, an oral biologist at Rutger.
It seems the contrast between fatty and sharp, acrid tastes allows us to eat fatty foods more easily – astringent food and drink reduce saliva, drying the mouth and cancelling out the greasy feeling created by fatty ones.
This, in turn, creates a clean feeling.
“This natural tendency for seeking balance in our mouths might have benefits for maintaining a diversity of foods in our diet,” says Prof. Paul Breslin.
It might also be good for our oral health, as it stops our mouths becoming too lubricated.
“This is necessary to keep our teeth from wearing down and our oral tissues healthy,” adds Prof. Paul Breslin.
Taste is an incredibly important and sometimes complicated, sense, playing a huge role in our enjoyment of life, says Shahzada Ahmed, a consultant ear, nose and throat surgeon at Queen Elizabeth Hospital and BMI The Priory Hospital, Birmingham.
Taste is the combination of different chemical signals on the tongue: sweet, sour, bitter, salty and umami (savory).
These are picked up by tastebuds – up to 10,000 of them.
Contrary to popular belief, they aren’t the lumps you see on your tongue – those are papillae.
The tastebuds are on or around the papillae.
Each bud contains 100 or so receptor cells, which respond to the taste chemicals and send impulses to the brain.
We reveal the latest revelations about how taste works, and how it affects your health . . .
The reason you hate healthy veg
Up to a quarter of us are what’s known as supertasters.
They have more tastebuds – more than 10,000 rather than the average 2,000. As a result they taste food far more intensely.
This can be a bonus. Many chefs and wine tasters are supertasters, able to differentiate flavor more readily than the rest of us.
But you can be too sensitive for your own good.
Nutrient-rich but bitter vegetables such as broccoli, cabbage and Brussels sprouts can be unpalatable.
To find out if you’re a supertaster, there’s an easy test. Punch a hole in the corner of a piece of card before putting a few drops of blue food coloring on your tongue.
Next, place the card on the front of your tongue and press gently.
“With a magnifying glass and mirror, count the papillae – these won’t pick up the dye, so will appear as pink dots against the blue,” says Shahzada Ahmed.
“If you have 35 or more, you may be a supertaster.”
Overweight? Blame dulled tastebuds
German researchers revealed last month that obese children have a less sensitive sense of taste than children of normal weight.
A study published in the Archives Of Disease In Childhood observed 99 obese children and 94 of normal weight aged between six and 18.
It found that obese children found it significantly more difficult to tell one taste sensation from another, and to identify the taste correctly.
“We are still unsure why this may occur and whether obesity causes a dulled sense of taste or if they have this to begin with, but having a dulled sense of taste probably means the children need increasing amounts of food and flavour to give them stimulation,” says Shahzada Ahmed.
There are tastebuds in your tummy, too
Taste cells aren’t found only on your tongue – they’re everywhere, from the roof of your mouth to your stomach and intestine.
Those in the mouth help us make those instant judgments about what we should be eating, while those in the gut ensure the digestive system is prepared for what happens next.
“If you were to eat something bitter and potentially toxic, gut cells would sound an alarm to slow down absorption or encourage you to be sick,” says Shahzada Ahmed.
And if you ate something sweet, these taste cells may then ensure the body boosts your insulin levels to cope with the extra sugar.
The tongue tip is more sensitive to sour tastes
For years, people thought we tasted different flavors on different parts of the tongue.
The so-called “tongue map” put sweet flavors at the tip, bitter at the back, and salty and sour at the sides.
This was based on misguided science from a century ago, says George Murty, a consultant ear, nose and throat specialist at University Hospital Leicester.
“However, studies do suggest that some parts of the tongue may be more sensitive to specific flavors,” he says.
A Japanese study found women were more sensitive to sourness on the tongue tip, and to salty and bitter tastes on the soft palate (the fleshy part at the back of the mouth).
Both sexes were less sensitive to a sour taste on the soft palate than the tongue tip.
It is thought hormones may play a role: poisons are bitter or sour, and a woman needs to be sensitive to harmful toxins, particularly when trying to get pregnant or when carrying a baby.
Ear infections can damage taste for good
It is well known that colds affect taste.
This is because 90% of the flavor of food comes from our sense of smell (particles of food are breathed into the nose, hitting sensory cells that send an electric signal to the brain).
If the nose is blocked, this is affected.
But ear infections, too, can cause problems.
“Repeated middle ear infections such as glue ear can affect the ability to taste,” says Shahzada Ahmed.
“This is because ear infections can damage the taste nerve, which runs up from the tongue right through the middle ear and into the brain.
“This damage can intensify the sensation of the texture of fatty foods, and as a result these people may put on weight.”
Other illnesses linked to a loss of taste include Sjogren’s Syndrome, an auto-immune condition that affects up to 4% of adults and causes the immune system to attack glands that secrete fluid, such as the saliva glands.
An underactive thyroid can also cause problems, possibly because the thyroid hormone helps maintain the health of the lining of the taste nerves.
Fortunately, hormone replacement tablets will help reverse any problems.
“Liver disease and kidney failure can also damage your sense of taste,” says Dr. George Murty.
These organs rid the body of toxins. If they stop functioning poisons can build up, affecting the tongue lining and nerves.
Why fatty foods are so moreish?
Who can stop at just one or two chips? Now scientists think they know why this is so.
University of California researchers discovered that when rats tasted something fatty, cells in their upper gut started producing endocannabinoids – marijuana-like chemicals that give a natural high.
Interestingly, the study showed sugars and proteins do not have the same effect.
Fats may be the only foodstuff to produce these chemicals because of evolution.
“Fats are the ultimate energy source,” says Carl Philpott, a consultant ear, nose and throat surgeon and rhinologist at James Paget University Hospital, Norfolk.
“So when we needed to survive long, cold winters, that was the type of food we needed to stock up on.”
Could your heart pills ruin the taste of food?
A number of drugs can interfere with our sense of taste. Anti-depressants can block taste messages reaching the brain, says Dr. George Murty.
Beta-blockers, taken for heart conditions and high blood pressure, can also cause problems.
These block the transmission of nerve impulses that cause blood vessels to narrow and the heart to beat faster, but they can also affect other nerves, including receptor nerves on the tongue.
Chemotherapy can also cause total loss of taste or alter it, so everything seems bitter, salty or metallic.
This is because chemo drugs target cells with a fast turnover rate. This includes tastebuds cells (and smell receptor cells).
However, normal taste generally returns within a couple of months of stopping chemo.
Good taste starts with your mother
What you like to eat might not be such a personal choice after all.
Certain foodstuffs – garlic and vanilla, for instance – have been shown to enter the womb through the amniotic fluid, giving the baby a preference for those foods after birth, says Carl Philpott.
Genes, too, play a part.
A study at Kings College, London compared the diets of 3,000 female twins with non-identical twins. Identical twins were found to share far more preferences, such as weaknesses for coffee, garlic or fruit and vegetables.
“This suggests genetics play a moderate part in the development of preferred foods,” says Professor Jane Wardle, who led the study.
It is possible that genes involved with taste, or the reward chemicals released by the brain in response to certain foods, play a role.
Marmite – you can make yourself love it!
It is possible to train yourself to like certain tastes – particularly important with children (who tend to default to sweet tastes when young, primarily because the growing body is programmed to go for high-energy food).
A lot of the time it’s simply psychological, taking cues from others. Try eating with people who enjoy your dreaded food type.
“Bringing out the sweetness of foods can also make them more palatable,” says Shahzada Ahmed.
“Roasting bitter broccoli will draw out its natural sugars.”
Finally, teaming it with something fatty – say cauliflower with a cheesy sauce – can also help.
“Fatty foods trigger receptors in the stomach that produce feel-good chemicals,” says Shahzada Ahmed.