London - We are reminded constantly that eating too much and exercising too little will ultimately lead to weight gain. But when you eat sensibly and work out diligently only to find the kilos still don’t drop off, what’s going wrong?
Scientists now have a better understanding of how the body responds to food and believe that, in some cases, failed dieters may be hard-wired to find weight loss more difficult. Everything from your nerves to your gut bacteria could be sabotaging your battle of the bulge. Here we find out how:
FATTY FOOD SWITCHES OFF STOMACH NERVES
Last month researchers announced that if you struggle to keep weight off, then your nerves could be to blame. According to scientists at the University of Adelaide, nerves in the stomach - called the gastric nerves -tell the brain when we are full after a meal.
But too much junk food can desensitise those gastric nerves so they stop working effectively. The result? You eat more to feel satisfied and trigger the nerves to respond.
In their study, the Australian team showed that the nerves were less responsive after fatty food. And two weeks after switching back to a normal diet, the gastric nerve response was still below normal.
“This means you would need to eat more food before you get the same degree of fullness as a healthy individual,” says study leader Amanda Page, associate professor of medicine at Adelaide. In their findings, published in the Journal of Obesity, Professor Page and her team suggested the lack of response was made worse by leptin, the so-called hunger hormone.
Though leptin normally helps to stem hunger pangs, when exposed to lots of high-fat foods, the hormone seems to affect the stomach nerves, dulling fullness signals to the brain. Although the study was on mice, Professor Page says a similar effect is likely to be seen in humans, and more research is needed to see if there are ways “to trick the stomach into resettling itself to normal” after a high-fat meal.
YOUR BRAIN IS MISWIRED
Scientists say it is not just overeating that makes people fat. Your brain may also play a role.
Last year, researchers at the University of Michigan reported that our brains are wired differently, and for some of us that means reduced response to the hunger hormone leptin that regulates appetite.
Leptin’s role is to signal to the brain when to reduce appetite and start burning calories. Previous studies have shown that people who don’t produce leptin are more likely to struggle with weight.
But Dr Alan Saltiel, director of Life Sciences at Michigan who led the study, found that in some people the brain receptors responsible for processing leptin just don’t work effectively.
A possible explanation for this is that these people produce too much leptin which effectively overloads their brain receptors and impairs the mechanisms that help to eliminate excess fat. Saltiel suggested that in these people a faulty mechanism means the hormone can’t bind to cells in the brain, so the full signals don’t get through.
Other researchers have shown that some women have a weakened “reward circuit” in their brains, the response that instructs them to stop eating when they have consumed something enjoyable. As a result, they are at a greater risk of weight gain over time.
In a study at the University of Oregon, some women given chocolate milkshakes had a blunted output of the neurotransmitter dopamine, released by the brain when food is enjoyed and vital to our “reward circuit”.
Previous studies have shown that obese people have fewer dopamine receptors and the Oregon researchers suggested that a low dopamine response to something tasty indicates a genetic flaw.
YOU'RE AN APPLE SHAPE, NOT A PEAR
Your body shape - whether apple or pear - could determine how easy it is to lose weight.
In a study of obese adults published in the Journal of the American Medical Association a few years ago, researchers found that people who carry their excess weight around their waist - the so-called apple shape - also rapidly secrete a lot of insulin (the hormone that controls blood sugar levels) after eating a little bit of sugar.
This suggests they respond more strongly to sweet food. They also struggled to lose weight on a low- fat diet and, the study found, would do better on a diet that restricted simple carbohydrates from sugary and starchy foods like cookies and potatoes.
People who carry their excess fat around their hips - the pear shape - secreted less insulin after eating sugary food and would lose weight equally well on either diet.
“There are a lot of studies looking at the way body shape influences weight loss,” says dietitian Louise Sutton of Leeds Metropolitan University.
“What this and other research has shown is that unstable insulin levels, such as those exhibited in the apple shapes in this study, create stronger hunger sensations, causing them to struggle with their weight and finding it hard to plan an appropriate diet.”
YOUR GUT LACKS THE RIGHT BACTERIA
Whether you have the right type and amount of bacteria in your stomach could hamper your dieting attempts.
Numerous studies in recent years have linked gut bacteria to hunger and metabolism. In the latest, conducted at Washington University, tests on mice which were given stomach bacteria from obese people showed that they became fatter than those receiving microbes from lean individuals.
Transplanting the gut microbes led to metabolic changes in the rodents associated with obesity, said the scientists behind the study, which was published in the journal Science.
The findings come after another study, published in the Proceedings of the National Academy of Sciences this year, found that the levels of a specific gut bacteria - called Akkermansia muciniphila - were lower in obese and type 2 diabetic mice. In this case, feeding the mice a prebiotic supplement, which provides food for the bacteria, boosted the bugs back to normal levels and reduced the risk of weight problems and diabetes.
Adding the beneficial bacteria changed the chemical signals coming from the digestive system - which led to changes in the way fat was processed elsewhere in the body.
Linia Patel, a spokesperson for the British Dietetic Association, says that gut bacteria have a crucial role in the body. “We do know that good bacteria have a pivotal role in gut health, as well as one’s ability to digest food well and possibly immunity.”
YOUR HEAD IGNORES YOUR STOMACH
Why is it that you are constantly wanting to snack when others are satisfied after a single meal?
To find out if our internal hunger pangs really are dramatically different, even from those of other family members, nurses at the University of Pennsylvania looked at the eating habits of children and their siblings.
Their findings showed that overweight and obese children ate an average 34 percent more calories from snacks than their normal weight brothers and sisters, even though they had all been offered the same meal.
Why? Dr Tanja Kral, the study leader, says the heavier children seemed to have an “impaired ability to adjust for calorie differences” and that they also ate more of a meal after a calorie-rich appetiser compared with their normal weight siblings.
“Our findings suggest some children are less responsive to their internal cues of hunger and fullness and will continue eating even when full,” Dr Kral says.
According to Linia Patel, parents often inadvertently help to confuse their child’s hunger cues by rewarding or consoling them with food when they are young.
Such practices, she says, dull the hunger sensation so that children eventually fail to recognise it. “Serve children appropriate servings of food and no adult portions,” Patel says. “And ask your child if his or her tummy is full at the end of a meal. Help them to recognise hunger and satiety.”
FASTING UPSETS YOUR IMMUNITY
If you feel your body is battling against your attempts to diet, it could be true.
Professor Gregory Freund, a nutritionist at the University of Illinois school of medicine, found that sudden attempts to slash calories or reduce food dramatically in a detox can trigger significant changes in our immune systems.
This could mean efforts backfire because weight loss is made more tricky. He says diets with one or more fasting or cleansing days a week are especially troublesome.
His studies showed that rapidly reducing intake seems to decrease the number of a type of immune cells called cytokines. These cells have been linked to weight loss, and low levels can increase the risk of piling on the pounds.
Professor Freund says that the reaction can be countered by taking “smaller steps to your weight loss” and not attempting severe calorie restriction or fasting. - Daily Mail