MIGUEL BOYAYANLying down on a stretcher, psychologist Eliana Sales das Dores waits anxiously while physiologist Carlos Eduardo Negrão pricks into her right leg, near to the knee, a needle that is finer than a strand of hair, some 4 centimeters in length. The needle is a microelectrode that is going to detect the nerve impulses that circulate over one of the nerves responsible for muscular contraction and controlling the diameter of the blood vessels. A 42-year old citizen of São Paulo, and then weighing 78 kilos (58 today), Eliana hardly notices the prick of the needle they say that it is less bothering than a mosquito bite amidst the movement of the other researchers, who are putting into her left arm two inflatable bags, one a bit above the elbow, and the other in the wrist. Between the elbow and the wrist, an elastic band records the volume of blood that passes through the forearm. Next, they ask her to come close, with her right hand, to the rods of a dynamometer, a V-shaped spring that measures the force applied to a movement.
By means of examinations like these, carried out over the last three years, a team from the University of São Paulo (USP), coordinated by Negrão and by endocrinologist Sandra Villares, discovered some physiological alterations in the organism of the obese that explain why over weight people have a greater propensity towards high blood pressure hypertension than those who are at peace with the scales. In the obese, the commands from the nerves that lead to a reduction in the diameter of the blood vessels of the arms and the legs are more active. For this reason, the arteries stay closed, without dilating, and the blood does not spread out through the muscles as would be desirable, during a mental or physical activity of moderate intensity a sprint to the car on a rainy day, for example, or even at rest. And as at these times the heart beats more quickly, the resistance of the blood vessels makes the pressure rise more than expected.
As if that were not enough, people with their weight above what is recommended live with another problem: their organism fails to use, with the desired efficiency, the hormone called insulin, which extracts sugar (glucose) from the blood and takes it to the cells of the muscles and other tissues, where it is converted into energy. This is the reason why those who are fat are more liable than the thin to type 2 diabetes, which increases the risk of circulation problems capable of affecting the heart or the brain. Analyzed in conjunction, these studies bring some encouraging news: the prospects for preventing and even treating both hypertension and insulin resistance. These two problems afflict more and more people, as a consequence of the increase in the number of obese persons in the country, which has grown more than twofold in the last two decades today, 17 million Brazilians weigh far more than is regarded as healthy.
But perhaps the way out is to tweak the nose of those who will not swap a feijoada (typical Brazilian stew made of black beans and pork) for a walk. According to an article published in September in the American Journal of Physiology Heart and Circulation Physiology and signed by Ivani Trombetta, Negrão, Sandra Villares and other researchers from USP, there is no other really effective way of reverting the consequences of overweight, other than associating a diet with physical exercises. Just reducing the size of the portions helps one to slim, but it does not reduce so much the risks of hypertension and diabetes as when a diet is added to exercises. And it is not enough to do just any physical exercise, like walking to the supermarket or going up the stairs, instead of taking the elevator.
“Physical exercise must be programmed and done regularly, respecting the physical and cardiac capacity of each person”, explains Negrão, who is responsible for the Cardiovascular Rehabilitation and Exercise Physiology Unit of the Heart Institute (InCor). It is not a little that you have to sweat. Other studies had already indicated that it is necessary to burn least 1,500 kilocalories a week to reduce the risk of diseases that affect the heart and the circulation which is equivalent to a sedentary person pedaling a bicycle for one hour, from three to five times a week. “But no one should venture to do exercise without beforehand having been through a cardiorespiratory test, to assess the physical capacity and workings of the heart and the circulation during exercise”, the researcher warns.
The studies carried out by Negrão and Sandra Villares indicate that eating less and doing more exercise, provided that this is with suitable intensity and proper guidance, not only helps to eliminate the little loves handles around the waist and the fat on the hips without losing the muscles. The double sacrifice is worth it for a more important reason: physical exercise modifies the workings of the cells of the muscles and makes the organism make better use of insulin. These changes revert insulin resistance and prevent type 2 diabetes, one of the most harmful consequences of overweight. To define who was obese, the researchers availed themselves of the so-called Body Mass Index, the BMI, which corresponds to weight divided by the square of the height. A woman with 66 kilos and 1.68 meters in height has a BMI of 23.4. This is within the range regarded as healthy, which goes up to 25. But if she weighed between 70.5 and 84.6 kilos she would be overweight, and obese, with a BMI higher than 30, if she weighedmore than 84.6 kilos.
The team from USP followed up 59 women aged between 20 and 40 years old, and weighing between 70 and 106 kilos an average level of obesity, separated into two groups. The first, with 24 women, only dieted: over four months, they consumed 600 kcal per day less than the minimum recommended for a Brazilian, 2,300 kcal. The other 25, besides eating less, did moderate physical exercise, equivalent to walking quickly or riding a bike, three times a week, for 60 minutes. In both groups, there was a decrease in insulin resistance, but exercises multiplied this benefit by two: sensitivity to insulin grew 50% amongst the women who walked and ate less, whilst the increase was 22% amongst those who just dieted. “We do not yet now how to explain the details of these processes, but the results are heartening”, Negrão recognizes.
After training, the volume of blood that reached the arms and legs of those who walked or pedaled was 50% greater. These alterations are due in part to the decrease in the activity of the sympathetic nervous system that controls the dilation of the blood vessels, allowing them to increase in diameter. With time, the heart also adapts itself to exercise and starts to respond in a more efficient way: it pumps more blood with each beat and thus works less. As a consequence, the irrigation of the muscles is improved and arterial pressure lowered. There was, however, one intriguing detail. In both groups, the women slimmed significantly ten kilos, on average. The researchers only noted one crucial difference when they analyzed the data in detail. Those who just dieted lost fat, of course, but they also consumed a portion of the muscles of the body by no means a desirable effect, since it lowers the consumption of energy, and, with time, can facilitate getting back part of the lost weight. But the women whodid both exercise and a diet burned only adipose tissue.
Head of the Child Obesity Outpatients Department at USP’s School of Medicine, Sandra decided to see whether these physiological alterations also happened with children. With the professor of physical education Maurício Maltez Ribeiro and physician Érika Parente, Sandra assessed 163 obese boys and girls between 7 and 11 years old in children and adolescents, the degree of obesity is determined by the body mass index, adjusted in relation to age. The data from these children was compared with the data from another ten, classified as thin, who were part of the control group. The researchers found that already in infancy obesity affects the working of the sympathetic nervous system: the flow of blood to the arms and legs of the obese children increased only 14%, while in the thin ones this increase rose to 43% during the test of mental stress, in which the children had to say in which color the name of another color was written: for example, the word red was written in blue ink. The chubby ones also showed a rise in their blood pressure higher than is normal for the age, and they were already suffering from insulin resistance. These values returned to normal levels amongst obese children after four months of training, in which they did one hour of physical activity exercises and games three times a week. “These discoveries may assist in the prevention and treatment of diabetes and hypertension in children as well”, Sandra comments.
World epidemic
The need for coupling diet and exercise is reiterated, in one way or another, in the issue of Science magazine of February 7 this year dedicated to obesity, the extent of which is dealt with there from the epidemiological, sociological and biochemical point of view. Obesity today is one of the ten main public health problems in the world, in the assessment of the World Health Organization (WHO). It is estimated that there are 700 million people overweight weighing a little bit more than is regarded as healthy and another 300 million of obese people, of which at least one third are in the developing companies. Excess weight is more visible in the richer and more industrialized companies, like the United States, England and the United Kingdom, where the number of obese persons has tripled in the last 20 years.
In the United States alone where the daily availability per capita is 3,800 kcal, 50% above what is recommended by the WHO, one third of the adult population is overweight and another 30% are obese. The American government, besides spending US$ 55 billion a year to treat problems deriving from obesity, sees this problem as an epidemic, tackled by national campaigns that, for example, encourage parents to take their children to school on foot, instead of using the car. But obesity is also expanding in European nations and in developing countries that are taking up the American life style, marked by sedentary days, rich meals and cookies in abundance, at any time in short, by the excessive intake of food rich in sugars and fats. As a consequence of the phenomenon nicknamed globesity, not even the French, who have always appreciated their slim figures, are managing to toe the line: over there, 11.3% of the population is now obese.
In Brazil, in a little over 20 years, from 1975 to 1997, the number of obese persons has more than doubled there are today almost 17 million persons (9.6% of the population) with a BMI of over 30. Studies by epidemiologist Carlos Augusto Monteiro, of the School of Public Health at USP, which guide the government in this field, make it clear: here too obesity is a public health problem. Monteiro availed himself of three population studies carried out by the Brazilian Institute of Geography and Statistics (IBGE). The first is from 1975, the second from 1989, both nationwide, and the third from 1997, limited to two contrasting regions, the Northeast, the poorest, and the Southeast, the richest, which are also representative for bringing together 70% of the almost 180 millions of Brazilians.
On the basis of this data, Monteiro found that the number of obese men has increased threefold in this period, to arrive at 6.4% of the adult male population, while the total of obese women has doubled and reached 12.4% of the universe of adult women in 1997, the date of the last survey that assessed the height and weight of Brazil’s inhabitants. Between 1989 and 1997, the number of people with excessive weight only decreased amongst the more wealthy women of the southeastern region, according to an article that the researcher from USP published in Public Health Nutrition in February 2002, written in partnership with Wolney Conde, from USP, and Barry Popkin, from the University of North Carolina, United States. One of the figures that was most alarming is the increase of obesity amongst children and adolescents. It is estimated that over the last two decades this figure has grown at a swift pace and increased five times, leaping up from 3% to 15% of the total of children. In more concrete terms, there arealmost 6.5 obese children in Brazil.
Sugar all the time
Between 1975 and 1997, the quantity of calories available for each Brazilian but not necessarily consumed by them all increased from 2,494 kcal per day to 2,967 kcal, according to the Food and Agriculture of the United Nations (FAO). It is a 20% growth that has not taken place in a homogeneous way: the availability of proteins grew by almost one third, and of fats by 55%. “Brazilians consume today almost twice as much sugar as they should”, says the epidemiologist. In a study published in July in Cadernos de Saúde Pública [Public Health Notebooks], Monteiro and Conde, from USP, and Inês Rugani de Castro, from the Annes Dias Nutrition Institute, of Rio de Janeiro, assessed the advance of obesity in relation to schooling. The conclusion is that from 1975 to 1989, the number of cases of obesity has doubled amongst men and women who went to school for longest. Then, in the next period, from 1989 to 1997, growth was greater amongst the portion with less schooling, and it decreased amongst women with more schooling, with at least 12 years studying.
Today, obesity has overtaken the levels of malnutrition, and the nutritional profile of the Brazilian finds itself in a phase of transition, in which malnutrition has decreased and obesity increased, approaching the American scene. In the last two decades, malnutrition has fallen from 8.3% to 3.5% amongst adult men, and from 13.4% to 6.5% amongst the women, but it still remains high (9.6%) amongst the poorest women of the Northeast. “Should this trend be maintained”, says Monteiro, “cases of obesity and the diseases related to it will shortly be concentrated on the less favored sectors of society.” The Ministry of Health has created a national policy for food and nutrition, which, amongst other measures, has made it obligatory to detail calories on the labels of processed foods and obliged municipal governments to employ 70% of the budget intended for feeding public school students in the purchase of fresh foods like fruit and vegetables.
There is thus taking shape a situation that Marion Nestle, Nutrition, Food Studies, Public Health Department of New York University, calls the great irony of the 21st century, in the editorial of the issue of Science dedicated to obesity: although millions of people are still going hungry, it has never been so easy to get food. In some countries at least, people eat more and expend less energy to get food. Nobody needs any more to grab their bow and arrow to set off hunting an antelope to eat meat – all you have to do is pick up the phone and order it from the restaurant on the corner. In 1962, American geneticist James Neel, one of the pioneers in human genetics, presented the idea that the capacity for accumulating fat was essential in an environment in which food was scarce and it was not possible to eat just anytime. But what used to be an advantage that made possible the survival of some populations in the course of the history of the human species is turning itself into a disadvantage, aggravated by the comfort of the armchair that is an invitation to the dolce fare niente while waiting for dinner.
But it is not only the fact that there is food to hand and the atavistic tendency to eat that are making the battle against obesity complex. There are at least 300 genes that, directly or indirectly, govern the ways by which the organism stores and consumes fat, the raw material for the production of energy. At USP’s School of Pharmaceutical Sciences, pharmacist Rosario Hirata recently identified in Brazilians two variations in the gene responsible for the production of the leptin hormone which favors the development of obesity and can serve as indicators of the propensity of each individual for putting on weight. It is still not known for sure how much all the genes contribute towards obesity, but the importance of some of them is now clear. “Of the genes linked to obesity, the one that most frequently appears altered is the MC4R, connected to complex biological processes that postpone the desire for eating”, says Sandra Villares. “Even so, this modification occurs in only 6% of the obese.”
Today, it is also known that, besides emotional and environmental factors, at least two biochemical mechanisms govern weight. One of them, more immediate, regulates the daily ingestion of food, and its control is essentially connected with two hormones produced in the digestive system, ghrelin and PYY. But the maintaining one’s weight for months or years seems to depend on leptin, produced by the fat cells, and on insulin, which regulates the consumption of sugar by the cells. Even scientists agree that it is not at all easy to resist the desire to take just one more bite of the sandwich: the biological mechanisms that induce us to eat seem to be stronger than those that lead us to stop. It is also clearer why it is difficult to keep one’s weight after slimming. In an article published in February’s Science, the American, Jeffrey Friedman, from Rockefeller University, United States, tells how reducing weight makes the level of the leptin hormone fall which is where the stimulus for eating more comes from. “The sensation of hunger is so intense”, reports Friedman, “that, without being so powerful as the need for breathing, it is probably no less potent than the need for drinking when one is thirsty.”
The Project
Genetic and Environmental Aspects of Obesity (98/15983-8); Modality: Thematic Project; Coordinator: Carlos Eduardo Negrão – USP; Investment: R$ 511,545.25
