New Delhi: Milind Watve, a professor of biology, has spent several decades unravelling the sex lives of microbes. He is now devoting his energy to understanding why people overeat, a question that has drawn scores of researchers and billions of dollars.
Preliminary results of a study by Watve on cashiers showed that human brains have started to respond to money in the same way our hunter-gatherer ancestors did to food.
Put simply, the more money you handle, the greater the chance that you may turn obese, according to Watve, who teaches at the Indian Institute of Science Education and Research in Pune. Even among the cashiers, those who handled their own money tended to be more overweight than the ones who counted out money as part of their job.
“In the modern lifestyle and social and economic structure, the importance of non-food rewards such as money is increasing,” Watve wrote in a paper published in Current Science earlier this month. “Frequent stimulation of the reward system by non-food rewards may eventually desensitize the reward centre which gives a sub-normal response to food and greater quantity of food is needed for generating adequate response.”
Since money plays a dominant role in our lives, people could be eating more to compensate for the diminished pleasure derived from food, Watve reasoned.
To test his hypothesis, Watve conducted an experiment in which he and his students interviewed 160 cashiers in Maharashtra. Among them were those who had money of their own, or owners, (and hence gained income proportionate to the cash they handled) and those who dealt with currency for pay. The researchers also tabulated the sums handled. The participants’ weight, height and waist-to-hip ratio, all standard metrics to measure obesity, as well as exercise regime were compared with the sums earned.
“What we found was that those who handled significantly higher amounts of cash, and owners, had significantly higher body mass index (BMI) whereas age, duration of service, exercise didn’t correlate with BMI,” said Watve. “The waist-to-hip ratio correlated significantly with money handled, exercise and the sex of the cashier.”
BMI is the ratio of weight to the square of height. While figures vary across countries on what constitutes ideal BMI, 23-25 kg/m2 is considered healthy, 25-30 is overweight and anything above that obese.
The results, according to Watve, were preliminary evidence, if not conclusive proof that those who had an incentive to handle cash were generally more obese and the more the cash handled, the greater the BMI. There was a slight, but statistically insignificant, increase in BMI among owners when compared with salaried cashiers who handled big sums of money.
“There is some fundamental role being played by money in the brain,” Watve reasoned. Perhaps because money rewards were stimulating neural pathways that responded to rewards, it required a greater amount of food to produce a compensatory response, he explained.
A majority of the researchers who have studied obesity and why humans would risk diseases such as diabetes by overeating, say the reasons are a mix of genetics, increased availability of food and sedentary lifestyles.
“The generally accepted explanations for the obesity epidemic are particular genes or that we are doing far less physical work than before, but that isn’t entirely true,” said Watve. “Doubly labelled water experiments show that our metabolic rates have hardly changed over millennia and there haven’t been enough years of evolution for significant genes to spread through the globe.”
Doubly labelled water is that in which constituent elements have been marked so they can be traced during experiments.
The World Health Organization estimated that, as of 2008, 1.5 billion adults aged 20 and above were overweight and that two of every five of them were obese. The demand for the surgical removal of fat, health food and anti-obesity drugs has surged and is estimated at about $20 billion (Rs 90,200 crore) annually.
Beginning 1982, American and British scientists have presented evidence to show that metabolic rates, or the speed at which the digestive system breaks down food molecules into energy, has remained fairly constant across societies, lifestyles and time.
Humans have become less active as they transitioned from a vigorous hunter-gatherer lifestyle to a more stable, but less-demanding agrarian life all the way up to the labour-saving standards of today. But there has been no attendant evolutionary decline in metabolic rates.
“That’s just not happened. You can therefore be fairly certain that it’s not that we are working less, we are probably just eating more,” Watve said.
Deep within—or scattered throughout, it’s still not clear —the brain’s oracular folds lie feedback receptacles called reward centres. Here, chemicals known as neurotransmitters such as dopamine “tell” the brain if the body is being taken care of. In ways that are still not entirely understood, they influence the degree to which we empathize, connive, drink, smoke and eat. The greatest reward that early humans got was food and the brain responded with bursts of dopamine. With a shift in lifestyles, regions of the brain that once responded to food alone now have also begun to respond to money, according to Watve.
To be sure, the idea that different regions in the brain may be playing roles different from what they were ordained for isn’t new.
Drugs that seek to manage obesity by killing hunger pangs tap into the mechanism of the brain’s reward systems to wean patients off overeating.
“They aren’t too popular, as most drugs such as Sibutramine have side effects and are banned in India,” said Anoop Misra, a diabetes researcher and chairman, Center of Excellence for Diabetes, Metabolic Diseases and Endocrinology at Fortis Hospitals.
Evolutionary biologists have observed several organisms that employed alternative uses for organs that were designed for different purposes, just as feathers evolved for regulating the body temperatures of birds, but then began to be used for flight.
“It’s called exaptation,” said Aditya Sinha, evolutionary biologist at the National Institute of Advanced Sciences, Bangalore. He said Watve’s work was exciting, most importantly because the data showed that nearly 18% of the variance, or divergence from the mean, in BMI and 25% of the variation in the waist-to-hip ratio could be explained by this one idea of exaptation. “Obesity is an extremely complex phenomenon with several factors thought to play a role. So if one factor can explain between one-fourth and one-fifth of the variation, it is pretty significant. We still though have no idea how exactly this works in the brain,” he said.
Also unclear is the degree to which food and money struggle for dominance over the brain’s reward circuitry.
Misra however isn’t convinced neural mechanisms play a significant overarching role in obesity.
“The paper presents an extremely interesting hypothesis, but I’m not convinced that the data set shows strong evidence that money is playing an important role in obesity, at least at the individual level,” he said.
The experiment doesn’t take into consideration the cashier’s family history of obesity, Misra said. His own research shows a wide variety of genes can explain nearly 60% of obesity incidence, and that in a majority of such cases exercise and diet can overcome even these genetic effects.
Watve isn’t the only one to study the effect of money on obesity. In April, Eric Stice and co-researchers at the Oregon Research Institute reported in The Journal of Neuroscience on a group of 60 lean adolescents who were at different risk levels of being prone to obesity (those with two obese parents were deemed to be at higher risk than those with one). They reacted differently to both food and money rewards. Those at higher risk levels had significantly higher levels of activation in the brain’s reward circuitry to food and money.
Watve plans to conduct more experiments to prove his hypothesis and is planning a conference in Pune to discuss behavioural influences related to obesity.
“Cashiers were chosen because they are more likely to be thinking ‘money-related’ thoughts over long periods and, therefore, the effects of money were easier to quantify,” he said. “That said we’re looking at collaborations to study other professions.”
•Researchers are looking at ideas in evolutionary biology to understand why obesity has become pandemic
•Biologist Milind Watve says one of the reasons for obesitymay be evolution and resulting changes that are occurring in the human brain.
•An experiment suggest that diminished returns from food may be causing people to overeat and, hence, put them at greater risk of being fat.