Trends in the obesity epidemic are deepening in seriousness worldwide, which is especially a worry among pediatricians. Currently 41 million children under five years of age are overweight and obese.
As they age, these children are predicted to develop cardiometabolic complications of their obesity, including Type 2 diabetes, about 90% of which is driven by excess body weight.
However, obesity-associated health risks are distributed unevenly among people who are obese. Significant numbers of adults who are obese (Body Mass Index ≥30 kg/m2) lack some of the major metabolic complications we normally associate with high body mass index (BMI) (hypertension, and in blood: abnormal lipid profile, high fasting glucose, high cholesterol). These adults (as many as 25%) have been called ‘metabolically healthy obese’ (MHO).
Conversely, other adults develop cardiovascular disease and diabetes despite non-obese BMI, and have been called ‘metabolically obese normal weight’ (MONW). Inflammation appears to make some of the difference here, and the higher risk groups tend to display higher chronic inflammation.
Prevalence of metabolically healthy obese individuals
The calculated prevalence of MHO adults depends in part on the clinical criteria used.
The calculated prevalence of MHO adults depends in part on the clinical criteria used. The Adult Treatment Panel III criteria definition of metabolic syndrome specifies a diagnosis of three or more of the following: elevated fasting glucose, increased waist circumference, elevated blood triglycerides, abnormal lipid profile, or elevated blood pressure.
However, the International Diabetes Foundation criteria are different and associate with different risk profiles for cardiometabolic disease. There is significant disagreement in the field. Some clinical commentators regard the MHO type as an illusion; primarily a semantic distinction between increasing classes of risk, with no subjects truly protected from steadily increasing cardiometabolic risk with increasing age and BMI.
On the other hand, there are important examples of adults who are obese or even morbidly obese, and who remain MHO for long periods of time. Perhaps physical activity is a critical variable that makes the difference between healthy and unhealthy obesity, but available data are limited.
They found that metabolic health tends to associate with, in order of importance: lower BMI, younger age, female gender, reduced likelihood of smoking, heavy drinking and physical inactivity.
How do these factors vary as a function of population, gender, occupation, diet, income and national/ethnic origin? Goday and co-authors studied a large number of Spanish workers (N = 451,432) and attempt to answer the question.
They found that metabolic health tends to associate with, in order of importance: lower BMI, younger age, female gender, reduced likelihood of smoking, heavy drinking and physical inactivity. These associations are not new, and re-affirm the importance of well known preventive measures to preserve health.
However, there are some provocative implications
First, children who live with one obese parent have a four-fold increased risk of developing obesity, whereas children who live with two obese parents have a thirteen-fold increased risk. What are the cardiometabolic risks for the children of these Spanish workers? And how will their risks change over time?
Second, diet and physical activity patterns are changing around with world, with dramatic increases in food consumption and reductions in exercise, among both adults and children, which are fueling a crisis in diabetes risks. These risks are heavily influenced by shifting patterns of globalization.
Diet and physical activity patterns are changing around with world, with dramatic increases in food consumption and reductions in exercise, among both adults and children.
Third, many European countries are currently experiencing an influx of guest workers and political/economic refugees of non-Caucasian origin (South Asians, North Africans, Afghans, Syrians or others of Indo-Chinese descent), who may be more likely to develop metabolic abnormalities at low BMI, according to the Asia-Pacific criteria.
Such potential MONW adults might be present among the small percentage of normal weight or underweight adults who are metabolically unhealthy in the Spanish study. This population is not traditionally a significant fraction of the Spanish workforce, but the proportions may change as immigration forces alter the composition of European populations.
It may be useful in future studies to evaluate the metabolism and BMI of these adults differently from Spaniards of Caucasian genetic background, rather than lumping everyone together.
Finally, the children of these new immigrants will likely have complex risk profiles for obesity and cardiometabolic disease as they reach adulthood in 10-20 years, because their Asia-Pacific genetic origins will interact with European diet and physical activity patterns in ways that are difficult to predict.
A large ‘natural experiment’ in energy metabolism and population genetics is currently underway, and European public health authorities should take steps now to capture data and understand health risks in each country, in order to plan properly for the future medical needs of these new Europeans.