Genetics of obesity
by Dr Angelo Pietrobelli
Recent years have seen an alarming rise in the incidence
of childhood obesity, not only in developed countries, but also in competitive economies,
such as Singapore, Malaysia and China.
How did this come about? According to experts, this epidemic is largely a result
of energy imbalance, that is, energy input in excess of energy output. This is not
surprising, especially in the more affluent societies, where food is abundant and
high technologies have reduced us to couch potatoes.
To address the many questions on childhood obesity is Dr Angelo Pietrobelli. Dr
Angelo Pietrobelli is a pediatric endocrinologist who worked with Dr. Heymsfield
for more than three years at the New York Obesity Research Center. Currently, he
is working as a consultant at the Newborn Intensive Unit Care in Verona Pediatric
Clinic, Verona University, Verona (ITALY) , while maintaining his research work
with the New York Obesity Research Center as the body composition consultant on
Dr. Faith NIH Pediatric Twin Grant. His research interests include the use of Dual
energy X-ray Absorptiometry (DXA) with pediatric samples and also other body composition
measurements. Currently, he is involved in several projects related to cardiac change
associated with weight loss, Leptin, as well as the treatment of Pediatric Obesity.
Q) How do you define overweight and obesity?
A) It is difficult to define overweight and obesity for children
and adolescents. A variety of criteria for overweight and obesity have been used
to evaluate the prevalence trends among children and adolescents.
A common definition, especially in Europe, is weight in excess of 20% above ideal
weight for age and gender. In USA, overweight can be defined as Body Mass Index
(BMI = kg/m2) >85th percentile for age and sex and obesity as BMI >95th percentile
for age and sex or skinfold thickness of the 85th percentile for age and sex. On
the other hand the definition of obesity is also an increase in fat mass, not just
an increase in body weight.
Q) What are the major causes of childhood obesity?
A) Obesity is a complex disease with genetic, metabolic and behavioral
determinants. Obesity results from an imbalance between energy intake and expenditure,
and there are genetic influences of these components of energy balance. However,
despite obesity having genetic determinants, the genetic composition of the population
does not change rapidly.
Increases in consumption of high fat, energy-dense foods and a reduction in physical
activity over the past decades are the most important environmental factors thought
to contribute to the current epidemic of obesity.
Q) Studies have cited TV watching as one of the causes
of childhood obesity. What is your opinion?
A) Recently, we published a paper (Pediatrics 2001; 107:1043-48)
on this issue. In our opinion, television viewing is a cause of obesity, due to
the presence of or/and a combination of these mechanisms:
• reduced physical activity and increased sedentary lifestyle,
• increased calorie consumption while watching and
• reduced resting metabolism.
Q) Please elaborate on the various methods of measuring
obesity?
A) There are various models and indirect methods for measuring fat
and fat-free mass. For example, techniques used in specialized research facilities
are total body electrical conductivity, total body potassium and magnetic resonance
imaging. Other more convenient and widely available techniques are dual energy X-ray
absorptiometry (DXA), bioelectrical impedance (BIA), skinfolds, and other very simple
anthropometric evaluations (i.e., weight for height, ideal body weight, BMI).
Q) Can we use the BMI as a means of measuring obesity
in children? If so, how does this differ from the standards used for adults? If
not, why not?
A) BMI is widely used in adult populations and a cut off point of
30 kg/m2 is recognized internationally as a definition of adult obesity. BMI index
in childhood changes substantially with age. At birth the median is as low as 13
kg/m2 and this increases to 17 kg/m2 at age 1, then decreases to 15.5 kg/m2 at age
6, and finally increases to 21 kg/m2 at age 20.
Because a cut off point related to age and sex is needed to define child obesity,
Cole and colleagues recently (BMJ 2000; 320:1240-43) provided centiles curves to
measure overweight and obesity in children and linked it to the accepted adult cut
off points of BMI of 25 and 30 kg/m2.
Q) What are the medical consequences of childhood obesity?
A) Obesity in childhood is associated with different consequences,
including cardiovascular disorders, metabolic, endocrinologic, and orthopedic, among
others. The medical consequences of pediatric obesity include elevated blood pressure,
glucose intolerance, hyperinsulinemia and dyslipidemias; all these are associated
with risks for cardiovascular disease.
Q) What are the social consequences of childhood obesity?
A) It is recognized that obese and overweight children demonstrate significantly
lower levels of self-esteem by early adolescence, than their normal weight peers.
In addition, these children exhibit higher rates of sadness, loneliness, and nervousness,
and they are also more likely to engage in high-risk behaviors such as smoking or/and-consuming
alcohol.
Q) What's your advice for parents with an obese child?
A) My advice to such parents are:
• Find reasons to praise their child's behavior
• Never use food as reward
• They can "reward" their children, in exchange for positive changes in their behavior
• Establish daily family meal and snack times
• They should determine what food is offered and when, and the child should decide
whether to eat
• Offer only healthy options
• Remove temptations
• Be a role model
• Be consistent
Q) What are your views on the use of appetite suppressants
or fat burners for the treatment of childhood obesity?
A) Treatment for obese children usually involves a program of behavioral
modification, caloric restriction, increased activity, and decreased sedentary behaviors.
Medication for pediatric obesity cannot be recommended at the present.
Q) What should parents do to prevent their children from
becoming overweight?
A) Parents should pay attention to food portion sizes and let their
children respond to their own hunger and fullness cues. Children should be included
in food shopping, food preparation and parents should encourage them to be more
interested in nutrition.
Parents should also set the example. If parents eat well, their children will eat
well too. The full family needs to adopt a healthy lifestyle, which includes healthy
eating habits and regular exercise.