ISLAMABAD  – Dieting makes people feel depressed because cutting out fatty foods alters their brain, a new study has claimed.

Scientists have found that ditching a high-fat diet triggers actual chemical changes in the brain that could make people enter a vicious cycle of poor eating. Since fatty and sugary foods cause chemical changes before obesity even occurs, the University of Montreal researchers likened going on a diet to drug withdrawal.

“By working with mice, whose brains are in many ways comparable to our own, we discovered that the neurochemistry of the animals who had been fed a high fat, sugary diet were different from those who had been fed a healthy diet,” Dr Stephanie Fulton said.

“The chemicals changed by the diet are associated with depression. A change of diet then causes withdrawal symptoms and a greater sensitivity to stressful situations, launching a vicious cycle of poor eating,” Fulton said.

The researchers fed one group of mice a low-fat diet and a high-fat diet to a second group over six weeks, monitoring how the different food affected the way the animals behaved. Fat represented 11 per cent of the calories in the low-fat diet and 58 per cent in the high-fat diet, causing the waist size in the second group to increase by 11 per cent, which is not yet obese.

The relationship between rewarding mice with food and their resulting behaviour and emotions was then measured, and the brains of the mice were studied to see if there had been any changes. Results showed mice that had been fed the higher-fat diet exhibited signs of being anxious - such as avoiding open areas - and their brains had been altered.

A molecule the researchers looked at was dopamine, which enables the brain to reward people with good feelings and encourages them to learn certain kinds of behaviour.

They found another molecule, CREB, involved in memory, which causes the production of dopamine, is more activated in the brains of the higher-fat mice.

“CREB is much more activated in the brains of higher-fat diet mice and these mice also have higher levels of corticosterone, a hormone that is associated with stress. This explains both the depression and the negative behaviour cycle,” Fulton said.

Simple ‘standing up’ test can predict mortality

A simple test which asks people who are middle aged and above to sit on the floor and stand up with as little support as possible can predict mortality, scientists claim. The ability to sit on the floor before rising to a standing position is closely linked to all causes of death, according to a new study.

Researchers found that adults who needed to use a number of aids such as their hands and knees to get off the floor were six times more likely to die than those who didn’t.

It supports previous research that found musculo-skeletal fitness is a strong predictor of health in the middle aged and above, the `Daily Mail` reported.

Tests on more than 2,000 men and women in Brazil were `remarkably predictive` or mortality rates.

“If a middle-aged or older man or woman can sit and rise from the floor using just one hand - or even better without the help of a hand - they are not only in the higher quartile of musculo-skeletal fitness but their survival prognosis is probably better than that of those unable to do so,” study leader Dr Claudio Arazjo, from the Exercise Medicine Clinic in Rio de Janeiro, said.

The test was a simple assessment of the subjects` ability to sit and then rise unaided from the floor. It was performed in 2,002 adults aged between 51 to 80 years.

The subjects were followed-up from the date of the baseline test until the date of death or 31 October 2011, a median follow-up of 6.3 years. Before starting the test, they were told that without worrying about the speed of movement, they have to try to sit and then rise from the floor, using the minimum support that they believe is needed.

Each of the two basic movements were assessed and scored out of five, with one point being subtracted from five for each support used (hand or knee, for example). Over the study period 159 subjects died, a mortality rate of 7.9 per cent.

The majority of these deaths occurred in people with low test scores - only two of the deaths were in subjects who gained a composite score of 10.

Overall, subjects in the lower score range of the sitting test had a five to six times higher risk of death than those in the higher groups.

Scores of eight and above had a particularly low risk of death in the tracking period, and each one point increase in score was related to a 21 per cent reduction in mortality.

Immune system changes make recurrent tumours more aggressive

The enhanced aggressiveness of recurrent tumours may be due to changes in the body`s immune response, scientists led by an Indian-origin researcher have claimed. The traditional view of recurrent tumours is that they are resistant to therapy because they`ve acquired additional genetic mutations that make them more aggressive and impervious to drugs.

Now, researchers at the Perelman School of Medicine at the University of Pennsylvania found in an animal model that the increased aggression of recurrent tumours could be due to changes in the body`s immune response.

“Typically when a patient has a tumour recurrence, their oncologist treats them, much like they treated them for the primary tumour - with drugs aimed at the tumour cells themselves,” said senior study author Sunil Singhal, assistant professor of Surgery and director, Thoracic Surgery Research Laboratory at the Perelman School of Medicine.

“But we`ve found that it might be better to attack the tumour cells and knock down the bad immune cells that are protecting the tumour,” Singhal said.

To assess the impact of anti-cancer vaccines on primary and recurrent tumours, the researchers immunised mice that had a primary or a recurrent tumour in their flank.

Although both groups of animals developed an immune response to the vaccine, only the primary-tumour animals showed tumour shrinkage in response to the vaccine. The recurrent tumours appeared unaffected by the vaccine response.

Despite the prevailing models of tumour recurrence - which emphasise genetic changes in the tumour cells themselves - Singhal and colleagues could not find substantial genetic or behaviour differences in the recurrent versus primary tumours that might account for the pattern of response.

By contrast, when they looked at the types of immune cells in and around the tumour, Singhal`s team saw a big difference. The recurrent-tumour mice had a large increase in the number of regulatory T cells, compared with primary-tumour animals.

That could be important, said Singhal, because T regulatory cells are responsible for holding other immune cells in check and blocking immune responses. Additionally, macrophages that protect the tumour cells from immune system also increased in number and activity in the recurrent-tumour animals.

Remarkably, when the researchers treated recurrent-tumour animals with drugs that block macrophage activity, tumour growth slowed significantly. However, the same drugs had no effect on primary-tumour animals.

Singhal said it is not clear exactly what triggers the immune system changes, but whatever it is appears to happen at the time of surgery. His group has already started looking for alterations in signalling molecules.